STRESS PROTEIN-CONTENT OF MATURE BRASSICA SEEDS AND THEIR GERMINATIONPERFORMANCE

Plants respond to sub-optimal conditions by the synthesis of specific 'stress' proteins, and these are thought to play a role in stress tole rance. Some of these proteins accumulate during late seed development, arguably to protect against damage during post-maturation drying and subsequent imbibition, prior to germination. Seed vigour is also deter mined during this late stage of seed development. High vigour seeds ar e those that can withstand the desiccation required for storage and su ccessfully germinate under sub-optimal conditions to establish healthy seedlings. If stress proteins are involved in tolerating stress condi tions, then they are likely to be important determinants of seed vigou r. In this work the relationship between seed vigour (measured by seed germination performance following rapid aging, or under water stress) in Brassica oleracea var. capitata and the content of two classes of stress protein (dehydrins and a low molecular weight heat shock protei n HSP17.6) at maturity was examined. Dehydrins did not show a positive relationship with seed performance. However, the protein HSP17.6 show ed a positive correlation with seed performance, and a treatment that reduced the amount of this protein in the seed also caused a reduction in subsequent seed performance.