Photosynthetic response of Chlamydomonas reinhardtii to short-term storage on ice in darkness. Dependence of the response on growth conditions

The effect of storage of the unicellular green alga Chlamydomonas reinhardtii (strain 137+) in the pelleted state in darkness on ice (0.2-0.5A degrees C) (further simply "SPDI-treatment") on its photosynthetic and respiratory activities was studied. To this end, the steady-state rates of O-2 exchange in darkness (dark respiration) and under saturating light (apparent photosynthesis) as well as the induction periods (IP) of apparent photosynthesis were measured at 25A degrees C in the SPDI-untreated and SPDI-treated for the period from similar to 0.5 to similar to 30 h algal cells. In contrast to expectations, the SPDI-treatment consistently affected the rate and IP of photosynthesis depending on the physiological state of C. reinhardtii. Dark respiration was affected by the SPDI-treatment as well. However, in absolute values the respiratory changes were much less than the photosynthetic ones, and they were insufficiently reproducible. The SPDI-treatment affected photosynthesis most significantly in high-CO2-grown cells (cells grown at 5% CO2 in white light). The rate of photosynthesis in these cells declined quasi-exponentially as a function of time during the SPDI-treatment with a t (1/2) similar to 1.5 h and finally became by about 60% lower than that before the SPDI-treatment. This decline of photosynthesis was accompanied by continuous and essential increase in the photosynthetic IP. The SPDI-induced photosynthetic changes in high-CO2-grown cells resulted from the firm disfunction of the photosynthetic apparatus. After switch from growth at 5% CO2 in white light to growth at similar to 0.03% CO2 (air) in white, blue, or red light, the alga gradually transited to a physiological state, in which the negative effects of the SPDI-treatment on the rate and IP of photosynthesis became weak and absent, respectively. Remarkably, this transition was faster in blue (a parts per thousand currency sign5 h) than in white and red light (> 10 h). Similar changes in the response of the alga to the SPDI-treatment occurred when high-CO2-grown cells (5% CO2, white light, 26A degrees C) were incubated in darkness (air, 24-26A degrees C) for 20-25 h. The results of study were analyzed in the light of literature data relating to the effects of CO2 concentration, darkness, and light quality on carbohydrates in plant organisms. The analysis led to suggestion that there is connection between the negative effect of the SPDI-treatment on C. reinhardtii and nonstructural carbohydrates presented in the alga: the more carbohydrates contain the alga, the more extensive inactivation of the photosynthetic apparatus occurs in it during its storage in the dense (pelleted) state in darkness on ice.