Exogenous 6-benzylaminopurine enhances waterlogging and shading tolerance after anthesis by improving grain starch accumulation and grain filling

Integrated physiological, transcriptomic and metabolomic analyses reveal the mechanism of peanut kernel weight reduction under waterlogging stress

Waterlogging stress (WS) hinders kernel development and directly reduces peanut yield; however, the mechanism of kernel filling in response to WS remains unknown. The waterlogging-sensitive variety Huayu 39 was subjected to WS for 3 days at 7 days after the gynophores touched the ground (DAG). We found that WS affected kernel filling at 14, 21, and 28 DAG. WS decreased the average filling rate and kernel dry weight, while transcriptome sequencing and widely targeted metabolomic analysis revealed that WS inhibited the gene expression in starch and sucrose metabolism, which reduced sucrose input and transformation ability. Additionally, genes related to ethylene and melatonin synthesis and the accumulation of tryptophan and methionine were upregulated in response to WS. WS upregulated the expression of the gene encoding tryptophan decarboxylase (AhTDC), and overexpression of AhTDC in Arabidopsis significantly reduced the seed length, width, and weight. Therefore, WS reduced the kernel-filling rate, leading to a reduction in the 100-kernel weight. This survey informs the development of measures that alleviate the negative impact of WS on peanut yield and quality and provides a basis for exploring high-yield and high-quality cultivation, molecular-assisted breeding, and waterlogging prevention in peanut farming.

Exogenous Chemicals Used to Alleviate or Salvage Plants under Flooding/Waterlogging Stress: Their Biochemical Effects and Perspectives

Plant flooding/waterlogging stress (FWS) can be a threat to food security worldwide due to climate change. To mitigate its potential devastation, numerous exogenous chemicals (ECs) have been used to demonstrate their effectiveness on alleviating FWS for the last 20 years. This review has summarized the most recent findings on use of various ECs as either nutrients or regulatory substances on crop plants under FWS and their roles involved in improving root respiration of seedlings, optimizing nutritional status, synthesizing osmotic regulators, enhancing the activity of antioxidant enzymes, adjusting phytohormone levels, maintaining photosynthetic systems, and activating flood-tolerance related gene expressions. The effect of ESs on alleviating plants under FWS proves to be beneficial and useful but rather limited unless they are applied on appropriate crops, at the right time, and with optimized methods. Further research should be focused on use of ESs in field settings and on their potential synergetic effect for more FWS tolerance.

Exogenous 6-BA enhances salt tolerance of Limonium bicolor by increasing the number of salt glands

KEY MESSAGE

Exogenous 6-BA can increase endogenous hormone content, improve photosynthesis, decrease Na+ by increasing leaf salt gland density and salt secretion ability, and reduce ROS content so that it can promote L. bicolor growth. 6-benzyl adenine (6-BA) is an artificial cytokinin and has been widely applied to improving plant adaptation to stress. However, it is rarely reported that 6-BA alleviates salt damage of halophytes. In this paper, we treated Limonium bicolor seedlings, a recretohalophyte with high medicinal and ornamental values, with 300 mM NaCl and different concentrations of 6-BA (0.5, 1.0, and 1.5 mg/L) and measured plant growth, physiological index, the density of salt gland, and the salt secretion ability of leaves. The results showed that exogenous applications 1.0 mg/L 6-BA significantly improved plant growth and photosynthesis, increased cytokinin and auxins contents, K+ and organic soluble matter contents, the activities of SOD, CAT, APX, and POD, and decreased Na+, H2O2, and O2- contents compared to that treated with 300 mM NaCl. Further research showed that exogenous 6-BA significantly increased the density of salt gland and the salt secretion ability of leaves by upregulating the expression of the salt gland developmental genes, therefore, can secrete more excess Na+, and thus reduces the Na+ concentration in leaves, which can alleviate Na+ damage to the species. In all, exogenous 1.0 mg/L 6-BA can increase endogenous hormone, improve photosynthesis, decrease Na+ by increasing secretion ability, and reduce ROS content of L. bicolor so that it can improve the growth. These results above systematically prove the new role of 6-BA in salt tolerance of L. bicolor.

Effects of 6-Benzyladenine (6-BA) on the Filling Process of Maize Grains Placed at Different Ear Positions under High Planting Density

Increasing grain weight under dense planting conditions can further improve maize yield. 6-BA is known to be involved in regulating grain development and influencing grain weight. Maize grain development is closely linked to starch accumulation and hormone levels. In this work, the effects of applying 6-BA at the flowering stage under high density on the grain filling characteristics, starch content, starch synthesis critical enzyme activity, and endogenous hormones levels of maize grains (including inferior grains (IGs) and superior grains (SGs)) of two high-yielding summer maize varieties widely cultivated in China were investigated. The findings indicated that applying 6-BA significantly improved maize yield compared to the control, mainly as a result of increased grain weight due to a faster grain filling rate. Additionally, the activities of enzymes associated with starch synthesis, including sucrose synthase (SuSy), ADP-glucose pyrophosphorylase (AGPase), granule-bound starch synthase (GBSS), soluble starch synthase (SSS), and starch branching enzyme (SBE), were all increased following 6-BA application, thus facilitating starch accumulation in the grains. Applying 6-BA also increased the zeatin riboside (ZR), indole-3-acetic acid (IAA), and abscisic acid (ABA) levels, and reduced the gibberellin (GA3) level in the grains, which further improved grain filling. It is worth noting that IG had a poorer filling process than SG, possibly due to the low activities of critical enzymes for starch synthesis and imbalanced endogenous hormones levels. However, IG responded more strongly to exogenous 6-BA than SG. It appears that applying 6-BA is beneficial in improving filling characteristics, promoting starch accumulation by enhancing the activities of critical enzymes for starch synthesis, and altering endogenous hormones levels in the grains, thus improving grain filling and increasing the final grain weight and yield of maize grown under crowded conditions. These results provide theoretical and technical support for the further utilization of exogenous hormones in high-density maize production.