Isozyme patterns in zygotic and somatic embryogenesis of carrot

Abstract

Isozyme patterns of carrot (Daucus carota L.) zygotic embryos between the torpedo stage up to 5-day-old seedlings have been compared with those of the similar stages from the embryogenic cell suspension culture to the late somatic plantlet. Somatic embryos blocked at the torpedo stage by β-cyclodextrine have also been analyzed. All these stages have been analyzed with respect to seven different enzyme systems: arylesterase, glucosephosphate isomerase, phosphogluconate dehydrogenase, alcohol dehydrogenase, isocitrate dehydrogenase, aspartate aminotransferase and phosphoglucomutase (EC 2.7.5.1, PGM). The relationships between the different stages of both types of embryogenesis have been visualized using an unrooted tree. Generally, profiles of somatic embryos were different from those of zygotic embryos. Interestingly however, a typical zygotic embryo pattern was found in the cyclodextrine-blocked somatic embryos. Only aspartate aminotransferase patterns revealed a similarity between zygotic and somatic torpedo embryos. Both plantlet types showed close patterns with common isozymes. Moreover, similarities were evident between somatic plantlets and cell suspensions. A few isozymes appeared to be stage specific markers: esterase 10–11 were specific to achenes and early germination, phosphogluconate dehydrogenase 8 was specific to 4–5 day-old seedlings and phosphoglucomutase 1 and 7 and alcohol dehydrogenase 4 were markers for zygotic embryos. No somatic embryogenesis specific isozyme could be found. We show that patterns can be associated with particular tissue formation: mainly, aspartate aminotransferase 2 and 1, phosphoglucomutase 8 and 9 and phosphogluconate dehydrogenase 7 coincided with apical meristem initiation and phosphoglucomutase 4 and 5, zones “b” and “d” of esterase and zone “b” of phosphogluconate dehydrogenase coincided with vascular bundle formation.