Effects of Potassium and Calcium on Root Exudates and Grain Quality During Grain Filling

The purposes of this study were to understand the root activity and root exudates of rice (Oryza sativa L.) in response to different levels of potassium (K) and calcium (Ca) nutrients and the effect of K and Ca on rice grain quality. Cultivars Yangdao 6 (indica) and Yangjing 9538 (japonica) were cultured in hydroponical solutions and treated with different Espino nutrition solutions from heading to maturity, which were supplemented with complete K and Ca (standard Espino nutrition solution, control), half K (1/2K), zero K (0K), half Ca (1/2Ca), and zero Ca (0Ca) nutrition. Compared to the control, the 0K treatment significantly decreased root activity, ATPase activity, and concentrations of citric acid, Ca2+, K+, and NH4+ in the root exudates, but accelerated root senescence; and the 0Ca treatment significantly decreased concentrations of oxalic acid, Ca2+, K+, and NH4+ in the root exudates. The oxalic acid concentration in root exudates was positively correlated (P < 0.01) with chalky grain percentage, chalkiness, and gel consistency of rice grain; whereas the citric acid concentration in exudates was negatively correlated (P < 0.01) with chalky grain percentage, chalkiness, and breakdown value, but positively correlated (P < 0.05) with setback value. At early (10 d after heading) and mid grain-filling (20 d after heading) stages, the concentrations of K+ and Ca2+ in root exudates were negatively correlated (P < 0.05) with chalky kernel percentage, chalkiness, and amylose contents, and the NH4+ concentration was also negatively correlated (P < 0.05) with amylose content of grain. This result indicates that root exudates are closely associated with grain quality. K and Ca nutrition regulate root exudates and consequently affect grain quality of rice.

摘 要以扬稻6号(籼稻)和扬粳9538(粳稻)为材料, 在水培条件下自抽穗至成熟设0K (不施K)、1/2K (标准Espino营养液的1/2K)、0Ca (不施Ca)、1/2Ca (标准Espino营养液的1/2Ca)以及对照(全K、Ca, 标准Espino营养液的K、Ca量) 5种处理, 研究了水稻根系及根系分泌物的变化及其与稻米外观品质、蒸煮食味品质的关系。结果表明, 与对照相比, 结实期无钾处理(0K)明显降低水稻根系活力、根系ATP酶活性和根系柠檬酸及Ca2+、K+和NH4+的分泌量, 加速根系的衰老; 无钙处理(0Ca)显著降低根系草酸及Ca2+、K+和NH4+的分泌。相关分析表明, 根系分泌的草酸与稻米的垩白米率、垩白度和胶稠度均呈极显著正相关; 根系分泌的柠檬酸与垩白米率、垩白度、崩解值呈极显著负相关, 而与消减值呈极显著正相关; 结实前中期(花后10 d, 20 d)根系分泌的[K+]、[Ca2+]与稻米垩白米率、垩白度和直链淀粉含量均呈显著或极显著负相关; 根系分泌的[NH4+]与直链淀粉含量也呈极显著负相关。表明根系分泌物与稻米品质有密切的关系, K、Ca营养水平对根系分泌物有调控作用, 进而影响稻米品质。