l h e radial distribution pattern of indole-3-acetic acid (IAA) was determined across the developing tissues of the cambial region in the stem of hybrid aspen (Populus tremula L. x Populus tremuloides Michx). IAA content was measured in consecutive tangential cryosections using a microscale mas spectrometry technique. Analysis was performed with wild-type and transgenic trees with an ectopic expression of Agrobacterium fumefaciens IAA-biosynthetic genes.In all tested trees IAA was distributed as a steep concentration gradient across the developing tissues of the cambial region. l h e peak level of IAA was within the cambial zone, where cell division takes place. Low levels were reached in the region where secondary wall formation was initiated. l h e transgenic trees displayed a lower peak level and a wider radial gradient of IAA compared with the wild type. This alteration was related to a lower rate of cambial cell division and a longer duration of xylem cell expansion in the transgenic trees, resulting in a decreased xylem production and a larger fiber lumen area. The results indicate that IAA has a role in regulating not only the rate of physiological processes such as cell division, but also the duration of developmental processes such as xylem fiber expansion, suggesting that IAA functions as a morphogen, conveying positional information during xylem development.The vascular cambium is responsible for xylem formation, which constitutes the bulk of secondary growth. Development of xylem elements involves severa1 consecutive phases, including division in the cambial zone, cell expansion, secondary wall formation, and autolysis of xylem elements destined for water transport and mechanical support (Larson, 1994). This development is coordinated in space, resulting in a radial pattern of discrete zones where the different developmental phases take place. The rate of xylem cell production, i.e. the number of divisions in the cambial zone per unit of time, is determined by two components: (a) the rate of cell cycling of the individual cambial zone cells and @) the number of dividing cells, which is determined by the duration of meristematic capacity for each xylem mother cell. Similarly, the rate and duration of expansion and secondary wall formation can modulate final cell size and wall thickness of the xylem elements. These aspects are important in forest trees, where they determine critica1 wood properties such as annual ring width and the seasonal pattem of earlywoodllatewood formation

No abstract

No abstract

a b s t r a c tGenetic analysis was carried out in order to provide insights into differentiation among populations of two interfertile oak species, Quercus petraea and Quercus robur. Gene flow between the two species, local adaptation and speciation processes in general, may leave differential molecular signatures across the genome. Three interspecific pairs of natural populations from three ecologically different regions, one in central Europe (SW Germany) and two in the Balkan Peninsula (Greece and Bulgaria) were sampled. Grouping of highly informative SSR loci was made according to the component of variation they express-interspecific or provenance specific. 'Species' and 'provenance discriminant' loci were characterized based on F ST s. Locus specific F ST s were tested for deviation from the neutral expectation both within and between species. Data were then treated separately in a Bayesian analysis of genetic structure. By using three 'species discriminant' loci, high membership probability to inferred species groups was achieved. On the other hand, analysis of genetic structure based on five 'provenance discriminant' loci was correlated with geographic region and revealed shared genetic variation between neighbouring Q. petraea and Q. robur. Small sets of highly variable nuclear SSRs were sufficient to discriminate, either between species or between provenances. Thus, an effective tool is provided for molecular identification of both species and provenances. Furthermore, data suggest that a combination of gene flow and natural selection forms these diversity patterns. 'Species discriminant' loci might represent genome regions affected by directional selection, which maintains species identity. 'Provenance specific' loci might represent genome regions with high interspecific gene flow and common adaptive patterns to local environmental factors.

No abstract