Do mitochondria in Dendrobium petal mesophyll cells form vacuole-like vesicles?

Abstract

Using transmission electron microscopy, we investigated the ultrastructure of mitochondria in petal mesophyll cells of the orchid Dendrobium cv. Lucky Duan, from the time of floral opening to visible petal senescence. Cells close to the vascular bundle contained many mitochondria, some of which showed internal degeneration. This inner mitochondrial breakdown was accompanied by an eightfold increase in mitochondrial volume. Small electron-dense granules (approximately 0.04 mum in diameter) at the periphery of the mitochondrial matrix remained. These granules were used as an indicator of still later stages of mitochondrial development in these cells. The apparent final stage of mitochondrial degeneration was a single-membrane-bound vesicle, resembling a vacuole. No evidence was found for the idea that mitochondria became transferred (intact or degenerated) into a lytic vacuole. Taken together, the data suggest the hypotheses that (a) mitochondria in cells close to the vascular bundle in petals of open Dendrobium cv. Lucky Duan flowers undergo large-scale internal degeneration and that (b) such degenerating mitochondria form vacuole-like vesicles.

Do plastids inDendrobiumcv. Lucky Duan petals function similar to autophagosomes and autolysosomes?

“…An overview of the anatomy of the petal, using light microscopy, has been shown in a previous paper. 30 Briefly, the upper epidermis had large cells, bulging to the exterior. The lower epidermis had somewhat smaller cells.…”

Ultrastructure of autophagy in plant cells

“…No half-life data seem available for plant mitochondria. 112 No evidence has thus far been shown in plants for a role of macroautophagy in the degradation of mitochondria. Uptake of mitochondria into the vacuole by microautophagy, and subsequent degradation, has been shown in organisms other than plants (mainly yeasts), but also have not been reported in plants.…”

“…The mitochondrial interior eventually becomes homogeneously electron-translucent. Kirasak et al 112 observed that small electron-dense granules (approximately 0.04 μm in diameter) remain visible at the periphery of the mitochondrial matrix during plant mitochondrion degeneration. Such granules are not found in any other organelle.…”

The Complexity of Vesicle Transport Factors in Plants Examined by Orthology Search

“…In line, mitochondrion internal vesicle-like structures have been reported in mitochondria of patients with defective gene functions which cause pathological conditions, or during reconstruction of the matrix compartment after extensive osmotic swelling [279], [280] as well as in degenerating mitochondria in vascular bundle in petals of open Dendrobium cv. Lucky Duan flowers [281]. Therefore, one can speculate that some of the components identified in this study as mitochondrial-localized factors are involved in the formation of cristae as the induction of membrane curvature is comparable to vesicle formation [282].…”