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 /J-glucosidase are increased dramatically, while other hydrolytic activities such as the actions of protease, aminopeptidase, a-glucosidase, phosphatase, esterase, and a-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 |3-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.

Gene expression in opening and senescing petals of morning glory (Ipomoea nil) flowers

“…The mitochondria and the nucleus, in contrast remain until a late stage. Autophagic processes are indicated by the degradation of various organelles in the vacuole, rupture of the tonoplast, and subsequent autolysis of the whole cell (Matile and Winkenbach 1971;Smith et al 1992).…”

“…This species and the closely related I. tricolor have been used in several previous studies on petal senescence (Matile and Winkenbach 1971;Kende and Baumgartner 1974;Baumgartner et al 1975;Yamada et al 2006). We previously determined the time line of various visible symptoms of programmed cell death (PCD; here taken to be synonymous to senescence) and processes such as DNA degradation, chromatin condensation, and nuclear fragmentation, during petal PCD in I. nil (Yamada et al 2006).…”

Programmed cell death during plant growth and development

“…Thus it appears that the organized disassembly program active in leaves during senescence maintains cellular compartmentation throughout most of senescence, with death occurring semisynchronously only at the very end of the process (Thomson and Platt-Aloia, 1987). In contrast, petal senescence is characterized by early wilting (Matile and Winkenbach, 1971;Smith et al, 1992) and/or a watersoaked appearance, indicating the loss of tonoplast integrity. Ultrastructural changes in senescing carnation petals confirm this apparent cellular disorganization including early rupture of the tonoplast and plasmalemma and dissolution of cell wall components leading to complete loss of cellular contents (Smith et al, 1992).…”

“…The end result according to either model would be the non-autonomous inhibition of protein synthesis leading to the observed arrest of cell growth (Herrero and Dickinson, 1981), and ultimately to death. Although RNase activity is one of several hydrolytic markers for autolysis during tracheary element differentiation (Ye and Droste, 1996) and for leaf (Taylor et al, 1993) and petal (Matile and Winkenbach, 1971) senescence, stylar S-RNase appears to be the sole lytic agent necessary (Dodds et al, 1996, and references therein) for a process that may be initiated by the action of a single cell death promoter ± the as yet unidentified pollen S-locus product.…”

Nuclear fragmentation and DNA degradation during programmed cell death in petals of morning glory (Ipomoea nil)

“…I. nil and the closely related I. tricolor have been widely used in previous studies on petal senescence (Winkenbach 1970;Matile and Winkenbach 1971;Baumgartner et al 1975;Beutelmann and Kende 1977). The purpose of the present paper was to establish if there is chromatin fragmentation or nuclear fragmentation during PCD in the petals of this species, and if so, how its time line is related to other PCD parameters.…”