Arie Altman

Gradual Soil Water Depletion Results in Reversible Changes of Gene Expression, Protein Profiles, Ecophysiology, and Growth Performance in Populus euphratica , a Poplar Growing in Arid Regions

The responses of Populus euphratica Oliv. plants to soil water deficit were assessed by analyzing gene expression, protein profiles, and several plant performance criteria to understand the acclimation of plants to soil water deficit. Young, vegetatively propagated plants originating from an arid, saline field site were submitted to a gradually increasing water deficit for 4 weeks in a greenhouse and were allowed to recover for 10 d after full reirrigation. Time-dependent changes and intensity of the perturbations induced in shoot and root growth, xylem anatomy, gas exchange, and water status were recorded. The expression profiles of approximately 6,340 genes and of proteins and metabolites (pigments, soluble carbohydrates, and oxidative compounds) were also recorded in mature leaves and in roots (gene expression only) at four stress levels and after recovery. Drought successively induced shoot growth cessation, stomatal closure, moderate increases in oxidative stress-related compounds, loss of CO2 assimilation, and root growth reduction. These effects were almost fully reversible, indicating that acclimation was dominant over injury. The physiological responses were paralleled by fully reversible transcriptional changes, including only 1.5% of the genes on the array. Protein profiles displayed greater changes than transcript levels. Among the identified proteins for which expressed sequence tags were present on the array, no correlation was found between transcript and protein abundance. Acclimation to water deficit involves the regulation of different networks of genes in roots and shoots. Such diverse requirements for protecting and maintaining the function of different plant organs may render plant engineering or breeding toward improved drought tolerance more complex than previously anticipated.

Gene expression and metabolite profiling of Populus euphratica growing in the Negev desert

BackgroundPlants growing in their natural habitat represent a valuable resource for elucidating mechanisms of acclimation to environmental constraints. Populus euphratica is a salt-tolerant tree species growing in saline semi-arid areas. To identify genes involved in abiotic stress responses under natural conditions we constructed several normalized and subtracted cDNA libraries from control, stress-exposed and desert-grown P. euphratica trees. In addition, we identified several metabolites in desert-grown P. euphratica trees.ResultsAbout 14,000 expressed sequence tag (EST) sequences were obtained with a good representation of genes putatively involved in resistance and tolerance to salt and other abiotic stresses. A P. euphratica DNA microarray with a uni-gene set of ESTs representing approximately 6,340 different genes was constructed. The microarray was used to study gene expression in adult P. euphratica trees growing in the desert canyon of Ein Avdat in Israel. In parallel, 22 selected metabolites were profiled in the same trees.ConclusionOf the obtained ESTs, 98% were found in the sequenced P. trichocarpa genome and 74% in other Populus EST collections. This implies that the P. euphratica genome does not contain different genes per se, but that regulation of gene expression might be different and that P. euphratica expresses a different set of genes that contribute to adaptation to saline growth conditions. Also, all of the five measured amino acids show increased levels in trees growing in the more saline soil.

Plant Biotechnology and In Vitro Biology in the 21st Century

During rooting of apple microcuttings, we applied 24h pulses with ACC (l-aminocyclopropane-I-carboxylic acid, an ethylene precursor) or STS (silverthiosulfate, an inhibitor of ethylene action). The timing of the pulse and the auxin concentration in the medium determined the effect (promotive, inhibitory, or no effect). Another major factor was submergence of the basal 4 mm of the stem in the medium: the results indicated that this led to entrapment and accumulation of ethylene in the basal part of the stem (the portion that produces the roots) at high auxin concentration. In stem-segments or slices that are both cultured on top of the medium, ethylene accumulation did not occur. The detrimental effect of auxin on shoot and roots was -at least partlydue to auxin-induced ethylene synthesis.

Forest-tree biotechnology: genetic transformation and its application to future forests

The wide use of forest-tree products and the progressive deterioration of natural forests mean that foresters can no longer rely on the exploitation of existing forests. Extensive accelerated-breeding programs are needed for reforestation and to improve existing forest-tree species. Plant genetic-transformation techniques and gene isolation and characterization are no longer serious problems; forest-tree species should be a major target for commercial genetic engineering and molecular breeding. We discuss some problems in forest-tree breeding and summarize developments in the transformation of tree species, including possible applications for improving and introducing novel traits into forest tree-species.

Genotypic difference in salinity and water stress tolerance of fresh market tomato cultivars

The physiological response and tolerance of four fresh-market, cultivated tomatoes (Lycopersicon esculentum cvs. ‘F121’, ‘F144’, Fireball and Patio) to water stress and salinity was determined. Under salinity, ion accumulation, osmotic potential and dry matter production were highly correlated. No such correlation was found under water stress. No correlation between plant tolerance and accumulation of proline could be determined.

Tree genetic engineering and applications to sustainable forestry and biomass production

Forest trees provide raw materials, help to maintain biodiversity and mitigate the effects of climate change. Certain tree species can also be used as feedstocks for bioenergy production. Achieving these goals may require the introduction or modified expression of genes to enhance biomass production in a sustainable and environmentally responsible manner. Tree genetic engineering has advanced to the point at which genes for desirable traits can now be introduced and expressed efficiently; examples include biotic and abiotic stress tolerance, improved wood properties, root formation and phytoremediation. Transgene confinement, including flowering control, may be needed to avoid ecological risks and satisfy regulatory requirements. This and stable expression are key issues that need to be resolved before transgenic trees can be used commercially.

Biology of root formation and development

Preface A. Altman, Y. Waisel. Diversity of Roots: The Place of Roots in Plant Development and the Diversity of Root Types P.W. Barlow, B. Palma. Induction of Roots and Their Development: Indissociable Chief Actors in the Inductive Phase of Adventitious Rooting T. Gaspar et al. Hormonal Control of Root Induction and Development: Increased Induction of Adventitious Rooting via Slow Release Auxins and Elicitors van der Krieken et al. Molecular Biology of Root Development: Auxin Induced Gene Expression During Rooting of Loblolly Pine Stem Cuttings B. Goldfarb et al. Ecological Aspects of Root Development: Shootborne Roots: An Adaptive Organ in Sand Dunes A. Danin. Applied Aspects of Root Development: Relations between Early Root Growth and Flower Yield of Clonal Rose Rootstocks D.P. de Vries, L.A.M. Dubois. Root Products: Insane Roots and Twisted Carrots: Physiology and Biochemistry of Root Specific Metabolites H.E. Flores. Models and Methods for Root Study: Morphological Structured Model for Hairy Root Culture I. Berzin et al. Concluding Remarks: A 1996 Overview of the Research Interests from the Jerusalem Symposium T. Gaspar. 71 additional articles. Index.

Photosynthetic response of Populus euphratica to salt stress

Abstract P. euphratica Olive and the hybrids (P. talassica Kom X (P. euphratica + Salix alba L)) seedlings were subjected to low (50 mM NaCl) and high salt (200 mM NaCl) treatments to determine their photosynthetic responses to salt stress. The photosynthetic pattern indicated that P. euphratica is a C3 plant with a high CO2 compensation point (150 μmol mol−1) and saturation point (900 μmol mol−1), but has some characteristics of C4 plants with a high light saturation point (2800 μmol m−2 s−1) in control conditions. CO2 compensation and saturation points increased with high salt treatment for both the hybrid and P. euphratica while light saturation point decreased with salt treatment. The net photosynthesis of P. euphratica with high salt treatment declined in the first 14 days and recovered to 70% that with control in day 21 when soil salt content was about 0.7% NaCl, while that of the hybrids did not recover when soil salt content was about 0.5% NaCl with hgih salt treatment. With increasing salt levels, Chlorophyll a contents and Chlorophyll a b ratio increased, while Chlorophyll b and carotenoid contents decreased by day 10, when photosynthesis was heavily depressed for both species. Fluorescence patterns confirmed that reduction of photosynthesis under high salt treatment was not due to damage of the photosynthetic apparatus, but more likely due to inhibition of the dark reaction.

Effect of NaCl on growth, photosynthesis, ion and water relations of four poplar genotypes

Abstract Cuttings of our poplar clones, Populus deltoides × P. nigra (Dode) Guinier cv. I-214 ( P . I-214), P. deltoides × P. nigra (Dode) Guinier f. robusta ( P . Robusta), P. berolinensis and P. simonii ×( P. pyramidalis × Salix matsudana ) cv. Popularis 35-44 ( P . Popularis) were treated with three salt levels (0, 0.5 or 1.0% w/v NaCl in sand culture for 21 days). Growth, photosynthesis, stomatal resistance, leaf water potential, and Na + and K + concentrations were all significantly affected by salinity. For all clones, leaf and height growth were significantly reduced after 3 and 5 days following exposure to salinity respectively. Physiological parameters (photosynthesis, stomatal resistance and pre-dawn leaf water potential) also showed rapid responses to salinity, but clonal differences were not significant. Growth, biomass partitioning and Na + and K + concentrations were also significantly affected by salinity. Reductions in leaf area growth were maintained throughout the duration of the experiment. Height and diameter growth were less sensitive but still showed significant differences between 0, and 0.5 and 1.0% NaCl. Proportionately less above ground biomass was produced compared with below ground (root) biomass. P . I-214 was more vigorous than other clones and had significantly lower leaf and root Na + concentrations than P . Popularis. Young leaf tissue had higher Na + and K + concentrations and Na:K ratios than older leaf or root tissue.

Transgenic Populus tremula: a step-by-step protocol for its Agrobacterium-mediated transformation

In recent years, Populus species have acquired an important place in basic and applied research of woody plants. The practical role of Populus species in world forestry and their importance to research as a woody-plant model have led to increasing interest in tissue-culture and molecular techniques, as well as the development of transformation procedures for this genus. A simple technical procedure is described here step-by-step, for the first time, as a routine method for transforming Populus tremula using a disarmed Agrobacterium tumefaciens hypervirulent strain. The procedure begins with the inoculation of stem explants with bacterial suspension, followed by a short period of co-cultivation on a highly regenerative medium. Transformed shoots are selected on regeneration medium containing antibiotics and the presence of the inserted target genes is checked using a rapid and efficient PCR test. Selected shoots are transferred to a rooting medium, under the same selection pressure, and propagated via stem cuttings. Selected plants can be hardened and transferred to the green-house within 4 months of inoculation. The method has proven efficient for several gene constructs, selection on Kan or Hyg, and three different Agrobacterium strains.