Changes in water status and proline and abscisic acid concentrations in developing somatic embryos of pedunculate oak (Quercus robur) during maturation and germination

Abstract

Somatic embryos of oak (Quercus robur L.) were matured on P24 media differing in gel strength (0.8, 0.9 and 1.0% (w/v) agar). Viscosity and osmotic potential (Psipi,medium) of the media were determined. Developing cotyledonary embryos were analyzed at maturity Stages I-III for water content, osmotic potential (Psipi,embryo) and concentrations of abscisic acid (ABA) and proline. Proliferation of embryogenic tissue, germination rates and the number of embryos formed were also determined in order to relate embryo quality to physiological parameters. Viscosity increased with agar concentration, a phenomenon apparently related to water availability. Many Stage III embryos with high germination potentials were obtained on P24 medium containing 1.0% agar. Embryo water content decreased progressively from 94 to 80% during embryo maturation. Stage I and II embryos that matured on media containing 0.8 or 0.9% agar had similar values of Psipi,embryo, whereas Psipi,embryo of Stage III embryos that matured on medium containing 1.0% agar was significantly lower, although Psipi,medium was unaffected by gel strength. Stage III embryos showed a nearly 16-fold increase in proline concentration and a 50% decrease in ABA concentration compared with Stage I embryos. We conclude that tissue water status and a complex relationship between ABA and proline concentrations, modulated by medium gel strength, are important factors in the maturation process and the quality of oak somatic embryos.

Physiological and morphological characteristics during development of pedunculate oak (Quercus robur L.) zygotic embryos

“…The protocol for the measurement of osmotic potential is described in Prewein et al (2004). Six samples harvested weekly with one repetition, were statistically analyzed using Duncan's test with a significance level (α) of 0.05.…”

“…The accumulation of embryo dry matter is closely connected to decline in moisture content and osmotic potential during development (Finch-Savage et al 1992). In addition, recent evidence suggests that low osmotic potential has an influence on the regulation of storage protein biosynthesis even during the latter stages of somatic embryo maturation (Sunderlikova and Wilhelm 2002;Prewein et al 2004). Seed storage proteins are abundant and characteristic for the final phase of the maturation process (Finkelstein et al 1985).…”

Isolation and characterization of an embryo-specific Em-like gene of pedunculate oak (Quercus robur L.) and its temporal and spatial expression patterns during somatic and zygotic embryo development

“…Diminished expression of QrEm in SEs after 30% dehydration resembles the patterns observed in their zygotic counterparts at the end of development, when natural water loss occurs. In addition, recent findings revealed that tissue water status and the complex relationship between ABA and proline levels, modulated by media gel strength, are important factors for influencing the maturation process in order to produce high quality oak SEs (Š underlíková and Wilhelm 2002;Prewein et al 2004). The expression of the QrEm gene was also affected by treatment with 6% sorbitol for 5 weeks.…”

“…The 6QR5 oak embryogenic culture line was maintained by means of repetitive embryogenesis on P 24 medium (Teasdale 1992) supplemented with 3% (w/v) sucrose, 0.89 lM BA and solidified with 0.8% (w/v) agar, as described previously (Endemann and Wilhelm 1999;Prewein et al 2004). Maturation was induced by culturing translucent SEs (size B5 mm) on P 24 medium supplemented with 6% (w/v) sorbitol for 5 weeks.…”

“…by somaclonal variation, genotypedependent characteristics, precociously germinated embryos, fused embryos, and namely by absence or underdeveloped apical meristems, leading to very low germination rates. Recently, attention has been given to the improvement of SE quality, resulting, in turn, in efficient plant conversion (Prewein et al 2004). The differing nature of somatic and zygotic embryos (ZEs) may cause deficient maturation.…”