Graduate Thesis Or Dissertation
 

Nature of calcium uptake by plants

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  • Cucumber, pea, bean, and corn excised roots were used to assess species differences in metabolic uptake of calcium It was found that Ca was mostly taken up by these root systems by non-metabolic processes. The apparent free space ranged from 26 to 28 percent of the total root volume and beyond that no large accumulation of Ca was observed. Although a small rate of increase was observed during the 12 hour experimental period, this was attributed to either an increase in the total non-metabolic component or to a manifestation of the small percentage of younger vacuolated segments of the roots. These results pointed out that the physiological maturity of the roots may be the controlling factor in Ca absorption and that mature root cells are relatively impermeable to Ca. Excised roots and intact plants of six-week-old tomato were compared to evaluate the influence of the top in the uptake of calcium. On a per unit of root basis, the uptake of calcium was 5.5 times faster for intact plants than for the most rapid sustained phase of absorption for excised roots. Intact plants absorbed calcium almost 39 times faster than the slower rate observed for the excised roots. Several hypotheses were advanced to explain these observations, Mass flow in the transpirational stream or migration along charged surfaces would represent non-metabolic processes. Another possibility is an indirect enhancement of metabolic uptake by transpiration due to a stimulation of bleeding in the root. A third possibility is the operation of a uni-directional transport of ions across the endodermis in intact plants which goes undetected in excised root systems because the stele is opened to the external solution.
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