THE INFLUENCE OF LOW TEMPERATURE ON DIEL PATTERNS OF CARBOHYDRATE METABOLISM IN LEAVES OF POA ANNUA L. AND POA×JEMTLANDICA (ALMQ.) RICHT.

Abstract

SUMMARYThe 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 xjemtlandica (a subarctic grass) was investigated. Exposure for 5 d to a temperature of 7 °C significantly reduced the rate of net photosynthesis of P. annua but had no effect that of P. xjemtlandica. 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. xjemtlandica compared with P. annua.During the 16 h photoperiod, the leaves of P. xjemtlandica stored twice as much photosynthate as the leaves of P. annua. However, the higher rate of export from the leaves of P. xjemtlandica 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. xjemtlandica. The activity of acid invertase was reduced by exposure in both species.

Daily photosynthetic and C‐export patterns in winter wheat leaves during cold stress and acclimation

“…The two primary functions of a source leaf are to fix energy during photosynthesis and export that chemical energy to the rest of the plant (Wardlaw 1990, Geiger and Servaites 1994, Leonardos and Grodzinski 2001). The importance of measuring export rates in the light period during stressful episodes has been noted by several groups (Borland and Farrar 1987, Farrar 1988, Geiger and Servaites 1994, Leonardos and Grodzinski 2001). The daily export patterns of the acclimated and stressed wheat leaves (Figs 2 and 4) show that at all conditions more 14 C‐assimilates were exported in the light during photosynthesis than in the dark.…”

“…The intracellular and intercellular movements of photoassimilates from the site of production to the main vascular channels can be inhibited reducing phloem loading and end‐product removal from the leaf (Webb 1970, Farrar 1988, van Bel 1993, Schrier et al 2000). However, few measurements exist that quantify the extent to which changes in temperature alter photosynthesis and concurrent export of newly fixed C from source leaves via the phloem (Borland and Farrar 1987, Jiao and Grodzinski 1996, 1998, Leonardos et al 1996, Grodzinski et al 2001, Leonardos and Grodzinski 2001).…”

Compartmentation and fluxes of carbon in leaf blades and leaf sheaths ofPoa annuaL. andPoa x jemtlandica(Almq.) Richt

“…It has been suggested that the rapid turnover of storage earbohydrate in slow-growing montane grasses may be crucial in maintaining a pool of soluble sugars in an envirotiment where photosynthesis is unpredictable (Atkinson & Farrar, 1983). Exposure to low temperature resulted in a significantly greater increase in fructan concentration in the leaves of P. x jemtlandiea than in P. annua (Borland & Farrar, 1987). Thus, the rapid turnover of fructans in the leaves of P. x jemtlandiea growing at 19°C may facilitate a more rapid response in fruetan metabolism to any treatment whieh afl"eets the growth of the plant than is possible in P. annua.…”