U053058.pdf (52.99 MB)
Photoregulation by the phytochrome family: A physiological study of transgenic plants.
thesis
posted on 2015-11-19, 09:09 authored by Alexandra Claire. McCormacChapter 1 reviews the evidence, to date, that the individual molecular species of phytochrome have distinct physiological roles and explains why the use of transgenic plants, which express an introduced phytochrome-encoding sequence, is adopted in this thesis as a novel approach to test this hypothesis. Chapter 2 describes the diversity of photomorphogenic responses of etiolated and light-grown wild-type plants. Chapters 3 to 6 detail the photophysiological responses of transgenic tobacco (Nicotiana tabacum) and Arabidopsis thaliana seedlings which, through expression of a transgene, accumulate supra-wild-type levels of either phytochrome A or phytochrome B; comparison is made with an Arabidopsis mutant specifically deficient in phytochrome B. The results indicate that endogenous phytochromes A and B have reciprocal and independent photosensory roles in seedling development, mediating responsiveness to continuous far-red and red, respectively. Persistent expression, in transgenic plants, of phytochrome A is seen to severely impair the shade-avoidance syndrome of light-grown plants, thus phytochrome A is discounted as the photoreceptor for red:far-red ratio perception. A transgene encoding phytochrome A is expressed in horseradish (Armoracia lapathifolia ) in order to supress the normal shade-avoidance responses, with implications for improved crop yield as discussed in Chapter 10. Transgenic overexpression of phytochrome A in Arabidopsis (but not in tobacco) results in enhanced sensitivity of the greening response to red light, relative to wild-type and also phytochrome B-overexpressing seedlings (see Chapter 7). Germination behaviour of transgenic Arabidopsis seed indicates a role for phytochrome B in mediating dark-germination. The action of a heterologous phytochrome A in photoregulation of germination in transgenic tobacco seed is less readily interpreted (see Chapter 8). Expression of a heterologous sequence encoding phytochrome A in the aurea mutant of tomato fails to rescue wild-type phenotype (see Chapter 9). Chapter 11 characterizes a single-cell system for the study of phytochrome activity. Chapter 12 discusses the potential for, and caveats against, the use of transgenic plants in investigations of phytochrome function.
History
Date of award
1993-01-01Author affiliation
BiologyAwarding institution
University of LeicesterQualification level
- Doctoral
Qualification name
- PhD