Current climate change scenarios require strategies that mitigate the effects of water deficits. Given that chitosan stimulates induced resistance responses, we tested the hypothesis that foliar application of this polysaccharide can have positive effects on the primary metabolite, antioxidant, and osmoregulatory metabolisms of sorghum, mitigating the effects of water deficit on grain yield. Sorghum plants were cultivated under either irrigated or water-deficit conditions and were either treated or untreated with chitosan, and we assessed the following responses: water potential, gas exchange, nutritional status, biosynthesis of primary and osmoregulatory metabolites, the activity of the antioxidant system constituents, and hydrogen peroxide and malondialdehyde contents. An active methodology was used to impose water stress on plants grown in pots with 20 kg of soil, 06 replications per treatment. Sorghum plants subjected to water deficit that were treated with chitosan exhibited higher stomatal conductance and transpiration than the untreated plants. Water restriction reduced the nutrient contents of leaves, but in the irrigated plants, chitosan treatment increased the tissue contents of certain nutrients and leaf concentrations of total proteins and total amino acids. In the plants under water-deficit conditions that were treated with chitosan, an elevated photosynthetic rate contributed to an increase in carbohydrate accumulation and a higher production of panicle and grain dry biomass compared with the untreated plants. The activity of catalase and ascorbate peroxidase also increased in response to chitosan. Overall, chitosan was effective in enhancing the water deficit tolerance of sorghum plants cultivated under water-deficit conditions by 57%. With this work, we generate perspectives for studies focusing on the development of water-deficit-resistant sorghum lineages, by means of chitosan elicitation.
Treatments that increase the germination potential and vigor of Glycine max seedlings are continuously being stimulated, with the aim of achieving a higher percentage of emergence and better performance in the field. Considering the relationship of tryptophan with germination-associated phytohormones, this study tested the hypothesis that exogenous supply of tryptophan to soybean seeds can affect germination, physiological vigor, and the accumulation of primary and oxidative metabolism molecules in seedlings. Soybean seeds were exposed to soaking solutions containing different concentrations of the amino acid (0, 25, 50, 100, and 200 µM), and the seedlings were evaluated at three time periods, at 8 h after sowing (HAS), and 5 and 14 days after sowing (DAS). Treated seeds showed better germination fitness and seedlings showed greater vigor, and these parameters increased with increasing concentrations of tryptophan. In the initial hours and days of germination process evaluation (14 HAS and 5 DAS), the activities of starch metabolism enzymes (α- and β-amylase) tended to be higher, resulting in increased contents of sucrose, reducing sugars, and total soluble solids at 8 DAS, constituting an important metabolic effect for seedling growth. On the other hand, the induction of germination and vigor promoted by exogenous tryptophan in soybean seedlings occurred by stimulating the metabolic pathways of oxidative stress, resulting in increased concentrations of H2O2, malondialdehyde, and proline in the tissues. Additionally, it led to increased activities of the antioxidant enzymes superoxide dismutase and ascorbate peroxidase. These parameters were responsive to increasing supplied concentrations of tryptophan. Thus, the metabolic stress in soybean seeds induced by auxin seems to be an important inductive pathway for germination and vigor of G. max seeds.
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