EX-SITU CONSERVATION OF TROPICAL RAIN-FOREST SEED - PROBLEMS AND PERSPECTIVES

The tropical forest flora of the world is being destroyed very rapidly putting in danger of extinction a great number of species, so it is n ecessary to find alternatives for their conservation. Seed storage is a good possibility that allows germoplasm preservation of valuable and endangered plants which consists in keeping seed viability in storage optimal conditions. In other plant communities, different from tropic al forests, seed storage at low temperature and dehydration conditions in seed banks is now a common procedure of germoplasm preservation ma inly in botanical gardens of developed countries. Knowledge about seed longevity is essential to forest technicians or to anyone working wit h forest ecology because the seed represents the natural means for pla nt reproduction and for the preservation of the genetic variability of plant populations. According to tolerance dessication, seeds can be d ivided basically in three groups: orthodox, intermediate and recalcitr ant. Dessication tolerance is controlled genetically and it may be con trolled by several compounds such as hormones like gibberellic acid or abscisic acid or the proteins called LEA. Recalcitrant seeds keep the ir metabolic activity during the quiescent period so it is not possibl e to store them for long periods of time at temperatures below 0 degre es C because seeds water content is converted into ice crystals. Inter mediate seeds can not resist freezing temperatures and only survive fo r some years at room temperature. Most tropical forest seeds are recal citrant because the conditions for germination and development on thei r natural environment are favourable almost all the time, so they did not evolve any resistance mechanism. Unfortunately, seed storage resea rch is scarce. For the seeds that can not be stored, in vitro culture techniques and cryopreservation are good alternatives that are being w ell studied by plant physiologist and biotechnologists and that in the future will complement ex situ storage techniques.