J Bacteriol. This indicates that heat and irradiance may share a common sensing/signaling pathway to regulate the stoichiometry and function of the photosynthetic apparatus in as well as a reduction in the number of PBSs and/or size of PBSs by a decrease of the peripheral biliprotein complexes (Raps et al., 1985; de Lorimier et al., 1992; Reuter and Muller, 1993; Garnier et al., 1994; Samson et al., 1994; Nomsawai et al., 1999). Moreover, some species may vary the composition of their PBS by induction of fresh polypeptides associated with PBS or modifications of the PBS parts (Reuter and Muller, 1993; Garnier et al., 1994; Samson et al., 1994; Nomsawai et al., 1999). The PSI to PSII percentage becomes higher under low irradiance and lower at high-light intensity, and PSI seems to be the variable component of the photosynthetic apparatus (Murakami and Fujita, 1991; Fujita et Arctiin al., 1994). Moreover, the activity or the amount of cytochrome c oxidase in the respiratory system is definitely modified concomitantly with the level of PSI (Adhikary et al., 1990; Murakami et al., 1997). Both terminal components of the electron transport system in cyanobacteria look like controlled in response to modulation of the redox state of the intersystem PQ pool and/or the cytochrome b6f complex. Alterations in the redox state of these intersystem electron transport parts may be induced by changes in either light quality, irradiance, CO2 availability, or Na+ stress (Murakami and Fujita, 1993; Fujita et al., 1994; Grossman et al., 1994; Murakami et al., 1997). Recently, Grossman et al. (2001) Rabbit Polyclonal to PDXDC1 have shown that the reactions to Arctiin both high light and nutrient stress in sp. PCC 7942 is definitely regulated by a two-component sensory system. NblR is the response regulator that appears to control PBS degradation in response to high light and nutrient stress. NblS is the sensor His kinase that regulates the phosphorylation on nblR (Grossman et al., 2001). Furthermore, the sensor for chromatic adaptation in cyanobacteria also is a two-component sensor His kinase related to that of flower phytochromes (Kehoe and Grossman, 1996). Recently, it has been suggested that low temps specifically induce damage to the PSI reaction Arctiin center in the cyanobacterium sp. PCC 6803 (Zak and Pakrasi, 2000). Growth of sp. PCC 6803 at low temps causes a destabilization of the PSI complex that, in turn, prospects to a degradation of the PSI core proteins, PsaA and PsaB. In contrast, the content and activity of PSII do not show significant changes under these conditions. The stability of the PSI reaction center seems to be dependent on the presence of the extrinsic thylakoid protein BtpA (Zak and Pakrasi, 2000). We have reported previously the filamentous cyanobacterium UTEX 485 produced at low heat/moderate irradiance (15C/150 mol m?2 s?1) mimicked the cells grown at moderate heat/high-light intensity (29C/750 mol m?2 s?1) with respect to pigmentation and photosynthetic characteristics (Miskiewicz et al., 2000). Cells produced under these conditions exhibited reduced cellular material of Chl and concomitantly higher levels of myxoxanthophyll, lower apparent quantum Arctiin yields of oxygen development, and enhanced resistance to photoinhibition under visible (Miskiewicz et al., 2000) as well mainly because UV light (Ivanov et al., 2000a). However, decreasing growth irradiance from 150 to 10 mol m?2 s?1 at 15C resulted in low temperature-grown cells that were photosynthetically indistinguishable from cells grown under control conditions of 29C and 150 mol m?2 s?1 (Miskiewicz et al., 2000). These results indicate that photosynthetic acclimation of is the result of the combined effects of growth heat and light, rather than because of either low heat or high light per se. A similar trend was reported for the green algae and (Huner et al., 1998). In the present study, we test the hypothesis that.