PARTITIONING OF C-14 ASSIMILATES BETWEEN SOURCES AND SINKS DURING DIFFERENT GROWTH-STAGES IN THE SYMPODIAL THIN-LEAVED ORCHID ONCIDIUM GOLDIANA

Distribution of C-14 assimilates from test leaves of a sympodial thin- leaved orchid hybrid, Oncidium Goldiana, was mapped using (CO2)-C-14 f eeding at three growth stages. Transport time of 33 h was suitable for studying patterns of C-14 assimilates partitioning to all plant parts on a single shoot. Oncidium Goldiana has a highly integrated pattern of source-sink assimilate partitioning in which ail test leaves suppli ed C-14 assimilates to every part of the plant. Both the inflorescence and the axillary bud are major sinks for all the leaves tested. Gener ally, all test leaves within each growth stage supplied similar amount s of C-14 assimilates to the respective major sinks. Pseudobulbs usual ly received significantly more C-14 assimilates from upper leaves (L1 and L2) than lower leaves (L3 and L4). Within each growth stage, the l ower leaf (L4) supplied more C-14 assimilates to the roots than the ot her leaves (L1, L2, and L3). Mature leaves are an important sink, espe cially after 6 h of (CO2)-C-14 feeding. The time-course study indicate s that pseudobulbs are important storage organs. Axillary buds and dev eloping inflorescences have significantly higher sink activities than mature inflorescences.