Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113-8657, Japan.
Ann Bot. 2011 Aug;108(2):253-61. doi: 10.1093/aob/mcr137.
When rice seeds germinate under complete submergence, only the coleoptile elongates efficiently. It has been reported previously that coleoptile elongation is reduced in the rice alcohol dehydrogenase 1 (ADH1)-deficient mutant, reduced adh activity (rad). The aim of this study was to elucidate how expressions of genes responsible for coleoptile elongation are affected by the ADH1 deficiency in the rad mutant under submergence.
To identify genes whose expressions are changed in the rad coleoptile at an early stage in germination (i.e. 1 d after imbibition), coleoptiles of the rad mutant and its wild type (WT) were isolated by laser microdissection, and their mRNA levels were examined with a microarray.
The microarray analysis identified 431 genes whose transcript levels were different between rad and WT. Interestingly, among the down-regulated genes in the rad coleoptile, 17·5 % were cell division-related genes and 5·1 % were cell elongation-related genes. It was found that cell division started at 1 d after imbibition and then gradually ceased, whereas in the WT coleoptile cell elongation started between 1 d and 2 d after imbibition and then continued. However, neither cell division nor cell elongation actively occurred in the rad coleoptile, in which the amounts of ATP were reduced.
These results indicate that cell division, as well as cell elongation, occur during coleoptile elongation in rice under complete submergence, and that the reduced ATP levels caused by the ADH1 deficiency repress both of them, thereby impairing coleoptile elongation in the rad mutant under submerged conditions.
当水稻种子在完全淹没的条件下发芽时，只有胚芽鞘能有效地伸长。此前有报道称，在缺乏醇脱氢酶 1 (ADH1) 的水稻突变体 rad 中，胚芽鞘伸长受到抑制，adh 活性降低 (rad)。本研究旨在阐明在淹没条件下，ADH1 缺乏对 rad 突变体胚芽鞘伸长的影响如何导致与胚芽鞘伸长相关的基因表达发生变化。
为了鉴定在萌发早期（即吸水后 1 天）rad 突变体胚芽鞘中表达发生变化的基因，通过激光微切割分离 rad 突变体及其野生型 (WT) 的胚芽鞘，并使用微阵列检测其 mRNA 水平。
微阵列分析鉴定出 431 个基因在 rad 和 WT 之间的转录水平不同。有趣的是，在 rad 胚芽鞘中下调的基因中，有 17.5%是细胞分裂相关基因，有 5.1%是细胞伸长相关基因。研究发现，细胞分裂在吸水后 1 天开始，然后逐渐停止，而在 WT 胚芽鞘中，细胞伸长在吸水后 1 天到 2 天之间开始，并持续下去。然而，在 rad 胚芽鞘中，既没有发生细胞分裂，也没有发生细胞伸长，因为 rad 胚芽鞘中的 ATP 含量减少。
这些结果表明，在完全淹没条件下，水稻胚芽鞘的伸长过程中既发生细胞分裂，也发生细胞伸长，而 ADH1 缺乏导致的 ATP 水平降低抑制了这两种过程，从而损害了 rad 突变体在淹没条件下的胚芽鞘伸长。
