ECOLOGICAL ASPECTS OF ASSIMILATE OUTFLOW .1. TEMPERATURE

The following tracks of assimilate outflow have been determined as a r esult of ultrastructural study of phloem terminal complexes: 1) throug h the unified endoplasmic network; and 2) by means of pinocytotic tran sport through the apoplast from one endoplasmic network to another. Bo th structural channels are dynamic: They are readily filled with assim ilates and contract with decline of the assimilate level. Measuring of the volume of these structures by methods of cell morphometry reveale d the temperature dependency of each type of outflow on three groups o f objects: with terminal complexes of the open type; with terminal com plexes of the closed type; and with terminal complexes of the combined type. Transport through the endoplasmic reticulum turned out to be ve ry sensitive in the range of low positive temperatures: it attained sa turation at 20-degrees-C, was appreciably inhibited at 15-degrees, and was shut down completely below 7-8-degrees. Inhibition is associated with contraction of the endoplasmic reticulum tubule in plasmodesmata to a rod. Pinocytotic transport through the apoplast, on the other ban d, is most active in the range of temperature depression of endoplasmi c transport (10-20-degrees), which confirms its compensatory nature fo r species with two-channel phloem loading.