GERMINATION OF SUNFLOWER SEEDS - INVOLVEMENT OF CALCIUM

An investigation on the role of calcium in the germination of sunflowe r seeds is reported. Germination was estimated as the elongation of th e root, after the reimbibition of seeds. It was observed, after the us e of metabolic inhibitors (actinomycin D, cycloheximide and colchicine ), that the primary root elongation was dependent of translation and w as independent of transcription or mitosis. We used the Ca2+ chelator EGTA, calcium competitors La3+, Co2+, and verapamil to show that free apoplastic Ca2+ is necessary for germination, as this phenomenon was i nhibited in their presence. When inhibitory concentrations of EGTA wer e used, germination was restored by exogenously added Ca2+. The same r eversible effects was observed if verapamil and Ca2+ were added succes sively to imbibing seeds. The involvement of ion import within die cel l was confirmed by the use of Ca2+ ionophore A23187 which favoured roo t elongation. As calmodilun antagonists TFP and W7 were also inhibitor s of the germinative process, our conclusion is that die triggering re action controlling cell expansion and germination of sunflower seeds i s under the dependence of Ca2+. However, inhibition was not complete i n their presence, so that die involvement of calmodulin was questioned .