Distribution of calcium absorbed by all or part of the root system of beans.

When either the whole root system or a single root of the bean plant (Phaseolus vulgaris L.), at different stages of maturity, was fed (45)Ca for a period of 6 hr, the leaves exhibited a definite pattern of (45)Ca acquisition with maximum acquisition for the primary, first, second, and third trifoliolate leaves at 12, 16, 18, and 22 days of growth, respectively. This maximum acquisition occurred when a leaf approached full expansion. A liquid scintillation spectrometer was employed for (45)Ca analysis.Autoradiograms indicated that when (45)Ca was applied to the terminal 5 cm portion of specific lateral roots for a period of 6 hr, specific areas of the shoot were preferentially supplied with (45)Ca. The amount of (45)Ca transported upward, when the terminal 5 cm portion of a single lateral root was treated, greatly decreased in plants older than 20 days, and the growth rate of these roots was also reduced at about the same time. When the whole lateral root was involved in (45)Ca uptake, the amount of (45)Ca transported to the shoot increased with increasing plant age until after day 22. A continuous increase in (45)Ca transport to the shoot occurred when the whole root system was subjected to (45)Ca treatment. One factor involved in the decreased movement of (45)Ca into a particular leaf may be a decreased absorptive capacity of that part of the root which preferentially supplies Ca to this leaf. Other possible factors are discussed.