| Popis: |
Seeds are classified as either: orthodox, seeds that tolerate dehydration; recalcitrant, seeds that are high in moisture content and cannot withstand intensive desiccation; or intermediate, seeds that survive dehydration but die during dry storage at low temperatures. Seed lifespan depends on the seed category and also varies from one species to another. The rate of loss of vigor and viability of orthodox seeds depends mainly on temperature and seed moisture content (MC); the lower the MC and storage temperature, the longer the longevity. Ultimately, storage in liquid nitrogen or seed ultra-drying by well-adapted processes should allow for long-term storage. The ageing of orthodox seeds is associated with numerous forms of cellular and metabolic damage (membrane integrity, energy metabolism, and the impairment of DNA, RNA, and proteins) in which reactive oxygen species play a prominent role. Interestingly, priming treatment can reinvigorate aged seeds by restoring the antioxidant systems. The storage of recalcitrant seeds is very difficult since they must be placed in a wet medium to avoid dehydration and at temperatures low enough to prevent germination but warm enough to avoid chilling injury. A better understanding of the mechanisms involved in ageing is necessary to identify markers in order to estimate seed longevity. |
