Gas Exchange Attributes Research Articles

Triacontanol regulates morphological traits and enzymatic activities of salinity affected hot pepper plants

Potential role of triacontanol applied as a foliar treatment to ameliorate the adverse effects of salinity on hot pepper plants was evaluated. In this pot experiment, hot pepper plants under 75 mM NaCl stress environment were subjected to foliar application of 25, 50, and 75 µM triacontanol treatments; whereas, untreated plants were taken as control. Salt stress had a significant impact on morphological characteristics, photosynthetic pigments, gas exchange attributes, MDA content, antioxidants activities, electrolytes leakage, vitamin C, soluble protein, and proline contents. All triacontanol treatments significantly mitigated the adversative effects of salinity on hot pepper plants; however, foliar application triacontanol at 75 µM had considerably improved the growth of hot pepper plants in terms of plant height, shoot length, leaf area, plant fresh/dry biomasses by modulating above mentioned physio-biochemical traits. While, improvement in gas exchange properties, chlorophyll, carotenoid contents, increased proline contents coupled with higher SOD and CAT activities were observed in response to 75 µM triacontanol followed by 50 µM triacontanol treatment. MDA and H2O2 contents were decreased significantly in hot pepper plants sprayed with 75 µM triacontanol followed by 50 µM triacontanol foliar treatment. Meanwhile, root and shoot lengths were maximum in 50 µM triacontanol sprayed hot pepper plants along with enhanced APX activity on exposure to salt stress. In crux, exogenous application triacontanol treatments improved hot pepper performance under salinity, however,75 µM triacontanol treatment evidently was more effective in mitigating the lethal impact of saline stress via controlling the ROS generation and increment in antioxidant enzyme activities.

Zinc Oxide Nanoparticles Interplay With Physiological and Biochemical Attributes in Terminal Heat Stress Alleviation in Mungbean (Vigna radiata L.).

Gradually rising atmospheric temperature is the vital component of the environment, which is anticipated as the riskiest abiotic stress for crop growth. Nanotechnology revolutionizing the agricultural sectors, notably, zinc oxide nanoparticles (nano-ZnO) has captured intensive research interests due to their distinctive properties and numerous applications against abiotic stresses. Mungbean (Vigna radiata L.), being a summer crop, is grown all over the world at an optimum temperature of 28–30°C. A rise in temperature above this range, particularly during the flowering stage, can jeopardize the potential performance of the plant. Hence, an outdoor study was performed to evaluate the effect of multiple suspensions of nano-ZnO (0, 15, 30, 45, and 60 mg l–1) on physicochemical attributes and yield of mungbean crop under heat stress. Heat stress was induced by fine-tuning of sowing time as: S1 is the optimal sowing time having day/night temperatures <40/25°C and S2 and S3 are late sown that were above >40/25°C during the flowering stage. In vitro studies on Zn release from nano-ZnO by inductively coupled plasma mass spectroscopy (ICPMS) disclosed that the Zn release and particles uptake from nano-ZnO were concentration-dependent. Exogenous foliar application of nano-ZnO significantly upstreamed the production of antioxidants and osmolytes to attenuate the shocks of heat stress in S2 and S3. Likewise, nano-ZnO substantially rebated the production of reactive oxygen species in both S2 and S3 that was associated with curtailment in lipid peroxidation. Adding to that, foliar-applied nano-ZnO inflates not only the chlorophyll contents and gas exchange attributes, but also the seeds per pod (SPP) and pods per plant (PPP), which results in the better grain yield under heat stress. Thus, among all the sowing dates, S1 statistically performed better than S2 and S3, although foliar exposure of nano-ZnO boosted up mungbean performance under both the no heat and heat-induced environments. Hence, foliar application of nano-ZnO can be suggested as an efficient way to protect the crop from heat stress-mediated damages with the most negligible chances of nanoparticles delivery to environmental compartments that could be possible in case of soil application.

The Impact of Bio-Stimulants on Cd-Stressed Wheat (Triticum aestivum L.): Insights Into Growth, Chlorophyll Fluorescence, Cd Accumulation, and Osmolyte Regulation.

It has been established that wheat (Triticum aestivum L.) has a higher Cd absorption capacity than other cereal crops causing an excess daily Cd intake and a huge threat for public health. Therefore, the reduction of Cd accumulation in wheat from the soil is a crucial food-security issue. A pot trial was performed on Cd-stressed wheat seedlings to evaluate the morphological and physio-biochemical responses via foliage spray of two different bio-stimulants, i.e., ascorbic acid (AsA) and moringa leaf extract (MLE). Two wheat cultivars (Fsd-08 and Glxy-13) were exposed to cadmium (CdCl2.5H2O) stress (0, 500, and 1,000 μM), along with foliar spray of AsA (0 and 50 mM) and MLE (0 and 3%). The most observable growth reduction was documented in plants that are exposed to a higher Cd concentration (1,000 μM), followed by the lower Cd level (500 μM). The wheat growth attributes, such as number of leaves per plant, number of tillers per plant, biomass yield, shoot/root length, and leaf area, were greatly depressed under the Cd stress, irrespective of the cultivar. Under the increasing Cd stress, a significant diminution was observed in maximum photochemical efficiency (Fv/Fm), photochemical quenching (qP), and electron transport rate (ETR) accompanied with reduced gas exchange attributes. However, Cd-induced phytotoxicity enhanced the non-photochemical quenching (NPQ) and internal carbon dioxide concentration (Ci), which was confirmed by their significant positive correlation with Cd contents in shoot and root tissues of both cultivars. The contents of proline, AsA, glycine betaine (GB), tocopherol, total free amino acid (TFAA), and total soluble sugar (TSS) were greatly decreased with Cd stress (1,000 μM), while MLE and AsA significantly enhanced the osmolytes accumulation under both Cd levels (especially 500 μM level). The Cd accumulation was predominantly found in the root as compared to shoots in both cultivars, which has declined after the application of MLE and AsA. Conclusively, MLE was found to be more effective to mitigate Cd-induced phytotoxicity up to 500 μM Cd concentration, compared with the AsA amendment.

Foliar application of potassium and moringa leaf extract improves growth, physiology and productivity of kabuli chickpea grown under varying sowing regimes.

Chickpea (Cicer arietinum L.) is of prime importance because of vital source of protein as major food legume. Globally, it is cultivated on large area to meet dietary requirements of humans. Climatic extremes (erratic rainfall, extreme high and low temperature) are key restrains for its production. Optimum sowing time is considered as an important factor to address climatic variations and to attain maximum yield. Foliar application of potassium (K) has also been reported to increase resistance against abiotic stresses. Similarly, exogenous application of plant based growth substances (bio-stimulants) like moringa leaf extract (MLE) are extensively used to enhance productivity of field crops. Therefore, current study was planned to evaluate the impact of foliar applied K and MLE on growth, physiology and productivity of kabuli chickpea grown under varying sowing dates. There were two sowing dates (normal sown; November 15 and late sown; December 15, 2020). Experiment was comprised of treatments i.e. control, water spray, foliar application of K at 1%, foliar application of MLE at 3% and combined application of K and MLE. Foliar applied K and MLE significantly improved physiological, biochemical and yield attributes of kabuli chickpea cultivated under normal and late sown conditions. Increase in growth and yield attributes like plant height, number of nodules per plant, nodules dry weight, branches and pods per plant, 100- grain weight, biological and grain yield were recorded in case of combined foliar application of K and MLE in normal and late sown chickpea. Maximum improvement in gas exchange attributes (stomatal conductance and transpiration rate), chlorophyll contents, antioxidants (catalase, superoxide dismutase and ascorbate peroxidase) and osmolytes (proline) were recorded with combined application of K and MLE in both sowing dates. Thus, combined applied K and MLE can be used to enhance productivity of kabuli chickpea.

Synchronisation of zinc application rates with arbuscular mycorrhizal fungi and phosphorus to maximise wheat growth and yield in zinc-deficient soil

Arbuscular mycorrhizal fungi (AMF) are found to be causing the most abundant symbioses between fungi and roots of terrestrial plants. AMF act as a biofertiliser that stimulate plant growth and increase plant productivity under poor soil fertility. In addition, unbalanced application of zinc (Zn) and the antagonistic relationship with phosphorus (P) also play an imperative role in decreasing crop productivity. It is necessary to synchronise Zn application rate with applied inorganic P and AMF to achieve optimum crop yield. For tha purpose, a pot trial was conducted on Zn-deficient soil with five application rates of Zn, i.e. 0, 30, 60, 90, 120 and 150 mg kg−1. Two levels of inorganic P [0 (P0) and 21 (P1) mg kg−1] were applied with and without AMF inoculation. Results showed that more AMF colonisation was observed under deficient Zn and P conditions. Higher soil Zn (Zn120 and Zn150) significantly decreased the germination rate and plant growth. However, a significant improvement in germination, plant height, biomass, transpiration rate and 100-grain weight validated the productive functioning of AMF over no AMF. AMF inoculation alleviated P-induced Zn deficiency and Zn-induced P deficiency. Application of P0Zn60 and P0Zn30 with and without AMF is a better treatment to maximise wheat growth, yield and gas-exchange attributes in Zn-deficient conditions. It is also recommended to apply low Zn, (30 or 60 mg kg−1 Zn) when AMF is used, with 21 mg kg−1 P, or half of the recommended dose of P.

Exogenous application of neem extract enhances the control of bacterial spot of tomato grown in soilless culture system through modulating gas exchange attributes, osmolytes, antioxidant machinery and genes expression

Exogenous application of neem extract enhances the control of bacterial spot of tomato grown in soilless culture system through modulating gas exchange attributes, osmolytes, antioxidant machinery and genes expression

Role of exogenous-applied salicylic acid, zinc and glycine betaine to improve drought-tolerance in wheat during reproductive growth stages

BackgroundDrought has become a dangerous threat to reduce crop productivity throughout the world. Exogenous applications of regulators, micronutrients, and/or osmoprotectants for inducing drought-tolerance in field crops have been effectively adopted. A controlled pot study was performed to investigate the relative efficacy of salicylic acid (SA), zinc (Zn), and glycine betaine (GB) as foliar applications on the growth, tissues pigments content, relative water content (RWC), leaf gas-exchange, antioxidant enzymes activity, reactive oxygen species (ROS) accumulation, osmolytes contents, and the yield parameters of wheat plants subjected to two soil water conditions (85% field capacity: well-watered, 50% field capacity: water-deficient) during reproductive growth stages.ResultsWater deficient conditions significantly decreased the growth, yield parameters, RWC, photosynthesis pigment, and gas-exchange attributes except for intercellular CO2 concentration. However, foliar applications remarkably improved the growth and yield parameters under water deficit conditions. Under drought condition, exogenous applications of SA, Zn, and GB increased the grain yield pot− 1 by 27.99, 15.23 and 37.36%, respectively, as compared to the control treatment. Drought stress statistically increased the contents of hydrogen peroxide (H2O2), superoxide anion radical (O2•−), and malonaldehyde (MDA), and elevated the harmful oxidation to cell lipids in plants, however, they were considerably reduced by foliar applications. Foliar applications of SA, Zn, and GB decreased MDA content by 29.09, 16.64 and 26.51% under drought stress, respectively, as compared to the control treatment. Activities of all antioxidant enzymes, proline content, and soluble sugar were increased in response to foliar applications under water deficit conditions.ConclusionsOverall, foliar application of GB, SA, and Zn compounds improved the drought-tolerance in wheat by decreasing the ROS accumulation, promoting enzymatic antioxidants, and increasing osmolytes accumulation. Finally, GB treatment was most effective in thoroughly assessed parameters of wheat followed by SA and Zn applications to alleviate the adverse effects of drought stress.

Chemical role of α-tocopherol in salt stress mitigation by improvement in morpho-physiological attributes of sunflower (Helianthus annuus L.)

Elevated concentrations of salts in soil and water represent abiotic stresses. It considerably restricts plant productivity. However, the use of alpha-tocopherol (α-toc) as foliar can overcome this problem. It can improve crop productivity grown under salinity stress. Limited literature is documented regarding its optimum foliar application on sunflower. That’s why the need for the time is to optimize α-toc foliar application rates for sunflower cultivated in salt-affected soil. A pot experiment was performed to select a better α-toc foliar application for mitigation of salt stress in different sunflower cultivars FH (572 and 621). There were 2 levels of salts, i.e., control (no salt stress) and sodium chloride (120 mM) and four α-toc foliar application (0, 100, 200, and 300 mg L−1). Results showed that foliar application of 100 mg/L- α-toc triggered the remarkable increase in fresh shoot weight, fresh root weight, shoot, and root lengths under salinity stress in FH-572 and FH-621 over 0 mg/L- α-toc. Foliar application of 200 mg/L- α-toc was most effective for improvement in chlorophyll a, chlorophyll b, total chlorophyll and carotenoids compared to 0 mg/L- α-toc. Furthermore, an increase in A was noted in FH-572 (17%) and FH-621 (22%) with α-toc (300 mg L−1) application under saline condition. In conclusion, the 100 and 200 mg/L- α-toc are the best application rates for the improvement in sunflower FH-572 and FH-621 growth, chlorophyll contents and gas exchange attributes. Further investigations are needed to select a better foliar application rate between 100 and 200 mg/L- α-toc at the field level under the different agro-climatic zone and soil types.

Exogenous Application of Biostimulants and Synthetic Growth Promoters Improved the Productivity and Grain Quality of Quinoa Linked with Enhanced Photosynthetic Pigments and Metabolomics

Modern agriculture is mainly concerned with maximum resource use efficiency linked with greater productivity to feed the growing global population. The exogenous application of biostimulants is considered a sustainable approach to improve the growth and productivity of field crops. The present study was carried out to explore the comparative impact of biostimulants and synthetic compounds on quinoa crop (cultivar UAF-Q7), as it has gained significant popularity among agricultural scientists and farmers throughout the world, due to its high nutritional profile. A two-year field experiment was carried out at the Research Area of Directorate of Farms, University of Agriculture, Faisalabad, Pakistan. Application of moringa leaf extract (MLE) produced the maximum total chlorophyll (5.11 mg g−1) and carotenoids (1.2 mg g−1), compared with the control. Antioxidants’ activities and gas exchange attributes were also recorded as the highest following MLE application. Mineral elements in root and in shoot were found highest in response to MLE application. Similarly, application of MLE significantly improved the growth and yield attributes of quinoa. Mineral elements of grain (Mg, Zn and Fe) were also significantly enhanced. MLE was found to be more responsive in improving the growth and quality compared with synthetic compounds.

English

Increased salinity stress in environment challenges the seed germination, emergence, and crop yield. The issue carefully demands the seed priming strategies to mitigate the drastic effects of salinity. Current study was conducted to appraise the modulation in germination, photosynthetic pigments, yield, and gas exchange attributes of sesame cultivars (TS-5 and TH-6) to pre-sowing seed treatment with glycinebetaine (GB) under salt stress. Seeds were treated with GB (25 mM) and water prior to sowing for 16 h. Ten seeds of each cultivar were laid down on moistened filter paper (0 mM and 70 mM NaCl) in petri plates to assess the germination attributes under salt stress. In a separate pot experiment, GB primed and water primed seeds were sown in 10 kg sand filled plastic pots. After two weeks of seed sowing, two concentrations of salinity (0 mM and 70 mM) were maintained by dissolving NaCl in full strength Hoagland nutrient solution. Data for germination, gas exchange and yield parameters were collected after one week, two week and ten weeks respectively. Salt stress decreased the germination percentage, plumule/radicle length, number of seeds/plant, Chl a, net photosynthetic rate (PN), stomatal conductance (gs) and transpiration rate (E), while intercellular CO2 concentration (Ci) and ratio of internal to atmospheric CO2 concentration Ci/Ca ratio were increased. However, seed mass/plant, Chl b and carotenoids remained unaffected under salinity. GB mitigated the saline effects by increasing the germination percentage, plumule length, number of seeds/plant and PN and showed nonsignificant effect on radicle length, seed mass per plant and Chl a, b and carotenoid contents. Sesame cultivar TH-6 showed better performance as compared to TS-5 under saline conditions. GB is powerful osmoregulator to minimize salt effect in sesame by enhancing physiological and yield attributes

Foliar application of zinc improves morpho-physiological and antioxidant defense mechanisms, and agronomic grain biofortification of wheat (Triticum aestivum L.) under water stress

Agronomic biofortification with zinc (Zn) may be engaged to improve the nutritious value of food crops along-with tolerance to water deficit conditions. The Zn may increase plant resistance to water stress by boosting physiological and enzymatic antioxidants defense mechanisms. Major objective of this study was to investigate the effect of foliar applied Zn on grain zin biofortification and drought tolerance in wheat. Treatments include application of Zinc at terminal growth phases (BBCH growth stage 49 and BBCH growth stage 65) with five levels: 0 (control-ck), water spray, 5, 10 and 15 mM under two levels of water regimes; well-watered (where 80% water holding capacity (WHC) was maintained in the soil) and water stress, (where 40% WHC was maintained in the soil). Results revealed that water stress significantly reduced relative water contents, gas exchange attributes, plant height, yield and yield related attributes of wheat. In contrast, hydrogen peroxide, free proline levels, activities of malondialdehyde, and concentration of soluble protein were markedly increased under water stress condition. Application of various levels of Zn significantly improved the CAT, SOD, POD and ASP activities at 40% WHC compared with control treatment. Foliarly applied 10 and 15 mM Zn predominantly reduced the damaging impact of water stress by improving the plant status in the form of plant height, RWC and gas exchange attributes. Likewise, wheat plant treated with 10 mM Zn under water stress condition increased the grain yield by improving number of grains per spike, 100 grain weight and biological yield compared with control. Moreover, increasing Zn levels also increased Zn concentration in grains and leaves. Overall, this study suggests that optimum level of Zn (10 mM) might be promising for alleviating the adverse impacts of water stress and enhance the grain biofortification in wheat.

Alleviating lead-induced phytotoxicity and enhancing the phytoremediation of castor bean (Ricinus communis L.) by glutathione application: new insights into the mechanisms regulating antioxidants, gas exchange and lead uptake

Heavy metals pollution represents a serious issue for cultivable lands and ultimately threatens the worldwide food security. Lead (Pb) is a menacing metal which induces toxicity in plants and humans. Lead toxicity reduces the photosynthesis in plants, resulting in the reduction of plant growth and biomass. The excessive concentration of Pb in soil accumulates in plants body and enters into food chain, resulting in health hazards in humans. The phytoremediation is eco-friendly and cost-efficient technique to clean up the polluted soils. However, to the best of our Knowledge, there are very few reports addressing the enhancement of the phytoremediation potential of castor bean plants. Therefore, the present study aimed to investigate the potential role of glutathione (GSH), as a promising plant growth regulator, in enhancing the lead stress tolerance and phytoremediation potential of castor bean plants grown under lead stress conditions. The results indicated that Pb stress reduced the growth, biomass, chlorophyll pigments and gas exchange attributes of castor bean plants, causing oxidative damage in plants. Pb stress induced the oxidative stress markers and activities of antioxidant enzymes. On the other hand, the application of GSH reduced oxidative stress markers, but enhanced the growth, biomass, photosynthetic pigments, gas exchange attributes, Pb accumulation and antioxidant enzymes activities of lead-stressed castor bean plants. Both Pb uptake and Pb accumulation were increased by increasing concentrations of Pb in a dose-additive manner. However, at high dose of exogenous GSH (25 mg L−1) further enhancements were recorded in the Pb uptake in shoot by 48% and in root by 46%; Pb accumulation was further enhanced in shoot by 98% and in root by 101% in comparison with the respective control where no GSH was applied. Taken together, the findings revealed the promising role of GSH in enhancing the lead stress tolerance and phytoremediation potential of castor bean (Ricinus communis) plants cultivated in Pb-polluted soils through regulating leaf gas exchange, antioxidants machinery, and metal uptake.

Role of exogenously applied putrescine in amelioration of cadmium stress in Coriandrum sativum by modulating antioxidant system

Abiotic stress reduces the plant growth and biomass production. Putrescine (Put) may be applied to alleviate numerous types of abiotic stresses in plants. The present research was intended to evaluate the role of exogenously applied Put in extenuation of cadmium (Cd) stress in coriander plants. Coriander seeds primed with 0.25, 0.5, and1 mM Put were allowed to grow in 50 mg kg−1 Cd contaminated soil for one month. Put treatment improved seed germination, gas exchange attributes, root growth and shoot growth of coriander. The improved activity of stress-responsive enzymes such as superoxide dismutase, catalase and peroxidase, besides amplification of proline was observed in Put treated seedlings under Cd stress. In addition, a reduced amount of total soluble protein and sugars content were noticed in Cd stressed seedlings. Nevertheless, Put reduced MDA level in treated plants. Our results demonstrated that Put mitigated Cd induced stress by modulating antioxidants and photosynthetic activity of coriander plants. Novelty statement Most of the researchers have studied the role of endogenous putrescine in alleviation of plant stress. However, during current study, we primed coriander seeds with putrescine. Our results elucidated very promising role of exogenously applied putrescine in stress mitigation and growth improvement of coriander seedlings under Cd stress. The findings of current study advocate the application of putrescine for stress alleviation in crop plants.

Improving thermotolerance in Gossypium hirsutum by using signalling and non-signalling molecules under glass house and field conditions

The climate change and global warming driven rise in temperature and unpredictable occurrence of heat waves impede cotton plants growth and development. Therefore, environmental friendly thermotolerance strategies are required to sustain optimum crop yield under stressful conditions. Reports on heat stress impacts on plant water relations, gas exchange attributes and physiological parameters, at different reproductive stages of cotton, under controlled and natural conditions are lacking. To investigate the impact of temperature and exogenous application of elicitors, a medium heat tolerant cotton genotype was exposed to control/optimal (30/20 °C), medium (38/24 °C) and high (45/30 °C) temperature stress at squaring, flowering and boll formation stages. Plants were staggered to April (early), May (normal) and June (late) sowing dates under field conditions. Growth regulators, salicylic acid (SA-50 ppm), bio-stimulant moringa leaf extract (MLE-30 times diluted) and signaling molecules, i.e. hydrogen peroxide (H2O2 -30 ppm) and ascorbic acid (ASA-70 ppm), were applied foliarly one day prior to temperature stress treatments. Several physio-biochemical parameters, such as leaf non-enzymatic antioxidant, gas exchange attributes and water relations were measured seven-days after exposure to medium and high temperature regimes. Elevated temperature (45/30 °C) increased the content of total soluble proteins (TSP), activity of glutathione reductase (GR), radical scavenging capacity (DPPH%) and H2O2 generation by 64 %, 26 %, 39 % and 57 %, respectively, compared with optimal temperature plants (control). Similarly, the stomatal conductance (GS), seed index and ginning out turn (GOT%) were reduced by 49 %, 47 % and 44 %, respectively under the high temperature regime compared with control temperature regime. Gas exchange components, water relations, seed index and GOT were also reduced under medium and high temperature regimes. Among the exogenous applications, H2O2 showed profound alleviation of temperature stress, followed by ASA and MLE. Foliar application of H2O2 increased TSP, GR and DPPH% by 1.16 folds, 70 % and 82 % (averaged across during three reproductive stages); while, GS, seed index and GOT were increased by 45 %, 20 %, 22 % under high temperature stress over the control plants of the same thermal regime. In conclusion, oxidative burst and antioxidant activities were increased, whereas stomatal conductance, seed index and GOT were reduced with increasing temperature from 30/20 °C to 38/24 °C and from 38/24 °C to 45/30 °C. On the other hand, H2O2 improved thermotolerance of cotton plants via maintaining cellular redox balance, gas exchange attributes, and further enhanced seed weight and ginning out turn under medium and high temperature regimes.

Foliar melatonin stimulates cotton boll distribution characteristics by modifying leaf sugar metabolism and antioxidant activities during drought conditions.

Drought is a severe abiotic stress affecting the plant's antioxidant system and interrupting compatible solute translocation processes, which leads to low productivity. Melatonin acts as a common growth regulator enhancing the plants defense system and regulates sugar metabolism in challenging environments. Melatonin treatments enable plants to be tolerant to abiotic stresses via enhancing their recovery potential, but its impact using various concentrations has not yet been studied in leaf physiological aspects when applied to cotton foliage during their peak flowering and boll loading stage. The overall objective of this research was to facilitate cotton boll distribution characteristics by modifying cotton leaf sugar metabolism and antioxidant activity by applying foliar melatonin (0, 25, 50, and 100 μmol l-1 ) under drought levels with a relative soil water content of 75%, 60%, and 45% ± 5 (FC1, FC2, and FC3, respectively). Higher rates of melatonin application (100 μmol l-1 ) enhanced boll distribution characteristics and controlled the boll shedding rate during drought conditions. An increase in melatonin rates proved to be more helpful in stimulating cotton sympodial leaf physiological attributes, including leaf gas exchange parameters, sugar metabolism, proline content, and antioxidants defense system as compared with less or no melatonin application during all FC conditions and showed the most significant effect at a higher melatonin concentration (M100) at 7-21 DAF. The total proline content and antioxidant activity were enhanced in the M100 treatment during all FC levels, which caused a reduction in the total malondialdehyde (MDA) contents and hydrogen peroxide (H2 O2 ) concentrations in cotton leaves. Moreover, sugar metabolism responsible genes GhSusA and SPS2 showed an upsurge in expression levels and enhanced sucrose degradation in M100 treatments during all FC levels. Furthermore, cotton boll attributes showed also a positive relation with leaf physiological and gas exchange attributes. The results suggested that foliar melatonin application during the flowering initiation stage improved the overall performance and is helpful for cotton crops productivity against drought stress.

Supplemental Effects of Biochar and Foliar Application of Ascorbic Acid on Physio-Biochemical Attributes of Barley (Hordeum vulgare L.) under Cadmium-Contaminated Soil

Biochar, prepared from organic waste materials, can improve the quality of contaminated soil areas. Biochar can be used as an economic centerpiece over other available resources and can properly utilize large amounts of waste. Soil contaminated with cadmium (Cd) is a worldwide problem that poses potential agricultural and human health hazards. Moreover, Cd toxicity causes serious problems for sustainable food production, especially in food crops like barley. High cadmium concentration in soil is phytotoxic and decreases plant growth and ultimately yields. Biochar and ascorbic acid in ameliorating Cd stress are economically compatible and consistent approaches in agriculture. The present study aimed to evaluate biochar’s and foliar-applied ascorbic acid’s influence on some growth and biochemical characteristics of barley (Hordeum vulgare L.) to Cd stress. The soil was supplemented with biochar 2% w/w and 20 mg Cd kg−1. The foliar application of 30 mM ascorbic acid was done on plants. The results revealed that Cd stress decreased chlorophyll a, chlorophyll b, total chlorophyll, and carotenoids. It also increased oxidative stress indicators, i.e., APX, COD, POD, flavonoids, anthocyanin, phenolics, and electrolyte leakage, in barley with Cd-contamination. A significant enhancement in root and shoot length, gas exchange attributes, and chlorophyll contents validated the effectiveness of Bio + Asa treatments over all other treatments under Cd contamination. In conclusion, the sole applications of biochar and Asa in Cd contamination are also effective, but Bio + Asa is a better amendment for Cd stress alleviation in barley plants.

Moringa leaf extract improves biochemical attributes, yield and grain quality of rice (Oryza sativa L.) under drought stress.

Changing climate, food shortage, water scarcity and rapidly increasing population are some of the emerging challenges globally. Drought stress is the most devastating threat for agricultural productivity. Natural plant growth substances are intensively used to improve the productivity of crop plants grown under stressed and benign environments. The current study evaluated whether leaf extract of different moringa (Moringa oleifera L.) could play a role in improving drought-tolerance of rice (Oryza sativa L.). Rice plants were grown under three drought conditions, i.e., no, moderate and severe drought (100, 75 and 50% field capacity, respectively). Moringa leaf extract (MLE) obtained from four landraces (Multan, Faisalabad, D. G. Khan and exotic landrace from India) was applied during critical crop growth stages, i.e., tillering, panicle initiation and grain filling. Drought stress adversely affected the gas exchange attributes, photosynthetic pigments, antioxidant enzymes’ activities, yield and quality parameters of rice. Application of MLE from all landraces significantly improved physiological, biochemical and yield parameters under stressed and normal environmental conditions. The highest improvement in gas exchange traits (photosynthetic rate, stomatal conductance and respiration rate), photosynthetic pigments (chlorophyll a, b and carotenoids) and enzymatic activities (superoxide dismutase, catalase) and oxidative marker (H2O2) was recorded with MLE obtained from Faisalabad landrace. The application of MLE of Faisalabad landrace also improved yield and grain quality of rice grown under drought stress as well as drought-free environment. Thus, MLE of Faisalabad can be successfully used to improve growth, productivity and grain quality of rice under drought stress.

Synergistic effects of plant growth promoting rhizobacteria and silicon dioxide nano-particles for amelioration of drought stress in wheat

Drought tolerant plant growth-promoting rhizobacteria (PGPR) can confer drought tolerance in plants, when inoculated, and this effect can be more pronounced by their combined application with silicon oxide nanoparticles (SiO2 NPs). In this research, drought-tolerant and plant growth-promoting rhizobacterial strains were isolated from the rhizospheric soil of wheat plants growing in the arid region of Pakistan. Out of 30 isolated strains, three rhizobacterial strains were selected based on their drought tolerance, higher phytohormones (indole acetic acid (IAA), abscisic acid (ABA), and cytokinin (CK), and osmolyte (proline and sugar) production ability. These strains were identified as Bacillus sp. Azospirillum lipoferum and Azospirillum brasilense by 16S rRNA sequencing and accession numbers (MT482404, MT742664, and MT 742666, respectively) were obtained. Inoculation of these strains, alone and in combination, improved the germination attributes of wheat seeds under drought stress conditions. However, the combination of all three bacterial strains gave the best results. SiO2 NPs were prepared from silicon dioxide and characterized by scanning electron microscopy (SEM), Energy dispersive X-rays pattern (EDX), and UV–visible spectrum. The effect of SiO2 NPs was also tested on wheat seeds under drought stress and it was observed that SiO2 NPs (150 mg/L) create pronounced drought ameliorative potential in wheat seedlings. In the pot experiment, the combined application of SiO2 NPs and PGPR exhibited a synergistic role and improved the growth and yield of wheat. The interaction between SiO2 NPs and bacterial combination improved biomass (fresh and dry weight), and chlorophyll-a, b content by 138.78%, 65.70%, 128.57%, and 283.33% respectively as compared to untreated but drought exposed plants. They also improved relative water content (71.66%), gas exchange attributes, increased nutrients uptake, and osmolytes production of wheat. Up-regulation of antioxidant enzymes; superoxide dismutase (60.49%), peroxidase (55.99%), and catalase (81.69%) was also observed. This research work suggested that the application of SiO2 NPs and PGPR strains induced drought tolerance in wheat by modulating different physiological and metabolic processes in plants which ultimately improved the growth and yield of wheat under drought stress.

Elucidating the role of silicon in drought stress tolerance in plants

Predicted changes in climate, with more severe droughts and more extreme weather variability, are gaining considerable attention from stakeholders because of the already stressed and seriously challenging agricultural ecosystems of the contemporary world. One of the greatest challenges faced by these unique ecosystems due to climate change is drought stress, which affects plant growth, development and metabolic processes, thus reducing production, yield, and quality of crop plants. Plants counter this stress by employing complex mechanisms through a series of physiological, cellular, and molecular processes. Among the myriad of stress tolerance mechanisms, the positive effects of Si on water status of plants have been widely appreciated. Here, we review the potential of Si supplementation in alleviating drought stress and highlight the imported mechanisms involved in Si mediated reduction of drought stress in plants. Si fertilization not only enhances the photosynthetic pigments, growth, biomass, antioxidant enzymes, gene expression, osmolyte concentrations and nutrient uptake but also improves crop production, yield and grain quality during drought stress. In addition, it provides insights on important mechanisms involved in the modification of gas exchange attributes, gene modification, nutritional homeostasis, control synthesis of compatible solutes, osmotic adjustment and stimulation of phytohormone biosynthesis and antioxidant enzymes under drought stress. We also highlight knowledge gaps and future research prospects to understand Si mediated role in alleviating drought stress.

Salicylic Acid-Induced Morpho-Physiological and Biochemical Changes Triggered Water Deficit Tolerance in Syzygium cumini L. Saplings

Fruit tree culture is at the brink of disaster in arid to semi-arid regions due to low water availability. A pot experiment was carried out to analyze whether foliar application of salicylic acid (SA) can improve water stress tolerance in Syzygiumcumini. Saplings were subjected to control (CK, 90% of field capacity, FC), medium stress (MS, 60% of FC) and high stress (HS, 30% of FC) along with foliar application of 0.5 and 1.0 mM of SA. Results showed that soil water deficit significantly decreased leaf, stem and total dry weight, leaf gas exchange attributes and chlorophyll a, b. However, root dry weight and root/shoot ratio increased under MS and HS, respectively. Contrarily, foliar application of SA significantly improved chlorophyll a, b, leaf gas exchange attributes, and dry weight production under soil water deficit. Concentration of oxidants like hydrogen peroxide and superoxide radicals, along with malondialdehyde and electrolyte leakage increased under soil water deficit; however, decreased in plants sprayed with SA due to the increase in the concentration of antioxidant enzymes like superoxide dismutase, peroxidase, catalase and ascorbate peroxidase. Results suggest that the foliar application of SA can help improve water stress tolerance in Syzygiumcumini saplings; however, validation of the results under field conditions is necessary.