<p>To sense light quality and quantity plants possess different groups of photoreceptors. This thesis describes the isolation and characterization of several photomorphogenic mutants in the model plant tomato. The use of a genetic approach to determine the roles of the different photoreceptors, in photomorphogenesis and to study their mode of action, is one of the most promising approaches used in photomorphogenic research. M <sub><font size="-1">2</font></sub> populations were screened for aberrant seedling phenotypes in blue and/or red light (R). This resulted in the isolation of two allelic mutants ( <em>fri <sup><font size="-1">1</font></SUP></em> and <em>fti <sup><font size="-1">2</font></SUP>)</em> that resembled the phytochrome A (phyA)-deficient mutants of <em>Arabidopsis</em> in their far-red light (FR) insensitivity. Immunochemically detectable phyA polypeptide is absent as is the bulk of the spectrophotometrically detectable labile phytochrome pool in etiolated <em>fri</em> seedlings. The <em>fri</em> locus mapped to chromosome 10 at a position similar to that of the <em>PhyA</em> locus <em></em> on the RFLP map. Four allelic mutants, that had longer hypocotyls under continuous R, were isolated. These mutants are only insensitive to R during the first two days upon transition from darkness to R and were designated <em>tri <sup><font size="-1">1</font></SUP></em> to <em>tri4</em> (temporarily led light insensitive). Immunochemically detectable phyB1 protein is either absent, reduced or truncated. The <em>tri</em> mutants differ from phyB-deficient mutants found in other species in their relatively normal end-of-day FR and supplementary daytime FR responses. The <em>tri</em> mutant gene and the <em>PhyB1</em> gene were mapped to the same position on the RFLP map of chromosome 1. The nature of the mutations in <em>au</em> and <em>yg-2</em> was analysed by crossing both mutants with a transgenic tomato line that overexpresses oat phyA-3. Immunochemically detectable oat PHYA-3 is present in both the <em>au,PhyA-3</em> and <em>yg-2,PhyA-3</em> 'double mutant'. However, spectrophotometrical analysis revealed that it is non active, as indicated by the long-hypocotyl phenotype of the 'double' mutants. The results were consistent with both mutants being disturbed in the phytochrome chromophore biosynthesis. The three remaining phytochrome genes <em>(PhyB2, E</em> and <em>F</em> ), for which no mutants have been found thus far, have also been mapped to the RFLP map of chromosomes 5, 2 and 7, respectively. In addition, it has been proved that there are two distinct <em>hp</em> loci, each with several alleles. The <em>hp-2</em> gene has been located on both the genetic and molecular linkage maps of chromosome 1.
|Qualification||Doctor of Philosophy|
|Award date||6 Dec 1996|
|Place of Publication||S.l.|
|Publication status||Published - 1996|
- molecular genetics