Gluconate enhanced the water uptake and improved the growth of rice seedlings under PEG-induced osmotic stress

Low-molecular-weight organic acid not only serves as a nutrient of plants or as a source of energy metabolism but also a bioactive molecule, which can be linked with hormones, nitrogen (N), and other signals to participate in regulating gene expression, stress response, growth, and development of plants via mechanisms that remain poorly understood. We investigated how the supply of gluconate and sulfate affects rice plant growth and water absorption at the same N supply under osmotic stress. Using a greenhouse hydroponic experimental approach, we assessed the physiology of rice seedlings supplied with C6H11O7NH4 (AG) and (NH4)(2)SO4 (AS) over multiple weeks. The root xylem sap rate in rice roots treated with AG increased significantly compared with AS treatment and the control under osmotic stress. The length of roots between 0.5 and 1.5 mm in diameter was obtained after treatment with polyethylene glycol (PEG) solutions containing AG, which was lower than those treated with PEG alone and PEG solutions containing AS. Compared with PEG alone and PEG solutions containing AS, AG induced a significant increase in root lignin under PEG-induced osmotic stress. However, relative to AS supply characteristics, the markedly reduced aerenchyma and porosity of roots, as well as higher root activity, increased fine root tips and length, and higher aquaporins and glutamate synthase (GS) activity in AG supply resulted in increased water uptake under osmotic stress. In addition, AG supply markedly increased leaf area and chlorophyll content. These results suggested that gluconate can enhance the water absorption capacity of the root system by promoting the growth and development of the root system, increasing the activity of aquaporin and GS and reducing the aeration tissue and porosity of the root system under osmotic stress.