The Action Mechanism Of Elongated-Uppermost-Internode Gene Eui In Rice(Oryza Sativa L.)

The eui rice, carrying elongated-uppermost-internode gene eui, elongates its uppermost internode very rapidly at heading stage. While rice plants with single recessive gene euil extend the uppermost internode up to 60 cm, rice plants with eui2 gene grow with an uppermost-internode length of 50cm. By contrast, plants with Eui gene have an uppermost internode length of 30cm long. Six allelic gene lines on Xieqingzao background, i.e. Xieqingzao maintainer lines XeB( I), XeB(2), XB possessing gene euil, eui2, Eui respectively, and their corresponding Xieqingzao CMS lines XeA( 1), XeA(2), XA, were used as materials. By determining the levels of endogenous plant hormones, GA,, IAA, ABA, in various organs at different growth stages; applying inhibitors and exogenous hormones to eui rice plants; as well as removing some organs of eui rice, the action mechanism of euil and eui2 were studied.Rice plants with euil gene contained fairly high GA1 contents in the panicles at the stage of the second internode elongation. The GA, level in the panicles of XeB(1) were 434.34 pmollg.FW, three times higher than that of XB. At heading stage, GA, level in the panicles of XeB(l) increased dramatically, being 5957.28 pmol/g.FW, 16 times the GA, amount of XB. During the same period, GA, amount in the flag leaves also raised to a level of 3792.72 pmol/g.FW, three times the GA, level of XB. When XeB(I) plants were treated with GA biosynthesis inhibitor S-3 307 at late booting stage, the plant growth of XeB( I) was greatly inhibited, with a reduction of 25 cm in plant height. When the panicles of XeB(1) were removed at late booting stage, the elongation of uppermost internode of XeB( 1) were inhibited substantially, having a length of 30cm, similar to that of XB. While both XeA(1) and XeB(l) showed more sensitivity to GA3 than XA and XB at seedling stage, only XeA(1) showed higher sensitivity at heading stage than XA. It can be concluded that the unusual increase of GA, levels both in the panicles and the flag leaves of ezdl rice promoted euil rice to have a great elongation in its uppermost internode. It is also can be inferred that as the panicles of rice plants with euil already contained higher GA1 content at the stage of second internode elongation, euil gene also promotes the second internode to elongate significantly. Since euil gene involved both GA, levels and sensitivity to GA3, euil gene is probably not a simple structural gene. Further study on euil is needed.Rice plants with eui2 gene had a great increase of GA1 content in the flag leaves. Having a GA, level of 31 74pmol/g.FW, XeB(2) contained twice more GA, amount than that of XB. Treatment with 5-3307 led to a noteble reduction in plant height of XeB(l), making its height close to that of XB. By contrast, when applying GA3 to XB plants, they grow rapidly and reached a bight similar to that of XeB(2). At late booting stage, the pariicles of a fewXeB(2) plants were removed and this resulted in a reduction of uppermost-internode length, but the degree of inhibition was significantly lower than that of XeB(1). The eui2 rice didn抰 show more sensitivity to GA3 than Eui2. Above results indicated: at heading stage eui2 promote rice plants to extend their uppermost internodes vigorously by enhancing the GA1 levels in the flag leaves of eui2 rice plants dramatically. The eui2 didn抰 show strong expression in the panicles, consequently, eu2 rice plants had an uppermost internode a little shorter than that of euil rice plants. Since eui2 only involved GA1 level, it was inferred that eui2 might be a structural gene, a gene related to GA biosynthesis.Since both euil and eui2 had relation with GA and so far few genes have been found which promote uppermost internode to elongate rapidly, it is suggested that eui rice could be used as a new model plant for studying stem elongation, and it will be of great value both in theroy and application to clone and transform euil and eui2 gene.