Influence of Translocation of Photosynthetic Efficiency of Phaseolus vulgaris L

Measurements of net photosynthesis show that in Phaseolus vulgaris L. the cultivar Michelite-62 exceeds the cultivar Red Kidney in net CO(2) uptake by 23 to 31%. Data on translocation of pulse label indicate that export of a pulse of photosynthetically assimilated (14)C from the source leaf of either M-62 or Red Kidney follows an exponential pattern and shows an initial rapid phase followed by a second slower phase. The steeper slope for both phases in M-62 suggests its rate of translocation of pulse label is higher than that of Red Kidney. Furthermore, only 38% of the (14)C remains in the leaf of M-62 after 8 hours, while Red Kidney retains up to 60% of the label. Leaf autoradiographs obtained after pulse labeling demonstrate a much faster rate of vein loading in M-62 and are considered evidence for the higher translocation efficiency of M-62. These results provide evidence for a positive correlation between photosynthetic efficiency and translocation efficiency in M-62 and Red Kidney and give support to our hypothesis that translocation is one of the important physiological factors controlling the varietal differences in photosynthetic efficiency in Phaseolus vulgaris.