Selective effect of hormones on nucleic acid metabolism during germination of pear embryos

Khan, Anwar A.; Heit, C. E.

doi:10.1042/bj1130707

Cited by 34 publications

(17 citation statements)

References 20 publications

(20 reference statements)

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“…Thus the cold treatment "prepares" hazel seeds for germination and hormonal changes occur mainly at germinating temperature. This seems not to be the case in pear embryos, since the ability of pear embryos to increase in the level of hormones (5,7,8). Increases in activities of peroxidases, as reported here, chromatin-bound RNA polymerase (5) and aminoacyl-tRNA synthetases (13) have been observed in pear embryo during stratification.…”

Section: Resultsmentioning

confidence: 59%

“…ABA has been shown to induce dormancy in pear embryos (7). The presence of 20 ,lM GA3 and 20 ,uM kinetin during stratification enhanced the activities of certain isoperoxidases and the presence of 20 ,LM ABA, showed an inhibitory effect (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Both kinetin and GA3 can partially release the dormancy in pear embryos (7). ABA has been shown to induce dormancy in pear embryos (7).…”

Section: Resultsmentioning

confidence: 99%

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Changes in Isoperoxidases during Cold Treatment of Dormant Pear Embryo

Tao¹,

Khan²

1976

Plant Physiol.

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The number of isoperoxidases and the intensity of certain isozymes increased with increasing periods of stratification of pear (Pyrus communis cv. Bartlett) embryos. The presence of GA3 or kinetin during stratification enhanced the activity of certain isoperoxidases, and these enhancements were blocked in the presence of ABA which by itself had an inhibitory effect. Enhancement in isoperoxidases of pear embryos during stratification was inhibited by 6-methylpurine and cycloheximide; and in the presence of either of these two inhibitors, stratification failed to release the dormancy. Pear embryos germinated for 3 days showed changes in the pattern of isoperoxidases depending on the length of stratification.Peroxidase may be important in the regulation of plant growth and development (2,3,12). Good correlation between seed viability and peroxidase activity was reported by MacLeod (9). Peroxidase activity increased during stratification in embryos of European mountain ash (1); however, no attempt has been made to study the isoperoxidase during stratification of seeds with a cold requirement. Rychter and Lewak (12) reported recently that the appearance of faster moving isoperoxidases in apple embryo was stimulated by stratification, GA3, and BA and inhibited by ABA or coumarin. Unfortunately, the peroxidases were isolated after 3 days of germination and the hormones were added at the beginning of germination. It is not certain whether the changes in isoperoxidases being measured were a result of growth alone, growth plus stratification, or growth plus hormonal treatment. The present study investigates the changes of isoperoxidases in pear embryos during stratification and germination. The data show changes in the isoperoxidase pattern during germination and stratification with or without the presence of hormones. MATERIALS AND METHODSPear seeds, Pyrus communis cv. Bartlett, were soaked at 5 C or 25 C on moist blotters for various lengths of time. Before and after the above treatments, seeds were soaked for 10 min in 2% sodium hypochlorite solution and then washed thoroughly with distilled H20. Embryos were then dissected out. In some experiments pear seeds were stratified (5 C) in the presence of 20 10 ungerminated embryos were ground in a mortar with 0.5 ml of phosphate buffer (50 mm, pH 7.8). The homogenate was centrifuged at 20,000g for 10 min. Saturated sucrose solution (0.1 ml) was added to each supernatant. All operations were carried out at 4 C.The electrophoresis was performed by a procedure adapted from McCown et al. (10). The 5.5% running gels with 4.4% spacer gels were prepared in glass tubes (0.6 x 7.8 cm) which were coated with diluted Photoflo solution. The gels were preelectrophoresed for I hr before applying 0.1 ml of supernatant (about 0.8 mg protein, except in germination experiment) on the top of each gel. The gel electrophoresis was conducted at 4 mamps/tube for approximately 2 hr in the 0.16 M tris-glycine buffer, pH 8.3, at 4 C. After electrophoresis, the gels were soaked in I M ace...

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Section: Resultsmentioning

confidence: 59%

Section: Resultsmentioning

confidence: 99%

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Changes in Isoperoxidases during Cold Treatment of Dormant Pear Embryo

Tao¹,

Khan²

1976

Plant Physiol.

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“…This increase in ER synthesis precedes and is very probably required for the gibberellic acid-induced synthesis The relatively rapid effect of abscisic acid in preventing the gibberellic acid-enhanced choline incorporation suggests a fairly direct role of abscisic acid in membrane biosynthesis and (or) assembly. Abscisic acid prevents the synthesis of a-amylase in the barley aleurone cells, but does not alter the rate of respiration or total RNA or protein synthesis (5), although it may inhibit specific RNA synthesis (21,22). Abscisic acid also prevents the gibberellic acid-enhanced increase in ER-bound polysomes (Evins, manuscript in preparation).…”

Section: Discussionmentioning

confidence: 99%

Hormone-Controlled Synthesis of Endoplasmic Reticulum in Barley Aleurone Cells

Evins

Varner

1971

Proc. Natl. Acad. Sci. U.S.A.

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The rate of synthesis of the endoplasmic reticulum in barley aleurone cells after treatment with gibberellic acid was determined by measurement of [14C1-choline incorporation into acid-insoluble material in a semipurified fraction containing the endoplasmic reticulum. 94% of the 14C incorporated into this fraction is extractable by lipid solvents and only 9% is removed by procedures for nucleic acid extraction. Gibberellic acid increases the rate of synthesis of the endoplasmic reticulum 4-to 8-fold, starting about 4 hr after addition of the hormone (at about the same time as polysome formation). Abscisic acid inhibits this gibberellic acid-enhanced increase in the rate of synthesis of endoplasmic reticulum.Isolated barley aleurone layers respond to exogenous gibberellic acid by synthesizing a-amylase and protease after an 8-to 10-hr lag period (1-3); abscisic acid prevents these characteristic responses to gibberellic acid (4, 5). During the lag period, gibberellic acid causes an increase in the number and proportion of ribosomes that can be isolated as polysomes in the hormone-treated cells, starting 3-4 hr after hormone addition (Evins, manuscript in preparation). The polysomes are, in vivo, probably bound to the endoplasmic reticulum (ER), because electron microscopy studies show extensive development of the rough ER in the aleurone cells of germinating barley (6) as well as changes in the rough ER of isolated barley aleurone layers during both the lag and synthesis phases of a-amylase production (7, 8, and personal communication from E. L. Vigil and M. Ruddat, University of Chicago). However, the quantitative determination of differences in the rate of ER synthesis between hormone-treated and control tissues and the time of the onset of ER synthesis after hormone addition are difficult to establish by electron microscopy. We now report the rate of ER synthesis estimated by the measurement of [14C]choline incorporation into a semipurified ER fraction (method of Nagley and Hallinan, ref. 9). With this method it can be shown that gibberellic acid increases the rate of ER synthesis 4-to 8-fold. This increase starts at about the same time as polysome formation. Abscisic acid inhibits the gibberellic acid-enhanced increase in the rate of ER synthesis within 2 hr after addition. METHODSFor each sample, 10-40 aleurone layers were prepared by the methods of Chrispeels and Varner (1) from barley seeds (Hordeum vulgare L. cv. Himalaya) and incubated for the times specified in 5 ml of 1 mM Na acetate buffer (pH 4.8)-20 mM CaClr-1MM gibberellin A3 on a Dubnoff metabolic shaker at 250C.The method of Nagley and Hallinan (9) was used to measure the rate of synthesis of ER. At the end of the incubation the aleurone layers were transferred for 30 min to a medium containing 5 ACi of [methyl-14C]choline chloride (New England Nuclear Corp., 8.25 Ci/mol) and either 10 mg of neutralized casein acid hydrolysate (per 40 layers) or 1 mM iserine and 1 mM L-methionine (A grade, Calbiochem). Trichloroacetic acid-precipitable m...

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“…An increase of RNA level, or prevention of its decrease during senescence by kinetin was found in Xanthium (22). Kahn and Heit (11) found that kinetin enhanced incorporation of 32p, mainly into the heavy ribosomal RNA, in germinating pear embryos.…”

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confidence: 97%

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato

Puri¹,

Tal²

1977

Plant Physiol.

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Plants of the wilty tomato (Lycopersicum esculentum) mutant,flacca, and of the normal cultivar Rheinlands Rubm growing under either "normal" or high humidity were used in this research. Under normal humidity, RNase activity was much higher in mutant plants in which abscisic acid (ABA) and water content were lower than in the normal plant. The mutant also contained less RNA and protein per cell and less soluble RNA relative to ribosomal RNA as compared with the normal genotype. In ABA-treated mutant plants, RNase activity decreased while RNA, protein, the ratio of soluble to ribosomal RNA and water content increased.Under high humidity, RNase activity in mutant plants was decreased, but was still somewhat higher than that in the normal plant, although water saturation deficit was equal in both plant types. Abscisic acid increased RNase activity in the mutant plants. The content of RNA and protein per cell was similar in both types, but the ratio of soluble to ribosomal RNA remained lower in the mutant. In ABA-treated mutant plants, although the content of DNA and RNA per fresh weight was similar to that of control mutant plants, the ratio of RNA to DNA decreased significandy. In addition, ABA caused an increase of the soluble to ribosomal RNA ratio toward the normal value in mutant plants.Contrary to ABA, kinetin increased RNase activity in the mutant under normal humidity and decreased it under high humidity.A similar incorporation of labeled uridine into RNA in normal, mutant, and ABA-treated mutant plants under normal humidity suggests that the difference between mutant and normal plats in respect to total, soluble, and ribosomal RNA results not from a different rate of RNA synthesis but from a different rate of RNA degradation, ie. RNase actvity.An increase of RNase activity (1,6,7,9,12,35) and a decrease of RNA level (8,12) was found in tomato and other plants subjected to water stress. The soluble fraction of RNA increased while the ribosomal fraction decreased in sugar beet under water stress (25). Low relative humidity appears to be associated with slow accumulation and reduced incorporation of labeled uracil into RNA in etiolated leaves of Jack bean (3).An association between RNase activity, RNA level, and hormone balance in the plant was also reported. Srivastava (29) found an increase of RNase activity in detached barley leaves treated with ABA and a decrease of this activity following treatment with kinetin. Similar hormonal effects on RNase activity were reported in other plants (5,13,28,39 The first attempt to elucidate the interrelations among RNase activity, water content, and hormone balance was made by Arad et al. (1). They found that in barley leaves, in which the water balance was not disturbed, ABA increased and kinetin decreased RNase activity. However, these hormonal effects were inverted in leaves subjected to water shortage i.e. ABA decreased and kinetin increased the activity. They interpreted these results to mean that above a certain optimal leaf water content, the specific ho...

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Selective effect of hormones on nucleic acid metabolism during germination of pear embryos

Cited by 34 publications

References 20 publications

Changes in Isoperoxidases during Cold Treatment of Dormant Pear Embryo

Changes in Isoperoxidases during Cold Treatment of Dormant Pear Embryo

Hormone-Controlled Synthesis of Endoplasmic Reticulum in Barley Aleurone Cells

Abnormal Stomatal Behavior and Hormonal Imbalance in flacca, a Wilty Mutant of Tomato

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