Drought stress-induced physiological mechanisms, signaling pathways and molecular response of chloroplasts in common vegetable crops.

Drought stress is one of the most adverse abiotic stresses that hinder plants' growth and productivity, threatening sustainable crop production. It impairs normal growth, disturbs water relations and reduces water-use efficiency in plants. However, plants have evolved many physiological and biochemical responses at the cellular and organism levels, in order to cope with drought stress. Photosynthesis, which is considered one of the most crucial biological processes for survival of plants, is greatly affected by drought stress. A gradual decrease in CO2 assimilation rates, reduced leaf size, stem extension and root proliferation under drought stress, disturbs plant water relations, reducing water-use efficiency, disrupts photosynthetic pigments and reduces the gas exchange affecting the plants adversely. In such conditions, the chloroplast, organelle responsible for photosynthesis, is found to counteract the ill effects of drought stress by its critical involvement as a sensor of changes occurring in the environment, as the first process that drought stress affects is photosynthesis. Beside photosynthesis, chloroplasts carry out primary metabolic functions such as the biosynthesis of starch, amino acids, lipids, and tetrapyroles, and play a central role in the assimilation of nitrogen and sulfur. Because the chloroplasts are central organelles where the photosynthetic reactions take place, modifications in their physiology and protein pools are expected in response to the drought stress-induced variations in leaf gas exchanges and the accumulation of ROS. Higher expression levels of various transcription factors and other proteins including heat shock-related protein, LEA proteins seem to be regulating the heat tolerance mechanisms. However, several aspects of plastid alterations, following a water deficit environment are still poorly characterized. Since plants adapt to various stress tolerance mechanisms to respond to drought stress, understanding mechanisms of drought stress tolerance in plants will lead toward the development of drought tolerance in crop plants. This review throws light on major droughts stress-induced molecular/physiological mechanisms in response to severe and prolonged drought stress and addresses the molecular response of chloroplasts in common vegetable crops. It further highlights research gaps, identifying unexplored domains and suggesting recommendations for future investigations.

Ethylene regulates sulfur acquisition by regulating the expression of sulfate transporter genes in oilseed rape.

To manage nutrient deficiencies, plants develop both morphological and physiological responses. The studies on the regulation of these responses are limited; however, certain hormones and signaling components have been largely implicated. Several studies depicted ethylene as a regulator of the response of some nutrient deficiencies like iron, phosphorous and potassium. The present study focused on the response of sulfur in the presence and absence of ethylene. The experiments were performed in hydroponic nutrient media, using oilseed rape grown with or without sulfur deficiency and ethylene treatments for 10 days. The ACC oxidase and ACC synthase were observed significantly reduced in sulfur-deficient plants treated with ethylene compared to control. The biomass and photosynthetic parameters, including the expression of multicomplex thylakoidal proteins showed a significant increase in sulfur deficient plants supplemented with ethylene. The enzymes related to sulfur regulation such as sulfate adenyltransferase, glutamine synthetase and O-acetylserine (thiol)lyase also showed similar results as shown by the morphological data. The relative expression of the sulfur transporter genes BnSultr1, 1, BnSultr1, 2, BnSultr4,1, BnSultr 4,2, ATP sulfurylase and OASTL increased in sulfur-deficient plants, whereas their expression decreased when ethylene was given to the plants. Fe and S nutritional correlations are already known; therefore, Fe-transporters like IRT1 and FRO1 were also evaluated, and similar results as for the sulfur transporter genes were observed. The overall results indicated that ethylene regulates sulfur acquisition by regulating the expression of sulfur transporter genes in oilseed rape (Brassica napus).

Comparative physiological and proteomic analysis deciphering tolerance and homeostatic signaling pathways in chrysanthemum under drought stress.

Drought is increasing prevalently, mostly due to global warming, and harmful effects associated with drought stress include a reduction in the developmental phases of the plant life cycle. Drought stress affects vital metabolic processes in plants such as transpiration, photosynthesis and respiration. The other physiological and cellular processes like protein denaturation and aggregation are also affected by drought. Drought stress severely affects the floral industry by reducing the yield of flowers and among them is chrysanthemum (Dendranthema grandiflorum). In this study, we determined the critical signaling pathways, tolerance mechanism and homeostatic maintenance to drought stress in chrysanthemum. We compared the proteome of chrysanthemum leaves under drought stress. Among 250 proteins on 2DE gels, 30 protein spots were differentially expressed. These proteins were involved in major signaling pathways including, stress response, flower development and other secondary metabolism like physiological transport, circadian rhythm, gene regulation, DNA synthesis and protein ubiquitination. A reduction in a biomass, flower development, photosynthesis, transpiration, stomatal conductance, PSII yield and stomatal index was also observed in our results. Moreover, the stress markers and leaf water potential were also analyzed to depict the level of stress tolerance in chrysanthemum. Our data suggested that chrysanthemum plants developed reactive oxygen species and revealed signaling pathways to cope with drought stress. These results, thus, provide crucial information about how chrysanthemum plants respond to drought stress to maintain homeostasis.

Target-Based Physiological Modulations and Chloroplast Proteome Reveals a Drought Resilient Rootstock in Okra (Abelmoschus esculentus) Genotypes.

As climate changes increase, drought stress is becoming a problem for all major horticultural crops; among them is okra (Abelmoschus esculentus). Despite its superior resilience to heat stress and high nutritional content, it is still underutilized in contrast to other vegetable crops. Moreover, the drought-resistant and drought-sensitive genotypes of okra are also not well known and require further exploration to improve their productivity. To investigate this in more detail, we performed comparative physiological and large-scale chloroplast proteomics on drought-stressed genotypes of okra. We evaluated four major genotypes of okra, viz., NS7774, NS7772, Green Gold, and OH3312 for drought resilient rootstock. The physiological modulations demonstrated a significant change by 50-76% in biomass, net-photosynthetic machinery, water transport, and absorption both in early and late stages of drought stress compared to well-watered crops in all genotypes. Maximum oxidative damage due to drought stress was observed for the genotypes NS7772, Green Gold and OH3312 as depicted by H2O2 and O2- determination. Greater oxidative stress was correlated to lesser antioxidant activity and expression of antioxidant enzymes, such as catalase and ascorbate peroxidase under stress in okra genotypes. The overall photosynthetic pigments, such as total chlorophyll, and total carotenoid content, were also decreased, and stomatal guard cells were disrupted and appeared closed compared to the control for the above three mentioned genotypes, except NS7774. A subsequent tissue-specific proteome analysis of chloroplasts and thylakoids analyzed by BN-PAGE (blue native polyacrylamide gel electrophoresis) revealed either over or under expression of specific proteins, such as ATPase, PSI, PSII core dimer, PSII monomer and ATP synthase. The expression of multiprotein complex proteins, including PSII-core dimer and PSII-core monomer, was slightly higher for the genotype NS7774 when compared to three other genotypes for both 5 and 10 days of drought stress. Further identification of specific proteins obtained in second dimension BN-PAGE provided descriptive detail of seven proteins involved in drought resistance across all genotypes. The identified proteins are majorly involved in photosynthesis under drought stress, suggesting NS7774 as a drought tolerant genotype. Further, the proteomic results were confirmed using Immunoblot by selecting specific protein such as PsaA. Overall, from our physiological modulations and chloroplast proteomics in all genotypes, we summarized NS7774 as a resilient rootstock and the other three genotypes (NS7772, OH3312, and Green Gold) as sensitive ones.

Proteomic Analysis Reveals the Dynamic Role of Silicon in Alleviation of Hyperhydricity in Carnation Grown In Vitro.

The present study depicted the role of silicon in limiting the hyperhydricity in shoot cultures of carnation through proteomic analysis. Four-week-old healthy shoot cultures of carnation "Purple Beauty" were sub-cultured on Murashige and Skoog medium followed with four treatments, viz. control (-Si/-Hyperhydricity), hyperhydric with no silicon treatment (-Si/+Hyperhydricity), hyperhydric with silicon treatment (+Si/+Hyperhydricity), and only silicon treated with no hyperhydricity (+Si/-Hyperhydricity). Comparing to control morphological features of hyperhydric carnations showed significantly fragile, bushy and lustrous leaf nature, while Si supply restored these effects. Proteomic investigation revealed that approximately seventy protein spots were differentially expressed under Si and/or hyperhydric treatments and were either up- or downregulated in abundance depending on their functions. Most of the identified protein spots were related to stress responses, photosynthesis, and signal transduction. Proteomic results were further confirmed through immunoblots by selecting specific proteins such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), PsaA, and PsbA. Moreover, protein-protein interaction was also performed on differentially expressed protein spots using specific bioinformatic tools. In addition, stress markers were analyzed by histochemical localization of hydrogen peroxide (H2O2) and singlet oxygen (O21-). In addition, the ultrastructure of chloroplasts in hyperhydric leaves significantly resulted in inefficiency of thylakoid lamella with the loss of grana but were recovered in silicon supplemented leaves. The proteomic study together with physiological analysis indicated that Si has a substantial role in upholding the hyperhydricity in in vitro grown carnation shoot cultures.

Leaf Physiological and Proteomic Analysis to Elucidate Silicon Induced Adaptive Response under Salt Stress in Rosa hybrida 'Rock Fire'.

Beneficial effects of silicon (Si) on growth and development have been witnessed in several plants. Nevertheless, studies on roses are merely reported. Therefore, the present investigation was carried out to illustrate the impact of Si on photosynthesis, antioxidant defense and leaf proteome of rose under salinity stress. In vitro-grown, acclimatized Rosa hybrida 'Rock Fire' were hydroponically treated with four treatments, such as control, Si (1.8 mM), NaCl (50 mM), and Si+NaCl. After 15 days, the consequences of salinity stress and the response of Si addition were analyzed. Scorching of leaf edges and stomatal damages occurred due to salt stress was ameliorated under Si supplementation. Similarly, reduction of gas exchange, photosynthetic pigments, higher lipid peroxidation rate, and accumulation of reactive oxygen species under salinity stress were mitigated in Si treatment. Lesser oxidative stress observed was correlated with the enhanced activity and expression of antioxidant enzymes, such as superoxide dismutase, catalase, and ascorbate peroxidase in Si+NaCl treatment. Importantly, sodium transportation was synergistically restricted with the stimulated counter-uptake of potassium in Si+NaCl treatment. Furthermore, two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) results showed that out of 40 identified proteins, on comparison with control 34 proteins were down-accumulated and six proteins were up-accumulated due to salinity stress. Meanwhile, addition of Si with NaCl treatment enhanced the abundance of 30 proteins and downregulated five proteins. Differentially-expressed proteins were functionally classified into six groups, such as photosynthesis (22%), carbohydrate/energy metabolism (20%), transcription/translation (20%), stress/redox homeostasis (12%), ion binding (13%), and ubiquitination (8%). Hence, the findings reported in this work could facilitate a deeper understanding on potential mechanism(s) adapted by rose due to the exogenous Si supplementation during the salinity stress.

Genotypic Variation under Fe Deficiency Results in Rapid Changes in Protein Expressions and Genes Involved in Fe Metabolism and Antioxidant Mechanisms in Tomato Seedlings (Solanum lycopersicum L.).

To investigate Fe deficiency tolerance in tomato cultivars, quantification of proteins and genes involved in Fe metabolism and antioxidant mechanisms were performed in "Roggusanmaru" and "Super Doterang". Fe deficiency (Moderate, low and -Fe) significantly decreased the biomass, total, and apoplastic Fe concentration of "Roggusanmaru", while a slight variation was observed in "Super Doterang" cultivar. The quantity of important photosynthetic pigments such as total chlorophyll and carotenoid contents significantly decreased in "Roggusanmaru" than "Super Doterang" cultivar. The total protein profile in leaves and roots determines that "Super Doterang" exhibited an optimal tolerance to Fe deficiency compared to "Roggusanmaru" cultivar. A reduction in expression of PSI (photosystem I), PSII (photosystem II) super-complexes and related thylakoid protein contents were detected in "Roggusanmaru" than "Super Doterang" cultivar. Moreover, the relative gene expression of SlPSI and SlPSII were well maintained in "Super Doterang" than "Roggusanmaru" cultivar. The relative expression of genes involved in Fe-transport (SlIRT1 and SlIRT2) and Fe(III) chelates reductase oxidase (SlFRO1) were relatively reduced in "Roggusanmaru", while increased in "Super Doterang" cultivar under Fe deficient conditions. The H⁺-ATPase relative gene expression (SlAHA1) in roots were maintained in "Super Doterang" compared to "Roggusanmaru". Furthermore, the gene expressions involved in antioxidant defense mechanisms (SlSOD, SlAPX and SlCAT) in leaves and roots showed that these genes were highly increased in "Super Doterang", whereas decreased in "Roggusanmaru" cultivar under Fe deficiency. The present study suggested that "Super Doterang" is better tomato cultivar than "Roggusanmaru" for calcareous soils.

Morphogenesis, Flowering, and Gene Expression of Dendranthema grandiflorum in Response to Shift in Light Quality of Night Interruption.

The impact of shifts in the spectral quality of light on morphogenesis, flowering, and photoperiodic gene expression during exposure to light quality of night interruption (NI) was investigated in Dendranthema grandiflorum. The circadian rhythms of plants grown in a closed walk-in growth chamber were interrupted at night for a total of 4 h, using light-emitting diodes with an intensity of 10 µmol·m⁻²·s⁻¹ PPF. The light quality of the NI was shifted from one wavelength to another after the first 2 h. Light treatments consisting of all possible pairings of blue (B), red (R), far-red (Fr), and white (W) light were tested. Plants in the NI treatment groups exposed to Fr light grew larger than plants in other treatment groups. Of plants in NI treatment groups, those in the NI-WB treatment grew the least. In addition, the impact of shifts in the light quality of NI on leaf expansion was greater in treatment groups exposed to a combination of either B and R or R and W light, regardless of their order of supply. Flowering was observed in the NI-RB, NI-FrR, NI-BFr, NI-FrB, NI-WB, NI-FrW, NI-WFr, NI-WR, and SD (short-day) treatments, and was especially promoted in the NI-BFr and NI-FrB treatments. In a combined shift treatment of B and R or B and W light, the NI concluded with B light (NI-RB and NI-WB) treatment induced flowering. The transcriptional factors phyA, cry1 and FTL (FLOWERING LOCUS T) were positively affected, while phyB and AFT were negatively affected. In conclusion, morphogenesis, flowering, and transcriptional factors were all significantly affected either positively or negatively by shifts in the light quality of NI. The light quality of the first 2 h of NI affected neither morphogenesis nor flowering, while the light quality of the last 2 h of NI significantly affected both morphogenesis and flowering.

Involvement of sulphur nutrition in modulating iron deficiency responses in photosynthetic organelles of oilseed rape (Brassica napus L.).

The aim of this study was to characterize the roles of sulphur (S) nutrition in modulating the responses to iron (Fe) deficiency in the photosynthetic organelles of oilseed rape. Eight-week-old plants grown hydroponically were fed with S-sufficient or S-deprived solution with or without Fe(III)-EDTA. Responses to four S and Fe combined treatments were analysed after 5 and 10 days. Leaf chlorosis was generated by either S- or Fe-deprivation, with a decrease in chlorophyll and carotenoid content. These negative effects were more severe in the absence of S. The expression of Fe²âº transporter (IRT1) and Fe(III) chelate reductase (FRO1) gene was induced for the first 5 days and decreased after 10 days in the S-deprived roots, but largely improved by S supply even in the absence of Fe. Lack of ferric chelate reducing activity in the Fe-deprived roots in the absence of S was largely improved by S supply. The activity of photosynthesis, RuBisCO and sucrose synthase was closely related to S status in leaves. Electron microscopic observation showed that the Fe-deficiency in the absence of S greatly resulted in a severe disorganisation of thylakoid lamellae with loss of grana. However, these impacts of Fe-deficiency were largely restored in the presence of S. The present results indicate that S nutrition has significant role in ameliorating the damages in photosynthetic apparatus caused by Fe-deficiency.

Transcriptional and physiological changes in relation to Fe uptake under conditions of Fe-deficiency and Cd-toxicity in roots of Vigna radiata L.

We investigated transcriptional and physiological changes in relation to Fe transport and uptake under various conditions of iron (Fe)-deficiency and cadmium (Cd) toxicity. Responses to four such Fe/Cd conditions were evaluated, revealing that oxidative stress was generated in the presence of Cd, followed by a decrease in Fe and an increase in Cd concentrations in green gram (Vigna radiata) material, whereas supplementation with Fe had a protective effect against Cd toxicity. The involvement of enzymes in Fe-uptake for the formation of root-nodules was largely reduced in the presence of Cd toxicity, a condition recovered by Fe-supplementation. Insufficient ferric chelate reducing activity in Fe-deprived roots in the presence of Cd was also largely improved by Fe supplementation. The expression of Fe(2+) transporters (IRT1, IRT2, and IRT3), Fe(III) chelate reductase (FRO1-FRO8) and phytochelatin synthase (PCS1, PCS2 and PCS3) genes was up regulated for the first 5 days and decreased after 10 days in roots in the presence of Cd toxicity, but was sustained with Fe-supplementation. Additionally, root biomass was fully recovered in plants in the presence of Fe during Cd toxicity. Our results suggest that Fe-status plays a significant role in ameliorating the damage in Fe transport for chelation and its uptake caused by Cd toxicity. This supports the hypothesis that leguminous plants, particularly those that are sensitive to Fe such as green gram, can cope to some extent with Cd toxicity by improving the uptake and transport of Fe.

Influence of green, red and blue light emitting diodes on multiprotein complex proteins and photosynthetic activity under different light intensities in lettuce leaves (Lactuca sativa L.).

The objective of this study was to investigate the response of light emitting diodes (LEDs) at different light intensities (70 and 80 for green LEDs, 88 and 238 for red LEDs and 80 and 238 µmol m-2 s-1 for blue LEDs) at three wavelengths in lettuce leaves. Lettuce leaves were exposed to (522 nm), red (639 nm) and blue (470 nm) LEDs of different light intensities. Thylakoid multiprotein complex proteins and photosynthetic metabolism were then investigated. Biomass and photosynthetic parameters increased with an increasing light intensity under blue LED illumination and decreased when illuminated with red and green LEDs with decreased light intensity. The expression of multiprotein complex proteins including PSII-core dimer and PSII-core monomer using blue LEDs illumination was higher at higher light intensity (238 µmol m-2 s-1) and was lowered with decreased light intensity (70-80 µmol m-2 s-1). The responses of chloroplast sub-compartment proteins, including those active in stomatal opening and closing, and leaf physiological responses at different light intensities, indicated induced growth enhancement upon illumination with blue LEDs. High intensity blue LEDs promote plant growth by controlling the integrity of chloroplast proteins that optimize photosynthetic performance in the natural environment.

Physiological and proteomic analysis in chloroplasts of Solanum lycopersicum L. under silicon efficiency and salinity stress.

Tomato plants often grow in saline environments in Mediterranean countries where salt accumulation in the soil is a major abiotic stress that limits its productivity. However, silicon (Si) supplementation has been reported to improve tolerance against several forms of abiotic stress. The primary aim of our study was to investigate, using comparative physiological and proteomic approaches, salinity stress in chloroplasts of tomato under silicon supplementation. Tomato seedlings (Solanum lycopersicum L.) were grown in nutrient media in the presence or absence of NaCl and supplemented with silicon for 5 days. Salinity stress caused oxidative damage, followed by a decrease in silicon concentrations in the leaves of the tomato plants. However, supplementation with silicon had an overall protective effect against this stress. The major physiological parameters measured in our studies including total chlorophyll and carotenoid content were largely decreased under salinity stress, but were recovered in the presence of silicon. Insufficient levels of net-photosynthesis, transpiration and stomatal conductance were also largely improved by silicon supplementation. Proteomics analysis of chloroplasts analyzed by 2D-BN-PAGE (second-dimensional blue native polyacrylamide-gel electrophoresis) revealed a high sensitivity of multiprotein complex proteins (MCPs) such as photosystems I (PSI) and II (PSII) to the presence of saline. A significant reduction in cytochrome b6/f and the ATP-synthase complex was also alleviated by silicon during salinity stress, while the complex forms of light harvesting complex trimers and monomers (LHCs) were rapidly up-regulated. Our results suggest that silicon plays an important role in moderating damage to chloroplasts and their metabolism in saline environments. We therefore hypothesize that tomato plants have a greater capacity for tolerating saline stress through the improvement of photosynthetic metabolism and chloroplast proteome expression after silicon supplementation.

Cadmium toxicity induced alterations in the root proteome of green gram in contrasting response towards iron supplement.

Cadmium signifies a severe threat to crop productivity and green gram is a notably iron sensitive plant which shows considerable variation towards cadmium stress. A gel-based proteomics analysis was performed with the roots of green gram exposed to iron and cadmium combined treatments. The resulting data show that twenty three proteins were down-regulated in iron-deprived roots either in the absence (-Fe/-Cd) or presence (-Fe/+Cd) of cadmium. These down-regulated proteins were however well expressed in roots under iron sufficient conditions, even in the presence of cadmium (+Fe/+Cd). The functional classification of these proteins determined that 21% of the proteins are associated with nutrient metabolism. The other proteins in higher quantities are involved in either transcription or translation regulation, and the rest are involved in biosynthesis metabolism, antioxidant pathways, molecular chaperones and stress response. On the other hand, several protein spots were also absent in roots in response to iron deprivation either in absence (-Fe/-Cd) or presence (-Fe/+Cd) of cadmium but were well expressed in the presence of iron (+Fe/+Cd). Results suggest that green gram plants exposed to cadmium stress are able to change the nutrient metabolic balance in roots, but in the mean time regulate cadmium toxicity through iron supplements.

Nanotechnology, a frontier in agricultural science, a novel approach in abiotic stress management and convergence with new age medicine-A review.

Climate change imposes various environmental stresses which substantially impact plant growth and productivity. Salinity, drought, temperature extremes, heavy metals, and nutritional imbalances are among several abiotic stresses contributing to high yield losses of crops in various parts of the world, resulting in food insecurity. Many interesting strategies are being researched in the attempt to improve plants' environmental stress tolerance. These include the application of nanoparticles, which have been found to improve plant function under stress situations. Nanotechnology will be a key driver in the upcoming agri-tech and pharmaceutical revolution, which promises a more sustainable, efficient, and resilient agricultural and medical system Nano-fertilizers can help plants utilise nutrients more efficiently by releasing nutrients slowly and sustainably. Plant physiology and nanomaterial features (such as size, shape, and charge) are important aspects influencing the impact on plant growth. Here, we discussed the most promising new opportunities and methodologies for using nanotechnology to increase the efficiency of critical inputs for crop agriculture, as well as to better manage biotic and abiotic stress. Potential development and implementation challenges are highlighted, emphasising the importance of designing suggested nanotechnologies using a systems approach. Finally, the strengths, flaws, possibilities, and risks of nanotechnology are assessed and analysed in order to present a comprehensive and clear picture of the nanotechnology potentials, as well as future paths for nano-based agri-food applications towards sustainability. Future research directions have been established in order to support research towards the long-term development of nano-enabled agriculture and evolution of pharmaceutical industry.

Circadian-based approach for improving physiological, phytochemical and chloroplast proteome in Spinacia oleracea under salinity stress and light emitting diodes.

Salt stress is a recognized annihilating abiotic stress that has a significant impact on agricultural and horticulture crop productivity. Plant development faces three distinct dangers as a result of salt stress: oxidative stress, osmotic stress, and ionic toxicity. It has been shown that plants can forecast diurnal patterns using the circadian clock; moreover, they can manage their defensive mechanism for the detoxification of reactive oxygen species (ROS). Circadian rhythmicity in gene expression assembles transcription and translation feedback networks to govern plant shape, physiology, cellular and molecular activities. Both external and internal variables influence the systemic rhythm via input routes. The Malav Jyoti (MJ) and Delhi Green (DG) genotypes of spinach (Spinacia oleracea) were grown in the plant growth chamber. The chamber had an optimized temperature of 25 °C and humidity of 65% containing light emitting diode (LED) having Red: Blue: white (one side) and White fluorescent (other side) under salinity stress. The samples were collected on the basis of 4 h intervals of circadian hours (0 h, 4 h, 8 h and 12 h) during Day-10 and Day-20 of salt treatments. Under salt stress, the circadian and light-emitting diode-based strategy had a substantial influence on spinach's anti-oxidative responses, stomatal movement, CO2 assimilation, PS-I and II efficiency, phytochrome pigment efficiency, and photosynthesis. Based on the findings of the free radical scavenging enzyme tests, the photoperiodic hours for the proteome analysis were set to 11 am and 3 pm on Day-20. When compared to white fluorescent, this study found that LED has the capacity to influence the entrainment cues of the circadian clock in the cultivation of salt-sensitive spinach genotypes. According to our findings, changing the cellular scavenging mechanism and chloroplast proteome has increased the survival rate of spinach genotypes under LED when compared to white fluorescent.

S-deficiency responsive accumulation of amino acids is mainly due to hydrolysis of the previously synthesized proteins - not to de novo synthesis in Brassica napus.

To characterize the mechanisms of amino acid accumulation under sulphur (S)-deficiency and its physiological significance in Brassica napus, stable isotopes (15) N and (34) S were employed. The plants were exposed for 9 days to S-deficient conditions (0.05 mM vs 1.5 mM sulphate). After 9 days of S-deficiency, leaf-osmotic potential and total chlorophyll content significantly decreased. S uptake decreased by 94%, whereas N uptake and biomass were not significantly changed. Using (15) N and (34) S labelling, de novo synthesis of amino acids and proteins derived from newly absorbed NO(3) (-) and SO(4) (2) (-) and the content of N and S in the previously synthesized amino acids and proteins were quantified. At the whole plant level, S-deficiency increased the pool of amino acids but resulted in strong decrease of incorporation of newly absorbed NO(3) (-) and SO(4) (2) (-) into amino acids by 22.2 and 76.6%, respectively, compared to the controls. Total amount of N and S incorporated into proteins also decreased by 28.8 and 62.1%, respectively. The levels of (14) N- and (32) S-proteins (previously synthesized proteins) strongly decreased, mainly in mature leaves. The data thus indicate that amino acid accumulation under short-term S-deficiency results from the degradation of previously synthesized proteins rather than from de novo synthesis.

Grafting enhances drought tolerance by regulating and mobilizing proteome, transcriptome and molecular physiology in okra genotypes.

Drought stress poses a serious concern to the growth, development, and quality of the okra crop due to factors including decreased yield, inadequate development of dietary fibre, increased mite infestation, and decreased seed viability. Grafting is one of the strategies that have been developed to increase the drought stress tolerance of crops. We conducted proteomics, transcriptomics and integrated it with molecular physiology to assess the response of sensitive okra genotypes; NS7772 (G1), Green gold (G2) and OH3312 (G3) (scion) grafted to NS7774 (rootstock). In our studies we observed that sensitive okra genotypes grafted to tolerant genotypes mitigated the deleterious effects of drought stress through an increase in physiochemical parameters, and lowered reactive oxygen species. A comparative proteomic analysis showed a stress responsive proteins related to Photosynthesis, energy and metabolism, defence response, protein and nucleic acid biosynthesis. A proteomic investigation demonstrated that scions grafted onto okra rootstocks increased more photosynthesis-related proteins during drought stress, indicating an increase in photosynthetic activity when plants were subjected to drought stress. Furthermore, transcriptome of RD2, PP2C, HAT22, WRKY and DREB increased significantly, specifically for grafted NS7772 genotype. Furthermore, our study also indicated that grafting improved the yield components such as number of pods and seeds per plant, maximum fruit diameter, and maximum plant height in all genotypes which directly contributed towards their high resistance towards drought stress.

Recent trends and advances of RNA interference (RNAi) to improve agricultural crops and enhance their resilience to biotic and abiotic stresses.

Over the last two decades, significant advances have been made using genetic engineering technology to modify genes from various exotic origins and introduce them into plants to induce favorable traits. RNA interference (RNAi) was discovered earlier as a natural process for controlling the expression of genes across all higher species. It aims to enhance precision and accuracy in pest/pathogen resistance, quality improvement, and manipulating the architecture of plants. However, it existed as a widely used technique recently. RNAi technologies could well be used to down-regulate any genes' expression without disrupting the expression of other genes. The use of RNA interference to silence genes in various organisms has become the preferred method for studying gene functions. The establishment of new approaches and applications for enhancing desirable characters is essential in crops by gene suppression and the refinement of knowledge of endogenous RNAi mechanisms in plants. RNAi technology in recent years has become an important and choicest method for controlling insects, pests, pathogens, and abiotic stresses like drought, salinity, and temperature. Although there are certain drawbacks in efficiency of this technology such as gene candidate selection, stability of trigger molecule, choice of target species and crops. Nevertheless, from past decade several target genes has been identified in numerous crops for their improvement towards biotic and abiotic stresses. The current review is aimed to emphasize the research done on crops under biotic and abiotic stress using RNAi technology. The review also highlights the gene regulatory pathways/gene silencing, RNA interference, RNAi knockdown, RNAi induced biotic and abiotic resistance and advancements in the understanding of RNAi technology and the functionality of various components of the RNAi machinery in crops for their improvement.

Mycorrhizal colonization alleviates drought-induced oxidative damage and lignification in the leaves of drought-stressed perennial ryegrass (Lolium perenne).

To investigate the effects of arbuscular mycorrhizal (AM) fungus Glomus intraradices on antioxidative activity and lignification under drought-stressed (DS) conditions, the enzyme activities, growth, lignin contents and some stress symptomatic parameters as affected by drought treatment were compared in AM colonized or non-colonized (non-AM) perennial ryegrass plants for 28 days. Drought significantly decreased leaf water potential (Ψ(w) ), photosynthesis rate and biomass. The negative impact of drought on these parameters was much highly relived in AM plants compared to non-AM ones. Drought increased H2O2, lipid peroxidation, phenol and lignin levels, with significantly higher in non-AM relative to AM plants at day 28 after drought treatment. The enhanced activation of guaiacol peroxidase (GPOX), coniferyl alcohol peroxidase (CPOX), syringaldazine peroxidase (SPOX) and polyphenol oxidase (PPO) was closely related with the decrease in Ψ(w) in both AM and non-AM plants. GPOX, CPOX, SPOX and PPO highly activated with a concomitant increase in lipid peroxidation and lignin as the Ψ(w) decreased below -2.11 MPa in non-AM plants, while much less activated by maintaining Ψ(w) ≥-1.15 MPa in AM ones. These results indicate that AM symbiosis plays an integrative role in drought stress tolerance by alleviating oxidative damage and lignification, which in turn mitigate the reduction of forage growth and digestibility under DS conditions.

Mycorrhizal colonisation and P-supplement effects on N uptake and N assimilation in perennial ryegrass under well-watered and drought-stressed conditions.

To compare the effect of arbuscular mycorrhiza (AM) and P-supplement on N uptake and N assimilation under well-watered or drought-stressed conditions, Glomus intraradices-colonised, P-supplemented non-mycorrhizal (P) and non-mycorrhizal (control) plants of Lolium perenne were exposed to 12 days of water treatment. Leaf water potential (Ψ (w)), photosynthetic ability, and N and P nutritional status were measured at the beginning (day 0) and end (day 12) of water treatment. N absorption, amino acid and protein synthesis were quantified using the isotopic tracer (15)N at day 12. Under well-watered conditions, growth response and physiological parameters were similar in AM and P plants, as compared to controls. Drought (10% water) significantly decreased these parameters in all three treatments. As compared to control plants, the negative impact of water deficit on the Ψ (w), photosynthesis, biomass, and N and P content was highly alleviated in AM plants, while only slightly improved or remained the same level in P plants. The effect of AM symbiosis on N absorption and N assimilation was greater than that of the P supplement under well-watered and drought-stressed conditions, and this effect was highly enhanced under drought-stressed conditions. At terminal drought stress on day 12, the effect of AM colonisation on de novo synthesis of amino acids and proteins was 4.4- and 4.8-fold higher than that of the P supplement. These results indicate that the AM symbiosis plays an integrative role in N nutrition by alleviating the negative impacts of drought on N or P uptake and N assimilation, whereas the efficiency of a direct P supplement is very limited under drought-stressed conditions.