Effect of Excessive Manganese Supply on Uptake and Translocation of Calcium in Bean Plants (Phaseolus vulgaris L.)

Abstract

In short- and long-term water culture experiments an excessive supply of manganese inhibited the calcium translocation into the leaves of bean plants (Phaseolus vulgaris L.). This inhibition was not based on a reduction of the transpiration rate, nor could it be explained by a simple cation competition for binding sites. Particularly in fast growing leaf tissue, the inhibition of calcium translocation was much more pronounced than that of other cations, for example potassium. Inhibited calcium translocation resulted in typical symptoms of calcium deficiency (e.g., «crinkle leaf») in the shoot apices and youngest leaves at toxic levels of manganese. Excessive manganese supply caused the cation exchange capacity in the leaf tissue to be distinctly reduced, and the calcium uptake into the AFS of isolated leaf segments from leaves showing manganese toxicity was lower. It is concluded that under conditions of manganese toxicity the IAA-oxidase-activity is increased with a concomitant decrease in auxin level. The lower auxin level causes inhibition of cell wall expansion and, in turn, a reduction in formation of new negative binding sites and thus decreased calcium translocation into this tissue.