西藏虎头兰和墨兰对强光的生理响应

Physiological Response to High Light in Cymbidium tracyanum and C.sinense

兰属植物(Cymbidium)是重要的观赏花卉。该属大多数种类生长在适度荫蔽的环境中,但附生型的西藏虎头兰(C.tracyanum)却能在阳光直射的环境下良好生长。为了探究西藏虎头兰适应强光的生理机制,研究选取同属的地生型墨兰(C.sinense)与其进行对照实验,测定了这两种植物在不同光照强度下的叶绿素荧光参数和P700氧化还原态。结果表明,在强光下,西藏虎头兰光系统I和II活性的下降程度比墨兰小,而环式电子传递的激发程度更高。环式电子传递的激发有助于增强西藏虎头兰在强光下的光保护,而墨兰因环式电子激发程度较低,使其不能适应强光。由于附生环境更容易出现间歇性的直射光,西藏虎头兰的这种适应强光的能力可能有助于它更充分地利用附生环境中的光照资源。

The members of the genus Cymbidium are important ornamental flowers. Most species of this genus prefer to grow on the shady places of the forest floor, while epiphytic C. tracyanum can grow well in the presence of direct sunlight. To explore the physiological mechanism underlying the adaptation of C. tracyanum to high light, we used terrestrial C. sinense as the control, and measured the chlorophyll fluorescence and P700 redox state in those two species grown at two different light regimes. Our results showed that the activities of photosystem Ⅰ and Ⅱ in C. sinense under high light decreased more strongly than those in C. tracyanum. The activation of cyclic electron flow （CEF） in C. tracyanum under high light could serve as a main mechanism of photoprotection. However, the weak of CEF in C. sinense limited its adaptation to high light. Since epiphytic habitats may suffer more intermittent direct sunlight than understory, the strong adaptability of C. tracyanum to high light may contribute to its utilization of light energy in epiphytic habitats.