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Nodulation phenotypes of Pisum sativum mutants


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Ferguson, Brett James 2005 , 'Nodulation phenotypes of Pisum sativum mutants', PhD thesis, University of Tasmania.

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Nitrogen-fixing bacteria, collectively referred to as rhizobia, are able to trigger
the organogenesis of novel organs on legumes, called nodules. The initiation and
development of nodules requires a complex signal exchange involving both plant and
bacterial compounds. Phytohormones have been implicated in this process, although
in many cases direct evidence is lacking. In the work reported here, the root and
nodulation phenotypes of various mutant lines of Pisum sativum L. are characterized,
including those having alterations in their phytohormone levels and/or perception,
and a homeotic mutant. Root systems having similar or elevated GA levels compared
with that of their wild type developed wild type numbers of nodules, whereas those
deficient in gibberellins or brassinosteroids exhibited reduced nodulation.
Gibberellin application or grafting to a wild type root or shoot restored the nodule
number of a gibberellin-deficient mutant to that of its wild type. In contrast, the
shoot controlled the number of nodules that formed in graft combinations of a
brassinosteroid-deficient mutant and its wild type. Interestingly, a strong correlation
between nodule and lateral root numbers was observed in all lines assessed,
consistent with a possible overlap in the early developmental pathways of the two
organs. Double mutants possessing the na mutation, which results in severe GAdeficiency,
and the sln mutation, which results in elevated seedling GA levels,
displayed abnormal nodules and a reduced capacity to autoregulate their nodule
numbers. Constitutive GA signalling mutants also produced significantly fewer
nodules than their wild type. However, these nodules were normal in appearance, and significantly greater in number compared with that of na plants, regardless of
whether or not they also possessed the na mutation. This indicates that intact GA
signalling pathways are required for nodule development. Additional double mutants
were created by crossing na with one of three independent mutations, nod3, sym28,
and sym29/nark/har-1, that result in a plants inability to regulate its nodule number.
Double mutant segregates from each of these crosses formed significantly more
nodules than na, but these structures maintained the aberrant na nodule morphology.
A significant increase in nodule numbers was also observed on na following
treatment with an ethylene biosynthesis inhibitor, but these nodules were also
aberrant. These findings suggest that GAs are required for late nodule development
and that ethylene has a role in nodule initiation. The histology of na nodules further
supported a role for gibberellins late in nodule development as the cells of the
infected zone failed to enlarge.
The nodulation phenotype of the homeotic mutant, cochleata, which has
stipules replaced by alternative leaf components, abnormal flowers and reduced
fertility, was also investigated. Although the root system dry weight, root lengths and
nodule numbers of cochleata were similar to those of its wild type, the nodulation
phenotype of the mutant was unique. The nodules typically dichotomously branched
and multiple callus and root structures emerged from their meristems. These nodule-roots
incorporated a peripheral vascular bundle of the nodule into their own central
vascular cylinder and both the nodules and roots of the hybrid structures appeared

Item Type: Thesis - PhD
Authors/Creators:Ferguson, Brett James
Keywords: Peas, Bacterial wilt diseases
Copyright Holders: The Author
Copyright Information:

Copyright 2005 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).

Additional Information:

Available for library use only and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2006. Includes bibliographical references

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