UTILIZATION OF ASSIMILATES FOR GROWTH AND RESPIRATION IN LOLIUM-MULTIFLORUM LAM PLANTS

Uptake, distribution, storage, and reutilization of C-14-assimilates w ere studied to evaluate the utilization of C-14-products for growth an d respiration in intact and defoliated (by mowing) Italian ryegrass (L olium multiflorum Lam.) plants. The long-term changes in C-14 losses r evealed a two-phase pattern. Rapid C-14 losses in the first hours afte r (CO2)-C-14 assimilation indicated a preferential utilization of ''yo ung'' assimilates for respiration. The slow C-14 losses proceeded for some weeks and apparently coincided with C-14 incorporation into the s tructural and reserve compounds. In the source-sink system of Italian ryegrass, the transitory assimilate reservoir was located in the culms . Stored C-14 compounds were rapidly reutilized only by the plants aft er defoliation, but remained almost unutilized in the intact plants. C -14-reutilization was accompanied by additional respiratory expenditur es related to biomass de novo production. The C-14-fraction withdrawn from transitory reservoir and used for the respiration during the regr owth after mowing was close in size to C-14-fraction used for the resp iration of intact plants after (CO2)-C-14 assimilation.