Stoichiometry of the photosynthetic apparatus and phycobilisome structure of the cyanobacterium Plectonema boryanum UTEX 485 are regulated by both light and temperature

The role of growth temperature and growth irradiance on the regulation of the stoichiometry and function of the photosynthetic apparatus was examined in the cyanobacterium Plectonema boryanum UTEX 485 by comparing mid-log phase cultures grown at either 29degreesC/150 mumol m(-2) s(-1), 29degreesC/750 mumol m(-2) s(-1), 15degreesC/150 mumol m(-2) s(-1), or 15degreesC/10 mumol m(-2) s(-1). Cultures grown at 29degreesC/750 mumol m-2 s-1 were structurally and functionally similar to those grown at 15degreesC/150 mumol m(-2) s(-1), whereas cultures grown at 29degreesC/150 mumol m(-2) s(-1) were structurally and functionally similar to those grown at 15 degreesC/10 mumol m(-2) s(-1). The stoichiometry of specific components of the photosynthetic apparatus, such as the ratio of photosystem (PS) I to PSII phycobilisome size and the relative abundance of the cytochrome bb/f complex, the plastoquinone pool size, and the NAD(P)H dehydrogenase complex were regulated by both growth temperature and growth irradiance in a similar manner. This indicates that temperature and irradiance may share a common sensing/signaling pathway to regulate the stoichiometry and function of the photosynthetic apparatus in P. boryanum. In contrast, the accumulation of neither the D1 polypeptide of PSII, the large subunit of Rubisco, nor the CFl alpha-subunit appeared to be regulated by the same mechanism. Measurements of P700 photooxidation in vivo in the presence and absence of inhibitors of photosynthetic electron transport coupled with immunoblots of the NAD(P)H dehydrogenase complex in cells grown at either 29degreesC/750 mumol m(-2) s(-1) or 15degreesC/150 mumol m(-2) s(-1) are consistent with an increased flow of respiratory electrons into the photosynthetic intersystem electron transport chain maintaining P700 in a reduced state relative to cells grown at either 29degreesC/150 mumol m(-2) s(-1) or 15degreesC/10 mumol m s(-1). These results are discussed in terms of acclimation to excitation pressure imposed by either low growth temperature or high growth irradiance.