Introduction Directory UMM :Data Elmu:jurnal:P:PlantScience:PlantScience_Elsevier:Vol157.Issue1.2000:

Plant Science 157 2000 129 – 137 Zygotic and somatic embryos of cucumber Cucumis sati6us L. substantially differ in their levels of abscisic acid Helena Gawronska a, , Wojciech Burza b,1 , Elzbieta Bolesta b,1 , Stefan Malepszy b,1 a Department of Plant Physiology, Faculty of Agriculture, Warsaw Agricultural Uni6ersity, Rakowiecka 26 - 30 , 02 - 528 Warsaw, Poland b Department of Plant Genetics, Breeding and Biotechnology, Faculty of Horticulture, Warsaw Agricultural Uni6ersity, Nowoursynowska 166 a, 02 - 787 Warsaw, Poland Received 15 November 1999; received in revised form 10 April 2000; accepted 13 April 2000 Abstract 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 ZE of the same cucumber line during embryogenesis and seed maturation. Different stages of seed development were selected according to days after pollination DAP: 21, 24, 28, 35, 42 and 42 plus 14 days of storage for diploid ZE and 35 and 42 plus 14 days of storage for triploid ZE. SE were collected at five growth stages from globular to late cotyledonary. Quantitative analysis of ABA was performed using an enzyme linked immunosorbent assay ELISA test. Both types of embryos — somatic and zygotic — essentially differed in their levels of ABA, always being the highest for 2n ZE and lowest for SE. Although the concentration of ABA in ZE of the triploid line was higher 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 diploid line. The pattern of developmental changes in the level of ABA in the diploid ZE was consistent with that known for other species. An increase was observed during embryo development with a peak 51.1 mg g − 1 FW or 0.95 mg 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-fold. SE differed substantially from their zygotic counterparts not only in that the concentration of ABA was extremely low 0.005 – 0.011 mg 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. © 2000 Published by Elsevier Science Ireland Ltd. All rights reserved. Keywords : Abscisic acid; Cucumber; Somatic; Zygotic; Diploid; Triploid embryos www.elsevier.comlocateplantsci

1. Introduction

Artificial seeds are an important part of plant biotechnology and somatic embryos SE are the basic component of it [1]. The knowledge of the physiology of SE development including their hor- monal status is among the major points for the successful application of artificial seed technology. Despite this, comparative studies on SE and ZE are scarce. Abscisic acid ABA plays a key role in embryo and seed development at each stage, both in a stimulatory and inhibitory manner [2,3]. ABA controls the proper embryo formation and matu- ration [4,5], is involved in initiation and progress- ing of tissue desiccation [6,7], as well, as in the acquisition of desiccation tolerance by embryo [8]. Several authors showed that ABA inhibits preco- cious seed germination [7,9] and regulates seed maturation and dormancy [6]. ABA is also in- Abbre6iations : ABA, abscisic acid; DAP, days after pollination; ELISA, enzyme linked immunosorbent assay; EtoAc, ethyl acetate; FW, fresh weight; MeOH, methanol; SE, somatic embryos; ZE, zygotic embryos. Corresponding author. Tel.: + 48-22-8499476; fax: + 48-22- 8491946. E-mail addresses : gawronskadelta.sggw.waw.pl H. Gawronska., malepszyalpha.sggw.waw.pl S. Malepszy 1 . 1 Tel.fax: + 48-22-8430982. 0168-945200 - see front matter © 2000 Published by Elsevier Science Ireland Ltd. All rights reserved. PII: S 0 1 6 8 - 9 4 5 2 0 0 0 0 2 7 7 - 6 volved in induction and regulation of a number of genes coding for storage and LEA proteins [4,10 – 12], as well as, enzymes in fatty acids and lipids metabolism in seeds [13]. It is also suggested that ABA plays an essential role in somatic embryoge- nesis and somatic embryos maturation [5,14,15]. Moreover, it has been shown for many, but not all the plant species, that exogenously applied ABA to the growth medium increases the number of properly developed SE and improves their quality [14,15]. Triploids, when compared with respective diploid lines, differ from them in several aspects of development and morphology including delayed and somewhat abnormal embryo and seed devel- opment [16]. Not much data are available in the literature, related to differences in ABA levels between so- matic and zygotic embryos and not between diploid and triploid lines having the same genetic background. To our knowledge, such data are not available for cucumber. Moreover, the limited data on the role of ABA in somatic embryogenesis of other plant species, as pointed out by Nomura and Komamine [15], are still controversial and not conclusive. The aim of this study was to examine changes in the level of ABA in SE and in ZE of highly inbred diploid and triploid lines of cucumber Cucumis sati6us L. during embryogenesis and seed maturation.

2. Material and methods