Embryogenesis was observed through light and transmission electron microscopy to elucidate the role of the cytoskeleton in the cellularization of the coenocytic endosperm in Helianthus annuus. Microtubules were not seen throughout the development of the endosperm despite the fact that nuclear division occurred frequently. The positioning of organelles in the cytoplasm in close proximity to the developing cell plate as well as the crooked appearance of the growing endosperm cell wall suggests that a traditional microtubular system, in which a phragmoplast controls wall formation, is not present in this species. The growth patterns exhibited by endosperm walls, similar to that of tip growing cells, may indicate that actin filaments are controlling the cellularization of the endosperm. To further investigate the role of microtubules in the development of the endosperm of H. annuus, inhibitory studies using 100 µM, 300 µM and 1 mM colchicine were conducted on ovules both in-vivo and in-vitro. Enlarged nuclei, partial collapse of the integumentary tapetum, and loss of organelles were observed in colchicine treated cells which indicates that colchicine affected the development of the endosperm. However, since little difference was seen between the various concentrations of colchicine and the cellularization of the endosperm was still observed in treated cell, this may indicate that either colchicine did not affect the cytoskeleton controlling endosperm development or that it did not successfully penetrate the embryo sacs. The minor effect seen by the application of colchicine may support the idea that actin plays a role in the cellularization of endosperm in H. annuus. / Thesis (Master, Biology) -- Queen's University, 2008-11-03 10:18:50.557

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.

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