Grossman A R, Schaefer M R, Chiang G G, Collier J L
Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305.
Microbiol Rev. 1993 Sep;57(3):725-49. doi: 10.1128/mr.57.3.725-749.1993.
Photosynthetic organisms can acclimate to their environment by changing many cellular processes, including the biosynthesis of the photosynthetic apparatus. In this article we discuss the phycobilisome, the light-harvesting apparatus of cyanobacteria and red algae. Unlike most light-harvesting antenna complexes, the phycobilisome is not an integral membrane complex but is attached to the surface of the photosynthetic membranes. It is composed of both the pigmented phycobiliproteins and the nonpigmented linker polypeptides; the former are important for absorbing light energy, while the latter are important for stability and assembly of the complex. The composition of the phycobilisome is very sensitive to a number of different environmental factors. Some of the filamentous cyanobacteria can alter the composition of the phycobilisome in response to the prevalent wavelengths of light in the environment. This process, called complementary chromatic adaptation, allows these organisms to efficiently utilize available light energy to drive photosynthetic electron transport and CO2 fixation. Under conditions of macronutrient limitation, many cyanobacteria degrade their phycobilisomes in a rapid and orderly fashion. Since the phycobilisome is an abundant component of the cell, its degradation may provide a substantial amount of nitrogen to nitrogen-limited cells. Furthermore, degradation of the phycobilisome during nutrient-limited growth may prevent photodamage that would occur if the cells were to absorb light under conditions of metabolic arrest. The interplay of various environmental parameters in determining the number of phycobilisomes and their structural characteristics and the ways in which these parameters control phycobilisome biosynthesis are fertile areas for investigation.
光合生物可以通过改变许多细胞过程来适应环境，包括光合装置的生物合成。在本文中，我们将讨论藻胆体，它是蓝细菌和红藻的光捕获装置。与大多数光捕获天线复合物不同，藻胆体不是整合膜复合物，而是附着在光合膜的表面。它由色素藻胆蛋白和非色素连接多肽组成；前者对于吸收光能很重要，而后者对于复合物的稳定性和组装很重要。藻胆体的组成对许多不同的环境因素非常敏感。一些丝状蓝细菌可以根据环境中普遍存在的光波长改变藻胆体的组成。这个过程称为互补色适应，使这些生物能够有效地利用可用光能来驱动光合电子传递和二氧化碳固定。在大量营养素限制的条件下，许多蓝细菌会以快速且有序的方式降解它们的藻胆体。由于藻胆体是细胞中的丰富成分，其降解可能为氮受限的细胞提供大量氮。此外，在营养受限生长期间藻胆体的降解可能会防止在代谢停滞条件下细胞吸收光时发生的光损伤。各种环境参数在决定藻胆体数量及其结构特征方面的相互作用，以及这些参数控制藻胆体生物合成的方式，都是有待研究的丰富领域。
