Targeting of organelles into vacuoles and ultrastructure of flower petal epidermis of Petunia hybrida

Abstract

Autophagy in flower petal epidermal cells is a little studied process. However, it is of interest regarding the physiology of chlorophylless plant tissues. We show that the utilization of organelles in the Petunia hybrida L. flower petal epidermis occurs via the autophagic-like organelle targeting into vacuole during the particular process of vacuole fragmentation and growth of secondary vacuoles (ATVF). It differs from macroautophagy (formation of autophagosome) and microautophagy. Peroxisomes were shown to be subjected to both macroautophagy (as single microbodies and their assemblies) and to ATVF when they are in complexes with mitochondria and chromoplasts. In addition, we have demonstrated that ATVF in flower petals is accompanied with the sequestration of the cytoplasmic sectors located between the neighboring cell wall ingrowths, the ultrastructure of which has been reported in the present work for the first time. It has been shown there are more numerous mitochondria, a more pronounced ATVF, and a thicker cytoplasmic layer in the blue tissues, possibly reflecting more intensive metabolic processes in them compared to white tissues. We assume that these differences may be of interest for the further studies and may be discussed including in terms of anthocyanin-dependent photochemical effects.