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Examines developmental and environmental conditions enhanced expression of the alternative oxidase (AOX) in higher plants. Analysis of the transcriptional regulation of AOX1; Dependence of the AOX1 expression on the nitrogen source; Stimulation of nitrate at the AOX protein and respiratory levels.

A psychrophilic green alga belonging to the Chloromonas genus and here named. ANT1 was collected in Antartica. The activities of two enzymes, nitrate reductase and argininosuccinate lyase, were measured at various temperatures and compared to thecorresponding enzyme activities in the mesophilic species Chlamydomonas reinhardtii dangeard. For both enzymes, the temperature for apparent optimal activity was about 20° Lower in ANT1 than in C. reinhardtii. The enzymes were also submitted to various heat treatments before measuring their activities. Both psychrophilic enzymes were more sensitive to heat than the corresponding mesophilic enzymes. It is worth stressing, however, that in both species nitrate reductase was much more sensitive to heat than argininosuccinate lyase, which probably indicates that the peculiar structure of each protein primarily determines its dependence to temperature. Secondary adaptations to low temperatures should then occur to confer the psychrophilic character. [ABSTRACT FROM AUTHOR]