Translocation and Metabolic Conversion of C-Labeled Assimilates in Detached and Attached Leaves of Phaseolus vulgaris L. in Different Phases of Leaf Expansion

Leaf excision greatly affected the actual levels of ¹⁴C-assimilates in laminas and petioles of primary bean leaves (Phaseolus vulgaris L.) following a transport period. However, it did not affect the percentage of starch in the insoluble residue; starch decreased from 20% of the insoluble residue after exposure to ¹⁴CO₂ to 3% after 5 hr in both attached and detached leaves. The transition from import to export of attached and detached leaves was at the same stage, i.e., when the cotyledons were 63 to 85% depleted. The composition of the ¹⁴C-assimilates in importing leaves was different from that in exporting leaves. In the former, only 5% of the soluble label was free sugar, while 74% was free sugar in the latter. The failure of importing leaves to export was not due to the labeled substances being nontransferable. Extracts from importing leaves applied to exporting leaves were exported; these extracts were high in amino acids and organic acids but low in free sugar. However, exporting leaves exposed to ¹⁴CO₂ appeared to export sugars more readily than amino acids. Cotyledon excision did not delay transition of leaves from import to export. Actually, excision seemed to enhance slightly the transition of the primary leaves from import to export.