Responses of photosynthetic activity in the drought-tolerant cyanobacterium, Nostoc flagelliforme to rehydration at different temperature

Photosynthetic activity during rehydration at four temperatures (5, 15, 25, 35 °C) was studied in a terrestrial, highly drought-tolerant cyanobacterium, Nostoc flagelliforme. At all the temperatures, the optimum quantum yield Fv/Fm increased rapidly within 1 h and then increased slowly during the process of rehydration. The increase in Fv/Fm at 25 and 35 °C was larger than that at 5 and 15 °C. In addition, the changes of initial intensity of fluorescence (F0) and variable fluorescence (Fv) were more significant at 25 and 35 °C than those at 5 and 15 °C. Chlorophyll a content increased with the increase of temperature during the course of rehydration, with this being more pronounced at 25 and 35 °C. The photosynthetic rates at 25 and 35 °C were higher than those at 5 and 15 °C. Induction of chlorophyll fluorescence with sustained rewetting at 5 and 15 °C had two phases of transformation, whereas at 25 and 35 °C it had a third peak kinetic phase and showed typical chlorophyll fluorescence steps on rewetting for 24 h, representing a normal physiological state. A comparison of the chlorophyll fluorescence parameters, chlorophyll a content, and the chlorophyll fluorescence induction led to the conclusion that N. flagelliforme had a more rapid and complete recovery at 25 and 35 °C than that at 5 and 15 °C, although it could recover its photosynthetic activity at any of the four temperatures.