Water Relation Parameters of Embryogenic Cultures and Seedlings of Larch

Abstract

Changes in the water relations parameters of developing somatic embryogenic and xygotic European larch (Larix decidua) were studied. Water release curves were generated by suspending tissue samples over unsaturated NaCI solutions until they reached vapor equilibration with the surrounding air. Twenty solutions were used whose water potentials ranged from -0.05 to -10 MPa. Water release curves were obtained by plotting paired values of tissue relative water content (RWC) and solution potential. Curves were derived for embryonic larch at various stages of development and for hypocotyls and roots from germinated zygotic and somatic embryos. The ability to resist dehydration increased markedly with development. Stage 1 tissue, which consisted of clusters of loosely associated nonchlorophyllous cells, had extremely low bulk elastic modulus (e) (1.91 MPa) and apoplastic water content (A) (0.023), relatively high osmotic potential (war) , and lost turgor at 0.56 RWC. In contrast, mature embryoids with primary roots, hypocotyl, and cotyledons (stage 3) had an almost 4-fold increase in A (0.089), significantly higher (3.49 MPa), and lower *,I (-0.88 MPa) and lost turgor at 0.66 RWC. Hypocotyl tissue from germinated somatic embryos lost turgor at 0.74 RWC and had higher E, A, and solute accumulation than pregerminated tissue. Hypocotyl tissue resisted dehydration more strongly than root tissue, and differences between root and hypocotyl water relation parameters were more pronounced in xygotic than in somatic seedlings. Highest dehydration resistance was in zygotic hypocotyls. The characterization of the water relations of tissue cultures should allow the development of more consistent and reliable desiccation protocols to induce maturation of embryos and produce synchronously germinating seed.Cultured cells are usually characterized by their morphological, ultrastructural, and biochemical traits. Generally, their physiological characteristics, in particular their water relations, receive much less attention (29) in spite of the obvious influence that the culture media must have on tissue water potential.Cultured cells are typically grown in a medium with a low *,, resulting from high concentrations of salts, organic nitrogen sources, and sugars. These potentials, which are lower than those encountered by roots in soil, may be critical in determining cell growth and differentiation. To date, few l Abbreviations: T,, osmotic potential; c, bulk elastic modules; A, apoplastic water content; I, water potential; RWC, relative water content.

Embryogeny of gymnosperms: advances in synthetic seed technology of conifers

“…Somatic embryos have subsequently survived rapid air-drying, and dried somatic embryos have survived frozen storage for over 1 year at -20°C in the absence of cryoprotectants (Attree & Fowke unpubl.). Livingston et al (1992) argued that somatic embryos subjected to a RH of 81% (and therefore a water potential of -28MPa) would be totally desiccated and no longer viable once full vapour equilibrium was reached; however, seeds naturally dry under more rigorous RH environm~nts, and once dried their water potential may exceed -100 MPa due to the high matric component of seeds (Bewley & Black 1985).…”

The measurement of water relations of plant cell culture. I. Water release in response to centrifuge‐induced water potentials

“…Preparation of cells was similar to that described for PEG-eqiiilibrated cells prior to the addition of PEG. Thereafter, cells were equilibrated over distilled water at 4°C following the method of Livingston et al (1992). After 48 h of equilibration, cells were removed, weighed and dried at 70"C for 48 h. Cells equihbrated to 100% relative humidity after removal of extracellular water were considered to have an RWC of 1 and a mass of M^.…”

“…The RWC of cells was determined by first centrifuging cells at high accelerations (> 19 300 m s'") to remove extracellular water and then equilibrating the cells at a relative humidity of 100% as described by Livingston et al, (1992), The RWC of these cells was assumed to be 1,0 and other water contents were normalized to this value. At accelerations below 19 300 m s"', the slope of RWC vs acceleration decreased with increasing acceleration (Fig, 3A), RWC was well described in the region from 1 206 m s~-to 19 300 m s"' by a hyperbolic function (r^ > 0,995 for 8 data sets; see Discussion), However, at accelerations > 19 300 m %', the relationship between RWC and acceleration was Hnear for all treatments (r^ > 0,99 for 8 data sets) regardless of the pressure applied by the plunger (see 'Added mass' .…”

“…Introduction ttibuted 60% of the water content of celt cultures of Nic-Plant cell suspension cultures are used as model systems otiana tabacum. La:-ge volumes of interstitial water do to study cell behavior (Chen and Gusta 1983, Dracup et not occur in typical terresttial plants as tension wili real, 1986, Livingston et al 1992, Reaney and Gusta 1987, move any bulk water fi-otn the ioterstices. lit terrestrial Tanino et al 1990), Plant culture, especially cell suspen-plants interstitial water content is usually miniscule (alsion cultures, hold large amounts of interstitial water by though obser\'able, e.g, Pearce and Beckett 1985) atid capillary action of cells and cell clusters.…”

A New Pressure Probe Method to Determine the Average Volumetric Elastic Modulus of Cells in Plant Tissue

“…Nonideality of the cell sap and negative cell pressures at low water contents could also lead to errors in the determination of eStat (P), although these errors are probably small (Tyree, 1981). Potentially, additional errors could arise from changes in cell solute content resulting from respiration and/or hydrolysis of starch (Livingston et al, 1992). Turner (1988) and Murphy and Smith (1994) reviewed and discussed some other sources of error in the determination of balance pressures and turgor pressures with the pressure chamber.…”