Barley aleurone

The shift in pattern of protein synthesis during anaerobiosis has been observed in root tissue of many other plant species including rice, sorghum, barley, pea, and carrot (see Sachs Ho, 1986). In anaerobically treated barley aleurone cells, lactate dehydrogenase (LDH) activity increases (Hanson Jacobsen, 1984) as does enzyme activity and mRNA levels for ADH (Hanson, Jacobsen Zwar, 1984). 

Belanger, F.C., Brodl, M.R. Ho, T.-H.D. (1986). Heat shock causes destabli-zation of specific mRNAs and destruction of endoplasmic reticulum in barley aleurone cells, Proceedings of the National Academy of Sciences, USA, 83, 1354-8. 

Hanson, A.D. Jacobsen, J.V. (1984). Control of lactate dehydrogenase, lactate glycolysis and a-amylase of O2 deficit in barley aleurone layers. Plant Physiology, 75, 566-72. 

A similar time course for translatable mRNA has been reported (lA) in barley aleurone layers, in response to glbberel-lic acid. Total poly(A) RNA was found to Increase dramatically in the first 12 hr after hormone application, followed by a rapid decline to 25% of the maximum at 18 hr. On the other hand, the accumulation of ovalbumin mRNA in response to progesterone in chick oviducts (15) is an example that does not appear to behave in this manner. 

There have been few studies of polymer interconnections within the primary wall of monocots. An arabinoxylan from the primary wall of cultured, barley-aleurone cells,61 and a glucuronoarabinoxylan from maize-coleoptile primary-wall,200 have been shown to bind reversibly to cellulose in vitro, Because xylans are, quantitatively, the major component of monocot primary cell-walls, this interconnection is an important finding it is very likely to occur through multiple hydrogen-bonds, analogous to the interconnection between xyloglucan and cellulose in dicot cell-walls.56,57,59 It is also possible that heteroxylans participate in binding other cell-wall polymers to cellulose. 

In contrast to these findings, a glucuronoarabinoxylan isolated from oat coleoptiles did not bind to cellulose in vitro under reaction conditions that allowed other heteroxylans to bind.53 This oat heteroxylan had, however, a high percentage of arabinosyl side chains that would be likely to hinder binding sterically. A similar inability to bind to cellulose is exhibited by an arabinose-rich arabinoxylan isolated from cultured, barley-aleurone cell-walls.61... 

Fig. 3. Translation products of barley aleurone layer mRNAs. Lanes 1-4, total products from layers treated in water (control), 1 jxm ABA, 1 pM GA3, or both hormones, respectively. The rab 6 protein is marked with an arrow. Lanes 5-8, immunoprecipitation of a-amylase (upper bands) and the a-amylase/subtilisin inhibitor (lower bands) from the translation products shown in lanes 1-4. mRNA extraction, translation and immunoprecipitation were performed as previously described (Mundy etal., 1986).

Hong, B., Uknes, S.J. Ho, T.-H.D. (1988). Cloning and characterization of a cDNA encoding mRNA rapidly induced by ABA in barley aleurone layers. Plant Molecular Biology 11, 495-506. 

Jacobsen, J.V. Beach, L.R. (1985). Control of transcription of a-amylase and rRNA genes in barley aleurone protoplasts by gibberellin and abscisic acid. Nature 316, 275-7. 

Mundy, J., Hejgaard, J., Hansen, A., Hallgren, L., Jprgensen, K. Munck, L. (1986). Differential synthesis in vitro of barley aleurone and starchy endosperm proteins. Plant Physiology 81, 630-6. 

Muthukrishnan, S., Chandra, G.R. Maxwell, E.S. (1979). Hormone-induced increase in levels of functional mRNA and a-amylase mRNA in barley aleurones. Proceedings of the National Academy of Sciences (USA) 76, 6181-5. 

Whittier, R.F., Dean, D.A. Rogers, J.C. (1987). Nucleotide sequence analysis of a-amylase and thiol protease genes that are hormonally regulated in barley aleurone cells. Nucleic Acids Research 15, 2515-35. 

Roles of Metabolites of Abscisic Acid. Nothing is known about the physiological role of PA and DPA in plants, although these two metabolites of ABA have been tested in several bioassays recently. In the cotton explant abscission assay PA had one-tenth of the activity of ABA (19). PA and DPA were equally effective in inhibiting a-amylase secretion by barley aleurone layers treated with glbberellin A3 DPA had approximately one-tenth of the activity of ABA in this system (74). The effect of PA on growth of bean embryos was negligible (75). 

Abscisic acid is a negative regulator in that it primarily antagonizes the action of cytokinins, auxins, and in particular, gibberellins. Abscisic acid decreased the activity of polymerase in radishes (52), peas (53), maize coleoptiles (54), and pear embryos (55). More detailed studies are needed before the question of ABA-induced "modification" of RNA polymerase (54) or "alterations" in the number of sites for template activity (56) can be answered. In barley aleurone cells, ABA-induced suppression of GA-induced <-amylase formation was presumed to involve the continuous synthesis of a short-lived RNA (57). 

For a hormone to have a specific effect on gene activity, any increase in enzyme activity must result from de novo synthesis by newly formed mRNA. This increase in enzyme activity may or may not precede any general increase in metabolic activity. From the foregoing discussion on chromatin activity, it is clear that plant hormones largely either increase the activity of polymerase I or increase the synthesis of total RNA s. Claims that the hormones "activate" chromatin-bound polymerases and "modulate" the number of active sites on the chromatin (21) have not been substantiated. There are only two known examples of hormone-induced synthesis of specific mRNA s. The classic example is the barley aleurone cells, in which GA treatment induces de novo synthesis and release of K-amylase (58, 59, 60), protease (61), and possibly as many as ten proteins (62). 

Control of the synthesis of amylase ntRNA s in barley aleurone cells and the synthesis of cellulase mRNAs in pea epicotyl cells are similar in some respects. The control of cellulase activity in pea epicotyl is the only known example of auxin-induced formation of specific mRNA molecules. The formation of cellulase mRNA was demonstrated by the isolation of poly A + RNA s and in vitro synthesis of cellulase (71) using the protein-synthesizing system of wheat germ (72). The formation of cellulase mRNA precedes the increase in cellulase levels by more than 12 hr. Thus, it appears that the increase in rate of synthesis of translatable cellulase mRNA s in the pea epicotyl (71) and that of -amylase mRNA s in barley aleurone cells (65,... 

It appears that cyclic AMP does not mediate the action of GA (83). Two reports (85, 86) rule out the involvement of cyclic adenosine 3 ,5 -monophosphate and adenylate cyclase in the hormonal regulation of plant growth processes. Although barley aleurone cells metabolize GA s, attempts to isolate GA-binding proteins have not been successful (84). 

Ho, D. T. Response of barley aleurone layers to abscisic acid. Plant Physiol., 1976, 57, 175-178. 

Jacobsen, J. V. Know, R. B. The proteins released by isolated barley aleurone layers before and after gibberellic-acid treatment. Planta, 1974, 115, 193-206. 

Jacobsen, J. V. Zwar, J. A. Gibberellic acid and RNA synthesis in barley aleurone layers metabolism of rRNA and tRNA and of RNA containing polyadenylic acid sequences. 

Chrispeels, M. J. Varner, J. E. Gibberellic acid-enhanced synthesis and release of -amylase and ribonuclease by isolated barley aleurone layers. Plant Physiol., 1967, 42(3), 398-406. 

Chandra, G. R. Effect of gibberellic acid on the tRNA methylase activity of barley aleurone cells. In Plant Growth Substances. Ed. D. J. Carr, Springer-Verlag, Berlin, Heilelberg, New York, 365-370, 1970. 

Locy, R. Kende, H. The mode of secretion of -amylase in barley aleurone layers. Planta, 1978, 143, 89-99. 

Musgrave, A. Kays, S. E. Kende, H. Uptake and metabolism of radioactive gibberellins by barley aleurone layers. 

Evidence that the increase in activity of at least four hydrolases induced by GA actually occurs as a result of de novo synthesis, rather than by activation of preformed enzyme, has been obtained in various ways. However, the most unequivocal proof comes from density labeling experiments, first performed by Filner and Varner in 1967 (13). Later Jacobsen and Varner (14) proved by the same procedures that protease also is synthesized de novo in response to GA. And Bennett and Chrispeels (15) proved, using D2O, GA-induced de novo synthesis of ribonuclease and 6-1,3-glucanase in barley aleurone cells. 

The mechanism of action of abscisic acid (ABA) has been studied to the greatest extent in the barley aleurone system (29), in which ABA counteracts the effect of GA in the induction of hydrolases. This action of ABA has largely been the basis for speculating that ABA may act specifically to inhibit, by some unknown mechanism, DNA-dependent RNA synthesis. Much evidence indicates that ABA acts at the transcriptional level, but it also has been proposed that the inhibition of induction of a-amylase synthesis is caused, at least in part, by an effect on translation because ABA still inhibited the formation of a-amylase at 12 hr when cordycepin (an inhibitor of RNA synthesis) no longer had an effect (30). 

Narasimhan, B., Pliska-Matyshak, G., Kinnard, R., Carstensen, S., Ritter, M.A., von Weymarn L., and Murthy, P.P.N., 1997, Novel phosphoinositides in barley aleurone cells, additional evidence for the presence of phosphatidyl-vn7/o-inositol. Plant Physiol. 113 1385-1393. 

Ritchie, S. and Gilroy, S., 1998, Abscisic acid signal transduction in the barley aleurone is mediated by phospholipase D activity. Proc. Natl. Acad. Sci. USA 95 2697-2702. 

Murthy, P.P.N., Renders, J.M., and Keranen, L.M., 1989, Phosphoinisitides in barley aleurone layers and gibberellic acid-induced changes in metabolism. Plant Physiol. 91 1266-1269. 

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