THE IMPORTANCE OF PHOTOASSIMILATE CONTRIBUTION FROM THE CURRENT SHOOTAND CONNECTED BACK SHOOTS TO INFLORESCENCE SIZE IN THE THIN-LEAVED SYMPODIAL ORCHID ONCIDIUM-GOLDIANA

Inflorescence size of the current shoot of the thin-leaved sympodial o rchid hybrid Oncidium Goldiana is dependent on the number of connected back shoot(s). Our study showed that the size of the inflorescence in creased progressively from plants having no, one, or two connected bac k shoot(s). The size of the inflorescence was not affected by more tha n two back shoots connected to the current shoot. Defoliation experime nts demonstrated that the leaves of the current shoot are the main sou rce of photoassimilates for the inflorescence on the current shoot its elf white the leaves of the connected back shoots are secondary source s of photoassimilates, Significantly lower dry mass of pseudobulbs for the defoliated current shoot indicated some degree of remobilization of storage reserves for inflorescence production. The relative importa nce of leaves on the current shoot and connected back shoots as a sour ce of photoassimilates was confirmed using (CO2)-C-14 feeding experime nts. The test leaf on the current shoot contributed significantly more C-14 assimilates (83%) to the inflorescence after a transport time of 57 h. All selected test leaves on back shoots exported 61%-72% of C-1 4 assimilates to the inflorescence of the current shoot. The connected shoots of O. Goldiana are physiologically interdependent in terms of carbon economy during the flowering stage as test leaves on all shoots exported C-14 assimilates to all plant parts within the connected sho ots, including the mature leaves. There was sufficient evidence to ind icate a polar movement of C-14 assimilates toward the major sink on th e current shoot with some bidirectional transfer of C-14 assimilates a mong the different Sshoots.