Aleurone cells

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. 

Experiment 5. Observation under transmission electron microscope We compared the TEM ultrastructure of the seed coat and endosperm of control and rue-treated seeds The palisade layer of treated seed appears thicker than in the control (Figs 6A and 7A), while comparison between aleuronic cells of the control and treated cells (Figs. 6B and 7B), reveals that the cells of the control are healthy with some evident organelles such as the nucleus and the rough endoplasmic reticulum and other structures, the plastid, the plasmodesmata, conspicous constrictions, protein bodies and... 

Fig. 6 TEM micrographs of seed coat and aleurone cells of radish control seed 18 h after sowing in water e, epidermis pi, pigment layer al, aleurone layer. (A) Bar = 30 pm Particulars of the aleurone cell showing some organelles nucleus (n), plasmodesmata (pd), protein bodies (pb) and lipid droplets (Id). (B, C). Bar = 5 mm. 

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... 

The antagonism of GA action by ABA can be seen in studies of steady-state mRNA accumulation in aleurone cells, a major site of a-amylase synthesis in germinating cereal seeds (Fig. 3). GA treatment promotes the accumulation of high levels of a-amylase, shown by immunoprecipi-tation, while ABA, alone or with GA, completely represses this accumulation. In contrast, ABA clearly promotes the accumulation of a-amylase inhibitor mRNA, as determined by specific immunoprecipi-tation, while GA alone slightly reduces the level of a-amylase inhibitor mRNA. However, GA, together with ABA, does not decrease the level... 

Khursheed, B. Rogers, J.C. (1988). Barley a-amylase genes. Quantitative comparison of steady-state mRNA levels from individual members of the two different families expressed in aleurone cells. Journal of Biological Chemistry 263, 18953-60. 

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. 

Steam-pelleting of wheat middlings increases the ME and CP utilization in poultry diets by rupturing the aleurone cells and exposing the content of the cells to attack by digestive enzymes. 

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). 

A large number of studies (33) support the thesis (59) that the function of GA may be that of a derepressor of gene activity. Giberellic acid has significant effect on the synthesis of all species of RNA s (63, 64), but the formation of < —amylase does not depend on new synthesis of ribosomal and transfer RNA s. Unequivocal proof for GA-induced formation of transcripts was provided by the in vitro synthesis of peptides that are immuno-logically similar to -amylase on poly A+RNA templates that were. isolated from hormone-treated aleurone cells (65, 66, 67). Of particular significance is the finding that detectable levels of -amylase mRNA s were formed within 2 hr of treatment with GA. 

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). 

Chandra, G. R.t Duynstee, E. E. Hormonal regulation of nucleic acid metabolism in aleurone cells. In Biochemistry and Physiology of Plant Growth Substances. Ed. F. Wightman,... 

Chandra, G. R. Duynstee, E. E. Methylation of ribonucleic acids and hormone-induced amylase synthesis in the aleurone cells. Biochem. Biophys. Acta., 1971, 232, 514-523. 

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. 

Okita, T. W. DeCaleya, R. Rappaport, L. Synthesis of a possible precursor of -amylase in wheat aleurone cells. Plant Physiol., 1979, 63, 195-200. 

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. 

Higgins at al. (17) provided a quite direct link between GA-stimulated dtt novo enzyme synthesis and appearance of the complementary mRNA. They demonstrated convincingly that the level of translatable a-amylase mRNA increased in GA-treated tissue in parallel with the increased rate of enzyme synthesis. These results provide still more evidence that GA acts to induce selective mRNA and de novo enzyme synthesis in aleurone cells. 

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. 

Many experiments have demonstrated the capacity of cellulases and of mixtures of cellulases, pectinases, and hemicellulases to break down or to soften plant cell walls. For human diets this would be beneficial in preparing infant or geriatric foods where reduced fiber content is desired. Recently treatment of wheat bran was found to increase the in vitro protein digestibility by 35% (63) and to increase weight gain of rats fed a bran-containing ration. The aleurone cell wall was the primary substrate for these enzymes. 

Rice Oryza sativd) is an important cereal with an annual production of over 500-800 million tons. To produce white rice, the hull is removed and the bran layer is abraded giving 8-10% of the rice grain. The bran contains the testa, cross cells, aleurone cells, part of the aleurone layer, and the germ and includes almost all of the oil of the rice coreopsis. Gopala Krishna (45) considers that there is a potential for over 5 million tons of rice bran oil per annum, but present production is only about 0.7 million tons and not all of this is of food grade. India (0.50 million tons), China (0.12 million tons), and Japan (0.08 million tons) are the major countries producing rice bran oil. 

If a similar longitudinal section of a soaked grain be mounted in dilute iodine solution, the contents of the aleurone cells will be colored yellow indicating their proteid nature, while the starch grains will take on a blue to violet coloration. The endosperm will be observed taking up most of the room within the seed coat. The contents of its cells are not baled out to the embryo until after germination begins. Indian Corn is therefore an albuminous seed. 

Figure 7.1 Chemical images of the same wheat kernel cross-section showing the population on the z-axis. (a) Lipid in the scutellum and aleurone cell walls (b) Protein in the embryonic axis and aleurone cells ...

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