The Action Mechanism Of Elongated-Uppermost-Internode Gene Regulation On Internode Elongaton Of Rice

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-intemode length of 50cm. By contrast, plants with Eui gene have an uppermost intemode 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, GA₁, 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 intemode elongation. The GA₁ level in the panicles of XeB(1) were 434.34 pmol/g. FW, three times higher than that of XB. At heading stage, GA₁ level in the panicles of XeB(1) increased dramatically, being 5957.28 pmol/g.FW, 16 times the GA₁ amount of XB. During the same period, GA₁ amount in the flag leaves also raised to a level of 3792.72 pmol/g. FW, three times the GA₁ level of XB. When XeB(1) plants were treated with GA biosynthesis inhibitor S-3307 at late booting stage, the plant growth of XeB(1) 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 intemode of XeB(1) were inhibited substantially, having a length of 30cm, similar to that of XB. While both XeA(1) and XeB(1) showed more sensitivity to GA3 than XA and XB at seedling stage, only XeA(1) showe higher sensitivity at heading stage than XA. It can be concluded that the unusual increase of GA₁ levels both in the panicles and the flag leaves of euil rice promoted euil rice to have a great elongation in its uppermost intemode. 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 intemode elongation, euil gene also promotes the second intemode to elongate significantly. Since euil gene involved both GA₁ 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 GA₁ level of 3174pmol/g. FW, XeB(2) contained twice more GA₁ amount than that of XB. Treatment with S-3307 led to a noteble reduction in plant height of XeB(1), making its height close to that of XB. By contrast, when applying GA₃ to XB plants, they grow rapidly and reached a hight similar to that of XeB(2). At late booting stage, the panicles of a few XeB(2) plants were removed and this resulted in a reduction of uppermost-intemode length, but the degree of inhibition was significantly lower than that of XeB(1). The eui2 rice didn't show more sensitivity to GA₃ than Eui2. Above results indicated: at heading stage eui2 promote rice plants to extend their uppermost intemodes vigorously by enhancing the GA₁ levels in the flag leaves of eui2 rice plants dramatically. The eui2 didn't show strong expression in the panicles, consequently, eui2 rice plants had an uppermost intemode a little shorter than that of euil rice plants. Since eui2 onlyinvolved GAi 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 intemode 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.