Bioaccumulation efficacy and physio-morphological adaptations in response to iron and aluminium contamination of Indian camphorweed (Pluchea indica L.) using different growth substrates.

The aim of this study was to assess the removal capability of Fe/Al contamination of Indian camphorweed (Pluchea indica; hereafter, P. indica) using different growth substrates (100% sand, gardening soil, vermiculite, and zeolite). In addition, the study aimed at observing the physio-morphological adaptation strategies of P. indica under excess Fe/Al levels in a controlled greenhouse environment. After a 4-week treatment, P. indica plants under excess Fe in the 100% sand substrate exhibited signs of decay and eventually death. In contrast, the growth performances of P. indica under gardening soil substrate remained sustained even when exposed to Fe/Al stress. Under zeolite substrate, Fe in the root tissues was 23.1 and 34.7 mg g-1 DW after 1 and 4 weeks of incubation, respectively. In addition, Al in the root tissues also increased to 1.54 mg g-1 DW after 1 week and 1.59 mg g-1 DW after 4 weeks, when subjected to 20 mM Al treatment. Zeolite was observed to be a promising substrate to regulate the uptake of Fe (3.31 mg plant-1) and Al (0.51 mg plant-1) by the root tissues. The restriction of Fe and Al in the root and a low translocation to the leaf organ was indicated by a low translocation factor (< 1.0). High Fe concentrations in the root and leaf tissues negatively affected root elongation, and the net photosynthetic rate decreased by > 40% compared to positive control. Gas exchange parameters and leaf temperature were found the most sensitive to Fe/Al stress. Moreover, the limited transpiration rate under Fe/Al stress caused an increase of the leaf temperature and crop stress index. The findings suggest that P. indica grown using zeolite substrate may serve as a good model system for constructed wetlands, storing excess Al in the root tissues without any significant growth inhibition.

Alleviation of water-deficit stress in turmeric plant (Curcuma longa L.) using phosphate solubilizing rhizo-microbes inoculation.

The objective of this study was to assess the effects of phosphate solubilizing rhizo-microbes inoculants on nutrient balance, physiological adaptation, growth characteristics, and rhizome yield traits as well as curcuminoids yield at the secondary-rhizome initiation stage of turmeric plants, subsequently subjected to water-deficit (WD) stress. Phosphorus contents in the leaf tissues of Talaromyces aff. macrosporus and Burkholderia sp. (Bruk) inoculated plants peaked at 0.33 and 0.29 mg g-1 DW, respectively, under well-watered (WW) conditions; however, phosphorus contents declined when subjected to WD conditions (p ≤ 0.05). Similarly, potassium and calcium contents reached their maximum values at 5.33 and 3.47 mg g-1 DW, respectively, in Burk inoculated plants under WW conditions, which contributed to sustained rhizome fresh weight even when exposed to WD conditions (p ≤ 0.05). There was an increase in free proline content in T. aff. macrosporus and Burk inoculated plants under WD conditions, which played a crucial role in controlling leaf osmotic potential, thereby stabilizing leaf greenness and maximum quantum yield of PSII. As indicators of drought stress, there were noticeable restrictions in stomatal gas exchange parameters, including net photosynthetic rate, stomatal conductance, and transpiration rate, accompanied by an increase in leaf temperature. These changes resulted in reduced total soluble sugar levels. Interestingly, total curcuminoids and curcuminoids yield in Burk inoculated plants under WD conditions were retained, especially in relation to rhizome biomass. Burk inoculation in turmeric plants is recommended as a promising technique as it alleviates water-deficit stress, sustains rhizome biomass, and stabilizes curcuminoids yield. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-024-03922-x.

Exogenous glycine betaine alleviates water-deficit stress in Indian pennywort (Centella asiatica) under greenhouse conditions.

Centella asiatica (Indian pennywort) is a green leafy vegetable containing centelloside' (triterpenoid), a key phytochemical component in traditional medicine. Being a glycophytic species, they exhibit decline in growth performance and yield traits when subjected to water-deficit (WD) conditions. Glycine betaine (GB) is a low molecular-weight organic metabolite that plays a crucial role in abiotic stress conditions in higher plants. The objective of this study was to investigate the potential of GB in alleviating water-deficit stress (in terms of morphological and physiological responses) in two different genotypes of Indian pennywort, "Nakhon Pathom" (NP; high centelloside-yielding genotype) and "Pathum Thani" (PT; low centelloside-yielding genotype). The genotypes of Indian pennywort were propagated by stolon cutting and transplanted into plastic bags containing 2 kg of garden soil. At the flower-initiation stage (30 days after transplantation), uniform plant material was treated exogenously with 0 (control), 25, and 50 mM GB at 100 mL per plant (one-time foliar spray) and then divided into two groups, 1) well watered (WW; irrigated daily with 400 mL fresh water; 98% field capacity) and 2) water deficit (WD; withheld water for 14 days; 72% field capacity). Foliar application of GB (25 mM) significantly improved leaf osmotic potential in NP under WD conditions via osmotic adjustment by free proline and fructose. Differences in leaf temperature (Tleaf) between WD and WW in NP were maximized (+ 1.93 °C) and the gap of Tleaf was reduced in the case of 25-50 mM GB application. Similarly, crop water stress index (CWSI) in NP and PT plants under WD condition was significantly increased by 1.95- and 1.86-fold over the control, respectively; however, it was significantly decreased by exogenous GB application. Increasing Tleaf and CWSI in drought-stressed plants was closely related to stomatal closure, leading to reduced gas exchange parameters, i.e., stomatal conductance (gs), transpiration rate (E), net photosynthetic rate (Pn), and intercellular CO2 concentration (Ci), and consequently decreased plant biomass and total centelloside yield. Overall physiological, morphological, and secondary metabolite traits were enhanced in NP under WD conditions using 25 mM GB exogenous application compared with the control. The study highlights the significance of GB in Indian pennywort production under limited water irrigation (water deficit) with higher vegetable yield and phytochemical stabilization.

Iron (Fe) toxicity, uptake, translocation, and physio-morphological responses in Catharanthus roseus.

Iron (Fe) toxicity in plant species depends on the availability of Fe in the soil, uptake ability by the root system, and translocation rate to other parts of the plant. The aim of this study was to assess Fe uptake by root tissues of Catharanthus roseus, translocation rate to leaf tissues, and the impairment of plant physio-morphological characteristics. Fe uptake by the roots (~ 700 µg g-1 DW) of C. roseus was observed during the early exposure period (1 week), and translocation factor from root to shoot was fluctuated as an independent strategy. A high level of Fe content in the root tissues significantly inhibited root length and root dry weight. Under acidic pH condition, an enrichment of Fe in the shoots (~ 400 µg g-1 DW) led to increase in leaf temperature (> 2.5 °C compared to control) and crop stress index (> 0.6), resulting in stomatal closure, subsequently decreasing CO2 assimilation rate and H2O transpiration rate. An increment of CSI in Fe-stressed plants was negatively related to stomatal conductance, indicating stomatal closure with an increase in Fe in the leaf tissues. High Fe levels in the leaf tissues directly induced toxic symptoms including leaf bronzing, leaf spotting, leaf necrosis, leaf chlorosis, and leaf senescence in C. roseus plants. In summary, C. roseus was identified as a good candidate plant for Fe phytoextraction, depending on Fe bioaccumulation, therefore 50 mM Fe treatment was designated as an excess Fe to cause the growth inhibition, especially in the prolonged Fe incubation periods. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-023-01379-5.

Toxicity, physiological, and morphological alterations of Indian camphorweed (Pluchea indica) in response to excess copper.

Indian camphorweed (Pluchea indica (L.) Less.) is used as herbal tea due to the presence of volatile aromatic oils and several phytochemical compounds. The aim of this study was to assess the impact of copper (Cu) contamination on the physiology and morphology of P. indica, and the health risks associated with its consumption as tea. The cuttings of P. indica were subjected to 0 mM (control), 5 mM (low Cu), and 20 mM (excess Cu) of CuSO4 treatments for 1, 2, and 4 weeks. Thereafter, Cu contamination as well as physiological and morphological parameters were assessed. Cu accumulation was higher in the root tissues of plants (25.8 folds higher as compared to the leaves) grown under 20 mM CuSO4 for 4 weeks. This increased Cu accumulation resulted in the inhibition of root length, root fresh weight, and root dry weight. Cu concentration was found maximum (1.36 µg g-1 DW) in the leaf tissues under 20 mM Cu exposure for 4 weeks, with the highest target hazard quotient (THQ = 1.85), whereas Cu was not detected in control. Under exposure to 20 mM Cu treatment for 4 weeks, leaf greenness, maximum quantum yield of photosystem II, and photon yield of photosystem II diminished by 21.4%, 16.1%, and 22.4%, respectively, as compared to the control. Leaf temperature was increased by 2.5 °C, and the crop stress index (CSI) exceeded 0.6 when exposed to 20 mM Cu treatment for 2 and 4 weeks; however, the control had a CSI below 0.5. This led to a reduced transpiration rate and stomatal conductance. In addition, the net photosynthetic rate was also found sensitive to Cu treatment, which resulted in decreased shoot and root growth. Based on the key results, it can be suggested that P. indica herbal tea derived from the foliage of plants grown under a 5 mM Cu level (0.75 µg g-1 DW) with a target hazard quotient below one aligns with the recommended dietary intake of Cu in leafy vegetables. The study recommends choosing cuttings from plants with a small canopy as plant material in the greenhouse microclimates to validate the growth performance in the Cu-contaminated soil and simulate the natural shrub architecture and life cycle.

Aluminum uptake, translocation, physiological changes, and overall growth inhibition in rice genotypes (Oryza sativa) at vegetative stage.

Aluminum (Al) contamination in acidic soil is a major problem in paddy field, causing grain yield loss, especially in central plains of Thailand. The objective of this study was to assess Al content in the root tissues, its translocation to the leaves, and Al toxicity in three genotypes of rice, RD35 (local acidic-tolerant), Azucena (positive-check Al-tolerant), and IR64 (high yielding) under 0 (control) or 1 mM AlCl3 (Al toxicity) at pH 4.5. Al content in the root tissues of rice cv. RD35 under 1 mM AlCl3 was peaked at 4.18 mg g‒1 DW and significantly translocated to leaf tissues (0.35 mg g‒1 DW), leading to reduced leaf greenness (SPAD) (by 44.9% over the control) and declined net photosynthetic rate (Pn) (by 54.5% over the control). In contrast, Al level in cvs. Azucena and IR64 was restricted in the roots (2.12 mg g‒1 DW) with low amount of translocation in the leaf tissues (0.26 mg g‒1 DW), resulting in maintained values of SPAD and Pn. In cv. RD35, root and shoot traits including root length, root fresh weight, shoot height, shoot fresh weight, and shoot dry weight in 1 mM Al treatment were significantly dropped by > 35% over the control, whereas these parameters in cvs. Azucena and IR64 were retained. Based on the results, RD35 rice genotype was identified as Al sensitive as it demonstrated Al toxicity in both aboveground and belowground parts, whereas Azucena and IR64 were found tolerant to 1 mM Al as they demonstrated storage of Al in the root tissues to reduce toxicity in the leaf tissues. The study suggests that root traits, shoot attributes, chlorophyll degradation, and photosynthetic reduction can be successfully employed for the screening of Al-tolerant genotypes in rice breeding programs.

Determination of traits responding to iron toxicity stress at different stages and genome-wide association analysis for iron toxicity tolerance in rice (Oryza sativa L.).

Rice is the staple food for more than half of the world's population. Iron toxicity limits rice production in several regions of the world. Breeding Fe-tolerant rice varieties is an excellent approach to address the problem of Fe toxicity. Rice responds differently to Fe toxicity at different stages. Most QTLs associated with Fe toxicity have been identified at the seedling stage, and there are very few studies on Fe toxicity across different stages. In this study, we investigated agro-morphological and physiological traits in response to Fe toxicity in a rice diversity panel at seedling, vegetative, and reproductive stages and applied GWAS to identify QTLs/genes associated with these traits. Among agro-morphological and physiological parameters, leaf bronzing score (LBS) is a key parameter for determining Fe toxicity response at all stages, and SDW could be a promising parameter at the seedling stage. A total of 29 QTLs were identified on ten chromosomes. Among them, three colocalized QTLs were identified on chromosome 5, 6, and 11. Several QTLs identified in this study overlapped with previously identified QTLs from bi-parental QTL mapping and association mapping. Two genes previously reported to be associated with iron homeostasis were identified, i.e., LOC_Os01g72370 (OsIRO2, OsbHLH056) and LOC_Os04g38570 (OsABCB14). In addition, based on gene-based haplotype analysis, LOC_Os05g16670 was identified as a candidate gene for the colocalized QTL on chromosome 5 and LOC_Os11g18320 was identified as a candidate gene for the colocalized QTL on chromosome 11. The QTLs and candidate genes identified in this study could be useful for rice breeding programs for Fe toxicity tolerance.

Evaluation of curcuminoids, physiological adaptation, and growth of Curcuma longa under water deficit and controlled temperature.

Turmeric (Curcuma longa L.; Zingiberaceae), an economically important crop and a major spice in Indian cuisine, produces natural yellow color (curcumin) as well as curcuminoids which are widely utilized in traditional and modern medicinal practices. During the turmeric culture, the fluctuations of precipitation and seasonal changes in the whole life cycle play a major role, especially water shortage and decreasing temperature (in winter season), leading to rhizome dormancy under extreme weather conditions. The objective of this investigation was to understand how the water deficit and reduced temperature affect turmeric growth, physiological adaptation, quantity, and quality of turmeric rhizomes. Four-month-old turmeric plants were subjected to four treatments, namely normal temperature and well-watered (RT-WW), or water-deficit (RT-WD) conditions in the greenhouse, 25 °C controlled temperature and well-watered (CT-WW), or water-deficit (CT-WD) conditions in glasshouse. Leaf osmotic potential considerably declined in 30 days CT-WD treatment, leading to chlorophyll degradation by 26.04%, diminution of maximum quantum yield of PSII (Fv/Fm) by 23.50%, photon yield of PSII (ΦPSII) by 29.01%, and reduction of net photosynthetic rate (Pn) by 89.39% over CT-WW (control). After 30 days water withholding, fresh- and dry-weights of rhizomes of turmeric plants grown under CT-WD declined by 30-50% when compared with RT-WW conditions. Subsequently, curcuminoid content was reduced by 40% over RT-WW plants (control), whereas transcriptional expression levels of curcuminoids-related genes (CURS1, CURS2, CURS3, and DCS) were upregulated in CT-WD conditions. In summary, the water withholding and controlled temperature (constant at 25 °C day/night) negatively affected turmeric plants as abiotic stresses tend to limit overall plant growth performances and curcuminoid yield.

Expression levels of genes involved in metal homeostasis, physiological adaptation, and growth characteristics of rice (Oryza sativa L.) genotypes under Fe and/or Al toxicity.

Acid sulphate soil contains high amounts of iron (Fe) and aluminum (Al), and their contamination has been reported as major problems, especially in rainfed and irrigated lowland paddy fields. Rice is sensitive to Fe and Al grown in acid soil (pH < 5.5), leading to growth inhibition and grain yield loss. The objective of this study was to evaluate Fe and/or Al uptake, translocation, physiological adaptation, metal toxicity, and growth inhibition in rice genotypes grown in acid soil. Fe and Al in the root tissues of all rice genotypes were enriched depending on the exogenous application of either Fe or Al in the soil solution, leading to root growth inhibition, especially in the KDML105 genotype. Expression level of OsYSL1 in KDML105 was increased in relation to metal uptake into root tissues, whereas OsVIT2 was downregulated, leading to Fe (50.3 mg g-1 DW or 13.1 folds over the control) and Al (4.8 mg g-1 DW or 2.2 folds over the control) translocation to leaf tissues. Consequently, leaf greenness (SPAD), net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (E) in the leaf tissues of genotype KDML105 under Fe + Al toxicity significantly declined by 28.4%, 35.3%, 55.6%, and 51.6% over the control, respectively. In Azucena (AZU; Fe/Al tolerant), there was a rapid uptake of Fe and Al by OsYSL1 expression in the root tissues, but a limited secretion into vacuole organelles by OsVIT2, leading to a maintenance of low level of toxicity driven by an enhanced accumulation of glutathione together with downregulation of OsGR expression level. In addition, Fe and Al restrictions in the root tissues of genotype RD35 were evident; therefore, crop stress index (CSI) of Fe + Al-treated plants was the maximum, leading to an inhibition of gs (53.6% over the control) and E (49.0% over the control). Consequently, free proline, total phenolic compounds, and ascorbic acid in the leaf tissues of rice under Fe + Al toxicity significantly increased by 3.2, 1.2, and 1.5 folds over the control, respectively, indicating their functions in non-enzymatic antioxidant defense. Moreover, physiological parameters including leaf temperature (Tleaf) increment, high level of CSI (>0.6), SPAD reduction, photon yield of PSII (ΦPSII) diminution, Pn, gs, and E inhibition in rice genotype IR64 (Fe/Al-sensitive) under Fe + Al treatment were clearly demonstrated as good indicators of metal-induced toxicity. Our results on Fe- and/or Al-tolerant screening to find out the candidate genotypes will contribute to present screening and breeding efforts, which in turn help increase rice production in the Fe/Al-contaminated acid soil under lowland conditions.

In vitro acclimatization of Curcuma longa under controlled iso-osmotic conditions.

In vitro acclimatization has been validated as the successful key to harden the plantlets before transplanting to ex vitro conditions. In the present study, we investigated the potential of different sugar types (glucose, fructose, galactose, sucrose) in regulating morphological, physiological and biochemical strategies, survival percentage and growth performance, and rhizome traits of turmeric under iso-osmotic potential. Leaf greenness (SPAD value) in acclimatized plantlets (4% glucose; -1.355 MPa osmotic potential) of 'ST018' was retained and greater than in 'PB009' by 1.69-fold, leading to maintain high Fv/Fm (maximum quantum yield of PSII), ΦPSII (photon yield of PSII) and Pn (net photosynthetic rate) levels, and retained shoot height, leaf length, leaf width, shoot fresh weight and shoot dry weight after one month upon transplanting to ex vitro conditions. In addition, Pn, Ci (intracellular CO2), gs (stomatal conductance) and E (transpiration rate) in acclimatized plantlets (6% sucrose; -1.355 MPa osmotic potential) of 'PB009' were stabilized as physiological adapted strategies, regulating the shoot and root growth and fresh and dry weights of mini-rhizome. Interestingly, the accumulation of total curcuminoids in mini-rhizome derived from 6% sucrose acclimatized plantlets of 'ST018' was greater than in 'PB009' by 3.76-fold. The study concludes that in vitro acclimation of turmeric 'PB009' and 'ST018' using 6% sucrose and 4% glucose, respectively, promoted percent survival, physiological adaptations, and overall growth performances under greenhouse conditions.