Galland P, Lipson E D
Proc Natl Acad Sci U S A. 1987 Jan;84(1):104-8. doi: 10.1073/pnas.84.1.104.
Phototropism in the fungus Phycomyces is mediated by two photosystems that are optimized for the low-intensity region (below 10(-6) W X m-2) and the high-intensity region (above 10(-6) W X m-2). These photosystems can be distinguished under special experimental conditions, in which sporangiophores grown in the dark are suddenly exposed to continuous unilateral light. With this treatment, the bending occurs in two steps. Below 10(-6) W X m-2, an early-response component (15-min latency) and a late-response component (50- to 70-min latency) are observed that are mediated by photosystem I. Above 10(-6) W X m-2, the early component is augmented by an intermediate component with a 40-min delay that is mediated by photosystem II. The two photosystems are distinguished further by their wavelength sensitivities and adaptation kinetics. Photosystem I is more effective at 334, 347, and 550 nm than photosystem II, but it is less effective at 383 nm. At wavelength 450 nm, the dark-adaptation kinetics associated with photosystem I are approximately half as fast as those associated with photosystem II. However, the light-adaptation kinetics of photosystem I are approximately equal to 3 times faster than the kinetics associated with photosystem II. The existence of two photosystems clarifies several behavioral features of Phycomyces and helps explain how the sporangiophore can manage the full range of 10 decades.
真菌毛霉目中的向光性由两个光系统介导，这两个光系统分别针对低强度区域（低于10^(-6) W·m^(-2)）和高强度区域（高于10^(-6) W·m^(-2)）进行了优化。在特殊实验条件下可以区分这两个光系统，即让在黑暗中生长的孢子囊柄突然暴露于连续的单侧光下。经过这种处理，弯曲分两步发生。在10^(-6) W·m^(-2)以下，观察到由光系统I介导的早期反应成分（延迟15分钟）和晚期反应成分（延迟50至70分钟）。在10^(-6) W·m^(-2)以上，早期成分会因一个延迟40分钟的中间成分而增强，该中间成分由光系统II介导。这两个光系统在波长敏感性和适应动力学方面也有进一步区别。光系统I在334、347和550 nm处比光系统II更有效，但在383 nm处效果较差。在450 nm波长下，与光系统I相关的暗适应动力学速度约为与光系统II相关的暗适应动力学速度的一半。然而，光系统I的光适应动力学速度约为与光系统II相关的光适应动力学速度的3倍。两个光系统的存在阐明了毛霉目的几个行为特征，并有助于解释孢子囊柄如何应对跨越10个数量级的光照范围。
