Biosíntesis, distribució, acumulació i funció de la vitamina e en llavorsmecanismes de control

Resumen

This PhD thesis has studied the distribution, accumulation, function and biosynthesis of tocopherols and tocotrienols (vitamin E) in seeds, as well as their control mechanisms. First, the seeds of the family Arecaceae were studied due to the great amount of lipid that accumulates and the diverse range of genera, allowing the exploration of evolutionary trends in the distribution of tocopherols and tocotrienols. The accumulation of tocotrienols is a preserved trait, while the ability to accumulate tocopherols has been lost in different genera throughout evolution. The differential accumulation of tocopherols and tocotrienols showed that vitamin E may protect lipid bodies in the endosperm and embryo, and may also protect polyunsaturated fatty acids (PUFA) of proplastids from lipid peroxidation. In the seed coat, vitamin E may protect against ROS caused by biotic or abiotic stresses. In Cistus albidus seeds we investigated how the mother plant age and environment can affect the production of seeds, its quality, the synthesis of hormones and vitamin E. Also, the possible influence of hormones and vitamin E on seed dormancy and germination capacity was studied. In controlled environmental conditions only the age of the mother plant can influence the content of vitamin E and hormones of seeds maintaining the germination capacity. However, probably the environment, but cannot rule out genotype effects, might impact the degree of seed dormancy influencing the levels of ABA, GAs, and vitamin E, maintaining the viability of the embryos. The seeds of Chamaerops humilis var. humilis allow us to examine the antioxidant function of tocotrienols and tocopherols in different physiological stages of seeds: while tocotrienols act as antioxidants during storage, dormancy and quiescence; tocopherols seem to play this role during germination. Tocopherols were synthesized de novo once germination started, with increasing hormones and hydrogen peroxide levels, suggesting a transcriptional regulation of their synthesis. This was confirmed by changes in the expression levels of genes involved in the synthesis of tocopherols and tocotrienols. This thesis concludes that due to its dual role (antioxidant and regulatory), vitamin E is essential during storage, seed dormancy and quiescence. In particular, tocopherols are essential for germination.