Distribution of Calcium and Phosphorus in Leaves of the Proteaceae

The overall aim of our research program is to discover the physiological basis of calcium toxicity in Proteaceae plant species that typically inhabit low-phosphorus, acidic soils and avoid calcareous (alkaline) soils. The phenomenon of Ca toxicity has been known for decades, but so far no clear mechanistic explanation is available. We propose that Ca toxicity in P-efficient Proteaceae is the result of a shift in cell type where P accumulates, from epidermal cells as seen in dicots generally to mesophyll cells in P-efficient Proteaceae species [1]. Conversely, we hypothesise that Ca toxicity is avoided in the few Proteaceae species that inhabit calcareous soils by shifting the accumulation of Ca from mesophyll cells, where dicots generally accumulate Ca, to epidermal cells so as to prevent interference with efficient P utilisation.