Inaug.-diss.--Utrecht.

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The ability to form embryos from somatic cells or somatic embryogenesis (SE) is a form of totipotency present in plants. The effect of light on SE is poorly understood. Somatic embryogenesis of Arabidopsis thaliana in the visible region was mainly induced by red light (660 nm). The red light receptor PHYTOCHROME E (PHYE) was the only PHY mutant that reduced SE. Transcriptional analysis of phyE and darkness showed several hundred fold reduction in CONSTITUTIVE PHOTOMORPHIC DWARF (CPD) expression, a rate limiting enzyme in brassinosteroid (BR) biosynthesis. Application of BR partially rescued AGAMOUS LIKE 15 (AGL15) expression, a key SE gene, under darkness and in the phyE mutant. The results support a model where red light acts through PHYE and subsequently brassinosteroid signalling to induce SE through AGL15.

Congeneric species occupying different habitats might be expected to have different seed dormancy strategies and germination requirements while those growing in the same habitats may be more similar. I tested this hypothesis with a broad survey of the germination of 51 Carex species from mesic deciduous forests, wet deciduous forests, and wetland or seasonally flooded areas in response to different controlled environmental conditions. A canonical discriminant analysis based on the responses of 29 species to various treatments showed clear differences among seeds from each habitat with respect to germination behaviour. Germination of seeds from mesic deciduous forest species was generally faster after moist stratification than after either submersion or dry storage. In seeds from most wet areas of deciduous forest, wetland, or seasonally flooded habitats, germination was similar or greater after submerged as compared to moist stratification. Total germination was significantly increased by light in all species except Carex pedunculata , an ant-dispersed species. Germination was not significantly different on a poorly drained peat soil than on a well-drained sandy loam. Seeds of most species were at least physiologically dormant at maturity and germination of fresh seeds was generally low. Spring germination was similar among species from all habitats and generally began in late May or early June, at fairly high temperatures (min 7°C, max 17°C), which is unusual for forest species but consistent among Carex species.

This study aimed to improve seed quality in cauliflower and cabbage, firstly though the development of rapid methods for the evaluation of germination and seed storage potential using measurements of seed leachates conductivity and secondly, through the application of seed treatments both as pre-storage treatments and to improve germination under stress conditions.  Significant negative correlations between germination and the conductivity of seed leachate were observed both when seed had high germinations after ageing and when a range of germinations resulted from either combinations of dead plus living seeds, or ageing.  This suggested that conductivity measurements could be applied to predict seed germination.  Seed quality declined during storage at two moisture contents (12% and 6.5%) and two temperatures (25^oC and 35^oC) as reflected by the increase in seed leachate conductivity and decline in germination and vigour.  Differences in seed storage potential were best predicted by the controlled deterioration (CD) test and by CD followed by measurements of leachate conductivity.   Other pre-storage assessments (laboratory germination, K_i, conductivity) were less consistent in prediction of storage potential.  The second approach used to improve seed quality was to apply pre-storage seed treatments to improve seed storage potential.  The most striking improvements in seed storage potential occurred after pre-storage hydration treatments, aerated hydration (AH) for 12h or 18h and water soaking for 3h or 6h, with smaller improvements after antioxidant treatments (0.1% <span lang=EN-GB style='font-family:Symbol'>a-tocopherol and 0.1% ascorbic acid).  Halogenation (I₂) treatment had no effects on storage potential.  Improved seed quality was also revealed after AH treatment by both the increased ability of seed to germinate at high temperature (35^oC) and more rapid germination at reduced water potential and under salinity stress.  AH treatment also increased the ability of seeds to recover from exposure to higher temperature (40^oC) and reduced water potential (-1.90 MPa).

The ability to form embryos from somatic cells or somatic embryogenesis (SE) is a form of totipotency present in plants. The effect of light on SE is poorly understood. Somatic embryogenesis of Arabidopsis thaliana in the visible region was mainly induced by red light (660 nm). The red light receptor PHYTOCHROME E (PHYE) was the only PHY mutant that reduced SE. Transcriptional analysis of phyE and darkness showed several hundred fold reduction in CONSTITUTIVE PHOTOMORPHIC DWARF (CPD) expression, a rate limiting enzyme in brassinosteroid (BR) biosynthesis. Application of BR partially rescued AGAMOUS LIKE 15 (AGL15) expression, a key SE gene, under darkness and in the phyE mutant. The results support a model where red light acts through PHYE and subsequently brassinosteroid signalling to induce SE through AGL15.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 95-103). Also available via the Internet.

Thesis (Ph. D.)--University of Chicago, 1913. / "Reprinted from The Botanical Gazette, Vol. LVII, No. 5." "Literature cited": p. 410-414. Also available on the Internet.