PATTERN OF PHOTOASSIMILATE PARTITIONING IN PSEUDOBULBOUS AND RHIZOMATOUS TERRESTRIAL ORCHIDS

Photoassimilate partitioning patterns in two terrestrial orchids, Spat hoglottis unguiculata and Bromheadia finlaysoniana, were mapped using a (CO2)-C-14, dosing technique. A highly integrated source-sink photoa ssimilate partitioning pattern was observed in both orchids. In S. ung uiculata, a pseudobulbous terrestrial orchid, all test leaves supplied similar percentages of C-14-assimilates to all plant parts on a singl e shoot. In both orchids, the inflorescence during the reproductive st age and the axillary bud during the vegetative stage had the highest s ink activity and percentage distribution of C-14-assimilates. A high p ercentage of C-14-assimilates was imported by the pseudobulb of S. ung uiculata. The pseudobulb accumulated a higher percentage of C-14-assim ilates (44%) during the vegetative stage than during the flowering sta ge (21-30%). In B. finlaysoniana, a rhizomatous terrestrial orchid, a high percentage of C-14-photoassimilates was observed in the stem inte rnodes at all three developmental growth stages (the vegetative stage (stage 1), the flowering stage (stage 2) and the fruiting stage (stage 4)). Sink activities of the rhizome were higher at stages 1 and 4 tha n at stage 2. A similar pattern of photoassimilate partitioning was ob served for B. finlaysoniana grown naturally in its habitat. A polar mo vement of C-14-assimilates towards the major sink (inflorescence) was observed in the current shoot of field plants with a competing sink (a xillary bud). (C) 1998 Published by Elsevier Science B.V. All rights r eserved.