穗分化期外施24-表油菜素内酯(EBR)促进水稻源、库及籽粒灌浆的生理机制

水稻产量高低与其籽粒灌浆能力的强弱密切相关, 而籽粒灌浆能力的强弱受源和库的影响。已有研究表明, 油菜素甾醇类化合物(brassinosteroids, BRs)对水稻生长发育和产量具有正向调节作用。为进一步阐明BRs调控水稻源强、库容和库活性的生理机制及其相互关系, 本研究在大田条件下, 以粳稻日本晴为试验材料, 在穗分化期喷施24-表油菜素内酯(24-epibrassinolid, EBR), 分析其相关影响。首先, 两种不同浓度的EBR处理通过促进光合产物的合成及其在灌浆过程中的转运提高了水稻的源强。其次, 两种浓度EBR处理均增大了水稻的库容, 但两种处理的影响方式存在差异, 低浓度处理(T1) 显著提高水稻籽粒的千粒重, 对穗粒数的影响较小; 高浓度处理(T2)则显著增加单位面积的穗数和穗粒数, 对千粒重的影响较小。再次, 两处理同时提高了水稻强、弱势粒的蔗糖裂解酶活性, 尤其对弱势粒酸性转化酶(acid invertase, AI)活性的影响较大, 有助于光合产物向弱势粒分配, 进而促进弱势粒淀粉合成和籽粒灌浆, 提高其充实度和结实率。最后, 两处理均显著增加了水稻的产量, T1和T2分别平均增加5.6%和15.2%, T2比T1平均增产9.1%。因此, 与低浓度EBR处理下的千粒重增大相比, 高浓度处理下穗粒数的增加对产量影响更大。综上所述, 穗分化期进行EBR处理能够增大水稻的源强、库容和库活性, 进而促进光合物质的积累和分配, 有利于籽粒灌浆; 在光合物质供应充足和库活性显著提高的基础上, 库容的增大有助于产量的明显提高。

Physiological Mechanisms of Promoting Source,Sink, and Grain Filling by 24-Epibrassinolide (EBR) Applied at Panicle Initiation Stage of Rice

Grain weight and yield of rice are clearly related to grain filling ability, which is strongly affected by source and sink. Studies of Brassinosteroids’ effects on growth, development and yield of rice have been reported. In order to further set forth the relative physiological characteristics and relationship, we set up field experiments to study the impacts of 24-epibrassinolid (EBR) sprayed at the panicle initiation stage of Nipponbare on source capacity, sink size, sink activity and grain filling. Both T1 (0.2 µmol L^-1 EBR) and T2 (1 µmol L^-1 EBR) treatments increased the source capacity by improving the accumulation of photosynthate and its translocation during grain filling stage. Both EBR treatments increased the sink size through different manners: T1 treatment increased the grain weight markedly but had little influence on panicle and grain amounts; and T2 treatment significantly increased number of panicles and grains per panicle whereas had little influence on grain weight. Two EBR treatments enhanced the sucrose lyase activity in both superior and inferior grains, especially for the activity of Acid Invertase (AI) in inferior grains. AI accelerated the transportation of photosynthate and the synthesis of starch in inferior grains. T1 and T2 significantly increased rice yield by an average of 5.6% and 15.2%, respectively, with 9.1% more in T2 than in T1. Therefore, compared with grain weight enhancement in T1, the increase of panicle and grain numbers in T2 had greater impact on rice yield. In summary, two EBR treatments at panicle differentiation stage can increase the source capacity, sink size and sink activity of rice, and then promote photosynthates accumulation and distribution, which is beneficial to grain filling. On the basis of sufficient photosynthates and strong sink activity, sink size enlargement can significantly increase the rice yield.