Study on chalky grain rice by establishing the long-term detached ear culture method

本研究旨在通过建立和利用长期离体穗培养方法来阐明垩白粒水稻的发生机理。在本研究的第一部分，作者研究了几种抗氧化剂和酸化剂添加到培养基中对水稻穗部生长的影响。即使没有建立长期的穗培养方法，但无论是0.01%的亚硫酸、5 mM的L抗坏血酸、1.5 mM的亚硫酸盐或硫酸盐或亚硫酸盐，似乎都能较长时间地促进穗的生长。另一方面，为了用离体穗培养法初步检验已有研究成果提出的与垩白粒发生有关的假说，作者在灌浆期进行了赤霉素类和赤霉素类生物合成抑制剂的田间应用试验。结果表明，外源赤霉素处理提高了水稻籽粒发育过程中的α-淀粉酶活性和垩白粒的亲缘关系，表明赤霉素和α-淀粉酶均参与了垩白粒的发生。由于赤霉素生物合成抑制剂的作用在本初步研究中还不清楚，因此有必要准确检测抑制剂的浓度、使用时机和使用方式对垩白粒发生的影响。

This study aimed to elucidate the mechanism about the occurrence of chalky grain rice by establishing and using the long-term detached ear culture method. In the first part of this study the author examined the effect of several anti-oxidants and acidifying reagents addition to culture medium on rice ear growth. Even though the long-term detached ear culture method has not been established, application of either 0.01% sulfurous acid, 5mM L-ascorbate, 1.5mM sulfite or sulfate or sulfite acid seemed to be effective far longer-period ear growth. On the other hand, in order to preliminarily examine hypothesis related to the chalky grain occurrence which has been suggested from research achievement so far using the detached ear culture method, the author conducted field trials on application of gibberellin and gibberellin biosynthesis inhibitors during grain filling period. The results showed that the exogenous gibberellin treatment increased the a-amylase activity of the developing rice seeds and the parentage of the chalky grains even at a rice plant population level (i.e. at a field level), suggesting that both gibberellin and α-amylase are involved in the occurrence of chalky grain. Because the effect of gibberellin biosynthesis inhibitors was not clear in this preliminary study, it will be necessary to precisely examine the influence of concentration, timing, and way of the inhibitor application on the occurrence of chalky grain.