Applications of polysaccharides (β-glucan) for physiological and biochemical parameters for evaluation rice tolerance under salinity stress at seedling stage

Effects of Exogenous Spermidine on Seed Germination and Physiological Metabolism of Rice Under NaCl Stress

Salt stress is one of the principal abiotic stresses limiting agricultural production and seriously inhibiting seed germination rates. This study selected the salt-tolerant rice variety HD961 and the salt-sensitive rice variety 9311 as experimental materials to investigate the physiological and metabolic effects of exogenous Spd seed priming on rice seeds and seedlings under NaCl stress. The experiment involved treating rice seeds with 0.1 mmol·L-1 Spd and then subjecting them to 100 mmol·L-1 NaCl stress for 24 h, with sampling for analysis at the 24 h and the four-leaf-one-heart stage. The results indicated that under NaCl stress, the rice's germination and vigor indices significantly decreased. However, exogenous Spd seed priming reduced the accumulation of malondialdehyde, enhanced the capacity for osmotic adjustment, and increased the amylase and antioxidant activity by 50.07% and 26.26%, respectively. Under NaCl stress, the morphological development of rice seedlings was markedly inhibited, whereas exogenous Spd seed priming improved the aboveground and belowground biomass of the rice under stress conditions, as well as the content of photosynthetic pigments. It also reduced the damage to seedlings from electrical conductivity, helped maintain ionic balance, and promoted the excretion of Na+ and Cl- and the absorption of K+ and Ca2+. In the salt-sensitive rice variety 9311, the soluble protein content increased by 15.12% compared to the salt-tolerant rice variety HD961, especially under 100 mmol·L-1 NaCl stress, when the effect of exogenous Spd seed priming was more pronounced. In summary, these findings might provide new research perspectives and strategies for improving the salt tolerance of rice under NaCl stress.

β-Glucan and its nanocomposites in sustainable agriculture and environment: an overview of mechanisms and applications

β-Glucan is an eco-friendly, biodegradable, and economical biopolymer with important roles for acquiring adaptations to mitigate climate change in crop plants. β-Glucan plays a crucial role in the activation of functional plant innate immune system by triggering the downward signaling cascade/s, resulting in the accumulation of different pathogenesis-related proteins (PR-proteins), reactive oxygen species (ROS), antioxidant defense enzymes, Ca2+-influx as well as activation of mitogen-activated protein kinase (MAPK) pathway. Recent experimental studies have shown that β-glucan recognition is mediated by co-receptor LysMPRR (lysin motif pattern recognition receptor)-CERK1 (chitin elicitor receptor kinase 1), LYK4, and LYK5 (LysM-containing receptor-like kinase), as well as different receptor systems in plants that could be plant species-specific and/or age and/or tissue-dependent. Transgenic overexpression of β-glucanase, chitinase, and/or in combination with other PR-proteins like cationic peroxidase, AP24,thaumatin-likeprotein 1 (TLP-1) has also been achieved for improving plant disease resistance in crop plants, but the transgenic methods have some ethical and environmental concerns. In this regard, elicitation of plant immunity using biopolymer like β-glucan and chitosan offers an economical, safe, and publicly acceptable method. The β-glucan and chitosan nanocomposites have proven to be useful for the activation of plant defense pathways and to enhance plant response/systemic acquired resistance (SAR) against broad types of plant pathogens and mitigating multiple stresses under the changing climate conditions.

Effects of strigolactone on photosynthetic and physiological characteristics in salt-stressed rice seedlings

Saline stress has been identified as the primary factor inhibiting rice seedling growth, which represents a complex abiotic stress process. Most plant hormones have been shown to alleviate the plant damage caused by salt stress. The effects of synthetic strigolactone (GR24) on Jinongda 667 rice seedlings treated with 200 mM NaCl were studied. Photosynthesis and its related physiological characteristics were analyzed in salt-stressed rice seedlings treated with GR24. NaCL stress inhibited the growth of the rice, including plant height and root length, by approximately 14% and 40%, respectively. Compared to the control check group (CK), the adverse effects of salt stress on the growth status, leaf photosynthesis, and physiological/biochemical indices in the rice seedlings were alleviated in the GR24 treatment group. With increases in the GR24 concentration, the plant height and root length of the seedlings increased. The plant height in the groups treated with 1/2 Hoagland's complete nutrient solution + 200 mM NaCl +1 μM GR24 (T4) and 1/2 Hoagland's complete nutrient solution + 200 mM NaCl +5 μM GR24 (T5) were significantly different than the 1/2 Hoagland's complete nutrient solution + 200 mM NaCl group (T1) (P < 0.05), and there were significant differences between the T5 and T1 groups in root length (P < 0.05).The chlorophyll content in the rice seedling leaves was significantly different between the T1 group and all other groups (P < 0.05). The net photosynthetic rate of the T1 group was not significantly different from the T2 group (P > 0.05). The transpiration rate, stomatal conductance, and intercellular CO₂ concentrations showed the same trends as the net photosynthetic rate. The MAD, POD, and SOD activities were significantly increased by 68%, 60%, 14%, respectively, compared to the CK group (P < 0.01). When the GR24 concentration was 1 μM, the rice seedlings were resistant to the adverse effects of high salt stress. Therefore, the addition of proper concentrations of GR24 could improve the rice yield in saline-alkali land.