Function of Lysosomes and Lysosomal Enzymes in the Senescing Corolla of the Morning Glory (Ipomoea purpurea)

Abstract

The rapid senescence of the Ipomoea corolla is characterized by the breakdown of protein and nucleic acids. At the onset of wilting the activities of deoxyribonuclease (DNase), ribonuclease (RNase), and β-glucosidase are increased dramatically, while other hydrolytic activities such as the actions of protease, aminopeptidase, α-glucosidase, phosphatase, esterase, and α-amylase are only slightly changed. Isolated corolla discs show a course of senescence similar to that of the intact organ. When floating on solutions of cycloheximide the activities of DNase, RNase, and β-glucosidase do not increase. Actinomycin D inhibits the increase in RNase activity. It is concluded that protein synthesis is a prerequisite for the changes in these enzyme activities in the senescing corolla. The function of the lysosomal compartment in the process of senescence is illustrated by electron micrographs showing the autophagic activity of vacuoles. The last phase of senescence is characterized by the breakdown of the tonoplast and complete digestion of the cytoplasmic constituents in the autolysing cells.