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Arsenic (As) poses a significant environmental threat as a metalloid toxin, adversely affecting the health of both plants and animals. Strigolactones (SL) and nitric oxide (NO) are known to play crucial roles in plant physiology. Therefore, the present experiment was designed to investigate the potential cumulative role of SL (GR24–0.20 μM) and NO (100 μM) in mitigating the adverse effect of AsV (53 μM) by modulating physiological mechanisms in two genotypes of tomato (Riogrand and Super Strain 8). A sample randomized design with four replicates was used to arrange the experimental pots in the growth chamber. 45-d old both tomato cultivars under AsV toxicity exhibited reduced morphological attributes (root and shoot length, root and shoot fresh weight, and root and shoot dry weight) and physiological and biochemical characteristics [chlorophyll (Chl) a and b content, activity of δ -aminolevulinic acid dehydratase activity (an enzyme responsible for Chl biosynthesis), and carbonic anhydrase activity (an enzyme responsible for photosynthesis), and enhanced Chl degradation, overproduction of reactive oxygen species (ROS) and lipid peroxidation due to enhanced malondialdehyde (MDA) content. However, the combined application of SL and NO was more effective in enhancing the tolerance of both varieties to AsV toxicity compared to individual application. The combined application of SL and NO improved growth parameters, biosynthesis of Chls, NO and proline. However, the combined application significantly suppressed cellular damage by inhibiting MDA and overproduction of ROS in leaves and roots, as confirmed by the fluorescent microscopy study and markedly upregulated the antioxidant enzymes (catalase, peroxidase, superoxide dismutase, ascorbate dismutase and glutathione reductase) activity. This study provides clear evidence that the combined application of SL and NO supplementation significantly improves the resilience of tomato seedlings against AsV toxicity. The synergistic effect of SL and NO was confirmed by the application of cPTIO (an NO scavenger) with SL and NO. However, further molecular studies could be imperative to conclusively validate the simultaneous role of SL and NO in enhancing plant tolerance to abiotic stress. [Display omitted] • AsV toxicity impaired growth performance of tomato genotypes. • Combined SL and NO application promoted plant health by combating AsV toxicity. • SL plus NO suppressed cellular damage by inhibiting ROS overproduction and MDA accumulation in tomato seedlings. • Application of SL and NO together improved the biosynthesis of Chl, TSCs and proline. • SL Plus NO upregulated antioxidant enzyme activity and NO formation. [ABSTRACT FROM AUTHOR]

Present investigation reports the role of calcium (Ca2+) and hydrogen sulfide (H 2 S) crosstalk associated with Vigna radiata seedlings subjected to K+ deficient conditions under short-term (24 h) and long-term (72 h) NaCl stress. Perusal of the data reveals that under short-term NaCl stress an initial decline in K+ level led to the elevation in Ca2+ and H 2 S levels along with improvement in antioxidant system and reduction in reactive oxygen species (ROS) production. Under long-term NaCl stress a further decline in K+ content was deleterious that led to a lower K+/Na+ ratio. This was followed by reduction in antioxidant system along with excessive accumulation of ROS and methylglyoxal content, and increased membrane damage. However, supplementation of the seedling roots with Ca2+ enhanced biosynthesis of H 2 S through enhancing cysteine pool. The present findings suggest that synergistic action of Ca2+ and H 2 S induced the activity of H+-ATPase that created H+ gradient which in turn induced Na+/H+ antiport system that accelerated K+ influx and Na+ efflux. All of these together contributed to a higher K+/Na+ ratio, activation of antioxidative defense system, and maintenance of redox homeostasis and membrane integrity in Ca2+-supplemented stressed seedlings. Role of Ca2+ and H 2 S in the regulation of Na+/H+ antiport system was validated by the use of sodium orthovanadate (plasma membrane H+-ATPase inhibitor), tetraethylammonium chloride (K+ channel blocker), and amiloride (Na+/H+ antiporter inhibitor). Application of Ca2+-chelator EGTA (ethylene glycol-bis(b-aminoethylether)- N,N,Nʹ,Nʹ -tetraacetic acid) and H 2 S scavenger hypotaurine abolished the effect of Ca2+, suggesting the involvement of Ca2+ and H 2 S in the alleviation of NaCl stress. Moreover, use of EGTA and HT also substantiates the downstream functioning of H 2 S during Ca2+-mediated regulation of plant adaptive responses to NaCl stress. To sum up, present findings reveal the association of Ca2+ and H 2 S signaling in the regulation of ion homeostasis and antioxidant defense during K+-deficient NaCl stress. Image 1 • Short term NaCl-induced potassium (K+) deficiency regulates NaCl-induced impairments. • Under long term NaCl stress, further decline in K+ content was deleterious. • Calcium (Ca2+) regulates Na+/H+ antiport and defense system under NaCl stress. • Ca2+-dependent regulation of plant response to NaCl stress is mediated by hydrogen sulfide (H 2 S). • H 2 S functions downstream of Ca2+ during plant adaptive responses to NaCl stress. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H 2 S) and nitric oxide (NO) have been known to affect vast number of processes in plants under abiotic stresses. Also, calcium (Ca) works as a second messenger in plants, which underpins the abiotic stress-induced damage. However, the sequence of action of these signaling molecules against cadmium (Cd)-induced cellular oxidative damage remains unidentified. Therefore, we studied the synergistic actions and/or relationship of signaling molecules and Ca-dependent activation of tolerance mechanisms in Vigna radiata seedlings under Cd stress. The present study shows that exogenous Ca supplemented to Cd-stressed V. radiata seedlings reduced Cd accumulation and improved the activity of nitrate reductase, and L/D-cysteine desulfhydrase (LCD/DCD) that resulted in improved synthesis of NO and H 2 S content. Application of Ca also elevated the level of cysteine (Cys) by upregulating the activity of Cys-synthesizing enzymes serine acetyltransferase and O -acetylserine(thiol)lyase in Cd-stressed seedlings. Maintenance of Cys pool under Cd stress contributed to improved H 2 S content which together with Ca and NO improved antioxidant enzymes and components of ascorbate-glutathione (AsA-GSH) cycle. All these collectively regulated the activity of NADPH oxidase and glycolate oxidase, resulting in the inhibition of Cd-induced generation of reactive oxygen species. The elevated level of Cys also assisted the Cd-stressed seedlings in maintaining GSH pool which retained normal functioning of AsA-GSH cycle and led to enhanced content of phytochelatins coupled with reduced Cd content. The positive effect of these events manifested in an enhanced rate of photosynthesis, carbohydrate accumulation, and growth attributes of the plants. On the contrary, addition of NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], H 2 S scavenger HT (Hypotaurine) and Ca-chelator EGTA (Ethylene glycol-bis(b-aminoethylether)- N,N,Nʹ,Nʹ -tetraacetic acid) again developed a condition similar to stress and positive effect of the signaling molecules was abolished. The findings of the study postulate that Ca in association with NO and H 2 S mitigates Cd-induced impairment and enhances the tolerance of the V. radiata plants against Cd stress. The results of the study also substantiate that Ca acts both upstream as well as downstream of NO signals whereas, H 2 S acts downstream of Ca and NO during Cd-stress responses of the plants. Image 1 • Cadmium (Cd)-toxicity hampered photosynthesis and growth of Vigna radiata. • Application of calcium (Ca) induced the biosynthesis of nitric oxide (NO) and hydrogen sulfide (H 2 S). • Synergistic action of NO and H 2 S requires Ca for activation of defense system of the plants. • Interaction of Ca, NO and H 2 S maintain redox homeostasis. • Ca plays central role in the cross talk of NO and H 2 S under Cd toxicity. [ABSTRACT FROM AUTHOR]

Chromium (Cr), a highly toxic redox-active metal cation in soil, seriously threatens global agriculture by affecting nutrient uptake and disturbing various physio-biochemical processes in plants, thereby reducing yields. Here, we examined the effects of different concentrations of Cr alone and in combination with hydrogen sulfide (H 2 S) application on the growth and physio-biochemical performance of two mungbeans (Vigna radiata L.) varieties, viz. Pusa Vishal (PV; Cr tolerant) and Pusa Ratna (PR; Cr sensitive), growing in a pot in hydroponics. Plants were grown in the pot experiment to examine their growth, enzymatic and non-enzymatic antioxidant levels, electrolyte balance, and plasma membrane (PM) H+-ATPase activity. Furthermore, root anatomy and cell death were analysed 15 days after sowing both varieties in hydroponic systems. The Cr-induced accumulation of reactive oxygen species caused cell death and affected the root anatomy and growth of both varieties. However, the extent of alteration in anatomical features was less in PV than in PR. Exogenous application of H 2 S promoted plant growth, thereby improving plant antioxidant activities and reducing cell death by suppressing Cr accumulation and translocation. Seedlings of both cultivars treated with H 2 S exhibited enhanced photosynthesis, ion uptake, glutathione, and proline levels and reduced oxidative stress. Interestingly, H 2 S restricted the translocation of Cr to aerial parts of plants by improving the nutrient profile and viability of root cells, thereby relieving plants from oxidative bursts by activating the antioxidant machinery through triggering the ascorbate-glutathione cycle. Overall, H 2 S application improved the nutrient profile and ionic homeostasis of Cr-stressed mungbean plants. These results highlight the importance of H 2 S application in protecting crops against Cr toxicity. Our findings can be utilised to develop management strategies to improve heavy metal tolerance among crops. [Display omitted] • Cr impairs growth, nutrient homeostasis and physiology of mungbean seedlings. • H 2 S enhanced photosynthetic pigments biosynthesis in mungbean genotypes. • H 2 S inhibits ROS production and increased nutrients accumulation. • H 2 S improves anatomical features, proline and antioxidant system of seedlings. • H 2 S application provides Cr stress tolerance in mungbean. [ABSTRACT FROM AUTHOR]