Long-term Partitioning, Storage and Re-mobilization of 14C Assimilated by Lolium perenne (cv. Melle)

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Abstract
The youngest fully expanded leaves of single tillers of vegetative perennial ryegrass plants were exposed to 14CO2. Thereafter, quantitative and fractional analysis of the partitioning, storage and re-mobilization after defoliation of the 14C-labelled assimilate was sequentially conducted over a 22 d period. In undefoliated plants, most 14C reached its final destination within 5–6 of feeding. Forty per cent of assimilated 14C was subsequently lost through respiration, while 13.5, 8.5 and 34 per cent remained in roots, stem bases and tops respectively. At least some 14C was distributed to tillers throughout the plant, but secondary tillers subtended by the fed tiller made the greatest demand on 14C translocated from the fed tiller. A small, but significant portion of 14C was invested into long term storage in undefoliated plants, four per cent of the total assimilated still being present in a labile chemical form in roots and stem bases 22 d after feeding. In plants that were severely defoliated 4 d after feeding, depletion of reserve 14C was observed relative to undefoliated plants. The depletion took place from stem bases, not roots, and both low and high molecular weight storage compounds were involved. A portion of the depleted 14C was incorporated into new growth after defoliation.