This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (14) Citing Articles via Google Scholar Google Scholar Articles by Taiz, L. Articles by Starks, J. E. Search for Related Content PubMed PubMed Citation Articles by Taiz, L. Articles by Starks, J. E. Agricola Articles by Taiz, L. Articles by Starks, J. E.

Articles

Gibberellic Acid Enhancement of DNA Turnover in Barley Aleurone Cells ¹

^a Division of Natural Sciences, Thimann Laboratories, University of California, Santa Cruz, California 95064

When imbibed, deembryonated halfseeds from barley (Hordeum vulgare L., var. Himalaya) are incubated in buffer, the DNA content of the aleurone layer increases 25 to 40% over a 24-hour period. In contrast, the DNA of isolated aleurone layers declines by 20% over the same time period. Gibberellic acid (GA) causes a reduction in DNA levels in both halfseed aleurone layers and isolated aleurone layers. GA also increases the specific radioactivity of [³H]thymidine-labeled halfseed aleurone layer DNA during the first 12 hours of treatment. Pulse-chase studies demonstrated that the newly synthesized DNA is metabolically labile.

The buoyant density on CsCl density gradients of hormone-treated aleurone DNA is identical with that of DNA extracted from whole seedlings. After density-labeling halfseed DNA with 5-bromodeoxyuridine, a bimodal absorption profile is obtained in neutral CsCl. The light band (1.70 g/ml) corresponds to unsubstituted DNA, while the heavy band (1.725-1.74 g/ml) corresponds to a hybrid density-labeled species. GA increases the relative amount of the heavy (hybrid) peak in halfseed aleurone layer DNA, further suggesting that the hormone enhances semiconservative replication in halfseeds.

DNA methylation was also demonstrated. Over 60% of the radioactivity from [³H-Me]methionine is incorporated into 5-methylcytosine. GA has no effect on the percentage distribution of label among the bases.

It was concluded that GA enhances the rate of DNA degradation and DNA synthesis (turnover) in halfseeds, but primarily DNA degradation in isolated aleurone layers. Incorporation by isolated aleurone layers is due to DNA repair. Semiconservative replication apparently plays no physiological role in the hormone response, since both isolated aleurone layers and gamma-irradiated halfseeds respond normally. The hypothesis was advanced that endoreduplication and DNA degradation are means by which the seed stores and mobilizes deoxyribonucleotides for the embryo during germination.

³ Present address: School of Medicine, University of California, Davis, Calif. 95616.

¹ This research was supported in part by National Science Foundation Grant BMS75-03391 and by a grant from the Committee on Research, University of California, Santa Cruz, to L. T.

This article has been cited by other articles:

				S. W. Rogers and J. C. Rogers Cloning and Characterization of a Gibberellin-Induced RNase Expressed in Barley Aleurone Cells Plant Physiology, April 1, 1999; 119(4): 1457 - 1464. [Abstract] [Full Text]