Developmental Expression of Violaxanthin De-Epoxidase in Leaves of Tobacco Growing under High and Low Light

Violaxanthin de-epoxidase (VDE) is a lumen-localized enzyme that catalyzes the de-epoxidation of violaxanthin in the thylakoid membrane upon formation of a transthylakoid pH gradient. We investigated the developmental expression of VDE in leaves of mature tobacco (Nicotiana tabacum) plants grown under high-light conditions (in the field) and low-light conditions (in a growth chamber). The difference in light conditions was evident by the increased pool size (violaxanthin + antheraxanthin + zeaxanthin, VAZ) throughout leaf development in field-grown plants. VDE activity based on chlorophyll or leaf area was low in the youngest leaves, with the levels increasing with increasing leaf age in both high- and low-light-grown plants. However, in high-light-grown plants, the younger leaves in early leaf expansion showed a more rapid increase in VDE activity and maintained higher levels of VDE transcript in more leaves, indicating that high light may induce greater levels of VDE. VDE transcript levels decreased substantially in leaves of mid-leaf expansion, while the levels of enzyme continued to increase, suggesting that the VDE enzyme does not turn over rapidly. The level of VDE changed in an inverse, nonlinear relationship with respect to the VAZ pool, suggesting that enzyme levels could be indirectly regulated by the VAZ pool.

紫黄质脱环氧化酶（Violaxanthin de-epoxidase, VDE）是一类定位于类囊体腔的酶，可在类囊体跨膜质子梯度形成时催化类囊体膜内的紫黄质发生脱环氧化反应。本研究针对田间高光条件与生长箱低光条件下培育的成熟烟草（Nicotiana tabacum）植株叶片中VDE的发育表达模式展开了系统探究。田间高光生长植株在整个叶片发育周期内，其VAZ库（紫黄质+花药黄质+玉米黄质，violaxanthin + antheraxanthin + zeaxanthin）的总含量显著提升，这一特征直观体现了光照环境对该色素库的调控差异。在最幼嫩的叶片中，基于叶绿素含量或叶面积测算的VDE活性处于较低水平；无论高光还是低光培育的植株，VDE活性均随叶龄增长而逐步升高。但高光生长植株的早期展开幼叶中，VDE活性的上升速度更快，且更多叶片中可检测到更高丰度的VDE转录本，这表明高光环境可能诱导VDE的表达水平上调。在叶片展开中期，VDE的转录本丰度显著下降，但酶活性仍持续升高，这提示VDE酶的蛋白周转速率较为缓慢。VDE的含量与VAZ库呈反向非线性相关关系，这暗示VAZ库可能间接参与调控VDE的表达水平。