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Molecular and physiological studies of Pisum mutants
thesisposted on 2023-05-27, 06:45 authored by Batge, SL
The characterisation of developmental mutants generates insights into plant growth processes. This thesis presents a molecular investigation of three phytochrome A mutants of Pisum sativum L. (garden pea), and a study of the influence of abscisic acid (ABA) on seed development in the gibberellin (GA)- deficient mutant lh-2. Phytochromes are plant biliproteins which sense red (R, 600 - 700 nm) and far-red (FR, 700 - 760 nm) light and act in concert with other photoreceptors to influence developmental processes, such as germination, seedling de-etiolation, daylength perception and transition to flowering, in response to environmental cues. Two allelic mutants at the funl locus are deficient in phytochrome A. Point mutations have now been identified within the PHYA structural gene of both fun1-1 and fun1-2. These cause premature stop codons, predicted to result in production of a truncated and inactive phytochrome A protein in the mutant plants. This is consistent with the demonstration that fun1-2 plants lack immunodetectable PHYA, and with the previously described phenotypes. Co-segregation between the fun1-2 mutant phenotype and the identified molecular lesion confirms that the funl mutant phenotype is the direct result of disruption to the PHYA structural gene. The funl mutants can now be used confidently in future rigorous analyses of the physiological and developmental roles of the phytochrome family in pea. The AF05 mutant phenotype is similar to that described for transgenic phytochrome A-overexpressing lines in other species. Results presented in this thesis indicate that there is no mutation in the PHYA gene of this mutant, either in the coding region or promoter. Possible explanations for the phenotype are discussed. In Arabidopsis and tomato, phytochrome A mediates a FR-light induced block of greening when seedlings are transferred from FR to white light. This response is considered with regard to the phytochrome A mutants of pea. Gibberellin (GA)-deficient lh-2 mutant plants of pea are dwarf in stature and show increased seed abortion and decreased seed weight, compared with seeds of the wild type. This aberrant seed development is associated with reduced levels of active GA, and with an accumulation of abscisic acid (ABA) in young seeds. Hormonal influence on seed development was investigated by construction of an lh-2 wil double mutant. The wi/ mutation blocks ABA biosynthesis, and reduces ABA levels in young seeds by 10-fold, such that introduction of the wi/ mutation reduces the endogenous ABA levels in young lh-2 seeds. However, this fails to rescue the seeds from abortion. This indicates that the effects of lh-2 on seed development are not mediated through increased ABA levels, and is consistent with previous evidence that GAs are the controlling factor underlying the lh-2 seed phenotype in pea.
Rights statementCopyright 2000 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 2000. Includes bibliographical references