The effect of the ma3R mutation on phytochrome, gibberellin metabolism and photoperiodism in Sorghum bicolor (L.) Moench /
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| Other Authors: | , , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1993.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | The Ma3 gene in sorghum (Sorghum bicolor) regulates photoperiod sensitivity. Sorghum with the ma3^R allele are essentially photoperiod insensitive, are greatly elongated and contain high concentrations of gibberellins. The hypothesis that the sorghum ma3^R allele results in abnormal phytochrome regulation of growth and maturity was tested. Phytochrome control of anthocyanin synthesis and R mediated deetiolation was not apparent in ma3^R sorghum. Sorghum contains two phytochromes with apparent molecular weights of 123 and 126 kD. Sorghum with ma3^R did not possess the 123-kD phytochrome. The 126-kD and 123-kD phytochromes were tentatively characterized as phytochromes A and B, respectively. Gibberellin levels are greater in ma3^R than in non-map sorghum. Phytochrome regulates gibberellin synthesis. Nonetheless, phytochrome control of gibberellin metabolism was found in ma3^R and non-ma3^R genotypes. Thus, at least two phytochromes must control gibberellin metabolism. Gibberellin metabolism was concluded to be more complicated than previously believed. Gibberellin levels were found to vary by both tissue and time of day. The 123-kD phytochrome was implicated in the differences that were seen in gibberellin concentrations between tissues. The integrity of the biological clock in ma3^R sorghum was tested. Chlorophyll a/b binding protein (CAB) mRNA was found to cycle circadianly in ma3^R and non-ma3R plants. The periods of CAB mRNA cycling in constant light were different in ma3^R and non-ma3^R plants, but during normal photoperiods, cycling was identical between the genotypes. The biological clock was thus shown to function properly in ma3^R sorghum, but the mechanism for entrainment in constant light is altered. Plants were grown under different photoperiods, and growth was measured. Photoperiods of 23 and 24 h were found to inhibit elongation of non-ma3^R sorghum. This high irradiance response (HIR) was not evident in ma3^R sorghum. However, floral initiation was significantly delayed in ma3^R plants by long photoperiods. Sorghum with ma3^R are photoperiod sensitive, but the degree of sensitivity is greatly reduced. Internode elongation occurred in ma3^R plants grown under long photoperiods. Thus, internode elongation was separated from flowering. This suggests that the premise that gibberellins control flowering is not valid. A model is presented to explain phytochrome control of photoperiodism in sorghum. |
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| Item Description: | Vita. "Major subject: Plant Physiology." The numeral 3 in title is subscript. The capital R in title is superscript. |
| Physical Description: | xi, 116 leaves : illustrations ; 28 cm |
| Bibliography: | Includes bibliographical references. |