Transpiration and Calcium Deposition by Unifoliate Leaves of Phaseolus vulgaris Differing in Maturity

Unifoliate leaves were individually enclosed in clear, plastic chambers for the 24 hour treatment periods and then sacrificed for Ca analysis. Two transpiration rates were obtained by passing dry air through the chambers tising flow rates of 160 and 260 cm3/min. A third rate was obtained by a combination of shade and the lower air flow rate. Neither the transpiration rate nor solution‐Ca concentration (0.5mM and 2.5 mM of 0.1, and 0.5 strength Hoagland solution) altered the amount of Ca deposited in the unifoliate leaves of 22 day old bean plants (Phaseolus vulgaris). The transpiration rate per unit area of leaf remained constant for all ages studied (1l–20 days) and was 1.8, 2.7, 3.6 g H2O per dm2 day for the three different imposed conditions. A definite pattern of Ca deposition occurred. With all the transpiration rates there was a maximum rate of calcium deposition at 13 days of growth and a gradual decrease thereafter. When the Ca concentration of the nutrient solution was 20 μg/ml the daily Ca deposition in terms of water transpired by the unifoliate leaves exceeded this amount, except for the oldest leaf tested, and, the maximum Ca to water ratios were 250, 320, and 430 (μg Ca/g) in order of decreasing transpiration rates. The uptake of Ca against a concentration gradient and approximately the same total uptake regardless of transpiration rates and solution concentrations used, firmly suggest that Ca secretion into root‐xylem elements from a surrounding low level Ca solution requires energy expenditure by the plant. A possible explanation was proposed for the decreased rate of Ca deposition by the unifoliate leaves subsequent to the 13th day.