Summary• We examined the relationships among productivity, water use efficiency ( WUE) and drought tolerance in 29 genotypes of Populus × euramericana ( Populus deltoides × Populus nigra ), and investigated whether some leaf traits could be used as predictors for productivity, WUE and drought tolerance.• At Orléans, France, drought was induced on one field plot by withholding water, while a second plot remained irrigated and was used as a control. Recorded variables included stem traits (e.g. biomass) and leaf structural (e.g. leaf area) and functional traits [e.g. intrinsic water use efficiency ( W i ) and carbon isotope discrimination ( ∆ )].• Productivity and ∆ displayed large genotypic variability and were not correlated. ∆ scaled negatively with W i and positively with stomatal conductance under moderate drought, suggesting that the diversity for ∆ was mainly driven by stomatal conductance.• Most of the productive genotypes displayed a low level of drought tolerance (i.e. a large reduction of biomass), while the less productive genotypes presented a large range of drought tolerance. The ability to increase WUE in response to water deficit was necessary but not sufficient to explain the genotypic diversity of drought tolerance.

The specific binding of N-acetylneuraminic acid to wheat-germ agglutinin is based on configurational similarities between N-acetylneuraminic acid and N-acetylglucosamine. The N-acetamido group and an adjacent hydroxyl group, both in an equatorial position are shown to be the main determinants. The N-acetylneuraminic acid -wheat-germ agglutinin interaction is increased by the removal of the last two carbons Cs and C9. The interaction between wheat-germ agglutinin and glycoconjugates containing N-acetylneuraminic acid is shown to be dependent on a charge effect and on an avidity effect. Succinylated wheat-germ agglutinin which is negatively charged at physiological pH, in contrast with wheat-germ agglutinin which is positively charged, does not bind cell surface glycoconjugates containing N-acetylneuraminic acid but does bind cell surface glycoconjugates containing N-acetylglucosamine. The use of wheat-germ agglutinin and of SUCcinylated wheat-germ agglutinin leads to the determination of the number of cell surface receptors containing N-acetylneuramipic acid Wheat-germ agglutinin is a plant lectin which agglutinates various types of animal cells, of malignant cells and of protease-treated cells [l-31. The agglutination of cells is inhibited by N-acetylglucosamine and its /3l-4 oligomers [2,4]. In addition, wheat-germ agglutinin has been claimed to bind N-acetylneuraminic acid on the basis of equilibrium dialysis [5] and nuclear magnetic resonance [6] studies. Furthermore, the agglutination of neuraminidasetreated cells usually requires a higher concentration of wheat-germ agglutinin than required for untreated cells [2,7] although in some instances the neuraminidase treatment does not lower the cell agglutinability by the lectin [8]. Immobilized wheat germ agglutinin binds membrane sialoglycoproteins [9,10] but fails to bind the related sialoglycopeptides [9]. In the present paper, we wish to report several data showing that N-acetylneuraminic acid, gangliosides and glycoAbbreviations. Glc, glucose; Gal, galactose, NeuAc, N-acetylneuraminic acid ; NeuGc, N-glycoloylneuraminic acid ; Cer, ceramide; GM3, NeuAca2+3Gal~l+4GlcCer; GMz, GalNAc(3tZa-NeuAc)~l+4Gal~1+4GlcCer; GMI, Ga1/31+ 3GalNAc(3+2a-N e u A c )~l + 4 G a l~I -4GlcCer; GDI,, NeuAca2-3GalP1+3-GalNAc(3t2ctNeuAc)fll+4Gal~1-r4GlcCer; GDlb, Galpl -r 3-GalNAc(3+2aNeuAcXt2aNeuAc)~l+4Gal~I + 4GlcCer; GTl, NeuAcn2+ 3Gal/1'1+ 3GalNAc(3 + 2aNeuAcX t 2aNeuAc)flI -j 4-Gal81 +4GlcCer, Nph, p-nitrophenyl-.

Leaf or stem explants of a hybrid poplar clone (Populus tremula X Populus alba), sensitive to Agrobacterium tumefaciens, were co-cultivated either by an octopine or a nopaline disarmed A. tumefaciens modified strain. Transformed poplar shoots were readily regenerated from explants. The protocol was improved using the nopaline disarmed strain C58/pMP90 with the binary vector pBI121. This protocol was then used to test three other vectors. The first one, possessing a nptII gene fused to the CaMV 19S promoter, permitted regeneration of transformed shoots in presence of 50 to 100 mg/l kanamycin. The two other vectors carried an additional nptII gene under the control of the CaMV 35S or CaMV 35S promoter with a double enhancer sequence (CaMV 70). CaMV 70 promoter provided consistently higher level of gene expression than the other promoters in both callus and leaf tissues.

Summary• Here we tested whether some leaf traits could be used as predictors for productivity in a range of Populus deltoides × P. nigra clones. These traits were assessed in 3-yr-old rooted cuttings from 29 clones growing in an open field trial, in a five randomized complete block design, under optimal irrigation.• Variables were assigned to four groups describing productivity (above-ground biomass, total leaf area), leaf growth (total number of leaves increment rate), leaf structure (area of the largest leaf, specific leaf area, carbon and nitrogen contents), and carbon isotope discrimination in the leaves ( ∆ ).• High-yielding clones displayed larger total leaf area and individual leaf area, while no correlation could be detected between productivity and either leaf structure or ∆ . By contrast, ∆ was negatively correlated with number of leaves increment rate and leaf N content.• Our study shows that there is a potential to improve water-use efficiency in poplar without necessarily reducing the overall productivity. IntroductionPoplars are among the fastest growing trees under temperate latitudes. Their large productivity is associated with large water requirements and, as a consequence, a tight dependency of productivity upon water availability (Ceulemans et al ., 1988;Tschaplinski & Blake, 1989;Barigah et al ., 1994;Tschaplinski et al ., 1994;Zsuffa et al ., 1996). To sustain the extension of poplar cultivation from flood plains and bottomlands towards uplands where soil water availability is subjected to seasonal changes, more water-use efficient hybrids are required. One functional trait that could be of interest as an index for improved or maintained productivity under reduced water availability is the intrinsic water-use efficiency (Wi), i.e. the ratio between net CO 2 assimilation and stomatal conductance. Wi can be indirectly estimated at leaf level, via the carbon isotope discrimination ( ∆ ), assuming the occurrence of a linear and negative correlation between ∆ and intrinsic water-use efficiency shown both for cereals (Farquhar & Richards, 1984;Farquhar et al ., 1989) and for trees (Ponton et al ., 2001). This trait is easily measurable, highly heritable and has been used as a selection criterion in crop breeding Rebetzke et al ., 2002). Among tree species, it also displays a high heritability (Brendel et al ., 2002) and a large variability at interspecific level (Guehl et al ., 1998;Bonal et al ., 2000;Ponton et al ., 2001) and provenance level (Lauteri et al ., 1997;Roupsard et al ., 1998) as well as at family level (Brendel et al ., 2002). Such a clonal diversity of ∆ has already been shown to occur among poplars (Zhang et al ., 2004;Marron et al ., 2005). The detection of clones combining satisfactory productivity and high

Responses to successive drought and re-watering cycles (1-3 cycles) were compared in greenhouse-grown cuttings of Populus x canadensis (Moench) clones, 'Luisa_ Avanzo' and 'Dorskamp.' Total leaf number increment rate, duration of leaf expansion, total and individual leaf area expansion rates and stomatal conductance were recorded periodically during the experiment. Soil water content (SWC) and predawn leaf water potential (Psi(WP)) were measured four times during each drought cycle. In parallel, relative leaf water content (RWC) and specific leaf area (SLA) were estimated on leaves collected from the top to bottom of each cutting. Under well-watered conditions, 'Luisa_Avanzo' and 'Dorskamp' differed in their patterns of leaf area expansion. Although duration of leaf expansion was similar between clones, 'Luisa_ Avanzo' exhibited higher total leaf number increment rates and individual leaf area increases than 'Dorskamp.' As a result, 'Luisa_Avanzo' cuttings reached larger individual and total leaf areas than 'Dorskamp.' 'Dorskamp' leaves had lower SLA than 'Luisa_Avanzo' leaves. In response to successive drought cycles, both clones underwent decreases in total leaf number increment rates and in total leaf area expansion rates, but both whole-plant and individual leaf areas were drastically reduced only in 'Luisa_Avanzo.' 'Dorskamp' maintained a constant leaf area as a result of an increase in the duration of leaf expansion during drought and a significant stimulation of individual leaf area expansion rate and total leaf number increment rate in response to re-watering. Drought caused a greater decrease in SLA in 'Luisa_Avanzo' than in 'Dorskamp.' Expanded leaves of 'Dorskamp' were constitutively dense or thick, or both, whereas leaves of 'Luisa_Avanzo' became dense or thick, or both, only in response to drought. In both clones, re-watering caused partial recovery of SLA to control values. Our data confirm previous field and greenhouse observations that 'Dorskamp' is more tolerant to successive drought and re-watering cycles than 'Luisa_Avanzo.' We conclude that this difference is mainly attributable to the plasticity of 'Dorskamp' after re-watering, rather than to clonal differences in drought responses.

To test if some leaf parameters are predictors of productivity in a range of Populus deltoides (Bartr.) Marsh. x P. nigra L. clones, we assessed leaf traits and productivity in 2-month-old rooted cuttings from 31 clones growing in 4-l pots in a greenhouse, under conditions of controlled temperature and optimal irrigation. We evaluated four groups of variables describing (1) productivity (total biomass), (2) leaf growth (total leaf number increment and total leaf area increment rate), (3) leaf structure (specific leaf area and nitrogen and carbon contents) and (4) carbon isotope discrimination (delta), which is negatively correlated with time-integrated water-use efficiency. High-yielding clones did not necessarily display high leaf growth rates, but they displayed a larger total leaf area, lower specific leaf area and lower leaf nitrogen concentration than clones with low productivity. Total leaf area was mainly controlled by maximal individual leaf area and total leaf area increment rate (r = 0.51 and 0.56, respectively). Carbon isotope discrimination did not correlate with total biomass, but it was associated with total number of leaves and total leaf area increment rate (r = 0.39 and 0.45, respectively). Therefore, leaf area and specific leaf area were better indicators of productivity than leaf growth traits. The observed independence of delta from biomass production provides opportunities for selecting poplar clones combining high productivity and high water-use efficiency.

We compared responses to drought and re-watering of greenhouse-grown cuttings of Populus x euramericana (Dode) Guinier clones, Luisa Avanzo and Dorskamp. Total leaf area, leaf number, leaf area increment and stomatal conductance were evaluated periodically during a 29-day drought period and for 16 days after re-watering. Soil water content and predawn leaf water potential (Psi(wp)) were measured on Days 29 and 45. On the same days, relative water content (RWC), specific leaf area (SLA), nitrogen, chlorophyll, soluble sugars, total phenols, flavanols and antioxidant activity were determined for leaves taken from the bottom to the top of each cutting. Leaves of Luisa Avanzo cuttings grew more rapidly than leaves of Dorskamp and exhibited higher SLA, but lower concentrations of nitrogen, chlorophyll and soluble sugars and lower antioxidant activity per unit area. On Day 29, after withholding water, both clones had closed their stomata, reduced rates of leaf growth, and lower Psi(wp) and RWC; however, the clones differed in their responses to soil water depletion. Compared to Dorskamp, Luisa Avanzo closed its stomata earlier and maintained higher Psi(wp), but lower RWC and leaf sugar concentrations. Antioxidant activity of leaf methanolic extracts decreased in response to water stress only in Luisa Avanzo. Leaf physiology and its modulation by water stress were age dependent in Luisa Avanzo.

No abstract