ROLE OF SUCROSE FOR THE ACQUISITION OF TOLERANCE TO CRYOPRESERVATION OF CARROT SOMATIC EMBRYOS

The action of sucrose for the induction of freezing tolerance of carro t somatic embryos was investigated. The cryoprotective efficiency of v arious sugars, proline and penetrating agents (glycerol and dimethysul foxide) was evaluated relative to the protection afforded by sucrose. Raffinose, sorbitol and maltose like sucrose led to germination rates of 60-80% after freezing for an optimal concentration of 0.3 -0.4M. Wh ile we observe a rapid water loss of embryos (30% of the initial water ) in the first 15 min of pretreatment, germination rate is still low ( about 20%). The embryo sucrose content strongly increased from 80 to 3 00 mg/g dw which can be linked in part with an increase in germination rates after freezing during the first-only 12h as confirmed by using pCMBS as sucrose transport inhibitor. The partial or complete replacem ent of sucrose by PEG 6000 and ABA showed that a mixture of PEG 20% 1 mu M ABA gave the same protection as 0.4M sucrose as the same osmoti c pressure of the solution (ie 1.43Mpa). We can conclude that sucrose acts by a osmotic effect, its accumulation in the embryos and the indu ction of metabolic changes which together give a high level of embryo cryoprotection.