Grain chalkiness is a highly undesirable trait that adversely affects rice quality. This chalkiness is easily influenced by the application of chemical nitrogen (N) fertilizer at the late growth stage. However, on the molecular mechanism underlying grain chalkiness caused by late N fertilization is not fully clear. In this study, proteomic differences in expression were determined in developing grains exposed to N topdressing (108 kg N ha⁻¹, N+) and a control (0 kg N ha⁻¹, N0), using the rice variety OM052, which has a high level of chalkiness. A total of 198 differentially expressed proteins (DEPs) were detected between the N+ and N0 treatments, including 9 up-regulated proteins and 189 down-regulated proteins. Of these DEPs, approximately half were associated with carbohydrate metabolism (glycolysis, tricarboxylic acid cycle, pentose phosphate pathway, fermentation and starch metabolism) and N metabolism (protein synthesis, folding, degradation and storage, amino acid synthesis and catabolism). A detailed pathway dissection revealed that multiple metabolic pathways during the grain filling stage were involved in the N-induced grain chalkiness. Reduced abundances of proteins associated with respiratory metabolism and energy metabolism drastically impaired the biosynthesis and deposition of starch in the developmental endosperms, which might be a crucial trigger for the increase in grain chalkiness. The disturbed N metabolism and differential expression of storage proteins up-regulated during the grain filling stage are able to partially explain the occurrence of grain chalkiness in rice.

谷物白垩度是非常不利的特性，会对稻米品质产生不利影响。这种垩白度很容易受到生长后期化学氮肥的影响。然而，关于由晚氮施肥引起的谷物垩白的分子机制尚不完全清楚。在这项研究中，在暴露于N追肥（108 kg N ha ^-1，N +）和对照（0 kg N ha ^-1）的发育中的谷物中确定了蛋白质组学差异，N0），使用高白垩度的水稻品种OM052。在N +和N0处理之间共检测到198个差异表达蛋白（DEP），包括9个上调蛋白和189个下调蛋白。在这些DEP中，大约一半与碳水化合物代谢（糖酵解，三羧酸循环，磷酸戊糖途径，发酵和淀粉代谢）和N代谢（蛋白质合成，折叠，降解和储存，氨基酸合成和分解代谢）有关。详细的途径解剖显示，在籽粒充实阶段，多个代谢途径都与氮诱导的谷粒垩白有关。与呼吸代谢和能量代谢有关的蛋白质丰度降低，严重损害了发育胚乳中淀粉的生物合成和沉积，这可能是谷物白垩度增加的关键触发因素。籽粒灌浆过程中氮代谢的紊乱和贮藏蛋白的差异表达能够部分解释水稻籽粒垩白的发生。