|Title||Seasonal changes in the pattern of photosynthate transport within elongating shoots of Populus grandidentata|
|Year of Publication||1970|
|Degree||Doctor of Philosophy|
|Number of Pages||65 pp.|
|University||University of Michigan|
|City||Ann Arbor, MI|
Individual leaves on 5-year-old bigtooth aspen (Populus grandidentata Michx.) suckers in northern Lower Michigan were exposed to 14 CO2 in order to detect seasonal changes in translocation of photosynthates. As new leaves developed at the base of currently-elongating long shoots, they at first acted as translocation sinks and utilized stored carbohydrates. Base (first-formed) leaves began to translocate significant quantities of photosynthate around June 1. By June 15, the direction of net transport had changed from acropetally (to the shoot tip) to basipetally (to the main stem). Leaves midway along the shoot continued to export mainly to the stem tip until early July. Tip (last-formed) leaves did not begin to translocate significant quantities of photosynthates until late July; photosynthates from these leaves were transported mainly toward the main stem. Leaves occupying all shoot positions tested (base, middle, and tip) transported assimilates into their axillary buds--base leaves mainly in June, middle leaves in July, and tip leaves in August. The terminal bud imported photosynthates from all leaves on the shoot, and accumulated several times more C-14 label than did axillary buds at the base of the shoot.