Calcium-Umlagerung in Bohnenfrüchten während des Samenwachstums

Summary Bean plants ( Phaseolus vulgaris L. var. «Saxa») were grown in water culture under controlled climatic conditions. The water transport in the xylem into the fruit and within the dorsal and ventral vascular strands of the fruit was traced with the dye Pyranin. Simultaneously the influx of 45 Ca into the fruit, its movement in the vascular strands of the fruit and its transfer from the pod into the developing seed was studied. With onset of seed growth the influx of water in the xylem and of Ca into the fruit sharply declines. This decline is more pronounced in the dorsal vascular strand, which is in direct contact with the seeds. Within both vascular strands of the fruit, however, distinct alternating fluxes of water in the xylem and of Ca in the basal and apical directions occur. In the dorsal vascular strand translocation in the basal direction, i.e. towards the fruit stem, dominates. During seed development the amount of Ca in the seeds increases continuously, whereas the amount of Ca in the pod decreases at a similar rate. The high mobility of Ca within the pod and the preferential uptake of Ca by the seed from the ventral side of the pod as compared to that from the dorsal side are further indications for a direct transfer of Ca from the pod tissue into the seed via the seedcoat, i.e. an apoplastic Ca transport. Within the bean fruit the seedcoat has both the highest Ca content and the highest cation exchange capacity. The oxalate content of the bean fruit tissue is very low. According to these results obtained from bean fruits, the Ca supply to the developing seed is effectively regulated by the demand of the seed. Redistribution of Ca from the pod through the seedcoat into the cotyledons is the dominating mechanism of Ca supply. In later stages of seed growth, in particular, there appears to be no long-distance transport of Ca in the vascular system into the seed.