Red light causes a reduction in IAA levels at the apical tip by inhibiting de novo biosynthesis from tryptophan in maize coleoptiles
Red light causes a reduction in IAA levels at the apical tip by inhibiting de novo biosynthesis from tryptophan in maize coleoptiles
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DOI：
10.1007/s00425-006-0311-3
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发表时间：
2006-11-01
期刊：
影响因子：
4.3
通讯作者：
Koshiba, Tomokazu
中科院分区：
文献类型：
--
作者：
Nishimura, Takeshi;Mori, Yukiko;Koshiba, Tomokazu
玉米胚芽鞘单侧暴露于红光(7.9mmolm~(-2)S~(-1)光照5min)后3h，胚芽鞘中生长素水平从上到下均有不同程度的下降，约为暗对照的60%。5 mm顶端区域的局部照射足以使顶端IAA的下降幅度与整个受照射的顶端相同。当用N-1-萘基邻苯二甲酸(NPA)处理胚芽鞘时，IAA在芽鞘尖端的积累和从芽鞘尖端扩散出来的IAA的减少。NPA处理的胚芽鞘中IAA的积累量明显低于暗对照。无论是暗处理还是光处理，NPA处理都不影响胚芽鞘顶端结合IAA的含量。当(C11N2)-C-13-N-15-色氨酸(Trp)被涂在胚芽鞘顶部时，在黑暗和红光处理的胚芽鞘顶端，大量的稳定同位素被结合到游离IAA中。红光处理的胚芽鞘顶端的掺入比例略低于黑暗对照。在标记的IAA中检测不到该标记。IAA的基膜转运速率约为10 mm h(-1)，红光不影响其转运速度。这些结果强烈地表明，红光并不影响游离IAA向共轭形式的转化或基瓣运输的速率，而只是降低了顶端的IAA水平，这可能是该区域从色氨酸合成IAA的抑制。
When maize coleoptiles were unilaterally exposed to red light (7.9 mu mol m(-2)s(-1) for 5 min), 3 h after treatment IAA levels in coleoptiles decreased in all regions, from top to basal, with levels about 60% of dark controls. Localized irradiation in the 5 mm top zone was sufficient to cause the same extent of IAA reduction in the tips to that in the tips of whole irradiated shoots. When coleoptiles were treated with N-1-naphthylphthalamic acid (NPA), an accumulation of IAA in the tip and a decrease of diffusible IAA from tips were simultaneously detected. IAA accumulation in red-light treated coleoptiles by NPA was much lower than that of dark controls. NPA treatment did not affect the content of conjugated IAA in either dark or light treated coleoptile tips. When (C11N2)-C-13-N-15-tryptophan (Trp) was applied to the top of coleoptiles, substantial amounts of stable isotope were incorporated into free IAA in dark and red-light treated coleoptile tips. The ratio of incorporation was slightly lower in red-light treated coleoptile tips than that in dark controls. The label could not be detected in conjugated IAA. The rate of basipetal transport of IAA was about 10 mm h(-1) and the velocity was not affected by red light. These results strongly suggest that red light does not affect the rates of conversion of free IAA to the conjugate form or of the basipetal transport, but just reduces the IAA level in the tips, probably inhibited by IAA biosynthesis from Trp in this region.