CARBOHYDRATE STORAGE AND MOBILIZATION BY THE CULM OF WHEAT BETWEEN HEADING AND GRAIN MATURITY - THE RELATION TO SUCROSE SYNTHASE AND SUCROSE-PHOSPHATE SYNTHASE

Wheat plants grown under non-stress conditions at a day/night temperat ure of 18/13 degrees C under glasshouse conditions from head emergence to maturity showed a maximum accumulation of water-soluble, non-struc tural carbohydrates 20-25 days after anthesis. This storage was largel y as fructans with the timing and amount of storage and mobilisation v arying between cultivars, although the maximum concentration (fructose equivalents per unit stem fresh weight) was similar in all cultivars. The main storage in the culm was located in the lower part of the ped uncle enclosed by the flag leaf sheath, in the penultimate internode a nd for one cultivar also in the flag leaf sheath. (CO2)-C-14 pulse-cha se studies showed that there was a considerable delay in the incorpora tion of flag leaf assimilates into stem fructans, a delay probably ass ociated with transfer and metabolic processes in the stem itself. At a nthesis, when soluble carbohydrates were rapidly accumulating in the c ulm, the level of activity of sucrose synthase (SS) in the penultimate internode was much greater than that of sucrose phosphate synthase (S PS). The activity of SS declined rapidly as active storage ceased. Thi s pattern was the reverse of that found in the leaf where SPS, rather than SS, was initially high and declined towards maturity. These chang es are discussed in relation to the possible role of sucrose synthesis ing enzymes, particularly SS, in the accumulation and mobilisation of stem reserves in wheat.