Exogenous abscisic acid and jasmonic acid restrain polyethylene glycol-induced drought by improving the growth and antioxidative enzyme activities in pearl millet.

Drought stress is one of the most immense and permanent constraints in agriculture, which leads to a massive loss of crop productivity. However, little is known about the mitigation role of exogenously applied abscisic acid (ABA) and jasmonic acid (JA) in pearl millet (Pennisetum glaucum L.) under PEG-induced drought stress. Therefore, the current study investigated the putative role of exogenous ABA and JA in improving drought stress tolerance in pearl millet. Thirteen-day-old seedlings were exposed to six different treatments as follow; control (ck), PEG-600 (20%), JA (100 µM), ABA (100 µM), PEG+JA, and PEG+ABA, and data were collected at 7 and 14 days after treatment (DAT). Results showed that PEG decreased plant growth while the oxidative damage increased due to over production of H2 O2 and MDA content as a result of decreased activities of the antioxidative enzymes including APX, CAT, and SOD in the leaves. However, exogenous ABA and JA positively enhanced the growth profile of seedlings by improving chlorophyll and relative water content under PEG treatment. A significant improvement was observed in the plant defense system resulting from increased activities of antioxidative enzymes due to exogenous ABA and JA under PEG. Overall, the performance of JA was found better than ABA under PEG-induced drought stress, and future investigations are needed to explore the potential effects of these phytohormones on the long-term crop management and productivity under drought stress.

Integrative roles of nitric oxide and hydrogen sulfide in melatonin-induced tolerance of pepper (Capsicum annuum L.) plants to iron deficiency and salt stress alone or in combination.

There seems to be no report in the literature on the effect of melatonin (MT) in relieving the detrimental effects of combined application of salt stress (SS) and iron deficiency (ID). Therefore, the effect of MT on the accumulation/synthesis of endogenous nitric oxide (NO) and hydrogen sulphide (H2 S) and how far these molecules are involved in MT-improved tolerance to the combined application of ID and SS in pepper (Capsicum annuum L) were tested. Hence, two individual trials were set up. The treatments in the first experiment comprised: Control, ID (0.1 mM FeSO4 ), SS (100 mM NaCl) and ID + SS. The detrimental effects of combined stresses were more prominent than those by either of the single stress, with respect to growth, oxidative stress and antioxidant defense attributes. Single stress or both in combination improved the endogenous H2 S and NO, and foliar-applied MT (100 µM) led to a further increase in NO and H2 S levels. In the second experiment, 0.1 mM scavenger of NO, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) and that of H2 S, hypotuarine (HT) were applied along with MT to get further evidence whether NO and H2 S are involved in MT-induced tolerance to ID and SS. MT combined with cPTIO and HT under a single or combined stress showed that NO effect was reversed by the NO scavenger, cPTIO, alone but the H2 S effect was inhibited by both scavengers. These findings suggested that tolerance to ID and SS induced by MT may be involved in downstream signal crosstalk between NO and H2 S.

Interactive Effects of Nutrients and Bradyrhizobium japonicum on the Growth and Root Architecture of Soybean (Glycine max L.).

Understanding the symbiotic performance of rhizobia and responses of plant root systems to mineral nutrient supply will facilitate the development of strategies to enhance effective rhizobia-legume symbioses. Interactive effect of nitrogen (N), phosphorus (P), and magnesium (Mg) on the symbiotic performance of soybean (Glycine max L.) with Bradyrhizobium japonicum, nodulation, root architecture, and the N concentration in plant tissue under hydroponic conditions were studied. Plant growth was significantly higher under a high N supply combined with Mg (HNHMg) than in combination with P (HNHP), which was attributed to the interaction between N and Mg ions. The plants grown at a low N concentration combined with either high or low P or Mg (LNHP, LNHMg, LNLP, and LNLMg) showed a higher nodule dry weight compared to those grown under a high N supply. We observed that the N content in the roots and shoots of soybean plants was significantly lower under LNHP or LNLP, but it was higher under HNHMg or LNHMg, indicating that Mg promotes N acquisition by the plant tissues. Neither root nor shoot growth responded significantly to P availability regardless of the N supply. We observed significant positive relationships between the number of nodules, the N content in plant tissues and the root system architecture of soybean plants grown with a variable supply of Mg combined with N, which highlights the importance of N and Mg availability in the growth medium in regulating root system architecture and nodule formation. The number of rhizobial cells colonizing soybean roots was highest under the HNHMg treatment (6.78 × 104 CFUs/cm of root tip), followed by the HNLMg (4.72 × 104 CFUs/cm of root tip) and LNHMg (4.10 × 104 CFU/cm of root tip) treatments, and lowest under the LNLMg (1.84 × 104 CFUs/cm of root tip) nutrient conditions. The results of this study contribute to new insights for the improvement of the root system and the symbiotic performance of rhizobia inoculated on legumes, stressing the importance of a balanced supply of nutrients.

Protective role of selenium against chromium stress involving metabolites and essential elements in Brassica juncea L. seedlings.

The present study aimed at the potential role of selenium in providing protection to plants subjected to chromium toxicity. The study was carried out on 15-day-old seedlings of Brassica juncea raised in the solutions of Cr (300 µM) and Se (2, 4 and 6 µM), both alone and in combinations under controlled laboratory environment. The effects were studied on growth, plant metabolites (involved in osmotic homeostasis and stress protection), and essential elements. The results showed that the exposure of B. juncea seedlings to 300 µM Cr led to an increase in the contents of total sugars, reducing sugars, non-reducing sugars, total phenols and flavonoids. However, a significant decline in growth characteristics, the contents of proteins and free amino acids was observed. The essential elements (Na, K, Ca, Mg, C, H, N) also decreased in response to Cr. Se application in binary combinations, on the other hand, aided in improving seed germination (19%), root (88.3%) and shoot (18.2%) lengths. It also helped to increase the contents of sugars [total (16.3%), reducing (21.6%) and non-reducing (15.2%)], phenols (36.7%) and flavonoids (27.4%), thereby aiding in alleviating the phytotoxicity of Cr. The profiling of polyphenols and amino acids, and histological study of phenols supported the above results. The contents of essential elements also showed a significant increase, while Cr uptake was observed to decline by Se supplementation. The observations from the present study indicate that Se has the ability to influence primary and secondary metabolism, improve mineral nutrition and reduce Cr uptake in B. juncea seedlings to combat the Cr phytotoxicity and enhance the tolerance against stress.

Mitigation of NaCl Stress by Arbuscular Mycorrhizal Fungi through the Modulation of Osmolytes, Antioxidants and Secondary Metabolites in Mustard (Brassica juncea L.) Plants.

Present work was carried out to investigate the possible role of arbuscular mycorrhizal fungi (AMF) in mitigating salinity-induced alterations in Brassica juncea L. Exposure to NaCl stress altered the morphological, physio-biochemical attributes, antioxidant activity, secondary metabolites and phytohormones in the mustard seedlings. The growth and biomass yield, leaf water content, and total chlorophyll content were decreased with NaCl stress. However, AMF-inoculated plants exhibited enhanced shoot and root length, elevated relative water content, enhanced chlorophyll content, and ultimately biomass yield. Lipid peroxidation and proline content were increased by 54.53 and 63.47%, respectively with 200 mM NaCl concentration. Further increase in proline content and decrease in lipid peroxidation was observed in NaCl-treated plants inoculated with AMF. The antioxidants, superoxide dismutase, ascorbate peroxidase, glutathione reductase, and reduced glutathione were increased by 48.35, 54.86, 43.85, and 44.44%, respectively, with 200 mM NaCl concentration. Further increase in these antioxidants has been observed in AMF-colonized plants indicating the alleviating role of AMF to salinity stress through antioxidant modulation. The total phenol, flavonoids, and phytohormones increase with NaCl treatment. However, NaCl-treated plants colonized with AMF showed further increase in the above parameters except ABA, which was reduced with NaCl+AMF treatment over the plants treated with NaCl alone. Our results demonstrated that NaCl caused negative effect on B. juncea seedlings; however, colonization with AMF enhances the NaCl tolerance by reforming the physio-biochemical attributes, activities of antioxidant enzymes, and production of secondary metabolites and phytohormones.