Benech-Arnold Roberto L, Gualano Nicolas, Leymarie Juliette, Côme Daniel, Corbineau Françoise
IFEVA-Cátedra de Cerealicultura Facultad de Agronomia, Universidad de Buenos Aires/CONICET, Av. San Martin 4453, 1417 Buenos Aires, Argentina.
J Exp Bot. 2006;57(6):1423-30. doi: 10.1093/jxb/erj122. Epub 2006 Mar 17.
Two mechanisms have been suggested as being responsible for dormancy in barley grain: (i) ABA in the embryo, and (ii) limitation of oxygen supply to the embryo by oxygen fixation as a result of the oxidation of phenolic compounds in the glumellae. The aim of the present work was to investigate whether hypoxia imposed by the glumellae interferes with ABA metabolism in the embryo, thus resulting in dormancy. In dormant and non-dormant grains incubated at 20 degrees C and in non-dormant grains incubated at 30 degrees C (i.e. when dormancy is not expressed), ABA content in the embryo decreased dramatically during the first 5 h of incubation before germination was detected. By contrast, germination of dormant grains was less than 2% within 48 h at 30 degrees C and embryo ABA content increased during the first hours of incubation and then remained 2-4 times higher than in embryos from grains in which dormancy was not expressed. Removal of the glumellae allowed germination of dormant grains at 30 degrees C and the embryos did not display the initial increase in ABA content. Incubation of de-hulled grains under 5% oxygen to mimic the effect of glumellae, restored the initial increase ABA in content and completely inhibited germination. Incubation of embryos isolated from dormant grains, in the presence of a wide range of ABA concentrations and under various oxygen tensions, revealed that hypoxia increased embryo sensitivity to ABA by 2-fold. This effect was more pronounced at 30 degrees C than at 20 degrees C. Furthermore, when embryos from dormant grains were incubated at 30 degrees C in the presence of 10 microM ABA, their endogenous ABA content remained constant after 48 h of incubation under air, while it increased dramatically in embryos incubated under hypoxia, indicating that the apparent increase in embryo ABA responsiveness induced by hypoxia was, in part, mediated by an inability of the embryo to inactivate ABA. Taken together these results suggest that hypoxia, either imposed artificially or by the glumellae, increases embryo sensitivity to ABA and interferes with ABA metabolism.
关于大麦籽粒休眠的原因，人们提出了两种机制：（i）胚中的脱落酸（ABA），以及（ii）颖片中酚类化合物氧化导致氧气固定，从而限制了胚的氧气供应。本研究的目的是探究颖片造成的低氧环境是否会干扰胚中的ABA代谢，进而导致休眠。在20℃下培养的休眠和非休眠籽粒以及在30℃下培养的非休眠籽粒（即不表现休眠时）中，在检测到发芽之前的培养前5小时内，胚中的ABA含量急剧下降。相比之下，休眠籽粒在30℃下48小时内发芽率低于2%，并且在培养的最初几个小时内胚ABA含量增加，然后保持在比未表现休眠的籽粒胚中ABA含量高2 - 4倍的水平。去除颖片后，休眠籽粒在30℃下能够发芽，并且胚中ABA含量没有出现最初的增加。将去壳籽粒在5%氧气条件下培养以模拟颖片的影响，恢复了ABA含量最初的增加，并完全抑制了发芽。在存在多种ABA浓度和不同氧气张力的情况下，对从休眠籽粒中分离出的胚进行培养，结果表明低氧使胚对ABA的敏感性提高了2倍。这种效应在30℃时比在20℃时更明显。此外，当将休眠籽粒的胚在10 microM ABA存在的情况下于30℃培养时，在空气中培养48小时后其内源ABA含量保持恒定，而在低氧条件下培养的胚中ABA含量则急剧增加，这表明低氧诱导的胚ABA反应性的明显增加部分是由胚无法使ABA失活介导的。综合这些结果表明，无论是人为施加还是由颖片造成的低氧环境，都会增加胚对ABA的敏感性并干扰ABA代谢。
