Physiological Effects of Gibberellic Acid. X. The Release of Gibberellin-Like Substances by Germinating Barley Embryos

ent-Kaurene biosynthesis as a prerequisite for gibberellin (GA) biosynthesis was studied in germinating Hordeum vulgare L., cv Himalaya caryopses and correlated, in time, with the appearance of a-amylase activity. The rate of ent-kaurene biosynthesis was estimated by inhibiting its further metabolism with plant growth retardants (triapenthenol or tetcyclacis) and measuring its accumulation by isotope dilution using combined gas chromatographymass spectrometry. In the inhibitor-treated caryopses, ent-kaurene accumulation began approximately 24 hours after imbibition and proceeded at a rate of about I to 2 picomoles per hour per caryopsis, depending on the batch of seeds. In the absence of inhibitor, ent-kaurene did not accumulate, indicating that it is normally turned over rapidly, presumably to further intermediates of the GA biosynthesis pathway and eventually to GAs. entKaurene accumulation occurred almost exclusively in the shoot, which is, therefore, probably the site of biosynthesis. a-Amylase production began between 30 and 36 hours after imbibition and, thus, correlated well with de novo GA biosynthesis, as estimated from ent-kaurene accumulation. However, inhibition of ent-kaurene oxidation by plant growth retardants did not reduce the aamylase production significantly, although it did reduce shoot elongation. We conclude that ent-kaurene is produced in the shoot and is continuously converted to GA, which is essential for normal shoot elongation, but not for the production of a-amylase in the aleurone layer.Paleg (15) and Yomo (23) discovered independently that GA3 could substitute for the embryo in initiating a-amylase formation in germinating barley grains. This finding and the demonstration by Chrispeels and Varner (4) that isolated aleurone layers produced a-amylase in response to added GA3 led to the well-known hypothesis that GA3 produced in the embryo diffuses to the aleurone tissue where it induces the formation of a-amylase and other hydrolytic enzymes. The induction of a-amylase in the aleurone layer in response to XSupported by grants from the Deutsche Forschungsgemeinschaft. 2Present address: Instand e.V., Johannes-Weyer-Str.

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confidence: 99%

ent-Kaurene Biosynthesis in Germinating Barley (Hordeum vulgare L., cv Himalaya) Caryopses and Its Relation to α-Amylase Production

Großelindemann¹,

Je²,

Stöckl³

et al. 1991

“…Brown and Morris (3) reviewed the work done during the nineteenth century. These early studies concentrated on finding optimum conditions for germination, and on the roles of endosperm and embryo as food source and food consumer respectively, and on the complex interactions between these 2 parts.More recent publications report the interactions between the embryo, which is the natural source of gibberellic acid, and the aleurone cells of the endosperm, which supply enzymes responsible for the degradation and mobilization of the reserve food (2,5,7,19). Most of these studies, however, have been conducted after seeds have been imbibed for 24 to 48 hr; thus the findings reflect the metabolic state of the seeds nmany hours after imbibition.…”

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confidence: 86%

Metabolism of Barley Seed During Early Hours of Germination

Abdul‐Baki¹

1969

Abstract. The growth process in germinating barley seeds and its inhibition by actinomycin D and puromycin were investigated. Soon after seeds are imbibed, thcir respiratory activity increases several fold, and the protein-and carbohydrate-synthesizing systems become active. The immediate activation of protein synthesis and its inhibition by actinomycin D and puromycin suggest that the dry seed has all the components necessary for protein synthesis.Although a good correlation exists between the rate of oxygen uptake and that of protein synthesis during the first 12 hr of germination, respiration appears to be independent of protein synthesis during the first 8 hr, as reflected by the insensitivity of the respiratory process to actinomycin D and puromycin. However, after 8 hr both antibiotics reduce oxygen uptake as well as subsequent seedling growth.The distribution of 14C, derived from labeled glucose during the early hours of barley germination, among various fractions of metabolites, indicated that 50 to 70 6/e of the utilized gluoose appeared in 14C02. The rest of the incorporated label appeared in hemicelluloses and starch, water-soluble ethanol-insoluble carbohydrates, and to a lesser extent in proteins and cellulose.The growth process in germinating barley has been under investigation for over a hundred years. Brown and Morris (3) reviewed the work done during the nineteenth century. These early studies concentrated on finding optimum conditions for germination, and on the roles of endosperm and embryo as food source and food consumer respectively, and on the complex interactions between these 2 parts.More recent publications report the interactions between the embryo, which is the natural source of gibberellic acid, and the aleurone cells of the endosperm, which supply enzymes responsible for the degradation and mobilization of the reserve food (2,5,7,19). Most of these studies, however, have been conducted after seeds have been imbibed for 24 to 48 hr; thus the findings reflect the metabolic state of the seeds nmany hours after imbibition.The present paper reports on glucose metabolism, protein synthesis, and respiration which take place in barley during the first 12 hr of germination. Knowledge of such early phases of growth could give an insight into the biosynthetic capacity of the seed and thus might be used to determine seed quality and predict seedling performance in much less time than that required by present methods. Seeds were washed in 1 % sodiuimi hvpochlorite (NaHClO) for 15 nmin and aseptically transferred into imbibing and incubation media containiing penicillin-G and streptomvcin sulfate (20 ug/ml of each).All pretreatments and incubations were performed in a constant-temperatture water batlh at 250 with shaking.Incorporation of Lezicinle-'4C lJuto Proteins. The time course for incorporation of leucine-14C into proteins was determined. Six lots of 60 seeds eachl were soaked in 1 % NaHCIO for 15 mmin, washed 6 tinmes in sterile water, then imbibed in water for 0, 2, 4, 6, 8, and 10 hr. Th...

“…enzymes (2). These enzymes make the carbon and nitrogen stored in the endosperm available to the developing seedlings.…”

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confidence: 99%

Effects of Helminthosporium victoriae Toxin on Germination and Aleurone Secretion by Resistant and Susceptible Seeds

Samaddar

Scheffer

1970

Oat seeds of cultivars susceptible and resistant to Helminthosporium victoriae were held for various times in pathogen-produced, host-specific toxin solutions; control seeds were in water. Seeds were then washed thoroughly and incubated on moist paper, or dried and stored for 2-3 weeks before germination was attempted. In both cases, germination of susceptible seeds was prevented by previous exposure to toxin for 1 hour or more. Control seeds and treated resistant seeds grew normally. Toxin Several lines of evidence show that resistance of oats (Avena sativa L.) to infection by Helminthosporium victoriae Meehan and Murphy is the same as resistance to the pathogen-produced, host-specific toxin (HV-toxin) (12, 18). Many of the data behind this conclusion were obtained from experiments with germinating seeds and young seedlings. The validity of the conclusion is further supported by the fact that toxin rather than the fungus can be used to screen for disease resistance (16). Experiments to determine action of toxin have relied heavily on use of young seedling shoot and root tissue (12). Even the standard bioassays for toxin depend on use of germinating seeds (7). Nevertheless, there is little detailed information on the effects of toxin on seed germination.We have attempted in this study to determine the effects of toxin on resting seeds, on the germination process, and on certain aleurone activities. Aided by National Science Foundation Grant GB-6560. enzymes (2). These enzymes make the carbon and nitrogen stored in the endosperm available to the developing seedlings. Aleurone cells separated from the embryo secrete no amylase until they are activated by an exogenous supply of GA (14).Results of the study should be considered in relation to several hypothetical concepts of disease and toxin resistance. According to one hypothesis, disease resistance is based on synthesis of antifungal substances by the host after contact with the pathogen. There is strong support for this hypothesis (4), but to date there is no conclusive evidence that it can account for disease resistance in general. An alternative hypothesis is that disease resistance is a constitutive, possibly passive, characteristic of certain plants. Constitutive rather than induced resistance would seem more plausible if seeds and aleurone cells in a resting condition would express resistance. In either case, the aleurone layer is a simplified system for resistance studies, and for studies on the effects of toxins on plant metabolism. A further advantage of the model is that susceptibility or resistance to HV-toxin (and to H. victoriae) is determined at a single gene locus (7,12). An abstract describing some of this work has been published (10). MATERIALS AND METHODSOat seeds susceptible (cv. Park) and resistant (cv. Clinton) to H. victoriae and to HV-toxin were used in all experiments. Aleurone cells were obtained by cutting seeds into two parts and discarding the part containing the embryo (14). For germination tests, the glumes were removed and...