Okawa Shigenori, Makino Amane, Mae Tadahiko
Department of Applied Plant Science, Graduate School of Agricultural Sciences, Tohoku University, Tsutsumidori-Amamiyamachi, Sendai 9818555, Japan.
Ann Bot. 2003 Sep;92(3):357-64. doi: 10.1093/aob/mcg147. Epub 2003 Jul 9.
Low irradiance in the early phase of grain filling in rice often results in a low grain yield, but its effects on the partitioning of previously or recently assimilated carbon within the plant or panicle have not been seriously examined. The objective of this study was to demonstrate the effect of shading during the different stages in the early phase of grain filling on the partitioning of previously or recently assimilated carbon among constituent organs and into superior and inferior spikelets of the panicle in rice (Oryza sativa L. 'Sasanishiki') plants using 13C as a tracer. Plants were grown either under low (shading) or moderate (non-shading) irradiance (120 and 800 micromol quantum m(-2) s(-1)) for 3 or 4 d before or after the 13CO2 feeding at heading, full-heading or milky stages during the early phase of grain filling. Four days after the 13CO2 feeding, the proportion of labelled (previously assimilated) carbon partitioned into the panicle was 17% higher in plants grown under low irradiance compared with plants grown under moderate irradiance at the full-heading stage (7-11 d after heading), while the proportion partitioned into the culm was 13% lower. The light treatments for 3 d were conducted before the 13CO2 feeding and partitioning of the labelled (recently-assimilated) carbon into spikelets was examined 6 h after feeding. The amount of labelled carbon partitioned into the spikelets of the secondary branch (inferior grains) in the plants grown under low irradiance was only 31% when compared with plants grown under moderate irradiance at the full-heading stage, although the partitioning of labelled carbon into the apical spikelets of the primary branch (superior grains) was not affected by the light treatments. These results clearly indicate that preferential partitioning of assimilated carbon into the panicle occurs under low irradiance at around 7-11 d after heading and that the priority of superior spikelets for assimilated carbon intensifies. This phenomenon is thought to be an important strategy for such rice cultivars as used in this study to achieve a certain proportion of ripened grains even under light limited conditions.
水稻灌浆初期光照不足常常导致产量降低，但其对植株或稻穗中先前或近期同化碳分配的影响尚未得到深入研究。本研究的目的是利用13C作为示踪剂，证明灌浆初期不同阶段遮光对水稻（Oryza sativa L.‘Sasanishiki’）植株中先前或近期同化碳在各组成器官间以及在稻穗的上位和下位小穗间分配的影响。在抽穗期、齐穗期或灌浆初期的乳熟期进行13CO2饲喂之前或之后，将植株分别置于低（遮光）或中等（不遮光）光照强度（120和800微摩尔量子·米-2·秒-1）下生长3或4天。在13CO2饲喂后4天，在齐穗期（抽穗后7 - 11天），与中等光照强度下生长的植株相比，低光照强度下生长的植株中分配到稻穗的标记（先前同化）碳比例高17%，而分配到茎秆的比例低13%。在13CO2饲喂前进行3天的光照处理，并在饲喂后6小时检测标记（近期同化）碳向小穗的分配情况。在齐穗期，与中等光照强度下生长的植株相比，低光照强度下生长的植株中分配到二次枝梗（下位籽粒）小穗的标记碳量仅为31%，尽管光照处理对分配到一次枝梗（上位籽粒）顶端小穗的标记碳没有影响。这些结果清楚地表明，抽穗后7 - 11天左右在低光照条件下，同化碳优先分配到稻穗中，并且上位小穗对同化碳的优先性增强。这种现象被认为是本研究所用的这类水稻品种即使在光照受限条件下仍能实现一定比例成熟籽粒的重要策略。
