Acid phosphatase activity in plastids (plastolysomes) of senescing embryo-suspensor cells

Autolysis of the suspensor, an embryonal haustorium, starts in the basal cells and proceeds in the direction of the embryo. InPhaseolus vulgaris, acid phosphatase activity is first found in transforming plastids, similar to the acid phosphatase activity inPh. coccineus [Nagl (1977) Z. Pflanzenphysiol.85, 45-51], although the ultrastructural details are different. InTropaeolum majus, autolysis begins in the most distal part of the suspensor, i.e., the chalazal or carpel haustorium. First the endoplasmic reticulum shows acid phosphatase activity, but neither the mitochondria, which undergo transformation similar to that observed in plastids ofPhaseolus, nor the leucoplasts show such activity. Later, however, the plastids exhibit low activity. Contrarily, the plastids in the suspensor cells adjacent to the embryo show increasing activity during senescence of the suspensor. During final autolysis, activity is found in all cytoplasmic membranes, while it is reduced in plastids. The visible ultrastructural transformations of various organelles into cytolysomes does not necessarily coincide with acid phosphatase activity. Our findings are a further indication of the high diversification and specialization of plastids during plant embryogenesis.