TEMPERATURE INDUCED PHOTOINHIBITION IN OUTDOOR CULTURES OF MONODUS SUBTERRANEUS

• Published in: Journal of phycology 2000-12, Vol.36 (s3), p.69-69
• Main Authors: Vonshak, A., Torzillo, G., Boussiba, S.
• Format: Article
• Language: English
• Subjects: Monodus subterraneus
• ISSN: 0022-3646; 1529-8817
• DOI: 10.1046/j.1529-8817.1999.00001-205.x

Outdoor algal cultures are continuously exposed to changes in environmental conditions, particularly irradiance and temperature. While the changes in light intensity take place in a range of one to two hours, the increase in temperature is a slower process and takes about four to five hours. This de‐synchronization between the two important environmental factors governing photosynthesis and growth of algae results in a unique stress condition where photoinhibition can be induced at relatively low light intensity. Outdoors the early morning culture temperature was found to be about 12 to 14° C, and reaches 25 to 28° C at mid‐day. In an experiment, such a natural temperature regime was compared to another one in which the morning temperature of the culture was increased to 20° C by using a heating system. A fast decline in the maximal photochemical efficiency of PSII (Fv/Fm) was observed starting as soon as sunrise. The decline was faster in the non‐heated culture and was to a lower value. The diurnal changes in the electron transfer rate (ETR) and in the non‐photochemical quenching (NPQ) of the cultures, indicated that the early morning exposure of cells to sub‐optimal temperature results in a fast inactivation of PSII activity which was reflected in an inhibition of the photosynthetic activity even when the two cultures finally reached the same temperature at mid‐day. Thus, under the same light and temperature mid‐day conditions the ETR was higher and the NPQ was significantly lower in the heated culture. Significant changes in productivity of the cultures also were observed.