PubMed Health⌕ Search

Biomedical subjects

A Fath

Publications and source records attributed to A Fath.

9 recordsLinked to original sources
PubMed2001

Enzymes that scavenge reactive oxygen species are down-regulated prior to gibberellic acid-induced programmed cell death in barley aleurone.

Gibberellins (GAs) initiate a series of events that culminate in programmed cell death, whereas abscisic acid (ABA) prevents this process. Reactive oxygen species (ROS) are key elements in aleurone programmed cell death. Incubation of barley (Hordeum vulgare) aleurone layers in H2O2 causes rapid death of all cells in GA- but not ABA-treated layers. Sensitivity to H2O2 in GA-treated aleurone cells results from a decreased ability to metabolize ROS. The amounts and activities of ROS scavenging enzymes, including catalase (CAT), ascorbate peroxidase, and superoxide dismutase are strongly down-regulated in aleurone layers treated with GA. CAT activity, protein, and Cat2 mRNA decline rapidly following exposure of aleurone layers to GA. In ABA-treated layers, on the other hand, the amount and activity of CAT and Cat2 mRNA increases. Incubation in ABA maintains high amounts of ascorbate peroxidase and superoxide dismutase, whereas GA brings about a rapid reduction in the amounts of these enzymes. These data imply that GA-treated cells loose their ability to scavenge ROS and that this loss ultimately results in oxidative damage and cell death. ABA-treated cells, on the other hand, maintain their ability to scavenge ROS and remain viable.

Abscisic Acid↗
PubMed2000

Programmed cell death in cereal aleurone.

Progress in understanding programmed cell death (PCD) in the cereal aleurone is described. Cereal aleurone cells are specialized endosperm cells that function to synthesize and secrete hydrolytic enzymes that break down reserves in the starchy endosperm. Unlike the cells of the starchy endosperm, aleurone cells are viable in mature grain but undergo PCD when germination is triggered or when isolated aleurone layers or protoplasts are incubated in gibberellic acid (GA). Abscisic acid (ABA) slows down the process of aleurone cell death and isolated aleurone protoplasts can be kept alive in media containing ABA for up to 6 months. Cell death in barley aleurone occurs only after cells become highly vacuolated and is manifested in an abrupt loss of plasma membrane integrity. Aleurone cell death does not follow the apoptotic pathway found in many animal cells. The hallmarks of apoptosis, including internucleosomal DNA cleavage, plasma membrane and nuclear blebbing and formation of apoptotic bodies, are not observed in dying aleurone cells. PCD in barley aleurone cells is accompanied by the accumulation of a spectrum of nuclease and protease activities and the loss of organelles as a result of cellular autolysis.

Apoptosis↗
PubMed1999

Hormonally regulated programmed cell death in barley aleurone cells

Cell death was studied in barley (cv Himalaya) aleurone cells treated with abscisic acid and gibberellin. Aleurone protoplasts incubated in abscisic acid remained viable in culture for at least 3 weeks, but exposure to gibberellin initiated a series of events that resulted in death. Between 4 and 8 days after incubation in gibberellin, >70% of all protoplasts died. Death, which occurred after cells became highly vacuolated, was manifest by an abrupt loss of plasma membrane integrity followed by rapid shrinkage of the cell corpse. Hydrolysis of DNA began before death and occurred as protoplasts ceased production of alpha-amylase. DNA degradation did not result in the accumulation of discrete low molecular weight fragments. DNA degradation and cell death were prevented by LY83583, an inhibitor of gibberellin signaling in barley aleurone. We conclude that cell death in aleurone cells is hormonally regulated and is the final step of a developmental program that promotes successful seedling establishment.

Journal Article↗
PubMed1999

Barley aleurone cell death is not apoptotic: characterization of nuclease activities and DNA degradation

Barley aleurone cells undergo programmed cell death (PCD) when exposed to gibberellic acid (GA), but incubation in abscisic acid (ABA) prevents PCD. We tested the hypothesis that PCD in aleurone cells occurs by apoptosis, and show that the hallmarks of apoptosis, namely DNA cleavage into 180 bp fragments, plasma membrane blebbing, and the formation of apoptotic bodies do not occur when aleurone cells die. We show that endogenous barley aleurone nucleases and nucleases present in enzymes used for protoplast preparation degrade aleurone DNA and that DNA degradation by these nucleases is rapid and can result in the formation of 180 bp DNA ladders. Methods are described that prevent DNA degradation during isolation from aleurone layers or protoplasts. Barley aleurone cells contain three nucleases whose activities are regulated by GA and ABA. GA induction and ABA repression of nuclease activities correlate with PCD in aleurone cells. Cells incubated in ABA remain alive and do not degrade their DNA, but living aleurone cells treated with GA accumulate nucleases and hydrolyze their nuclear DNA. We propose that barley nucleases play a role in DNA cleavage during aleurone PCD.

Journal Article↗
PubMed1999

Barley aleurone cell death is not apoptotic: characterization of nuclease activities and DNA degradation.

Barley aleurone cells undergo programmed cell death (PCD) when exposed to gibberellic acid (GA), but incubation in abscisic acid (ABA) prevent PCD. We tested the hypothesis that PCD in aleurone cells occurs by apoptosis, and show that the hallmark of apoptosis, namely DNA cleavage into 180 bp fragments, plasma membrane blebbing, and the formation of apoptotic bodies do not occur when aleurone cells die. We show that endogenous barley aleurone nucleases and nucleases present in enzymes used for protoplast preparation degrade aleurone DNA and that DNA degradation by these nucleases is rapid and can result in the formation of 180 bp DNA ladders. Methods are described that prevent DNA degradation during isolation from aleurone layers or protoplasts. Barley aleurone cells contain three nucleases whose activities are regulated by GA and ABA. CA induction and ABA repression of nuclease activities correlate with PCD in aleurone cells. Cells incubated in ABA remain alive and do not degrade their DNA, but living aleurone cells treated with GA accumulate nucleases and hydrolyze their nuclear DNA. We propose that barley nucleases play a role in DNA cleavage during aleurone PCD.

Abscisic Acid↗
PubMed1998

Characterization of a calmodulin-binding transporter from the plasma membrane of barley aleurone.

We have used Arabidopsis calmodulin (CaM) covalently coupled to horseradish peroxidase to screen a barley aleurone cDNA expression library for CaM binding proteins. The deduced amino acid sequence of one cDNA obtained by this screen was shown to be a unique protein of 702 amino acids with CaM and cyclic nucleotide binding domains at the carboxyl terminus and high similarity to olfactory and K+ channels. This cDNA was designated HvCBT1 (Hordeum vulgare CaM binding transporter). Hydropathy plots of HvCBT1 showed the presence of six putative transmembrane domains, but sequence alignment indicated a pore domain that was unlike the consensus domains in K+ and olfactory channels. Expression of a subclone of amino acids 482-702 in Escherichia coli generated a peptide that bound CaM. When a fusion protein of HvCBT1 and green fluorescent protein was expressed in barley aleurone protoplasts, fluorescence accumulated in the plasma membrane. Expression of HvCBT1 in the K+ transport deficient Saccharomyces cerevisiae mutant CY162 showed no rescue of the mutant phenotype. However, growth of CY162 expressing HvCBT1 with its pore mutated to GYGD, the consensus sequence of K+ channels, was compromised. We interpret these data as indicating that HvCBT1 acts to interfere with ion transport.

Amino Acid Sequence↗
PubMed1993

High affinity binding of a glycopeptide elicitor to tomato cells and microsomal membranes and displacement by specific glycan suppressors.

We have previously isolated glycopeptides derived from yeast invertase that acted as highly potent elicitors in suspension-cultured tomato cells, inducing ethylene biosynthesis and phenylalanine ammonia-lyase activity, and we have found that the high mannose oligosaccharides released from the pure glycopeptide elicitors by endo-beta-N-acetylglucosaminidase H acted as suppressors of elicitor activity (Basse, C. W., Bock, K., and Boller, T. (1992) J. Biol. Chem. 267, 10258-10265). One of the elicitor-active glycopeptides (gp 8c) was labeled with t-butoxycarbonyl-L-[35S]methionine and purified by reversed phase high performance liquid chromatography resulting in a specific radioactivity of the derivative of about 900 Ci/mmol. This radiolabeled glycopeptide showed specific, saturable, and reversible binding to whole tomato cells under conditions in which cells are responsive to elicitors as well as to microsomal membranes derived from these cells. Ligand saturation experiments, performed with microsomal membranes, gave a dissociation constant (Kd) of 3.3 nM as determined by Scatchard analysis. Various glycopeptide elicitors and preparations from yeast invertase were compared with respect to their abilities to compete for binding of 35S-labeled gp 8c to tomato membranes and to induce ethylene biosynthesis in tomato cells. These studies revealed a high degree of correlation between elicitor activities in vivo and displacement activities in vitro. In both tests, a high activity depended on the presence of glycan side chains consisting of more than 8 mannosyl residues. The high mannose oligosaccharides that acted as suppressors of elicitor activity in vivo competed for binding of the labeled elicitor also. The suppressor-active glycan Man11GlcNAc and the elicitor-active gp 8c exhibited very similar displacement activities, and the inhibitory constant (Ki) of the glycan Man11GlcNAc was very similar to the Kd value calculated for 35S-labeled gp 8c, indicating that the glycopeptide elicitors and the glycan suppressors derived from these elicitors competed with similar affinities for the same binding site. The suppressor-inactive glycan Man8GlcNAc had a 200-fold lower capacity to compete for binding of 35S-labeled gp 8c to tomato membranes compared with the suppressor-active glycan Man11GlcNAc. Our results demonstrate the existence of a specific elicitor binding site in tomato cell membranes and suggest that glycopeptides and glycans act as agonists and antagonists for induction of the stress response, respectively, by competing for this binding site.

Amino Acid Sequence↗