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Morphological, physiological and biochemical aspects of flower initiation and development in Boronia megastigma Nees.


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Roberts, N J(Nicholas John) 1989 , 'Morphological, physiological and biochemical aspects of flower initiation and development in Boronia megastigma Nees.', PhD thesis, University of Tasmania.

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This study investigated flower initiation and development in
Boronia megastigma Nees.

Detailed morphological descriptions of flower, vegetative, and
reverted buds have been given. Flowers were found to initiate from
uncommitted axillary buds in the axils of mature leaves on current
seasons laterals. Flower buds usually initiated in autumn and
continued to differentiate slowly over winter, reaching anthesis in
early spring.

Photosynthesis and respiration rates were measured at a range of
temperatures (using infra red gas analysis) on both fully expanded and
immature leaves of current seasons laterals. Apparent photosynthesis
was highest in the mature tissue and peaked at 20°C for both types of
leaves. The dark respiration rate was greater in the immature leaves
and continued to increase with temperature. True photosynthesis was
highest at 25°C. A light saturation curve was carried out on fully expanded
leaves (at 20°C) and occurred between 400-600µmol m-2 s-1 .
This data was used to estimate photosynthetic rates in the glasshouse
and also to calculate uptake rates when labelling with 14CO2.

The effects of a night break, PFD, temperature, and daylength on
flower initiation and development were studied. As a consequence,
low night temperatures (<10°C) in combination with short days (10hrs)
and 50 to 100 percent full sunlight was termed "inductive" conditions,
whereas moderate night temperatures (>l5°C) and long days (16hrs) was
called "noninductive" conditions. Boronia does not appear to be a
photoperiodically sensitive plant, and providing PFD is not limiting
it has little effect on flowering under "inductive" conditions.
Night temperature had a dominant effect on the initiation and
development of the flowers. Flower development rather than flower
initiation seemed to be more affected by the environmental parameters.
The same environments that favoured flower bud initiation also
resulted in the highest percentage of flowers that reached anthesis.
Some degree of antagonism appeared to exist between apical activity
and the initiation of generative buds and their development.

Correlative inhibition by the vegetative apex was investigated by
removal of the most apical three pairs of leaves in "inductive" and
"noninductive" conditions before and after floral initiation. On
previously non-flowering laterals the rapid re-establishment of apical
dominance prevented floral bud initiation in the most apical remaining
pair of leaf axils. On pre-induced laterals the removal of the apex
enhanced flower differentiation particularly in the most apically
remaining leaf axils, and the extent of this was modified by the
environment .

Autoradiography was used to follow the distribution of 14C
photosynthate during flower initiation and development under
"inductive" and "noninductive" conditions. This method was used
also to study the reversion of floral differentiation, and the effect of
apex removal. The partitioning of labelled 14CO2 into a chloroform
soluble fraction, proteins, sugars, starch, free amino acids and
amides, organic acids and phosphates, and structural residue was
measured (using liquid scintillation counting). Mature leaves and
immature leaves were analyzed separately during the first 70 days of
"inductive" conditions. Quite distinct differences in the
partitioning patterns of some of the fractions were noted between the
two types of tissue, and the differences were reduced after 40-50
days. The level of partitioning into the amino acid fraction in both
types during the first 20 days of "inductive" conditions.
Consequently the fluctuation of free amino acids and amides in the
mature leaves was measured by HPLC during the first 30 days of
inductive conditions. The major amino acids and amides were found to
be alanine, asparagine, methionine, and proline. The concentration
of many amino acids was affected by the change in environment and
there were several changes of concentration over a period of time.

In vitro techniques were used to investigate apical dominance,
tissue maturity, and the influence of daylength and temperature on
flower initiation and development. The highest percentage of flowers
was found on explants that had fully expanded leaves and no vegetative
apex. Fewer flowers on these explants reverted or aborted before
reaching anthesis. No floral initiation occurred on explants that
retained the vegetative apex or that did not have fully expanded
leaves. The environmental influence on initiation and subsequent
differentiation and development was similar to the results found in
the in vivo experiments. Some competition between flowering and
vegetative vigour was demonstrated in vitro and on whole plants.

The effects of cytokinin and auxin were also studied in vivo and
in vitro. The effects of cytokinin and auxin were modified by the
environmental parameters used. Increased cytokinin concentration
enhanced the initiation and rate of differentiation of floral and
vegetative buds, however, many flower buds reverted with higher rates
of cytokinin (4-10 mg BAP/l) and it was thought that normal
differentiation and development to anthesis possibly requires less BAP
than does initiation. The presence of IAA appeared to be unnecessary
for flower initiation, differentiation, and development. In
"noninductive" conditions higher levels of IAA (3 mg/l) were promotive
to rooting.

The process(es) of flower initiation and development were
discussed in light of the experiments detailed above.

Item Type: Thesis - PhD
Authors/Creators:Roberts, N J(Nicholas John)
Keywords: Flowers, Flowers, Wild flowers
Copyright Holders: The Author
Copyright Information:

Copyright 1989 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:

Thesis (Ph.D.)--University of Tasmania, 1990. Bibliography: p. 227-251

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