Apoptosis in Plants: Specific Features of Plant Apoptotic Cells and Effect of Various Factors and Agents

Abstract

Apoptosis is an integral part of plant ontogenesis; it is controlled by cellular oxidative status, phytohormones, and DNA methylation. In wheat plants apoptosis appears at early stages of development in coleoptile and initial leaf of 5- to 6-day-old seedlings. Distinct ultrastructural features of apoptosis observed are (1). compaction and vacuolization of cytoplasm in the apoptotic cell, (2). specific fragmentation of cytoplasm and appearance in the vacuole of unique single-membrane vesicles containing active organelles, (3). cessation of nuclear DNA synthesis, (4). condensation and margination of chromatin in the nucleus, (5). internucleosomal fragmentation of nuclear DNA, and (6). intensive synthesis of mitochondrial DNA in vacuolar vesicles. Peroxides, abscisic acid, ethylene releaser ethrel, and DNA methylation inhibitor 5-azacytidine induce and stimulate apoptosis. Modulation of the reactive oxygen species (ROS) level in seedling by antioxidants and peroxides results in tissue-specific changes in the target date for the appearance and the intensity of apoptosis. Antioxidant butylated hydroxytoluene (BHT) reduces the amount of ROS and prevents apoptosis in etiolated seedlings, prolongs coleoptile life span, and prevents the appearance of all apoptotic features mentioned. Besides, BHT induces large structural changes in the organization of all cellular organelles and the formation of new unusual membrane structures in the cytoplasm. BHT distorts mitosis and this results in the appearance of multiblade polyploid nuclei and multinuclear cells. In roots of etiolated wheat seedlings, BHT induces differentiation of plastids with the formation of chloro(chromo)plasts. Therefore, ROS controlled by BHT seems to regulate mitosis, trigger apoptosis, and control plastid differentiation and the organization of various cellular structures formed by endocytoplasmic reticulum.