Mineral partitioning in the phloem during autumn senescence of beech leaves

Summary During the period of leaf senescence in fall, the minerals Mg, Ca, K, P, Cl, S, and Si were compared for occurrence and density in tissue compartments of leaf blade, petiole, and subtending stem of beech (Fagus sylvatica L.). Measurements were made by energy-dispersive X-ray microanalysis. The plant material was collected on 2,9, 16 and 23 October, and showed green, greenyellow, yellow, and red-brown autumn leaf coloration. Mg, K, and P were retrieved from the leaf blade prior to shedding, and deposited mainly in cortex and pith tissues of the stem. S and Ca remained in the leaf, and Si and Cl appeared to accumulate in the leaf prior to shedding. During the four stages of leaf senescence, the phloem compartments of the petiole showed considerable changes in mineral content. In addition, leaf senescence in several cases was accompanied by ion shifting from symplastic to apoplastic compartments and vice versa.