During seed maturation and germination, major changes in physiological status, gene expression, and metabolic events take place. Using chlorophyll sorting, osmopriming, and different drying regimes, Brassica oleracea seed lots of different maturity, stress tolerance, and germination behavior were created. Through careful physiological analysis of these seed lots combined with gene expression analysis using a dedicated cDNA microarray, gene expression could be correlated to physiological processes that occurred within the seeds. In addition, gene expression was studied during early stages of seed germination, prior to radicle emergence, since very little detailed information of gene expression during this process is available. During seed maturation expression of many known seed maturation genes, such as late-embryogenesis abundant or storagecompound genes, was high. Notably, a small but distinct subgroup of the maturation genes was found to correlate to seed stress tolerance in osmoprimed and dried seeds. Expression of these genes rapidly declined during priming and/or germination in water. The majority of the genes on the microarray were up-regulated during osmopriming and during germination on water, confirming the hypothesis that during osmopriming, germination-related processes are initiated. Finally, a large group of genes was up-regulated during germination on water, but not during osmopriming. These represent genes that are specific to germination in water. Germination-related gene expression was found to be partially reversible by physiological treatments such as slow drying of osmoprimed seeds. This correlated to the ability of seeds to withstand stress.Reproduction through seeds is a prominent feature of higher plants. Seeds are adapted to survive for periods of time under adverse conditions until conditions favorable for seedling establishment are encountered. Usually, mature seeds have low moisture contents, reduced metabolic activity, and have accumulated protective compounds to help them survive under rather severe conditions. In the course of seed maturation, various events happen including the accumulation of storage products, the suppression of precocious germination, the acquisition of desiccation tolerance, and often the induction of dormancy (for review, see Bewley and Black, 1994). Seeds become quiescent at desiccation and can often be stored for a long time. When nondormant dry seeds imbibe water, they can germinate to start a new lifecycle. During germination, a series of events occurs, such as the activation of respiration (Bewley and Black, 1994), the repair of macromolecules (Osborne, 1993), reserve mobilization (Gallardo et al., 2001), reinitiation of the cell cycle (De Castro et al., 1995; Vásquez-Ramos and Sánchez, 2004), and weakening of covering structures to allow radicle protrusion (Groot and Karssen, 1987). At the same time, seeds lose longevity during germination and desiccation tolerance upon radicle protrusion (Hong and Ellis, 1992). Our study focuses on these early events d...

No abstract

No abstract

This chapter discusses the gene expression under stress tolerance and in the absence of stress tolerance at seed priming and drying. An experimental model set up using cabbage seeds of different physiological qualities is described. The topics discussed include: effects of priming on germination rate and storability; sensitivity to ultra-drying; seed maturity; and gene expression studies using cDNA microarrays.