Insights into the alleviation of cadmium toxicity in rice by nano-zinc and Serendipita indica: Modulation of stress-responsive gene expression and antioxidant defense system activation.

The adversities of cadmium (Cd) contamination are quite distinguished among other heavy metals (HMs), and so is the efficacy of zinc (Zn) nutrition in mitigating Cd toxicity. Rice (Oryza sativa) crop, known for its ability to absorb HMs, inadvertently facilitates the bioaccumulation of Cd, posing a significant risk to both the plant itself and to humans consuming its edible parts, and damaging the environment as well. The use of nanoparticles, such as nano-zinc oxide (nZnO), to improve the nutritional quality of crops and their counteractive implications against HMs, have gained substantial attention among scientists and farmers. While previous studies have explored the individual effects of nZnO or Serendipita indica (referred to as S.i) on Cd toxicity, the synergistic action of these two agents has not been thoroughly investigated. Therefore, the gift of nature, i.e., S. indica, was incorporated alongside nZnO (50 mg L-1) against Cd stress (15 µM L-1) and their alliance manifested as phenotypic level modifications in two rice genotypes (Heizhan43; Hz43 and Yinni801; Yi801). Antioxidant activities were enhanced, specifically peroxidase (61.5 and 122.5% in Yi801 and Hz43 roots, respectively), leading to a significant decrease in oxidative burst; moreover, Cd translocation was reduced (85% for Yi801 and 65.5% for Hz43 compared to Cd alone treatment). Microstructural study showed a decrease in number of vacuoles and starch granules with ameliorative treatments. Overall, plants treated with nZnO displayed gene expression pattern (particularly of ZIP genes), different from the ones with alone or combined S.i and Cd. Inferentially, the integration of nZnO and S.i holds great promise as an effective strategy for alleviating Cd toxicity in rice plants. By immobilizing Cd ions in the soil and promoting their detoxification, this novel approach contributes to environmental restoration and ensures food safety worldwide.

Nutrient and mycoremediation of a global menace 'arsenic': exploring the prospects of phosphorus and Serendipita indica-based mitigation strategies in rice and other crops.

KEY MESSAGE: Serendipita indica induced metabolic reprogramming in colonized plants complements phosphorus-management in improving their tolerance to arsenic stress on multifaceted biological fronts. Restoration of the anthropic damage done to our environment is inextricably linked to devising strategies that are not only economically sound but are self-renewing and ecologically conscious. The dilemma of heavy metal (HM) dietary ingestion, especially arsenic (As), faced by humans and animals alike, necessitates the exploitation of such technologies and the cultivation of healthy and abundant crops. The remarkable symbiotic alliance between plants and 'mycorrhizas' has evolved across eons, benefiting growth/yield aspects as well as imparting abiotic/biotic stress tolerance. The intricate interdependence of Serendipita indica (S. indica) and rice plant reportedly reduce As accumulation, accentuating the interest of microbiologists, agriculturists, and ecotoxicological scientists apropos of the remediation mechanisms of As in the soil-AMF-rice system. Nutrient management, particularly of phosphorus (P), is also praised for mitigating As phytotoxicity by deterring the uptake of As molecules due to the rhizospheric cationic competition. Taking into consideration the reasonable prospects of success in minimizing As acquisition by rice plants, this review focuses on the physiological, metabolic, and transcriptional alterations underlying S. indica symbiosis, recuperation of As stress together with nutritional management of P by gathering case studies and presenting successful paradigms. Weaving together a volume of literature, we assess the chemical forms of As and related transport pathways, discuss As-P-rice interaction and the significance of fungi in As toxicity mitigation, predominantly the role of mycorrhiza, as well as survey of the multifaceted impacts of S. indica on plants. A potential strategy for simultaneous S. indica + P administration in paddy fields is proposed, followed by future research orientation to expand theoretic comprehension and encourage field-based implementation.

Pan-transcriptomic Profiling Demarcates Serendipita Indica-Phosphorus Mediated Tolerance Mechanisms in Rice Exposed to Arsenic Toxicity.

Inadvertent accumulation of arsenic (As) in rice (Oryza sativa L.) is a concern for people depending on it for their subsistence, as it verily causes epigenetic alterations across the genome as well as in specific cells. To ensure food safety, certain attempts have been made to nullify this highest health hazard encompassing physiological, chemical and biological methods. Albeit, the use of mycorrhizal association along with nutrient reinforcement strategy has not been explored yet. Mechanisms of response and resistance of two rice genotypes to As with or without phosphorus (P) nutrition and Serendipita indica (S. indica; S.i) colonization were explored by root transcriptome profiling in the present study. Results revealed that the resistant genotype had higher auxin content and root plasticity, which helped in keeping the As accumulation and P starvation response to a minimum under alone As stress. However, sufficient P supply and symbiotic relationship switched the energy resources towards plant's developmental aspects rather than excessive root proliferation. Higher As accumulating genotype (GD-6) displayed upregulation of ethylene signaling/biosynthesis, root stunting and senescence related genes under As toxicity. Antioxidant defense system and cytokinin biosynthesis/signaling of both genotypes were strengthened under As + S.i + P, while the upregulation of potassium (K) and zinc (Zn) transporters depicted underlying cross-talk with iron (Fe) and P. Differential expression of phosphate transporters, peroxidases and GSTs, metal detoxification/transport proteins, as well as phytohormonal metabolism were responsible for As detoxification. Taken together, S. indica symbiosis fortified with adequate P-fertilizer can prove to be effective in minimizing As acquisition and accumulation in rice plants.

Phosphorus and Serendipita indica synergism augments arsenic stress tolerance in rice by regulating secondary metabolism related enzymatic activity and root metabolic patterns.

The multifarious problems created by arsenic (As), for collective environment and human health, serve a cogent case for searching integrative agricultural approaches to attain food security. Rice (Oryza sativa L.) acts as a sponge for heavy metal(loid)s accretion, specifically As, due to anaerobic flooded growth conditions facilitating its uptake. Acclaimed for their positive impact on plant growth, development and phosphorus (P) nutrition, 'mycorrhizas' are able to promote stress tolerance. Albeit, the metabolic alterations underlying Serendipita indica (S. indica; S.i) symbiosis-mediated amelioration of As stress along with nutritional management of P are still understudied. By using biochemical, RT-qPCR and LC-MS/MS based untargeted metabolomics approach, rice roots of ZZY-1 and GD-6 colonized by S. indica, which were later treated with As (10 µM) and P (50 µM), were compared with non-colonized roots under the same treatments with a set of control plants. The responses of secondary metabolism related enzymes, especially polyphenol oxidase (PPO) activities in the foliage of ZZY-1 and GD-6 were enhanced 8.5 and 12-fold, respectively, compared to their respective control counterparts. The current study identified 360 cationic and 287 anionic metabolites in rice roots, and the commonly enriched pathway annotated by Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was biosynthesis of phenylalanine, tyrosine and tryptophan, which validated the results of biochemical and gene expression analyses associated with secondary metabolic enzymes. Particularly under As+S.i+P comparison, both genotypes exhibited an upregulation of key detoxification and defense related metabolites, including fumaric acid, L-malic acid, choline, 3,4-dihydroxybenzoic acid, to name a few. The results of this study provided the novel insights into the promising role of exogenous P and S. indica in alleviating As stress.

Nanobionics: A Sustainable Agricultural Approach towards Understanding Plant Response to Heavy Metals, Drought, and Salt Stress.

In the current scenario, the rising concentration of heavy metals (HMs) due to anthropogenic activities is a severe problem. Plants are very much affected by HM pollution as well as other abiotic stress such as salinity and drought. It is very important to fulfil the nutritional demands of an ever-growing population in these adverse environmental conditions and/or stresses. Remediation of HM in contaminated soil is executed through physical and chemical processes which are costly, time-consuming, and non-sustainable. The application of nanobionics in crop resilience with enhanced stress tolerance may be the safe and sustainable strategy to increase crop yield. Thus, this review emphasizes the impact of nanobionics on the physiological traits and growth indices of plants. Major concerns and stress tolerance associated with the use of nanobionics are also deliberated concisely. The nanobionic approach to plant physiological traits and stress tolerance would lead to an epoch of plant research at the frontier of nanotechnology and plant biology.

Physiological and TMT-based quantitative proteomic responses of barley to aluminium stress under phosphorus-Piriformospora indica interaction.

Barley (Hordeum vulgare L.) is one of the most important cereal crop in the world, and is also the one being seriously affected by heavy metals, particularly aluminium (Al). Keeping in view the utility of barley as food, fodder and raw material for traditional beer brewing, the top-notch quality and higher production of this crop must be sustained. Phosphorus (P) has a quintessential role in plant growth with a potential to relieve symptoms caused by Al poisoning. Displaying a phytopromotive and stress alleviatory potential, Piriformospora indica (P. indica) can improve the stress tolerance in crops. Several studies have been conducted to evaluate the mechanism of Al translocation in a variety of crops including barley, however, the bio-remediative studies related to detoxification and/or sequestration of metals are scarce. Therefore, the current study was carried out to elucidate the tolerance mechanism of an Al-sensitive barley cultivar ZU9 following the colonization with P. indica and exogenous P supply by physio-biochemical, elemental, leaf ultrastructural and root proteome analyses. When compared to the Al alone treated counterparts, the Al + P + P.i treated plants exhibited 4.1-, 1.38-, 2.7 and 1.35-fold improved root and shoot fresh and dry weights, respectively. With the provision of additional phosphorus, the content of P in the root and shoot for Al + P + P.i group was reportedly higher (71.6% and 49.5%, respectively) as compared to the control group. Moreover, inoculation of P. indica combined with P improved barley leaves' cell arrangement and also maintained normal cell wall shape. The root protemics experiment was divided into three groups: Al, Al + P.i and Al + P + P.i. In total, 28, 598, and 823 differentially expressed proteins were found in Al + P.i vs. Al and Al + P + P.i vs. Al, and phenylpropanoid biosynthesis was the most prominently enriched pathway, which contributed significantly to the recuperating effects of P-P. indica interaction. Conslusively, it was found that the percentage of protein related to peroxidase was 70/359 (Al + P + P.i vs. Al) and 92/447 (Al + P + P.i vs. Al + P.i), respectively, which indicated that P. indica in combination with P might be involved in the regulation of peroxidases, increasing the adaptability of barley plants by enhanced reactive oxygen species (ROS) scavenging mechansism.

Nitrogen metabolic rate and differential ammonia volatilization regulate resistance against opportunistic fungus Alternaria alternata in tobacco.

Nutritional correlations between plants and pathogens can crucially affect disease severity. As an essential macronutrient, the availability of nitrogen (N) and the types of N content play a fundamental part not only in energy metabolism and protein synthesis but also in pathogenesis. However, a direct connection has not yet been established between differences in the level of resistance and N metabolism. Pertinently, former studies hold ammonia (NH3) accountable for the development of diseases in tobacco (Nicotiana tabacum L.) and in some post-harvest fruits. With a purpose of pinpointing the function of NH3 volatilization on Alternaria alternata (Fries) Keissl pathogenesis and its correlation with both N metabolism and resistance differences to Alternaria alternata infection in tobacco, leaf tissue of two tobacco cultivars with susceptibility (Changbohuang; CBH), or resistance (Jingyehuang; JYH) were analyzed apropos of ammonia compensation point, apoplastic NH4 + concentration, pH value as well as activities of key enzymes and N status. At the leaf age of 40 to 60 d, the susceptible cultivar had a significantly higher foliar apoplastic ammonium (NH4 +) concentration, pH value and NH3 volatilization potential compared to the resistant one accompanied by a significant reduction in glutamine synthetase (GS), which in particular was a primary factor causing the NH3 volatilization. The NH4 + concentration in CBH was 1.44 times higher than that in JYH, and CBH had NH3 compensation points that were 7.09, 6.15 and 4.35-fold higher than those of JYH at 40, 50 and 60 d, respectively. Moreover, the glutamate dehydrogenase (GDH) activity had an upward tendency related to an increased NH4 + accumulation in both leaf tissues and apoplast but not with the NH3 compensation point. Collectively, our results strongly suggest that the accumulation of NH3 volatilization, rather than NH4 + and total N, was the primary factor inducing the Alternaria alternata infection in tobacco. Meanwhile, the susceptible cultivar was characterized by a higher N re-transfer ability of NH3 volatilization, in contrast to the disease-resistant cultivar, and had a stronger capability of N assimilation and reutilization. This study provides a deeper understanding of the pathogenicity mechanism induced by Alternaria alternata, which is useful for breeding Alternaria alternata-resistant varieties of tobacco, at the same time, our research is also conducive to control tobacco brown spot caused by Alternaria alternata in the field.

Tandem application of endophytic fungus Serendipita indica and phosphorus synergistically recuperate arsenic induced stress in rice.

In the context of eco-sustainable acquisition of food security, arsenic (As) acts as a deterring factor, which easily infiltrates our food chain via plant uptake. Therefore, devising climate-smart strategies becomes exigent for minimizing the imposed risks. Pertinently, Serendipita indica (S. indica) is well reputed for its post-symbiotic stress alleviatory and phyto-promotive potential. Management of phosphorus (P) is acclaimed for mitigating arsenic toxicity in plants by inhibiting the uptake of As molecules due to the competitive cationic exchange in the rhizosphere. The current study was designed to investigate the tandem effects of S. indica and P in combating As toxicity employing two rice genotypes, i.e., Guodao-6 (GD-6; As-sensitive genotype) and Zhongzhe You-1 (ZZY-1; As-tolerant genotype). After successful fungal colonization, alone and combined arsenic (10 µ M L-1) and phosphorus (50 µ M L-1) treatments were applied. Results displayed that the recuperating effects of combined S. indica and P treatment were indeed much profound than their alone treatments; however, most of the beneficial influences were harnessed by ZZY-1 in comparison with GD-6. Distinct genotypic differences were observed for antioxidant enzyme activities, which were induced slightly higher in S. indica-colonized ZZY-1 plants, with or without additional P, as compared to GD-6. Ultrastructure images of root and shoot exhibited ravages of As in the form of chloroplasts-, nuclei-and cell wall-damage with enlarged vacuole area, mellowed mostly by the combined treatment of S. indica and P in both genotypes. Gene expression of PHTs family transporters was regulated at different levels in almost all treatments across genotypes. Conclusively, the results of this study validated the promising role of S. indica and additional P in mitigating As stress, albeit corroborated that the extent of relevant benefit exploitation is highly genotype-dependent. Verily, unlocking the potential of nature-friendly solutions will mend the anthropogenic damage already been done to our environment.

Spatio-Temporal Variation in the Phyllospheric Microbial Biodiversity of Alternaria Alternata-Infected Tobacco Foliage.

Phyllospheric microbial composition of tobacco (Nicotiana tabacum L.) is contingent upon certain factors, such as the growth stage of the plant, leaf position, and cultivar and its geographical location, which influence, either directly or indirectly, the growth, overall health, and production of the tobacco plant. To better understand the spatiotemporal variation of the community and the divergence of phyllospheric microflora, procured from healthy and diseased tobacco leaves infected by Alternaria alternata, the current study employed microbe culturing, high-throughput technique, and BIOLOG ECO. Microbe culturing resulted in the isolation of 153 culturable fungal isolates belonging to 33 genera and 99 bacterial isolates belonging to 15 genera. High-throughput sequencing revealed that the phyllosphere of tobacco was dominantly colonized by Ascomycota and Proteobacteria, whereas, the most abundant fungal and bacterial genera were Alternaria and Pseudomonas. The relative abundance of Alternaria increased in the upper and middle healthy groups from the first collection time to the third, whereas, the relative abundance of Pseudomonas, Sphingomonas, and Methylobacterium from the same positions increased during gradual leaf aging. Non-metric multi-dimensional scaling (NMDs) showed clustering of fungal communities in healthy samples, while bacterial communities of all diseased and healthy groups were found scattered. FUNGuild analysis, from the first collection stage to the third one in both groups, indicated an increase in the relative abundance of Pathotroph-Saprotroph, Pathotroph-Saprotroph-Symbiotroph, and Pathotroph-Symbiotroph. Inclusive of all samples, as per the PICRUSt analysis, the predominant pathway was metabolism function accounting for 50.03%. The average values of omnilog units (OUs) showed relatively higher utilization rates of carbon sources by the microbial flora of healthy leaves. According to the analysis of genus abundances, leaf growth and leaf position were the important drivers of change in structuring the microbial communities. The current findings revealed the complex ecological dynamics that occur in the phyllospheric microbial communities over the course of a spatiotemporal varying environment with the development of tobacco brown spots, highlighting the importance of community succession.

Stress signaling convergence and nutrient crosstalk determine zinc-mediated amelioration against cadmium toxicity in rice.

Consumption of rice (Oryza sativa L.) is one of the major pathways for heavy metal bioaccumulation in humans over time. Understanding the molecular responses of rice to heavy metal contamination in agriculture is useful for eco-toxicological assessment of cadmium (Cd) and its interaction with zinc (Zn). In certain crops, the impacts of Cd stress or Zn nutrition on the biophysical chemistry and gene expression have been widely investigated, but their molecular interactions at transcriptomic level, particularly in rice roots, are still elusive. Here, hydroponic investigations were carried out with two rice genotypes (Yinni-801 and Heizhan-43), varying in Cd contents in plant tissues to determine their transcriptomic responses upon Cd15 (15 µM) and Cd15+Zn50 (50 µM) treatments. High throughput RNA-sequencing analysis confirmed that 496 and 2407 DEGs were significantly affected by Cd15 and Cd15+Zn50, respectively, among which 1016 DEGs were commonly induced in both genotypes. Multitude of DEGs fell under the category of protein kinases, such as calmodulin (CaM) and calcineurin B-like protein-interacting protein kinases (CBL), indicating a dynamic shift in hormonal signal transduction and Ca2+ involvement with the onset of treatments. Both genotypes expressed a mutual regulation of transcription factors (TFs) such as WRKY, MYB, NAM, AP2, bHLH and ZFP families under both treatments, whereas genes econding ABC transporters (ABCs), high affinity K+ transporters (HAKs) and Glutathione-S-transferases (GSTs), were highly up-regulated under Cd15+Zn50 in both genotypes. Zinc addition triggered more signaling cascades and detoxification related genes in regulation of immunity along with the suppression of Cd-induced DEGs and restriction of Cd uptake. Conclusively, the effective integration of breeding techniques with candidate genes identified in this study as well as economically and technologically viable methods, such as Zn nutrient management, could pave the way for selecting cultivars with promising agronomic qualities and reduced Cd for sustainable rice production.

Improvement of morpho-physiological, ultrastructural and nutritional profiles in wheat seedlings through astaxanthin nanoparticles alleviating the cadmium toxicity.

Heavy metal accumulation in arable lands and water bodies has become one of the serious global issues among multitude of food security challenges. In particular, cadmium (Cd) concentration has been increasing substantially in the environment that negatively affects the growth and yield of important agricultural crops, especially wheat (Triticum aestivum L.). No doubt, nanotechnology is a revolutionary science but the comprehension of nanoparticle-plants interaction and its potential alleviatory role against metal stress is still elusive. Here, we investigated the mechanistic role of astaxanthin nanoparticles (AstNPs) in Cd stress amelioration and their interaction with wheat under Cd-spiked conditions. The AstNPs fabrication was confirmed through ultraviolet visible spectroscopy, where the particles showed characteristic peak at 423 nm. However, Fourier transform infrared, X-ray diffraction, scanning electron microscopy and transmission electron microscopy analyses confirmed the presence of stabilized spherical-shaped nanocrystals of AstNPs within the size range of 12.03-30.37 nm. The hydroponic application of AstNPs (100 mg L-1) to Cd-affected wheat plants increased shoot height (59%), shoot dry weight (31%), nitrogen concentration (42%), and phosphorus concentration (26%) as compared to non-treated Cd affected seedlings. Moreover, AstNPs-treated plants showed reduction in acropetal Cd translocation (29%) in contrast to plants treated with Cd only. Under Cd-spiked conditions, AstNPs-treated plants displayed an improved nutrient profile (P, N, K+ and Ca2+) with a relative decrease in Na+ content in comparison with non-treated plants. Interestingly, it was found that AstNPs restricted the translocation of Cd to aerial plant parts by negatively regulating Cd transporter genes (TaHMA2 and TaHMA3), and relieved plants from oxidative burst by activating antioxidant machinery via triggering expressions of TaSOD and TaPOD genes. Consequently, it was observed that the application of AstNPs helped in maintaining the nutrient acquisition and ionic homeostasis in Cd-affected wheat plants, which subsequently improved the physiochemical profiles of plants under Cd-stress. This study suggests that AstNPs plausibly serve as stress stabilizers for plants under heavy metal-polluted environment.

Mechanistic Insights into Potassium-Conferred Drought Stress Tolerance in Cultivated and Tibetan Wild Barley: Differential Osmoregulation, Nutrient Retention, Secondary Metabolism and Antioxidative Defense Capacity.

Keeping the significance of potassium (K) nutrition in focus, this study explores the genotypic responses of two wild Tibetan barley genotypes (drought tolerant XZ5 and drought sensitive XZ54) and one drought tolerant barley cv. Tadmor, under the exposure of polyethylene glycol-induced drought stress. The results revealed that drought and K deprivation attenuated overall plant growth in all the tested genotypes; however, XZ5 was least affected due to its ability to retain K in its tissues which could be attributed to the smallest reductions of photosynthetic parameters, relative chlorophyll contents and the lowest Na+/K+ ratios in all treatments. Our results also indicate that higher H+/K+-ATPase activity (enhancement of 1.6 and 1.3-fold for shoot; 1.4 and 2.5-fold for root), higher shoot K+ (2 and 2.3-fold) and Ca2+ content (1.5 and 1.7-fold), better maintenance of turgor pressure by osmolyte accumulation and enhanced antioxidative performance to scavenge ROS, ultimately suppress lipid peroxidation (in shoots: 4% and 35%; in roots 4% and 20% less) and bestow higher tolerance to XZ5 against drought stress in comparison with Tadmor and XZ54, respectively. Conclusively, this study adds further evidence to support the concept that Tibetan wild barley genotypes that utilize K efficiently could serve as a valuable genetic resource for the provision of genes for improved K metabolism in addition to those for combating drought stress, thereby enabling the development of elite barley lines better tolerant of abiotic stresses.

Modulation of Cellular Redox Status and Antioxidant Defense System after Synergistic Application of Zinc Oxide Nanoparticles and Salicylic Acid in Rice (Oryza sativa) Plant under Arsenic Stress.

The objective of this research was to determine the effect of zinc oxide nanoparticles (ZnONPs) and/or salicylic acid (SA) under arsenic (As) stress on rice (Oryza sativa). ZnONPs are analyzed for various techniques viz., X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). All of these tests established that ZnONPs are pure with no internal defects, and can be potentially used in plant applications. Hence, we further investigated for better understanding of the underlying mechanisms and the extent of ZnONPs and SA induced oxidative stress damages. More restricted plant growth, gas exchange indices, significant reduction in the SPAD index and maximum quantum yield (Fv/Fm) and brutal decline in protein content were noticed in As-applied plants. In contrast, foliar fertigation of ZnONPs and/or SA to As-stressed rice plants lessens the oxidative stress, as exposed by subordinate levels of reactive oxygen species (ROS) synthesis. Improved enzymatic activities of catalase (CAT), peroxidase (POX), and superoxide dismutase (SOD), proline and total soluble protein contents under ZnONPs and SA treatment plays an excellent role in the regulation of various transcriptional pathways participated in oxidative stress tolerance. Higher content of nitrogen (N; 13%), phosphorus (P; 10%), potassium (K; 13%), zinc (Zn; 68%), manganese (Mn; 14%), and iron (Fe; 19) in ZnONPs and SA treated plants under As-stress, thus hampered growth and photosynthetic efficiency of rice plants. Our findings suggest that toxicity of As was conquering by the application of ZnONPs and SA in rice plants.

Physio-ultrastructural footprints and iTRAQ-based proteomic approach unravel the role of Piriformospora indica-colonization in counteracting cadmium toxicity in rice.

Due to its immense capability to concentrate in rice grain and ultimately in food chain, cadmium (Cd) has become the cause of an elevated concern among agriculturists, scientists and the environmental activists. Symbiotic association of Piriformospora indica (P. indica) has been characterized as a potential aid in combating heavy metal stress in plants for sustainable crop production but our scant knowledge regarding ameliorative tendency of P. indica against Cd, specifically in rice, necessitates an in-depth investigation. This study aimed at elaborating the underlying mechanisms involved in P. indica-mediated tolerance against Cd stress in two rice genotypes, IR8 and ZX1H, varying in Cd accumulation pattern. Either colonized or un-inoculated with P. indica, seedlings of both genotypes were subjected to Cd stress. The results showed that P. indica colonization significantly supported plant biomass, photosynthetic attributes and chlorophyll contents in Cd stressed plants. P. indica colonization sustained chloroplast integrity and reduced Cd translocation (46% and 64%), significantly lowering malondialdehyde (MDA) content (11.3% and 50.4%) compared to uninoculated roots under Cd stress in IR8 and ZX1H, respectively. A genotypic difference was evident when a 2-fold enhancement in root peroxidase (POD) activity was recorded in P. indica colonized IR8 plants as compared to ZX1H. The root proteomic analysis was performed using isobaric tags for relative and absolute quantification (iTRAQ) and the results showed that P. indica alleviates Cd stress in rice via down-regulation of key glycolysis cycle enzymes in a bid to reduce energy consumption by the plants and possibly re-directing it to Cd defense response pathways; and up-regulation of glutamine synthetase, a key enzyme in the L-Arg-dependent pathway for nitric oxide (NO) production, which acts as a stress signaling molecule, thus conferring tolerance by reduction of NO-mediated modification of essential proteins in response to Cd stress. Conclusively, both the tested genotypes benefited from P. indica symbiosis at varying levels by an enhanced detoxification capacity and signaling efficiency in response to stress. Hence, a step forward towards the employment of an environmentally sound and self-renewing approach holding the hope for a healthy future.

Transcriptome analysis reveals the tolerant mechanisms to cobalt and copper in barley.

Cobalt (Co) and copper (Cu) co-exist commonly in the contaminated soils and at excessive levels, they are toxic to plants. However, their joint effect and possible interaction have not been fully addressed. In this work, a hydroponic experiment was performed to investigate the combined effects of Co and Cu on two barley genotypes at transcriptional level by RNA-seq analysis. The results identified 358 genes inclusively expressed in both genotypes under single and combined treatments of Co and Cu, with most of them being related to metal transport, stress response and transcription factor. The combined treatment induced more differently expressed genes (DEGs) than the single treatment, with Yan66, a metal tolerant genotype having more DEGs than Ea52, a sensitive genotype. The pathways associated with anthocyanin biosynthesis, MAPK signaling, glutathione biosynthesis, phenylalanine metabolism, photosynthesis, arginin biosynthesis, fatty acid elongation, and plant hormone signal transduction biosynthesis were induced and inhibited in Yan66 and Ea52, respectively. Furthermore, flavonoid biosynthesis was much more largely enhanced and accordingly more free flavonoid components (naringin, narirutin and neohesperidin) were accumulated in Yan66 than in Ea52. It may be suggested that high tolerance to both Co and Cu in Yan66 is attributed to its high gene regulatory ability.

High accumulation of phenolics and amino acids confers tolerance to the combined stress of cobalt and copper in barley (Hordeum vulagare).

Cobalt (Co) and copper (Cu) co-exist in the metal contaminated soils and cause the serious toxicity to crops, while their interactive effect on plant growth and development is still poorly understood. In this work, a hydroponic experiment was carried out to reveal the interactive effect of Co and Cu on photosynthesis and metabolite profiles of two barley genotypes differing in metal tolerance. The results showed that both single and combined treatments of Co and Cu caused a significant reduction in chlorophyll content and photosynthetic rate of the two barley (Hordeum vulgare) genotypes, with the effect being greater for the combined treatment and the sensitive genotype (Ea52) being more affected than the tolerant genotype (Yan66). Compared to Cu or Co treatment alone, the combined treatment significantly increased the levels of phenolic components, including cinnamic derivatives (caffeic, chlorogenic, ferullic, p-coumaric); benzoic derivatives (p-hydroxybenzoic, vanillic, syringic, sallicilic, protocatechuic acid) as well as free amino acids, with Yan66 having more accumulation than Ea52. Meanwhile, under the combined treatment, the phenylalanine ammonialyase-related gene (HvPAL) was highly regulated along with the genes involved in the synthesis of malate (HvMDH) and citrate (HvCSY), with Ya66 showing the higher expression of these genes than Ea52. It can be concluded that higher Cu and Co stress tolerance in Yan66 is attributed to more accumulation of the metabolites including phenolics and amino acids.

Zinc alleviates cadmium toxicity by modulating photosynthesis, ROS homeostasis, and cation flux kinetics in rice.

Understanding of cadmium (Cd) uptake mechanism and development of lower Cd crop genotypes are crucial for combating its phytotoxicity and meeting 70% increase in food demand by 2050. Bio-accumulation of Cd continuously challenges quality of life specifically in regions without adequate environmental planning. Here, we investigated the mechanisms operating in Cd tolerance of two rice genotypes (Heizhan-43 and Yinni-801). Damage to chlorophyll contents and PSII, histochemical staining and quantification of reactive oxygen species (ROS), cell viability and osmolyte accumulation were studied to decipher the interactions between Cd and zinc (Zn) by applying two Cd and two Zn levels (alone as well as combined). Cd2+ and Ca2+ fluxes were also measured by employing sole Cd100 (100 µmol L-1) and Zn50 (50 µmol L-1), and their combination with microelectrode ion flux estimation (MIFE) technique. Cd toxicity substantially reduced chlorophyll contents and maximal photochemical efficiency (Fv/Fm) compared to control plants. Zn supplementation reverted the Cd-induced toxicity by augmenting osmoprotectants and interfering with ROS homeostasis under combined treatments, particularly in Yinni-801 genotype. Fluorescence microscopy indicated a unique pattern of live and dead root cells, depicting more damage with Cd10, Cd15 and Cd15+Zn50. Our results confer that Cd2+ impairs the uptake of Ca2+ whereas, Zn not only competes with Cd2+ but also Ca2+, thereby modifying ion homeostasis in rice plants. This study suggests that exogenous application of Zn is beneficial for rice plants in ameliorating Cd toxicity in a genotype and dose dependent manner by minimizing ROS generation and suppressing collective oxidative damage. The observations confer that Yinni-801 performed better than Heizhan-43 genotype mainly under combined Zn treatments with low-Cd, presenting Zn fortification as a solution to increase rice production.

iTRAQ-based comparative proteomic analysis reveals high temperature accelerated leaf senescence of tobacco (Nicotiana tabacum L.) during flue-curing.

Tobacco (Nicotiana tabacum) is extensively cultivated all over the world for its economic value. During curing and storage, senescence occurs, which is associated with physiological and biochemical changes in postharvest plant organs. However, the molecular mechanisms involved in accelerated senescence due to high temperatures in tobacco leaves during curing need further elaboration. We studied molecular mechanisms of senescence in tobacco leaves exposed to high temperature during curing (Fresh, 38 °C and 42 °C), revealed by isobaric tags for relative and absolute quantification (iTRAQ) for the proteomic profiles of cultivar Bi'na1. In total, 8903 proteins were identified, and 2034 (1150 up-regulated and 1074 down-regulated) differentially abundant proteins (DAPs) were obtained from tobacco leaf samples. These DAPs were mainly involved in posttranslational modification, protein turnover, energy production and conversion. Sugar- and energy-related metabolic biological processes and pathways might be critical regulators of tobacco leaves exposed to high temperature during senescence. High-temperature stress accelerated tobacco leaf senescence mainly by down-regulating photosynthesis-related pathways and degrading cellular constituents to maintain cell viability and nutrient recycling. Our findings provide a valuable inventory of novel proteins involved in senescence physiology and elucidate the protein regulatory network in postharvest organs exposed to high temperatures during flue-curing.

Resemblance and Difference of Seedling Metabolic and Transporter Gene Expression in High Tolerance Wheat and Barley Cultivars in Response to Salinity Stress.

To elucidate inter-specific similarity and difference of tolerance mechanism against salinity stress between wheat and barley, high tolerant wheat cv. Suntop and sensitive cv. Sunmate and tolerant barley cv. CM72 were hydroponically grown in a greenhouse with 100 mM NaCl. Glutathione, secondary metabolites, and genes associated with Na+ transport, defense, and detoxification were examined to discriminate the species/cultivar difference in response to salinity stress. Suntop and CM72 displayed damage to a lesser extent than in Sunmate. Compared to Sunmate, both Suntop and CM72 recorded lower electrolyte leakage and reactive oxygen species (ROS) production, higher leaf relative water content, and higher activity of PAL (phenylalanine ammonia-lyase), CAD (cinnamyl alcohol dehydrogenase), PPO (polyphenol oxidase), SKDH (shikimate dehydrogenase), and more abundance of their mRNA under salinity stress. The expression of HKT1, HKT2, salt overly sensitive (SOS)1, AKT1, and NHX1 was upregulated in CM72 and Suntop, while downregulated in Sunmate. The transcription factor WRKY 10 was significantly induced in Suntop but suppressed in CM72 and Sunmate. Higher oxidized glutathione (GSSG) content was accumulated in cv. CM72 and Sunmate, but increased glutathione (GSH) content and the ratio of GSH/GSSG were observed in leaves and roots of Suntop under salinity stress. In conclusion, glutathione homeostasis and upregulation of the TaWRKY10 transcription factor played a more important role in wheat salt-tolerant cv. Suntop, which was different from barley cv. CM72 tolerance to salinity stress. This new finding could help in developing salinity tolerance in wheat and barley cultivars.

Comparative Proteomic Analysis by iTRAQ Reveals that Plastid Pigment Metabolism Contributes to Leaf Color Changes in Tobacco (Nicotiana tabacum) during Curing.

Tobacco (Nicotiana tabacum), is a world's major non-food agricultural crop widely cultivated for its economic value. Among several color change associated biological processes, plastid pigment metabolism is of trivial importance in postharvest plant organs during curing and storage. However, the molecular mechanisms involved in carotenoid and chlorophyll metabolism, as well as color change in tobacco leaves during curing, need further elaboration. Here, proteomic analysis at different curing stages (0 h, 48 h, 72 h) was performed in tobacco cv. Bi'na1 with an aim to investigate the molecular mechanisms of pigment metabolism in tobacco leaves as revealed by the iTRAQ proteomic approach. Our results displayed significant differences in leaf color parameters and ultrastructural fingerprints that indicate an acceleration of chloroplast disintegration and promotion of pigment degradation in tobacco leaves due to curing. In total, 5931 proteins were identified, of which 923 (450 up-regulated, 452 down-regulated, and 21 common) differentially expressed proteins (DEPs) were obtained from tobacco leaves. To elucidate the molecular mechanisms of pigment metabolism and color change, 19 DEPs involved in carotenoid metabolism and 12 DEPs related to chlorophyll metabolism were screened. The results exhibited the complex regulation of DEPs in carotenoid metabolism, a negative regulation in chlorophyll biosynthesis, and a positive regulation in chlorophyll breakdown, which delayed the degradation of xanthophylls and accelerated the breakdown of chlorophylls, promoting the formation of yellow color during curing. Particularly, the up-regulation of the chlorophyllase-1-like isoform X2 was the key protein regulatory mechanism responsible for chlorophyll metabolism and color change. The expression pattern of 8 genes was consistent with the iTRAQ data. These results not only provide new insights into pigment metabolism and color change underlying the postharvest physiological regulatory networks in plants, but also a broader perspective, which prompts us to pay attention to further screen key proteins in tobacco leaves during curing.