FRUCTAN METABOLISM IN EXPANDING LEAVES, MATURE LEAF SHEATHS AND MATURE LEAF BLADES OF LOLIUM-PERENNE - FRUCTAN SYNTHESIS, FRUCTOSYLTRANSFERASE AND INVERTASE ACTIVITIES

Accumulation of water-soluble carbohydrates was studied in leaf tissue s of 8-wk-old plants of perennial ryegrass (Lolium perenne L. var. Bra ve). The roots and leaf bases were cooled to low temperatures to reduc e sink activity while source activity was enhanced by continuous illum ination of the shoots. This resulted in accumulation of fructans, firs t in sheaths, subsequently in expanding leaves, and finally in blades. Fructan concentration increased from 6 to 23 mg g(-1) f. wt in sheath s, from 8 to 30 mg g(-1) f. wt in expanding leaves and from 6 to only 17 mg g(-1) f. wt in mature leaf blades. Increase in concentration of low-DP fructans preceded accumulation of high-DR fructans. Expanding l eaves accumulated significantly more glucose and fructose than did mat ure leaf tissue. Leaf blades contained a higher concentration of sucro se than either leaf sheaths or expanding leaves. Expanding leaves exhi bited the greatest activity of SST (0.77 nkat g(-1) f. wt), the mature leaf blades the least (0.09 nkat g(-1) f. wt), whilst that of mature leaf sheaths was intermediate (0.27 nkat g-l f. wt). In each leaf tiss ue, invertase activity was higher than SST activity. Under conditions of fructan accumulation, SST activity increased threefold in mature le af sheaths and 1.2-fold in expanding leaves. In mature leaf blades, ho wever, the activity remained constant at a low level. Invertase activi ty never increased. Inhibitors of protein synthesis (cycloheximide) an d of RNA metabolism (actinomycin D) prevented any increase of SST acti vity in leaf sheaths. The results are discussed in relation to fructan metabolism in leaf tissues of Lolium perenne.