Zygotic and somatic embryos of cucumber (Cucumis sativus L.) substantiallydiffer in their levels of abscisic acid

In this work we studied the changes in the level of abscisic acid (ABA) in the somatic embryos (SE) and in the diploid and triploid zygotic embryos (Z E) of the same cucumber line during embryogenesis and seed maturation. Diff erent stages of seed development were selected according to days after poll ination (DAP): 21, 24, 28, 35, 42 and 47 plus 14 days of storage for diploi d ZE and 35 and 42 plus 14 days of storage for triploid ZE. SE were collect ed at five growth stages from globular to late cotyledonary. Quantitative a nalysis of ABA was performed using an enzyme linked immunosorbent assay (EL ISA) test. Both types of embryos - somatic and zygotic - essentially differ ed in their levels of ABA, always being the highest for 2n ZE and lowest fo r SE. Although the concentration of ABA in ZE of the triploid line was high er when compared with the same DAP, when the comparison was based on embryo development, both the concentration and content of ABA was higher in the d iploid line. The pattern of developmental changes in the level of ABA in th e diploid ZE was consistent with that known for other species. An increase was observed during embryo development with a peak (51.1 mu g g(-1) FW or 0 .95 mu g per embryo) at the final stage of embryo formation between 21 and 24 DAP. A sharp decrease in the ABA level then took place (more than 3-fold within 4 days) and was followed by a further reduction as the seed matured . The maximal and minimal values for ABA concentration differed about 35-fo ld. SE differed substantially from their zygotic counterparts not only in t hat the concentration of ABA was extremely low (0.005-0.011 mu g g(-1) FW) but also that no significant changes occurred during embryo development and no peak of ABA concentration was observed. Other tissues of the ovule and ovary also contained ABA and could be a source of ABA for the embryo. (C) 2 000 Published by Elsevier Science Ireland Ltd. All rights reserved.