The effect of growth temperature on enzyme activities in the brown alga Laminaria saccharina

Abstract

The effect of changes in growth temperature on the extractable activities of several key enzymes of carbon and nitrogen metabolism was studied in the brown alga Laminaria saccharina. Standard enzyme activities (measured at 20°C) were found to respond in one of three ways, being (i) unaffected by growth temperature (aspartate: 2-oxyglutarate aminotransferase, malate dehydrogenase, mannitol-1-phosphate dehydrogenase and phosphoenol-pyruvate carboxykinase), (ii) inversely proportional to growth temperature (glyceraldehyde-3-phosphate dehydrogenase (NAD- and NADP-dependent) and ribulose-1,5-bisphosphate carboxylase) or (iii) following changes in growth rate which was maximal at 10°C (glutamine synthetase and nitrate reductase). The photosynthetic capacity of L. saccharina sporophytes responded in a manner similar to the Calvin cycle enzymes glyceraldehyde-3-phosphate dehydrogenase (NADP-dependent) and ribulose-1,5-bisphosphate carboxylase with standard photosynthetic rates (measured at 15°C) being inversely proportional to growth temperature. The inverse relationship between photosynthetic capacity (measured at standard temperature) and growth temperature enabled Laminaria saccharina to maintain almost constant rates of actual photosynthesis (measured at growth temperature), and hence growth, over the temperature range from 5- to 20°C. The significance of the data is discussed with reference to the regulation of metabolic activities in field populations of Laminaria spp.