Water Relations Parameters and Tissue Development in Somatic and Zygotic Embryos of Three Pinaceous Conifers

Abstract

There is increasing interest in using somatic embryogenesis to meet the demand for high quality seedlings. However, in vitro production of propagules on a large scale depends on the optimization of the maturation and germination steps promoted by desiccation and subsequent imbibition of the embryo, respectively. It is therefore important to characterize zygotic and somatic embryos in terms of their water relations. Bound water, elastic modulus, osmotic potential at full turgor. and relative water content at turgor loss point were determined for somatic and zygotic embryos of western larch and loblolly pine and somatic embryos of white spruce at two developmental stages. These water relations parameters were derived from waterrelease curves obtained by suspending tissue samples in sealed vials over unsaturated NaCI solutions of known water potential. There was little difference in water relations parameters among species but marked stage dependency for bound water and elastic modulus. The amount of bound water was lowest in western larch somatic embryos (0.02-0.07) and highest in zygotic loblolly pine embryos (0.10-0.18). Elastic modulus ranged from 2.5 to 6.2 MPa in somatic embryos but varied between 1.4 and 1.8 MPa in zygotic embryos. The osmotic potential was lower in somatic embryos than in their zygotic counterparts. Our results show that water relations parameters are remarkably conservative across species but that, within a given species, these parameters are stage specific. It would seem, therefore, that desiccation protocols might be developed for a given developmental stage and applied across a range of species without the confounding effects of differences in water relations parameters.

Influence of a stationary magnetic field on water relations in lettuce seeds. Part II: Experimental results

“…We wanted to demonstrate experimentally the action of the magnetic ®eld on the water relations in the ®rst phase (hydration) of the germination process, since in this phase the biochemical reactions to be originated later by the germination have still not begun [Bradford, 1990;Dumont-DeBoux et al, 1996;Shackel and Tunner, 1998;Welbaum et al, 1998;Chen and Bradford, 1999]. In this ®rst phase the osmotic pressure plays a fundamental role [Steudle, 1992;Obroucheva et al, 1993;Welbaum et al, 1998;Ramahaleo et al, 1999], therefore if we make measurements only in this phase, we can demonstrate the alteration undergone by the osmotic pressure.…”

“…In this ®rst phase the osmotic pressure plays a fundamental role [Steudle, 1992;Obroucheva et al, 1993;Welbaum et al, 1998;Ramahaleo et al, 1999], therefore if we make measurements only in this phase, we can demonstrate the alteration undergone by the osmotic pressure. Later on, a series of complex processes begin in the seeds [biochemical, physiological, and genetic], which mask the direct action on the osmotic pressure [Bradford, 1990;Cosgrove, 1993;Dumont-DeBoux et al, 1996;Shackel and Turner, 1998;Welbaum et al, 1998;Chen and Bradford, 1999]. A clear dependence between the mass of water absorbed by seeds at absorption time t and the magnetic induction B of the magnetic ®eld, with which it was treated before absorbing water, are shown in Figures 1 and 2.…”