THE INFLUENCE OF LOW-TEMPERATURE ON DIEL PATTERNS OF CARBOHYDRATE-METABOLISM IN LEAVES OF POA-ANNUAL AND POA X JEMTLANDICA (ALMQ) RICHT

The effect of low temperature on diel changes in net gas exchange, carbohydrate content and export, and on the extractable activities of sucrose phosphate synthase and acid invertase from leaves of Poa annua (a ruderal grass) and Poa .times. jemtlandica (a subarctic grass) was investigated. Exposure for 5 d to a temperature of 7.degree. C significantly reduced the rate of net photosynthesis of P. annua but had no effect that of P. .times. jemtlandica. In both species, soluble sugars constituted 20% of the dry weight and showed net accumulation over 24 h. There was approximately twice the concentration of fructans in the leaves of P. .times. jemtlandica compared with P. annua. During the 16 h photoperiod, the leaves of P. .times. jemtlandical stored twice as much photosynthate as the leaves of P. annua. However, the higher rate of export from the leaves of P. .times. iemtlandica in the dark compared to P. annua resulted in the allocation of similar proportions of photosynthate to the processes of storage, respiration and export in leaf blades of both species over a 24 h period. Low temperature resulted in a decrease in the extractable activity of sucrose phosphate synthase from P. annua but not from P. .times. jemtlandica. The activity of acid invertase was reduced by exposure in both species.