A previous analysis showed that Gammaproteobacteria could be the sole recoverable bacteria from surface-sterilized nodules of three wild species of Hedysarum. In this study we extended the analysis to eight Mediterranean native, uninoculated legumes never previously investigated regarding their root-nodule microsymbionts. The structural organization of the nodules was studied by light and electron microscopy, and their bacterial occupants were assessed by combined cultural and molecular approaches. On examination of 100 field-collected nodules, culturable isolates of rhizobia were hardly ever found, whereas over 24 other bacterial taxa were isolated from nodules. None of these nonrhizobial isolates could nodulate the original host when reinoculated in gnotobiotic culture. Despite the inability to culture rhizobial endosymbionts from within the nodules using standard culture media, a direct 16S rRNA gene PCR analysis revealed that most of these nodules contained rhizobia as the predominant population. The presence of nodular endophytes colocalized with rhizobia was verified by immunofluorescence microscopy of nodule sections using an Enterobacter-specific antibody. Hypotheses to explain the nonculturability of rhizobia are presented, and pertinent literature on legume endophytes is discussed.

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Two-year-old Fagus sylvatica L. seedlings were subjected to natural winter chilling or were overwintered in a heated greenhouse. Plants were then grown in controlled environment chambers with photoperiods of 9 or 13 h. Renewal of bud growth was found to be mainly determined by winter chilling. There was a slight interaction between chilling and photoperiod. Sprouting of apical buds took two to three times as long in unchilled plants as in chilled plants. Shoot elongation was influenced by chilling and was also greater in the 13-h photoperiod than in the 9-h photoperiod, but this may have been due at least in part to the higher irradiance. Chilling resulted in rapid dormancy loss and changed the growth pattern from basitonal to acrotonal.

-In this study, pressure/volume curves were performed on 24-week-old seedlings of eight European provenances of Pinus halepensis Mill. subsp. halepensis after one week of water stress (-0.033, -0.4, -0.8, -1.2, -1.6 MPa). P. halepensis showed osmotic adjustments as a response to water stress, although the response varied between the provenances. Apoplastic water remained relatively constant. The elasticity module did not differ significantly. Water deficit at incipient plasmolysis and water content decreased as the stress increased. Water potential was markedly negative, even in seedlings not subjected to stress. The provenances from less xeric sites behaved similarly to species from non-arid sites, while those from more xeric sites displayed the strategy typical of drought-tolerant species. The impact on all provenances of one week of low-intensity water stress (-0.4 MPa) was slight. As the stress increased, the response varied between the provenances: N-Eubea > Kassandra > Litorale tarantino ≅ Guardiola > Otricoli ≅ E-Bouches du Rhône ≥ Hérault ≅ N-Vaucluse (in decreasing order).Aleppo pine / drought resistance / geographic variation / pressure-volume curves / provenances Résumé -Résistance au stress hydrique des plantules appartenant à huit provenances européennes de Pinus halepensis Mill. Sur des plantules âgées de 24 semaines, appartenant à 8 provenances de Pinus halepensis (Mill.) subsp. halepensis, des courbes pression-volume ont été effectuées après une semaine de stress hydrique (-0,033, -0,4, -0,8, -1,2, -1,6 MPa). P. halepensis a montré des ajustements osmotiques en réponse au stress hydrique, bien que de façon différenciée parmi les provenances. L'eau apoplastique a été relativement constante. Le module d'élasticité n'a pas différé significativement. Le déficit hydrique en début de plasmolyse et la teneur en eau ont baissé avec l'augmentation du stress. Le potentiel hydrique a été très négatif, même en absence de stress. Les semences provenant des milieux les moins secs se sont comporté de façon identique aux espèces des milieux non arides, tandis que les provenances originaires des milieux les plus secs ont révélé la stratégie caractéristique des espèces tolérant la sécheresse. En conclusion les provenances ont été insuffisamment influencées par une semaine de stress hydrique de faible intensité. En présence d'un accroissement du stress, les réponses ont permis de différencier les provenances : N-Eubea > Kassandra > Litorale tarantino ≅ Guardiola > Otricoli ≅ E-Bouches du Rhône ≥ Hérault ≅ N-Vaucluse (en ordre décroissant).courbes pression-volume / Pin d'Alep / provenances / résistance à la sécheresse / variation géographique Ann. For. Sci. 58 (2001) [663][664][665][666][667][668][669][670][671][672] 663

Summary -Italian populations of beech, originating from zones of similar altitudes but different latitudes (38°16'-43°49'N), were studied. The seedlings, 1 and 2 years old, were grown in Florence (43°45') under natural conditions or in climate-controlled chambers with short (SD) or long day (LD) after having been exposed, or not, to winter chilling (CH and NCH, respectively