Genetic analysis of seed development in Arabidopsis thaliana = [Genetische analyse van de zaadontwikkeling in Arabidopsis thaliana]

This thesis deals with the genetic aspects of seed development in Arabidopsisthaliana. Mutants affected in several aspects of seed development and, more specifically, in seed maturation have been isolated by various selection procedures. The mutants have been analyzed genetically, physiologically, and morphologically. Some of the mutants are impaired in the biosynthesis or sensitivity to the plant hormone, abscisic acid (ABA). All ABA-related mutants show reduced seed dormancy, indicating the important role of this hormone in the establishment of dormancy. In a direct screen for reduced dormancy, two mutants (rdo) with reduced dormancy were found. These were not ABA-deficient and showed the same sensitivity to ABA, ethylene, auxin, and cytokinin as the wild-type. In contrast to this embryo-determined reduced dormancy, reduced dormancy can also originate in an altered seed coat (testa), like in the altered testa shape ( ats ) mutant. Here, the altered testa shape is caused by a defect in the development of the integuments. Extreme ABA-insensitive mutants ( abi3 ) have green seeds that fail to complete many other aspects of seed maturation, including the induction of dormancy and desiccation tolerance, and the accumulation of seed storage proteins and lipids. In addition to abi3 mutants, lec and fus mutants exhibit such a severely disturbed seed maturation as well, with dark purple seeds due to anthocyanin accumulation. The fus3 mutant shows normal ABA-sensitivity. These various seed maturation mutants indicate that specific genes, some acting dependently and some acting independently from ABA, are responsible for seed maturation programs. The seed maturation mutants were subjected to a physiological and biochemical analysis. A GA-deficient mutant was combined with these mutants. Analysis of these double mutants indicated that seeds of the abi3 and lec mutants did not require GA for germination, in contrast to fus3 seeds. This correlates with ABA-sensitivity for germination. The composition of storage proteins and carbohydrates in abi3 , lec, and fus3 mutant seeds has been compared. The abi3 , lec, and fus3 mutants all showed severely reduced storage proteins. The desiccation intolerance of these seed maturation mutants was not correlated with the lack of specific carbohydrates. Furthermore, the mutants had a higher total content of carbohydrates. This is probably a consequence of the lower levels of storage lipids and proteins.