Apoptosis in barley aleurone during germination and its inhibition by abscisic acid

Abstract

During germination of barley grains, DNA fragmentation was observed in the aleurone. The appearance of DNA fragmentation in the aleurone layer, observed by TUNEL staining in aleurone sections, started near the embryo and extended to the aleurone cells far from the embryo in a time dependent manner. The same spatial temporal activities of hydrolytic enzymes such as alpha-amylase were observed in aleurone. DNA fragmentation could also be seen in vitro under osmotic stress, in isolated aleurone. During aleurone protoplast isolation, a very enhanced and strong DNA fragmentation occurred which was not seen in protoplast preparations of tobacco leaves. ABA was found to inhibit DNA fragmentation occurring in barley aleurone under osmotic stress condition and during protoplast isolation, while the plant growth regulator gibberellic acid counteracted the effect of ABA. Addition of auxin or cytokinin had no significant effect on DNA fragmentation in these cells. To study the role of phosphorylation in ABA signal transduction leading to control of DNA fragmentation (apoptosis), the effects of the phosphatase inhibitor okadaic acid and of phenylarisine oxide on apoptosis were studied. We hypothesize that the regulation of DNA fragmentation in aleurone plays a very important role in spatial and temporal control of aleurone activities during germination. The possible signal transduction pathway of ABA leading to the regulation of DNA fragmentation is discussed.

Barley Aleurone Cells Contain Two Types of Vacuoles: Characterization of Lytic Organelles by Use of Fluorescent Probes

“…This organelle is present in the aleurone cell during incubation in both GA and ABA, and imaging with pH-sensitive probes indicates that the organelle is more acidic in GA-treated cells than in ABAtreated cells. This observation may have far-reaching implications, because GA brings about programmed cell death in aleurone and ABA prevents it (Kuo et al, 1996;Wang et al, 1996). Lower pH within the secondary vacuoles of GAtreated cells may be associated with increased rates of hydrolysis within this organelle and a commensurate increase in the rate of autophagy.…”

“…Jones, unpublished data). Our working hypothesis is that the secondary vacuole is involved in autophagy and may be part of the process leading to programmed cell death of the aleurone cell (Wang et al, 1996).…”

Programmed cell death during vascular system formation

“…Phytohormones sometimes function in the induction of developmentally programmed cell death. For example, the death of aleurone cells is induced by gibberellic acid (GA) and suppressed by abscisic acid (ABA) (Kuo et al, 1996;Wang et al, 1996b). In contrast, GA inhibits the cell death process in pea ovary senescence (Vercher et al, 1987).…”

Mycotoxins reveal connections between plants and animals in apoptosis and ceramide signaling

“…In addition, appearance of TUNEL staining has been reported in cells that die to form the aleurone layer of barley and wheat grains (Wang et al, 1996), a gibberellin induced process that is blocked by okadaic acid (Kuo et al, 1996), and in microspore cells during diploid parthenogenesis of Norway spruce (Havel and Durzan, 1996). This suggests that DNA fragmentation, consistent with an apoptotic process, occurs in these situations where death clearly is a programmed and necessary part of normal development of the plant.…”

“…Programmed cell death in plants: occurrence in development, disease and genetic lesions Programmed cell death regimes in plants are recognized to occur at specific points during development including senescence (Woodson et al, 1992;Smart, 1994), pollination (O'Neill et al, 1993;Zhang and O'Neil, 1993); tracheary element development (Chasan, 1994;Demura and Fukuda, 1994;Fukuda, 1994) and in the formation of aleurone cells in barley and wheat (Wang et al, 1996;Kuo et al, 1996). Analogous to apoptosis in animals, cell death may be triggered in response to pathogens (see reviews by Dangl, 1995;Keen, 1990;Lamb, 1994;Jones and Dangl, 1996;Morel and Dangl, 1997).…”