Photosynthetic acclimation of the filamentous cyanobacterium, Plectonema boryanum UTEX 485, to temperature and light

Photosynthetic acclimation to temperature and irradiance was studied in the filamentous, non-heterocystous cyanobacterium Plectonema boryanum UTEX 485 . Growth rates of this cyanobacterium measured at ambient CO2 were primaril y influenced by temperature with minimal effects of irradiance, Both growth temperature and irradiance affected linolenic (18:3) and linoleic acid (18 :2) levels in the four major lipid classes in an independent but additive m anner. In contrast, photosynthetic acclimation was not due to either growth temperature or irradiance per se, but rather, due to the interaction of th ese environmental factors. P. boryanum grown at low temperature and moderat e irradiance mimicked cells grown at high light. Compared to cells grown at either 29 degrees C/150 mu mol m(-2) s(-1) (29/150) or 15/10, P. boryanum grown at either15/150 or 29/750 exhibited: (1) reduced cellular levels of C hi a and phycobilisomes (PBS), and concomitantly higher content of an orang e-red carotenoid, myxoxanthophyll; (2) higher light saturated rates (Pmax) when expressed on a Ch1 a basis but lower apparent quantum yields of oxygen evolution and (3) enhanced resistance to high light stress. P. boryanum gr own at 15/150 regained normal blue-green pigmentation within 16 h after a t emperature shift to 29 degrees C at a constant irradiance of 150 mu mol m(- 2) s(-1). DBMIB and KCN but not DCMU and atrazine partially inhibited the c hange in myxoxanthophyll/Ch1 a ratio following the shift from 15 to 29 degr ees C, We conclude that P. boryanum responds to either varying growth tempe rature or varying growth irradiance by adjusting the ability to absorb ligh t through decreasing the cellular contents of Ch1 a and light-haFvesting pi gments and screening of excessive light by myxoxanthophyll predominantly lo calized in the cell wall/cell membrane to protect PSII from over-excitation . The possible role of redox sensing/signalling for photosynthetic acclimat ion of cyanobacteria to either temperature or irradiance is discussed.