<br/>Plant morphogenesis is influenced greatly by the irradiance, quality, direction and periodicity of the ambient light. At least three different photomorphogenic photoreceptors have been distinguished: (i) the red light (R)- and far-red light (FR)- absorbing phytochromes; (ii) the UV-A and blue light (B)-absorbing cryptochromes; and (iii) the UV-B photoreceptor. The phytochromes, which are the best characterized photosensory photoreceptors, are encoded by a small multigene family. In tomato <em>(Lycopersicon esculentum</em> Mill.) five phytochrome genes have been cloned: <em>PHYA, PHYB1, PHYB2, PHYE</em> and <em>PHYF.</em> In this thesis a genetic approach is used to assign functions to the different phytochrome types in tomato. Two classes of phytochrome mutants in tomato were analyzed both molecularly and physiologically: (i) phytochrome photoreceptor mutants: <u>f</u> ar- <u>r</u> ed light- <u>i</u> nsensitive <em>(fri)</em> mutants, deficient in phytochrome A (phyA); <u>t</u> emporarily <u>r</u> ed light- <u>i</u> nsensitive <em>(tri)</em> mutants, deficient in phytochrome B1 (phyB1) and a phytochrome chromophore biosynthesis mutant <em>aurea (au);</em> (ii) signal transduction chain mutants: <u>h</u> igh- <u>p</u> igment- <u>1</u><em>(hp-1),</em><u>h</u> igh- <u>p</u> igment- <u>2</u><em>(hp-2), <u>a</u> tro <u>v</u> iolacea (atv)</em> and <u>I</u> ntensive <u>p</u> igmentation ( <em>Ip</em> ). In adult plant stages <em>fri</em> mutants are hardly phenotypically distinguishable from wild type (WT) in white light (WL). The phyB1 -deficient <em>tri</em> mutants are only insensitive during the first two days upon transition from darkness to R. The <em>tri</em> mutants are slightly taller than the WT when grown in WL. The kinetics of stem elongation rate of these mutants were determined very precisely using a custom-built plant growth-measuring apparatus as well as their response to vegetational shade light. The immature fruits of <em>hp-1</em> and <em>hp-2</em> mutants have higher chlorophyll levels and are darker-green in colour than WT. The signal transduction chain mutants all exhibit exaggerated phytochrome responses, <em>i.e.</em> high anthocyanin synthesis and short hypocotyl length compared to WT. Anthocyanin biosynthesis that accumulated during a 24-h period of different monochromatic irradiations was determined. At 660 nm the fluence rate-response relationships for induction of anthocyanin in WT are complex, showing a low fluence rate response (LFRR) and a fluence rate dependent high irradiance response (HIR), which have been attributed to phyA and phyB 1, respectively. The <em>hp-1</em> mutant exhibits a strong amplification of both the LFRR and HIR. The <em>atv</em> mutant shows strongest amplification of the HIR component. The <em>Ip</em> mutant exhibits an exaggerated anthocyanin response in B. The results are discussed in relationship to the published work on photomorphogenesis.
|Qualification||Doctor of Philosophy|
|Award date||20 Dec 1996|
|Place of Publication||S.l.|
|Publication status||Published - 1996|
- plant pigments
- solanum lycopersicum
- genetic variation