Barley embryos

The specific role of organic osmoticum in cultured plant cells remains unclear. Recent results, however, have provided some evidence as to their possible function. Cultured barley embryos were treated with exogenous... 

Lone, M.I., Kueh, J.S.H., Wyn Jones, R.G. Bright, S.W.J. (1987). Influence of proline and glycinebetaine on salt tolerance of cultured barley embryos. Journal of Experimental Botany, 38, 479-90. 

Bartels, D., Engelhardt, K., Roncarati, R., Schneider, K., Rotter, M. Salamini, F. (1991). An ABA and GA modulated gene expressed in the barley embryo encodes an aldose reductase related protein. The EMBO Journal 10, 1037-43. 

More specifically, compounds like podolactone A (Fig. 10.1) inhibit proton efflux from plant cells induced by fusicoccin, without affecting ATP levels.42 The related compound, podolactone E is a strong inhibitor of 6-aminolevulinic acid and chlorophyll synthesis.34 The authors concluded that this was caused by suppression of synthesis of proteins needed in the porphyrin pathway because podolactones also inhibited gibberellic acid-induced a-amylase synthesis in barley embryos. The molecular target site(s) of this class of terpenoid phytotoxins remains to be determined. 

The demonstration166 that the side-chains of 24-methylenecycloartanol (96), 24-methylenelophenol, and campesterol incorporated two deuterium atoms, whilst those of 24-ethylidenecycloartanol, stigmasterol, and sitosterol contained a maximum of four deuterium atoms when biosynthesized by cultures of barley embryo in the presence of [Me-2H3]methionine, provides further evidence for the intermediacy of 24-methylene- and 24-ethylidene-compounds in the biosynthesis of C28 and C29 phytosterols. The barley system was also able to convert labelled 24-ethylidenelophenol into radioactive sitosterol efficiently. These results, and those obtained from feeding experiments with [2-14C,(4R)-4-3Hi]MVA, are consistent with a pathway (Scheme 9) to stigmasterol (97) involving isomerization of (98) to a... 

Apart from 24-methylene cycloartanol (2-F) and cyclolaudenol (2-G), which in maize and barley embryos could give rise to 24a- and 24 -methyl sterols respectively, a further primary product of methylation, cyclosadol (2-T) has recently been foimd in maize and barley embryos. Its significance in the major pathway of sterol synthesis is still under investigation, but minor components such as 4-T and 8-T have also been reported in maize. The overall pattern of the type of compounds formed by the first attack of 5-adenosyl methionine on cycloartenol is outlined in Fig. 7. 

For the sulfhydration reaction, C>-phosphohomoserine is the most active substrate under assay conditions optimal for activity with this compound. When the activities were determined under conditions optimal for O-acetylhomoserine, activity with O-acetylhomoserine was increased to 17% of that with O-phosphohomoserine, while the relative activity with O-succinylhomoserine remained unchanged. Sulfhydrase activities with O-phosphohomoserine and O-acetylhomoserine showed different patterns of development during early growth of excised barley embryos, suggesting that activities with the two substrates may be catalyzed by separate enzymes (Datko et al., 1977). Purification of these activities will be required to determine whether this suggestion is correct. 

Recently, Kannangara and Jenson (1975) elegantly showed that [ CJbio-tin, when added to aseptically germinating barley embryos, was rapidly incorporated into the lamellar membranes of chloroplasts from newly formed leaves. 

Higgins, C. F., and J. W. Payne Peptide transport by germinating barley embryos Evidence for a single common carrier for di- and oligopeptides. Planta 138, 217 (1978). 

Boisen, S., and Djurtoft, R. (1982). Protease inhibitor from barley embryo inhibiting trypsin and trypsin-like microbial proteases. Purification and characterisation of two isoforms. J. Sci. 

Figure 1. Time course of lipoxygenase activity in the embryo of barley upon germination. The ratio of 9- and 13-HPOD formed from linoleic acid by extracts from barley embryos is indicated within the bars.

Figure 2. Patterns of loxA (Fig. 2a), and loxC mRNA (Fig. 2b) in barley embryos in the course of germination as determined by Northern blotting. Each lane contains 7.5 ng of total RNA.

A very early metabolic event during imbibition, occurring in less than 15 min, appears to be the reformation of keto acids from amino acids by deamination and transamination reactions [37]. Keto acids important for respiratory pathways (e.g. a-ketoglutarate and pyruvate) may be absent from dry seeds such as wheat [70] and peanut cotyledons [138]. They are known to be chemically unstable and it has been suggested [37] that they are stored in the dry seed as the appropriate amino acid, and then reformed on rehydration. This might occur also in barley embryos, seeds of Sinapis alba, and axes and cotyledons of Phaseolus vulgaris [36, 37]. 

Loreti, E., Bellincampi, D., Millet, C., Alpi, A., and Perata, P. (2002). Elicitors of defence responses repress a gibberellin signalling pathway in barley embryos. /. Plant Physiol 159, 1383-1386. 

Very recently it has been shown that although the barley embryo produces gibberellin, nevertheless its growth is enhanced by 10 M GA. When barley embryos are moistened they begin to synthesise protein within 30 min by contrast, no new RNA is synthesised for some 12 hr, so that presumably masked m-RNA is present in the dry embryo and is activated during the initial imbibition of water by the embryo. The GA addition which enhances growth enhances the initial rate of protein synthesis in the embryo, but apparently not by promoting precocious RNA synthesis or the effectiveness of the ribosomes. This may be a similar phenomena to that of the GA... 

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