Apoptosis in Wheat Seedlings Grown under Normal Daylight

Abstract

Apoptosis was observed in the coleoptile and initial leaf in 5-8-day-old wheat seedlings grown under normal daylight. Apoptosis is an obligatory event in early wheat plant ontogenesis, and it is characterized by cytoplasmic structural reorganization and fragmentation, in particular, with the appearance in vacuoles of specific vesicles containing intact organelles, chromatin condensation and margination in the nucleus, and internucleosomal fragmentation of nuclear DNA. The earliest signs of programmed cell death (PCD) were observed in the cytoplasm, but the elements of apoptotic degradation in the nucleus appeared later. Nuclear DNA fragmentation was detected after chromatin condensation and the appearance in vacuoles of specific vesicles containing mitochondria. Two PCD varieties were observed in the initial leaf of 5-day-old seedlings grown under normal daylight: a proper apoptosis and vacuolar collapse. On the contrary, PCD in coleoptiles under various growing (light) conditions and in the initial leaf of etiolated seedlings is only a classical plant apoptosis. Therefore, various tissue-specific and light-dependent PCD forms do exist in plants. Amounts of O2*- and H2O2 evolved by seedlings grown under normal daylight are less than that evolved by etiolated seedlings. The amount of H2O2 formed in the presence of sodium salicylate or azide by seedlings grown under normal daylight was increased. Contrary to etiolated seedlings, the antioxidant BHT (ionol) did not inhibit O2*- formation and apoptosis and it had no influence on ontogenesis in the seedlings grown under normal daylight. Thus, in plants grown under the normal light regime the powerful system controlling the balance between formation and inactivation of reactive oxygen species (ROS) does exist and it effectively functions. This system is responsible for maintenance of cell homeostasis, and it regulates the crucial ROS level controlling plant growth and development. In etiolated plants, this system seems to be absent, or it is much less effective.

Combined Effect of Water Deficit and Salt Stress on the Structure of Mesophyll Cells in Wheat Seedlings

“…During the chromatin condensation, the nuclear DNA in wheat coleoptile cells undergoes an internucleosomal fragmentation [33]. A similar chromatin condensation is shown in Figure 5(a).…”

Effect of “External” Superoxide Anion on Apoptosis in Coleoptiles of Wheat Seedlings

“…Margination of chro matin is clearly demonstrated in the sections (Fig. They had the same set of cytochromes as normal mitochondria, but were specified by the intense synthesis of heavy (ρ = 1.718 g/cm 3 ) mitochondrial DNA [10,11]. Mitochondria inside vesicles, or mitochondrial vesicles, were earlier detected by us in vacuoles of parenchyma cells of apical zones of 4 day old wheat seedling coleop tiles [4].…”

Programmed cell death during the transition from multicellular structures to globular embryos in barley androgenesis

“…Prior to exine wall rupture, the cytoplasm of the small cells is very dense, whereas the nucleus shows condensed chromatin structure. Condensation of nuclear chromatin and an electron-dense cytoplasm have been pointed as morphological markers of plant PCD (Pennel and Lamb 1997;Domı´nguez et al 2001;Aleksandrushkina et al 2004). However, in the small cell domain of barley MCSs, these characteristics appear to be inherent to their generative cell origin rather than induced by PCD, since they were observed prior to any PCD event had started.…”