INFLUENCE OF EXOGENOUS ABSCISIC-ACID ON GERMINATION AND PLANTLET CONVERSION FREQUENCIES OF HYBRID LARCH SOMATIC EMBRYOS (LARIX X LEPTOEUROPAEA) - RELATION WITH IN PLANTA ABSCISIC-ACID AND ABSCISIC-ACID GLUCOSEESTER LEVELS

The effect of exogenous abscisic acid, provided to somatic embryos dur ing the maturation step, on endogenous abscisic acid and its main conj ugated form (abscisic acid glucose ester), germination and conversion frequencies is presented in this paper. Abscisic acid measurements wer e obtained after a methanolic extraction, a fractionation through high performance liquid chromatography, quantitation with an immunoassay a nd identification of the quantitated compound using gas chromatography -mass spectrometry. Results show that endogenous abscisic acid and abs cisic acid glucose ester levels are clearly correlated with the exogen ous abscisic acid concentration provided to the embryos. Maturation wa s clearly enhanced by exogenous abscisic acid, but no correlation was found between abscisic acid concentration and germination frequency. C onversely, development of the aerial part of the germinated somatic em bryos was dependent upon the abscisic acid concentration in the cultur e medium and results suggest that this dependence could be related to the endogenous abscisic acid content.