生长素调控种子的休眠与萌发

植物种子的休眠与萌发,是植物生长发育过程中的关键阶段,也是生命科学领域的研究热点。种子从休眠向萌发的转换是极为复杂的生物学过程,由外界环境因子、体内激素含量及信号传导和若干关键基因协同调控。大量研究表明,植物激素脱落酸(Abscisic acid, ABA)和赤霉素(Gibberellin acid, GA)是调控种子休眠水平,决定种子从休眠转向萌发的主要内源因子。ABA与GA在含量和信号传导两个层次上的精确平衡,确保了植物种子能以休眠状态在逆境中存活,并在适宜的时间启动萌发程序。生长素(Auxin)是经典植物激素之一,其对向性生长和组织分化等生物学过程的调控已有大量研究。但最近有研究证实,生长素对种子休眠有正向调控作用,这表明生长素是继ABA之后的第二个促进种子休眠的植物激素。本文在回顾生长素的发现历程、阐释生长素体内合成途径及信号传导通路的基础上,重点综述了生长素通过与ABA的协同作用调控种子休眠的分子机制,并对未来的研究热点进行了讨论和展望。     

Accumulation and leakage of abscisic acid during embryo development and seed dormancy in wheat

Seed dormancy develops latein embryogenesis after a period of potential prematuregermination and has been associated with levels ofabscisic acid (ABA) in, and sensitivity to, ABA ofembryos. In wheat (Triticum aestivum L.)embryos, there are two peaks in levels of ABA duringdevelopment: the first occurs 25 days afterpollination (DAP) and the second from 35 to 40 DAP. The first peak of ABA appears to be associated withthe development of the embryo's sensitivity to ABAsince such sensitivity was altered in seeds on earsthat were incubated in a solution of ABA from 15 and20 DAP. In the embryos of Kitakei wheat, a line thatexhibits dormancy, the second peak, at around 35 DAP,was more prolonged in comparison to Chihoku, anon-dormant line. The results support the proposedinvolvement of ABA in the formation and maintenance ofseed dormancy during middle and late embryogenesis. When developing embryos were incubated in water,embryonic ABA leaked out from the embryos, inparticular between 30 and 40 DAP. Prematuregermination observed between 30 and 40 DAP might berelated to such leakage of ABA from embryos.     

Antagonism between abscisic acid and gibberellins is partially mediated by ascorbic acid during seed germination in rice

The antagonism between abscisic acid (ABA) and gibberellin (GA) plays a key role in controlling seed germination,^1,2 but the mechanism of antagonism during this process is not known. In the associated study,³ we investigated the relationship among ABA, reactive oxygen species (ROS), ascorbic acid (ASC) and GA during rice seed germination. ROS production is reduced by ABA, which hence results in decreasing ASC accumulation during imbibition. GA accumulation was also suppressed by a reduced ROS and ASC level, whereas application of exogenous ASC can partially rescue seed germination from ABA treatment. Further results show that production of ASC, which acts as a substrate in GA biosynthesis, was significantly inhibited by lycorine which thus suppressed the accumulation of GA. Consequently, expression of GA biosynthesis genes was suppressed by the low levels of ROS and ASC in ABA-treated seeds. These studies reveal a new role for ASC in mediating the antagonism between ABA and GA during seed germination in rice.     

低温层积与外源GA3对肉苁蓉种子萌发及其内源GA和ABA含量的影响

研究低温层积对肉苁蓉种子胚率、内源赤霉素（GA）和脱落酸（ABA）含量以及外源赤霉素（GA3）对低温层积不同时间种子萌发率影响的结果表明：低温层积可以提高种子的胚率及其GA的含量,降低其ABA含量;层积120～150d的肉苁蓉种子经外源GA3处理后,其萌发率可以达到70%以上;层积120d是外源GA3促进种子萌发的临界点。     

套袋对红肉脐橙果肉中色素、糖及内源激素的影响

以红肉脐橙为试材,研究幼果期套袋至果实着色前拆袋对果肉中色素、糖及内源激素的影响.结果表明, 套袋显著或极显著地提高了成熟果实的番茄红素、β-胡萝卜素含量;套袋处理与对照果实的GA和ABA含量变化趋势一致,表现为GA含量在果实膨大期迅速下降,着色期至果实成熟期保持在较低水平,ABA含量在拆袋时达到最高峰,然后迅速下降,于果实成熟前又出现一小高峰;套袋极显著降低了脐橙果肉的葡萄糖含量,显著降低了果糖含量,提高了蔗糖含量,但总糖含量与对照无显著差异.     

Abscisic acid and gibberellic acid-regulated responses of embryos and aleurone layers isolated from dormant and nondormant barley grains

Dormant and nondormant isogenic barley grains were obtained by maturing grains under short day (SD) or long day (LD) growth conditions, respectively. Hormonal responses of isolated embryos and aleurone layers from these grains were studied. Addition of abscisic acid (ABA) reduced germination rate and percentage of embryos, and induced Rab (ABA-responsive) mRNA in aleurone layers from both types of grain. Embryos and aleurone layers from dormant grains responded stronger to ABA than those from nondormant grains. Gibberellic acid (GA₃) increased the germination rate and percentage of embryos from dormant grains and counteracted the ABA-induced inhibition of embryo germination. GA₃ did not affect the amount of Rab mRNA in aleurone layers, suggesting that expression of the Rab gene has no direct correlation with germination. The stronger response of embryos and aleurone layers from dormant grains to ABA may not be explained by higher endogenous ABA levels, but might be due to differences in hormone signal transduction. Aleurone protoplasts from dormant grains had a higher cytosolic pH than those from nondormant grains. To inhibit the ABA-induced Rab mRNA, a much higher concentration of weak acid was required for aleurone layers from dormant grains than for those from nondormant grains. A possible difference in ABA signal transduction between dormant and nondormant grains is discussed.     

经低温贮藏的兰州百合种球种植后的鳞茎生长过程中GA3和ABA含量变化

6℃下贮藏67和101d的兰州百合种球种植后,于花蕾伸出顶端2-3cm时将其摘除,以后定期取样,检测鳞茎膨大成熟过程中GA3和ABA含量的结果表明：6℃下处理101d的母鳞茎中GA3含量先上升后下降,而处理67d的则相反;新鳞茎中GA3含量呈升高趋势,处理101d的含量高于处理67d的。母鳞茎中ABA含量先下降后上升,处理67d的高于处理101d的,新鳞茎中则相反。母鳞茎中GA3／ABA比值先升高后下降,处理101d的高于处理67d的;新鳞茎中则显著下降。据此认为,在百合鳞茎膨大成熟过程中,GA3和ABA之间的含量和作用并不全是互为消长的关系。     

外源ABA和GA3对红肉脐橙果皮色素含量的影响

测定红肉脐橙果实发育期间和果实转色期间施用外源ABA和GA3的果皮中叶绿素和总类胡萝卜素含量变化的结果表明:红肉脐橙果皮中叶绿素总量于9月20日出现最大值,为0.1469 mg·g-1(FW);类胡萝卜素总量于12月21日达到最大值,为0.0321 mg·g-1(FW);转色期用外源ABA处理后果皮叶绿素降解加速,而类胡萝卜素积累受抑;转色期施用GA3并不能延缓果皮叶绿素的降解,但能抑制类胡萝卜素的积累,因而阻碍了果皮类胡萝卜素的合成.     

外源脱落酸和赤霉素对红肉脐橙果肉糖含量的影响

在红肉脐橙幼果期和着色前分2次喷施不同浓度的外源ABA和GA3,研究其对红肉脐橙果肉糖含量的影响.结果表明:10mg.L-1ABA处理显著或极显著提高了果实成熟时的葡萄糖、果糖和总糖含量,50mg.L-1ABA处理极显著提高了果实蔗糖含量,而100mg.L-1ABA处理极显著降低了果实葡萄糖含量;中低浓度的GA3(10、50和250mg.L-1)极显著提高了果实蔗糖含量,10mg.L-1GA3处理对果实葡萄糖和果糖含量无明显影响,但极显著提高了果实总糖含量,50、250和500mg.L-1GA3处理极显著降低了果实葡萄糖、果糖和总糖含量.表明着色前较低浓度的外源ABA处理(10和50mg.L-1)可提高果实中一种或几种糖的含量,而较高浓度的GA3处理(250和500mg.L-1)则严重阻碍了果肉中糖的积累.