The Mechanism Of Hormonal Regulation Of The Transformation Between Germination And Dormancy Of Rice Tiller Buds

Tillering is an important agronomic trait of rice, and the tillering regulation is an effective means for the establishment of excellent population. In the present study, we conducted a series of experiments in the nutrient solution, pot and field, and external nitrogen, external hormones and panicle removal were used to construct a series of rice population which were difference for the tiller buds growth. The hormonal changes and the expression levels of the genes related to rice tiller buds growth were emphatically measured, and the objects of the present study were to investigate the relationship of hormones and genes during the transformation between dormancy and germination of rice tiller buds, and the mechanism of hormonal regulation of the transformation between dormancy and germination of the tiller buds. The main results of the study are listed below.(1) The endogenous CTK and IAA play important roles in regulating the tiller buds growth. The CTK is the direct regulator for tiller buds growth, and the IAA is the indirect factor. In general, CTK promoted the growth of rice tiller buds, and IAA inhibited that. However, the transformation of dormancy and germination of tiller bus was not only regulated by the contents of IAA and CTK, but also regulated by the balance of them. The high IAA/CTK ratio promoted the transformation from germination to dormancy of the tiller bus, however, the low IAA/CTK ratio promoted the transformation from dormancy to germination of the tiller buds. The agronomic measures such as nitrogen, hormones and panicle removal all regulated the growth of tiller buds by regulated the contents and balance of the IAA and CTK. The low nitrogen inhibited the growth of tiller buds by inhibited the increasing of CTK and increased the ratio of IAA/CTK, and the promoting effect of high nitrogen and 6-BA on the tiller buds growth was significantly related to the increasing of the CTK contents and the decreasing of the ratio of IAA/CTK. The panicle removal increased the CTK contents and decreased the IAA contents, and then decreased the ratio of IAA/CTK and by this to promote the growth of tiller buds. External application of GA3 and IAA decreased the CTK contents and increased the IAA contents, and then increased the ratio of IAA/CTK and by this to inhibit the growth of tiller buds. The external NAA inhibited the growth of tiller buds by inhibited the increasing of CTK and increased the ratio of IAA/CTK. Besides IAA and CTK, ABA also regulated the growth of rice tiller buds, but ABA may not be the determining factor for the tiller buds growth.(2) IAA has a notable positional effect on the regulation of rice tiller bud growth, and the positional effect of IAA was closely related to its polar transport. In tillering stage, the basal internodes of rice are not elongated, and this structural characteristic may lead to a deficiency in polar transport of IAA in the aboveground organs. IAA applied to different leaves all can transport to nodes through polar transport, and then decreased the CTK content and increased the ratio of IAA/CTK, and by this to inhibited the growth of tiller buds. However, the IAA applied to root cannot transport to nodes by polar transport, this lead to that applied IAA to roots has no significant effect on tiller buds growth. Contrary to the basal internodes, the upper internodes elongated after heading and that structural characteristic separate its nodes from one another and lead to an enhance in polar transport of IAA in the aboveground organs. IAA applied to the leaves above the buds or the leaves at which the buds locate can be transported to the node. IAA can then inhibit the increase in CTK levels and increased the ratio of IAA/CTK, thus inhibiting the growth of the bud. However, IAA applied to the leaf below the bud cannot be transported to the node by polar transport; this may be the main reason why applied IAA to the leaf below the bud could not inhibit the growth of the bud. In contrast to IAA, CTK had no positional effect on rice tiller bud growth. Application of 6-BA to different leaves and roots significantly promoted the growth of rice tiller buds at both unelongated and elongated nodes.(3) The CTK which promotes the germination of rice tiller buds is biosynthesis mainly in the nodes and delivery to tiller buds, and then regulated the growth of tiller buds by regulated the expression of OsTBl. The agronomic measures such as external applied IAA regulated the growth of tiller buds by regulated the biosynthesis of CTK in nodes. Besides CTK, the external IAA also might have regulated the expression level of OsD3, OsD10 and OsD27 in tiller buds and by this to regulating the tiller bud growth. These results suggested that the rice have more than one ways to regulate the growth of tiller buds.