WATER PERMEABILITY DURING THE EARLY PHASE OF INCUBATION OF RAPHANUS-SATIVUS SEEDS - EFFECTS OF A MEDIUM WITH LOW WATER POTENTIAL AND FUSICOCCIN

During the first 42 h of incubation of radish (Raphanus sativus L.) se eds, growth and diffusional water permeability (P-w) changed with time in a medium with low water potential (psi(w), medium: -0.67 MPa, 300 mM mannitol) and/or fusicoccin (FC). During the first 12 h, the low ps i(w) medium decreased both seed growth and P-w; FC increased both seed growth and P-w; changes in growth and P-w were accompanied by changes in seed water parameters and K+ reabsorption capability (i.e. transpo rt mechanisms). Seed water potential (psi(w seed)) reached equilibrium with the psi(w) medium in all conditions within the first 2 h. Seed s olute potential (psi(s seed)) was more negative in the low psi(w) medi um (as expected and in agreement with the lower value of P-w), while i n FC at first it became more negative (in agreement with the higher ca pability For K+ reabsorption), then more positive (in agreement with i ncreased values of P-w and the possible FC-dependent increase in cell- wall loosening). Seed pressure potential (psi(s seed)) was low in the low psi(w) medium, in agreement with the low value of P-w, even if psi (s seed) was more negative, while in FC psi(p seed) became at first mo re positive, in agreement with changes in psi(s seed), then dropped in relation to the increased value of P-w and to the possible FC-promote d cell-wall loosening. FC had the same effect (although less marked an d with a longer delay) also in the low psi(w) medium. After the 12th h , there were increased effects on growth of both low psi(w) medium and FC; the growth was correlated not with the values of P-w, but with th e capability to sustain psi(s seed). In R. sativus seeds, different gr owth rates due to a low psi(w) medium and/or FC seem to be correlated with the physical parameter 3