Carbon assimilation and partitioning into non-structural carbohydrate in contrasting varieties of Lolium perenne

Rates of photosynthetic carbon assimilation and the partitioning of carbon into different sugar fractions have been compared in Aurora and Perma, two varieties of perennial ryegrass (Lolium perenne L.). Perma had a higher photosynthetic rate than Aurora at all irradiances, and numerically a considerably higher apparent maximum quantum yield although this was not statistically significant. On a leaf area basis Perma had heavier leaves that contained more chlorophyll a, chlorophyll b and carotenoid. Carbohydrate was predominantly present in the leaves of both varieties as sucrose and fructan. Fructose, glucose and starch were undetectable or only present in trace amounts. Perma leaf blades and sheaths contained more sucrose and more small (DP3) fructan than Aurora, but less polymeric fructan. Following depletion of carbohydrate pools in low light, excised leaves were induced to accumulate fructan at high light. Perma accumulated 88 % more water-soluble carbohydrate and 90 % more starch than Aurora. However after 24 h the polymeric fructan content of Perma leaves was still lower than that of Aurora. The increase in carbohydrate content of Aurora leaves was nearly all explained by the increase in polymeric fructan, whereas Perma partitioned less into polymeric fructan and contained significantly more glucose, sucrose and DP3 fructan. Additionally, the average chain length of Perma polymeric fructan was shorter than that of Aurora.