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The role of Calcium ions (Ca2+) in the phytochrome-controlled unrolling of 6-d-old etiolated barley leaf sections was evaluated through the manipulation of light treatments, Ca2+ levels and antagonists and agonists of Ca2+ metabolism. The Ca2+-chelator ethyleneglycol-bis-(Baminoethylether) - N, N, N', N', - tetraacetic acid (EGTA) inhibited the response. Ca2+ restored responsivity when supplied within 1h of light treatment. Subsequent escape from responsivity to Ca2+ involved uncoupling of measurable phytochrome from response level. A second Red- light treatment (R) given, with Ca2+, to EGTA-treated sections following Ca2+ escape from the initial R effect induced full unrolling. Similar results were obtained with the relatively independent phytochrome- controlled nitrate reductase activity induction in the sections. It is proposed that Ca2+ escape arises from phytochrome signal attenuation. Measurable Pfr and response recoupled following Ca2+-escape for the second R, given with Ca2+. This relationship was identical to that observed with a single light treatment without EGTA, despite a 50% reduction in phytochrome levels at the time of the second R. This indicated that either the ratio of Pfr/Ptot governs response induction, or that the majority of detectable phytochrome is functionally irrelevant. It is suggested that phytochrome deactivation is reversible via phytochrome cycling. A23187-induced movement of Ca2+ also induced unrolling. This, and the R effect appeared to be separate, thus Ca2+ does not mediate the phytochrome signal via simple amplitude modulation. Treatment with 1.2-Diacylglycerol (1,2,-DG) induced unrolling. The interaction of 1,2-DG and A23187 demonstrated Ca2+ sensitivity modulation, indicating involvement of Protein Kinase C. The interaction of A23187 and phytochrome did not show this. It is suggested that the induction of unrolling centres around protein phosphorylation via separate 1,2,-DG, Ca2+-sensitive and phytochrome regulated kinases.

No description available.

Leaf discs of Saintpaulia ionantha x confusa hybrids (African Violets) were cultured and transferred between hormonal free medium (MS basal medium) and shoot-inducing medium (SIM) to determine whether there is a window of competence in shoot regeneration. The results showed that cultured cells were not responsive to shoot-inducing signals (i.e. not competent) until 3-5 days after explant isolation but the ability to regenerate shoots was not lost in surviving cells/tissues cultured on basal medium. Light microscopic observations found that first periclinal divisions of epidermal cells occurred at 3-5 days on SIM. Meristemoids were then formed from the derivatives of the original epidermal cells. It is proposed that cellular competence for shoot regeneration is acquired in culture. The pre-competent period consists of a resting phase and a "dedifferentiation" phase in which epidermal cells divide periclinally to form "dedifferentiated" cells which are the true target cells for shoot induction. Mutagenic treatments and propagation of a chimeral African Violet cultivar were carried out to study cell origin of adventitious shoots in African Violet leaf culture. The results suggest that adventitious shoots may originate from either multiple cells or single cells. The multiple cell origin is in contrast to the hypothesis of exclusively single cell origin for adventitious shoots proposed in several studies. Several factors were studied to identify the source of variations in shoot regeneration among individual explants and to define conditions favourable for shoot regeneration in African Violet in vitro culture. These factors include donor plant growth temperature, the presence of light and the quality of light in culture, the role of chlorophyll in cultured tissues, position of explants in leaves, age of explant materials, source and type of explants, wounding and leaf disc orientation on media. It was found that the presence of light in culture, age of leaf explants, source (in vitro cultured vs pot plant) and type (leaf vs petiole) of explants, wounding and leaf disc orientation on media all had a statistically significant effect on shoot production.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 197-236). Also available in electronic version. Access restricted to campus users.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 147-160). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Chicago, Dept. of Biology. / Includes bibliographical references. Also available on the Internet.