Moore K. B., Oishi K. K.
Department of Molecular and Cellular Biology (K.B.M., K.K.O.), Departmemnt of Plant Sciences,(K.K.O.), and Committee on Genetics (K.K.O.), University of Arizona, Tucson, Arizona 85721.
Plant Physiol. 1994 May;105(1):119-125. doi: 10.1104/pp.105.1.119.
During seed maturation the levels of the rate-limiting enzyme of isoprenoid biosynthesis, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) decrease while the levels of the isoprenoid compund abscisic acid (ABA) increase. In the present study, we demonstrate that HMGR specific activity is inversely correlated with endogenous ABA levels in Zea mays endosperm during seed development. HMGR specific activity and ABA levels were measured in the endosperm of the maize vivipary mutuants vp2, vp5, and vp7, which are defective in ABA biosynthesis, and vp1, which is defective in an ABA response element. Reduced ABA levels were observed in the endosperm of vp2, vp5, and vp7, whereas HMGR activity levels were higher compared with wild-type sibling endosperm activity. HMGR activities were increased by as much as 37% (vp2), 45% (vp5), and 58% (vp7) in the mutants. Endosperm HMGR activity in the vp1 mutant was also increased (41%) relative to wild-type siblings, even though vp1 does not have reduced ABA levels. In addition, exogenous ABA inhibits HMGR activity 34 to 50% in maize roots. These results sugggest the HMGR activity levels during seed development are regulated via a Vp1-dependent signal transduction pathway that is affected by the reduced ABA content of vp2, vp5, and vp7 endosperm.
在种子成熟过程中，类异戊二烯生物合成的限速酶3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR）的水平下降，而类异戊二烯化合物脱落酸（ABA）的水平上升。在本研究中，我们证明了在玉米种子发育过程中，玉米胚乳中HMGR的比活性与内源ABA水平呈负相关。在ABA生物合成有缺陷的玉米 vivipary 突变体vp2、vp5和vp7以及ABA反应元件有缺陷的vp1的胚乳中测量了HMGR比活性和ABA水平。在vp2、vp5和vp7的胚乳中观察到ABA水平降低，而与野生型同胞胚乳活性相比，HMGR活性水平更高。在突变体中，HMGR活性分别提高了37%（vp2）、45%（vp5）和58%（vp7）。相对于野生型同胞，vp1突变体胚乳中的HMGR活性也有所提高（41%），尽管vp1的ABA水平没有降低。此外，外源ABA在玉米根中抑制HMGR活性34%至50%。这些结果表明，种子发育过程中的HMGR活性水平是通过一条依赖Vp-1的信号转导途径来调节的，该途径受vp2、vp5和vp7胚乳中ABA含量降低的影响。
