Gene Expression Programs during Brassica oleracea Seed Maturation, Osmopriming, and Germination Are Indicators of Progression of the Germination Process and the Stress Tolerance Level

Abstract

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...

Screening of Antioxidant Compounds During Sprouting of Brassica oleracea L. var. costata DC

“…Previous work with B. oleracea sprouts concerned the genetic characterization of seed germination [25,26], monitorization of cell cycle modifications during the first divisions of the seeds [6], sensitivity to hypoxia [18], and the ability of seeds produced under a drought to germinate normally [27]. Other studies have dealt with the ability of seeds to biosynthesize and incorporate erucic acid into triacylglycerols [28] and the activity and distribution of peroxidases isozymes in germinating seeds [29].…”

Protein expression upon desiccation and imbibition of Magnolia ovata A. St.-Hil seeds

“…Down-regulated expression in a set of genes related to maturation was also observed when the drying maturation phase started in Medicago truncatula seeds (Gallardo et al, 2003). Some genes with high expression during the maturation of Brassica oleracea seeds are a sub-group of lateembryogenesis abundant and storage proteins (Soeda et al, 2005). In spite of the exact function of several downregulated genes being unknown, the logical presumption is that some genes are down-regulated because of the fact that their product might not be suited to the new physiological condition caused by dehydration stress (Ramanjulu and Bartels, 2002).…”

Cross-Tolerance Mechanism Induction in Melon Seeds by Priming Prior Drying

“…Seeds dried at different rates (slow or fast) after priming showed differential gene expression, similar to what occurs with genes that act to protect DNA and promote tolerance to stress (Soeda et al, 2005).…”