Hatakeyama Yuto, Wakamatsu Kenichi, Tanaka Akio, Tanogashira Taku, Nonami Hiroshi, Nakano Hiroshi, Wada Hiroshi
Kyushu Okinawa Agricultural Research Center, National Agriculture and Food Research Organization, Chikugo, Fukuoka, Japan.
Graduate School of Agriculture, Ehime University, Matsuyama, Ehime, Japan.
Planta. 2025 Aug 13;262(4):79. doi: 10.1007/s00425-025-04793-z.
The regulation of vacuolar compartmentation and protein synthesis during the early ripening stage might be responsible for rice appearance at high temperature. High temperature at the early ripening stage disrupts protein synthesis to arrest starch and storage protein accumulation in the rice endosperms, leading to the occurrence of chalky kernels (CK), such as white-back kernels (WBK) and basal-white kernels (BWK). In contrast, adequate nitrogen (N) application might sustain protein synthesis and reduce chalky kernels. These processes might be associated with the regulation of vacuolar compartmentation and protein synthesis during heat adaptation, yet the exact cellular dynamics behind the reduction of endosperm air space when applying N have not been examined in the fields. In this study, plants at different N levels were treated under the same high temperatures in the fields and morphological analysis were carried out to examine the time course of changes in organelles compartmentation during the N-enhanced mitigation process. Light and transmission electron microscopic observations were conducted at dorsal and basal endosperm cells, at which chalky formation was presumed to occur under low N conditions during kernel development at high temperature. Results show that CK reached 25.0% in no N-applied plants under heat, whereas N treatment contrastingly decreased CK formation down to 10.7%. In the mature kernels, the areas of chalky cells, amyloplasts, and protein bodies (PBs) were smaller in chalky cells, compared with translucent cells. At the middle ripening stage, volumetric enlargement of protein storage vacuole concomitant with the arrested amyloplast development were both observed in the putative growing chalky cells, resulting in the formation of CK at the late ripening stage. In contrast, N application ameliorated the effect on rice appearance by diminishing the vacuolar size and enhancing protein synthesis to ensure cell size and amyloplast and PB development, increasing the transparency. Therefore, it is proposed that regulation of vacuolar compartmentation and protein synthesis at the ripening stage might be responsible for rice appearance under field conditions.
早熟期液泡区隔化和蛋白质合成的调控可能是导致水稻在高温下外观变化的原因。早熟期的高温会破坏蛋白质合成，从而阻止淀粉和贮藏蛋白在水稻胚乳中的积累，导致垩白粒（CK）的出现，如白背粒（WBK）和基部白粒（BWK）。相比之下，适量施氮可能维持蛋白质合成并减少垩白粒。这些过程可能与热适应过程中液泡区隔化和蛋白质合成的调控有关，但在田间尚未研究施氮时胚乳气腔减少背后的确切细胞动态。在本研究中，将不同氮水平的植株在田间相同高温条件下处理，并进行形态分析，以研究氮增强缓解过程中细胞器区隔化的时间变化过程。在背侧和基部胚乳细胞进行了光镜和透射电镜观察，在高温下籽粒发育的低氮条件下，推测这些细胞会发生垩白形成。结果表明，高温下不施氮植株的垩白粒率达到25.0%，而施氮处理则将垩白粒形成率显著降低至10.7%。在成熟籽粒中，与半透明细胞相比，垩白细胞中垩白细胞、淀粉体和蛋白体（PBs）的面积较小。在灌浆中期，在假定正在生长的垩白细胞中观察到蛋白质贮藏液泡的体积增大，同时淀粉体发育停滞，导致在灌浆后期形成垩白粒。相比之下，施氮通过减小液泡大小和增强蛋白质合成来改善对水稻外观的影响，以确保细胞大小以及淀粉体和PB的发育，从而提高透明度。因此，提出在田间条件下，成熟期液泡区隔化和蛋白质合成的调控可能是导致水稻外观变化的原因。
