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PubMed2005

Species distinction in Irish populations of Quercus petraea and Q. robur: morphological versus molecular analyses.

BACKGROUND AND AIMS: Populations of oak (Quercus petraea and Q. robur) were investigated using morphological and molecular (AFLP) analyses to assess species distinction. The study aimed to describe species distinction in Irish oak populations and to situate this in a European context. METHODS: Populations were sampled from across the range of the island of Ireland. Leaf morphological characters were analysed through clustering and ordination methods. Putative neutral molecular markers (AFLPs) were used to analyse the molecular variation. Cluster and ordination analyses were also performed on the AFLP markers in addition to calculations of genetic diversity and F-statisitcs. KEY RESULTS: A notable divergence was uncovered between the morphological and molecular analyses. The morphological analysis clearly differentiated individuals into their respective species, whereas the molecular analysis did not. Twenty species-specific AFLP markers were observed from 123 plants in 24 populations but none of these was species-diagnostic. Principal Coordinate Analysis of the AFLP data revealed a clustering, across the first two axes, of individuals according to population rather than according to species. High F(ST) values calculated from AFLP markers also indicated population differentiation (F(ST) = 0.271). Species differentiation accounted for only 13 % of the variation in diversity compared with population differentiation, which accounted for 27 %. CONCLUSIONS: The results show that neutral molecular variation is partitioned more strongly between populations than between species. Although this could indicate that the populations of Q. petraea and Q. robur studied may not be distinct species at a molecular level, it is proposed that the difficulty in distinguishing the species in Irish oak populations using AFLP markers is due to population differentiation masking species differences. This could result from non-random mating in small, fragmented woodland populations. Hybridization and introgression between the species could also have a significant role.

Cluster Analysis↗
PubMed2005

Mating patterns of a subdivided population of the andean oak (Quercus humboldtii Bonpl., Fagaceae).

Mating patterns play a critical role in the maintenance of genetic variation. We analyzed the mating system in a recently fragmented population of the Andean oak (Quercus humboldtii) using four microsatellite loci. Five fragments in northeastern Colombia, South America, were selected consisting of 30.4 trees on average. We sampled about 30 seeds from three target trees in each fragment and genotyped them with four microsatellite loci with a total of 40 alleles across loci. Progenies were analyzed under the mixed mating system model (MLTR program) and the TwoGener pollen pool structure analyses. The number of unshared pollen donors per family (Nu) was estimated using gametotypic counts with the program HAPLOTYPES. Low selfing (3%) is occurring at the population and fragment level. Biparental inbreeding is present (4.9%), but reduced, in the largest fragment. The average pollen neighborhood size (Nep = 5.1 to 6.1) appears comparable to other oak species in sparse landscapes. In contrast, Nu consists of 2 to 4 main donors, although up to 12 are possible, with the mode positively correlated with fragment size. The Andean oak appears to be a resilient species capable of tolerating population subdivision, provided landscapes include large fragments.

Colombia↗
PubMed2006

Source populations of Quercus glauca in the last glacial age in Taiwan revealed by nuclear microsatellite markers.

In this work, we attempted to study genetic differentiation between populations of Quercus glauca in Taiwan using nuclear microsatellite markers to infer the potential refugium in the last glaciation stage. Four microsatellite loci for 20 individuals each in 10 populations of Taiwan were analyzed. We found that Q. glauca has relatively high within-population diversity (H(E) = 0.741) and low population differentiation (F(ST) = 0.042) but shows isolation by distance. The most divergent populations, according to the average F(ST) for individual populations in comparison with every other population, were found in populations Cy, Sa, and Hy in southern Taiwan and Pa in north-central Taiwan. Moreover, populations Cy, Sa, and Pa were recognized as being the source populations for gene recolonization after the last glaciation stage. In addition, the three sites of Wu, Ym, and Cy exhibited the highest gene diversities that coincided with populations with the highest chloroplast DNA variations. This may have resulted from an admixture of colonization routes. In conclusion, observations of the most divergent populations and source populations suggest that southern and probably north-central Taiwan may have potentially been refugia for Q. glauca in the last glaciation. This agrees with the possible refugium in southern Taiwan revealed by a previous study using chloroplast DNA markers.

Base Sequence↗
PubMed2006

Mating patterns of black oak Quercus velutina (Fagaceae) in a Missouri oak-hickory forest.

Wind-pollinated forest trees usually have high outcrossing rates, but allogamy does not necessarily translate into high pollen movement. The goal of this study was to determine the outcrossing rates, pollen pool genetic structure, and the size of the effective pollination neighborhood in a population of black oak, Quercus velutina, in a Missouri oak-hickory forest. Based on 6 allozyme loci, 12 maternal trees, and 439 progenies sampled along a transect of 1300 m, we found complete outcrossing (t(m) = 1.000, P < 0.001) and small amounts of biparental inbreeding. Using a TwoGener analysis of the pollen gene pool, we found significant structure across maternal plants (Phi(FT) = 0.078, P < 0.001), which when corrected for adult inbreeding translates into Phi(FT) = 0.066 that corresponds to an effective number of pollen donors of 7.5 individuals. Assuming a bivariate normal distribution and an adult density of 16.25 trees ha(-1), we estimated that the effective pollination neighborhood area had a radius of 41.9 m. Even assuming that our estimates may be conservative, these findings join a growing body of evidence that suggest that the local neighborhood of wind-pollinated forest tree populations may be relatively small creating opportunities for local selection and genetic drift.

Crosses, Genetic↗
PubMed2006

The bulk elastic modulus and the reversible properties of cell walls in developing Quercus leaves.

We examined the relationship between the bulk elastic modulus (epsilon) of an individual leaf obtained by the pressure-volume (P-V) technique and the mechanical properties of cell walls in the leaf. The plants used were Quercus glauca and Q. serrata, an evergreen and a deciduous broad-leaved tree species, respectively. We compared epsilon and Young's modulus of leaf specimens determined by the stretch technique at various stages of their leaf development. The results showed that epsilon increased from approximately 5 to 20 MPa during leaf development, although other potential determinants of epsilon such as the apoplastic water content in the leaf and the diameter of a palisade tissue cells remained almost constant. epsilon in these two species was similar at every developmental stages, although the apparent mechanical strength of the leaf lamina and thickness of mesophyll cell walls were greater in Q. glauca. There were significant linear relationships between Young's modulus and epsilon (P < 0.01; R (2) = 0.78 and 0.84 in Q. glauca and Q. serrata, respectively) with small y-intercepts. From these results, we conclude that epsilon is closely related to the reversible properties of the cell walls. From the estimation of epsilon based on a physical model, we suggest that the effective thickness of cell walls responsible for epsilon is smaller than the observed wall thickness.

Biomechanical Phenomena↗
PubMed2001

Photosynthetic light response of flooded cherrybark oak (Quercus pagoda) seedlings grown in two light regimes.

Two-year-old cherrybark oak (Quercus pagoda Raf.) seedlings raised in full or partial (27%) sunlight were flooded for 30 days to study the effects of light availability and root inundation on photosynthetic light response. Compared with seedlings receiving full sunlight, seedlings receiving partial sunlight developed leaves with 90% greater blade area, 26% less mass per unit volume, and 35% lower nitrogen (N) concentration per unit area, leading to a 15% reduction in leaf photosynthetic capacity when carbon exchange rates were based on blade area. However, when carbon exchange rates were based on leaf mass, leaves acclimated to partial sunlight exhibited a 15% greater photosynthetic capacity realized primarily through an increased initial slope of the photosynthetic light response (A/PPFD) curve and increased net photosynthesis at leaf saturation (Amax). Short-term flooding increased leaf mass per unit area more than 19%, reduced foliar N concentrations per unit dry mass by 19%, and initiated reductions in Amax and apparent quantum yield (phi) of seedlings in both light regimes. Greatest impairment of Amax (56% area basis, 65% mass basis) and phi (40%) were observed in leaves receiving full sunlight, and the declines were concomitant with a 35% decrease in chlorophyll concentration. Flooding also depressed instantaneous photosynthetic N-use efficiency (PPNUE) such that Amax decreased 54%, and the initial slope of PPNUE/PPFD curves decreased 33 and 50% for leaves acclimated to partial and full sunlight, respectively. The A/PPFD patterns indicated that the magnitude of flood-induced inhibition of the photosynthetic mechanism of cherrybark oak seedlings is determined partly by the light environment.

Light↗
PubMed2001

Canopy structure and light interception in Quercus petraea seedlings in relation to light regime and plant density.

Foliage structure was measured on 1- and 2-year-old Quercus petraea (Matt.) Liebl. seedlings grown in 100 or 18% sunlight at a planting density of 2.8 or 25 plants per m(2). A three-dimensional digitizing device was used to acquire the spatial position and orientation of all leaves within the seedlings and of all seedlings within the plot. The data were used to obtain (1) quantitative information on canopy structure, including leaf area index (LAI), seedling leaf area, number of leaves, leaf area density and leaf orientation; and (2) structural information on foliage arrangement from virtual images to estimate light interception by individual seedlings (STAR) and light partitioning among seedlings. During the second year, shading significantly reduced total leaf area and number of leaves but increased individual leaf area. The STAR was greater for seedlings in shade than in full sunlight because of the more horizontal orientation of leaves. Leaf area density was unaffected by the full sun treatments, and changes in leaf area dispersion had no effect on light-interception efficiency. No plant density effect was observed during the first year. During the second year, only the high plant density treatment induced mutual shading between seedlings, resulting in greater competition for light among seedlings in the full sun treatment than in the shade treatment. The small treatment-induced changes in light interception indicate that Q. petraea has low morphological plasticity of foliage structure compared with other species.

Light↗
PubMed2001

Characterization of the responses of cork oak (Quercus suber) to iron deficiency.

We studied responses of cork oak (Quercus suber L.) to iron (Fe) deficiency by comparing seedlings grown hydroponically in nutrient solution with and without Fe. Seedlings grown without Fe developed some responses typical of the Strategy I group of Fe-efficient plants, including two- and fourfold increases in plasma membrane ferric chelate reductase activity of root tips after 2 and 4 weeks of culture in the absence of Fe, respectively. Moreover, seedlings grown hydroponically for 2 weeks without Fe caused marked decreases in the pH of the nutrient solution, indicating that root plasma membrane ATPase activity was induced by Fe deficiency. Iron deficiency also caused marked decreases in leaf chlorophyll and carotenoid concentrations, and chlorophyll concentrations were decreased more than carotenoid concentrations. Iron deficiency resulted in an 8% decrease in the dark-adapted efficiency of photosystem II and a 43% decrease in efficiency of photosystem II at steady-state photosynthesis. No major root morphological changes were observed in seedlings grown without Fe, although seedlings grown in Fe-deficient nutrient solution had light-colored roots in contrast to the dark brown color of control roots.

Iron Deficiencies↗
PubMed2001

Interactive effects of elevated CO2 concentration and nitrogen supply on partitioning of newly fixed 13C and 15N between shoot and roots of pedunculate oak seedlings (Quercus robur).

Pedunculate oak (Quercus robur L.) seedlings were grown for 3 or 4 months (second- and third-flush stages) in greenhouses at two atmospheric CO2 concentrations ([CO2]) (350 or 700 micromol mol(-1)) and two nitrogen fertilization regimes (6.1 or 0.61 mmol N l(-1) nutrient solution). Combined effects of [CO2] and nitrogen fertilization on partitioning of newly acquired carbon (C) and nitrogen (N) were assessed by dual 13C and 15N short-term labeling of seedlings at the second- or third-flush stage of development. In the low-N treatment, root growth, but not shoot growth, was stimulated by elevated [CO2], with the result that shoot/root biomass ratio declined. At the second-flush stage, overall seedling biomass growth was increased (13%) by elevated [CO2] regardless of N fertilization. At the third-flush stage, elevated [CO2] increased growth sharply (139%) in the high-N but not the low-N treatment. Root/shoot biomass ratios were threefold higher in the low-N treatment relative to the high-N treatment. At the second-flush stage, leaf area was 45-51% greater in the high-N treatment than in the low-N treatment. At the-third flush stage, there was a positive interaction between the effects of N fertilization and [CO2] on leaf area, which was 93% greater in the high-N/elevated [CO2] treatment than in the low-N/ambient [CO2] treatment. Specific leaf area was reduced (17-25%) by elevated [CO2], whereas C and N concentrations of seedlings increased significantly in response to either elevated [CO2] or high-N fertilization. At the third-flush stage, acquisition of C and N per unit dry mass of leaf and fine root was 51 and 77% greater, respectively, in the elevated [CO2]/high-N fertilization treatment than in the ambient [CO2]/low-N fertilization treatment. However, there was dilution of leaf N in response to elevated [CO2]. Partitioning of newly acquired C and N between shoot and roots was altered by N fertilization but not [CO2]. More newly acquired C and N were partitioned to roots in the low-N treatment than in the high-N treatment.

Biomass↗
PubMed2001

Effect of elevated CO2 on monoterpene emission of young Quercus ilex trees and its relation to structural and ecophysiological parameters.

We investigated growth, leaf monoterpene emission, gas exchange, leaf structure and leaf chemical composition of 1-year-old Quercus ilex L. seedlings grown in ambient (350 microl l(-1)) and elevated (700 microl l(-1)) CO2 concentrations ([CO2]). Monoterpene emission and gas exchange were determined at constant temperature and irradiance (25 degrees C and 1000 micromol m(-2) s(-1) of photosynthetically active radiation) at an assay [CO2] of 350 or 700 microl l(-1). Measurements were made on intact shoots after the end of the growing season between mid-October and mid-February. On average, plants grown in elevated [CO2] had significantly increased foliage biomass (about 50%). Leaves in the elevated [CO2] treatment were significantly thicker and had significantly higher concentrations of cellulose and lignin and significantly lower concentrations of nitrogen and minerals than leaves in the ambient [CO2] treatment. Leaf dry matter density and leaf concentrations of starch, soluble sugars, lipids and hemi-cellulose were not significantly affected by growth in elevated [CO2]. Monoterpene emissions of seedlings were significantly increased by elevated [CO2] but were insensitive to short-term changes in assay [CO2]. On average, plants grown in elevated [CO2] had 1.8-fold higher monoterpene emissions irrespective of the assay [CO2]. Conversely, assay [CO2] rapidly affected photosynthetic rate, but there was no apparent long-term acclimation of photosynthesis to growth in elevated [CO2]. Regardless of growth [CO2], photosynthetic rates of all plants almost doubled when the assay [CO2] was switched from 350 to 700 microl l(-1). At the same assay [CO2], mean photosynthetic rates of seedlings in the two growth CO2 treatments were similar. The percentage of assimilated carbon lost as monoterpenes was not significantly altered by CO2 enrichment. Leaf emission rates were correlated with leaf thickness, leaf concentrations of cellulose, lignin and nitrogen, and total plant leaf area. In all plants, monoterpene emissions strongly declined during the winter independently of CO2 treatment. The results are discussed in the context of the acquisition and allocation of resources by Q. ilex seedlings and evaluated in terms of emission predictions.

Carbon Dioxide↗
PubMed2001

Light- and cold-stress effects on the greening process in epicotyls and young stems of red oak (Quercus rubra) seedlings.

Protochlorophyllide (Pchlide) and protochlorophyll (Pchl) were found in epicotyls of 14-day-old dark-germinated seedlings and in 100-day-old dark-grown stems of red oak (Quercus rubra L.). Fluorescence spectroscopy measurements of epicotyls at 77 K showed that the majority of Pchlide and Pchl is present as a shorter wavelength-emitting monomer with a fluorescence emission maximum at 629-631 nm. A small amount of a monomeric form emitting at 635-636 nm was also present. Minor amounts of Pchlide were aggregated into larger complexes with fluorescence emission maxima at 640, 644-646 and 652-654 nm, as seen in etiolated leaves. Flash illumination transformed the 652-654-nm-emitting form to chlorophyllide, but not those forms with emission maxima at 629-631, 635-636 and 644-646 nm. These shorter wavelength-emitting forms were transformed to chlorophyllide by continuous illumination, but the process took several hours. Epicotyls and young stems were light sensitive, with exposure to full daylight causing strong pigment bleaching and tissue destruction. Complete greening took place only at low irradiances. Light sensitivity was greater at 4 degrees C than at room temperature. We conclude that the monomeric arrangement of the pigments accounted for the light and temperature sensitivity of the greening process in epicotyls and stems.

Chlorophyll↗
PubMed2001

Vertical distribution of fine root density, length density, area index and mean diameter in a Quercus ilex forest.

We used minirhizotrons to determine the vertical distribution of fine roots in a holm oak (Quercus ilex L.) forest in a typical Mediterranean area over a 3-year period (June 1994-March 1997). We measured fine root density (number of roots per unit area), fine root length density (length of roots per unit area), fine root area index (area of roots per unit area) and fine root mean diameter. Variables were pooled for each 10-cm depth interval to a depth of 60 cm. Fine roots tended to decrease with increasing depth except between 0 and 10 cm, where the values of all fine root variables were less than in the 10-cm stratum below. Fine root vertical distribution was compared with soil water content and soil temperature at different depths in the soil profile.

Plant Roots↗
PubMed2002

Reduced photosynthesis in old oak (Quercus robur): the impact of crown and hydraulic architecture.

We tested the hypothesis that changes in crown architecture of old pedunculate oak trees (Quercus robur L. ssp. robur Kl. et Kr. et Rol.) reduce leaf specific hydraulic conductance of shoots, thereby limiting stomatal conductance and assimilation of affected shoots. At the end of summer 1999, hydraulic conductance and leaf specific hydraulic conductance, measured with a high-pressure flow meter in 0.5- to 1.5-m long shoots, were 27 and 39% lower, respectively, in shoots of low vigor compared with vigorously growing shoots in a 165-year- old stand in southeastern Germany. Two types of bottlenecks to water transport can be identified in shoots of old oak trees, namely nodes and abscission zones. The reduction in hydraulic conductance was especially severe in shoots with diameters of less than 2 mm. Maximum stomatal conductance and maximum net assimilation rate increased significantly with hydraulic conductance and leaf specific hydraulic conductance. Our data support the hypothesis that changes in shoot and consequently crown architecture observed in aging trees can limit photosynthesis by reducing shoot hydraulic conductance. Thus, in addition to increasing pathway length and lower conductivity of xylem in old trees, structural changes in shoot and crown architecture need to be considered when analyzing water relations and photosynthesis in mature and declining trees.

Photosynthesis↗
PubMed2003

Patterns of stomatal conductance among blue oak (Quercus douglasii) size classes and populations: implications for seedling establishment.

Quercus douglasii Hook. & Arn. (blue oak) is a deciduous white oak that is currently failing to regenerate throughout much of its range in California, USA. Patterns of water use were observed in adult trees, saplings and seedlings to determine if ontogenetic changes in water use occur, which might be important in the establishment of this long-lived perennial species in a Mediterranean-type system. Seasonal and diurnal stomatal conductance (g(s)), late-season predawn xylem water potentials (Psi(pre)), carbon isotopic ratio (delta(13)C) and soil water status were compared among the three size classes at three sites differing in mean precipitation and soil water characteristics. Comparisons were also made between microsites with and without regeneration (defined by the presence or absence of saplings). Overall patterns of water use were consistent among the three sites, except that, at the site with the highest rainfall, Q. douglasii plants had higher g(s) and more positive Psi(pre) values. Although no differences in water use patterns were found between regeneration and non-regeneration microsites, the observed ontogenetic differences in water use may have important implications for Q. douglasii establishment. Compared with adult trees and saplings, seedlings had higher gas exchange rates during periods of high soil water content (early in the season and in the morning). Seedling g(s) was correlated with percent extractable soil water (ESW) throughout the season; adult tree and sapling g(s) was correlated with ESW between June and September. Despite experiencing greater water stress (indicated by more negative Psi(pre) values) than older trees, seedlings had more negative delta(13)C values, implying lower water-use efficiencies.

California↗
PubMed2003

Seasonal trends in photosynthetic parameters and stomatal conductance of blue oak (Quercus douglasii) under prolonged summer drought and high temperature.

Understanding seasonal changes in photosynthetic parameters and stomatal conductance is crucial for modeling long-term carbon uptake and energy fluxes of ecosystems. Gas exchange measurements of CO2 and light response curves on blue oak leaves (Quercus douglasii H. & A.) were conducted weekly throughout the growing season to study the seasonality of photosynthetic capacity (Vcmax) and Ball-Berry slope (m) under prolonged summer drought and high temperature. A leaf photosynthetic model was used to determine Vcmax. There was a pronounced seasonal pattern in Vcmax. The maximum value of Vcmax, 127 micromol m(-2) s(-1), was reached shortly after leaf expansion in early summer, when air temperature was moderate and soil water availability was high. Thereafter, Vcmax declined as the soil water profile became depleted and the trees experienced extreme air temperatures, exceeding 40 degrees C. The decline in Vcmax was gradual in midsummer, however, despite extremely low predawn leaf water potentials (Psipd, approximately -4.0 MPa). Overall, temporal changes in Vcmax were well correlated with changes in leaf nitrogen content. During spring leaf development, high rates of leaf dark respiration (Rd, 5-6 micromol m(-2) s(-1)) were observed. Once a leaf reached maturity, Rd remained low, around 0.5 micromol m(-2) s(-1). In contrast to the strong seasonality of Vcmax, m and marginal water cost per unit carbon gain (partial partial differential E/ partial partial differential A) were relatively constant over the season, even when leaf Psipd dropped to -6.8 MPa. The constancy of partial partial differential E/ partial partial differential A suggests that stomata behaved optimally under severe water-stress conditions. We discuss the implications of our findings in the context of modeling carbon and water vapor exchange between ecosystems and the atmosphere.

California↗
PubMed2003

Effects of desiccation on the physiology and biochemistry of Quercus alba acorns.

Seeds that lose viability when dried to a water content of less than 12% are said to be recalcitrant. We subjected acorns of Quercus alba L., a species with recalcitrant seeds, to desiccation to determine the effects of drying on lipids, proteins and carbohydrates of the embryonic axis and cotyledon tissues. Samples of fresh seed and seed dried for selected intervals were analyzed for water content and germination, and for lipids, proteins and carbohydrates by Fourier transform-infrared (FT-IR) spectroscopy. Carbohydrates were further analyzed by gas chromatography (GC). The FT-IR analysis revealed that membrane lipid structure initially exhibited reversible shifts between gel and liquid crystalline phases in response to drying and rehydration; however, reversibility declined as viability was lost. Changes in carbohydrate concentration were observed based on peak height comparisons; sucrose concentration in the embryonic axis increased dramatically after 5 days of drying. The most sensitive indicator of desiccation damage was the irreversible change in protein secondary structure in embryonic axes and cotyledon tissue. These changes were illustrated by shifts in amide absorbance near 1650 cm(-1). Gas chromatography indicated an abundance of sucrose in both the embryonic axes and the cotyledon tissue. Although sucrose concentrations in these tissues were initially similar, sucrose concentration in the embryonic axes became significantly greater than in the cotyledons as the acorns dried. We hypothesize that, in drying acorns, increased concentration of sucrose does not prevent loss of viability, but acts as a glycoprotectant against cell collapse and cell wall membrane damage as water stress increases.

Chromatography, Gas↗
PubMed2003

Thinning effects on carbon allocation to fine roots in a Quercus ilex forest.

The dynamics of the fine root system are relevant to calculations of the carbon balance of the ecosystem, and there is also a need to quantify changes in this component caused by disturbances. Mediterranean forest systems have historically been coppiced to obtain charcoal. As a result of the resprouting capacity of holm oaks (Quercus ilex L.), these forests present more than 50% of their biomass below ground (stump + roots > 1 cm in diameter), but the effects of thinning on the fine root system are unknown. Fine root biomass, production, mortality and longevity were studied in a control and a thinned Mediterranean holm oak forest by minirhizotron methodology. Observations of fine roots started 2 years after thinning and continued for almost 3 years. Extraction of 80% of the former basal area of the forest greatly affected carbon allocation patterns. Biomass increased by more than 100%, production increased by 76%, mortality increased by 32% and longevity decreased by around 2 weeks. The greatest differences between treatments were associated with differences in growth during autumn months in the top 40 cm of soil, particularly between 10 and 20 cm depth.

Biomass↗
PubMed2003

Developmental stages during the rooting of in-vitro-cultured Quercus robur shoots from material of juvenile and mature origin.

In-vitro-cultured shoots of clones initiated from shoots of the basal parts (BS) and the crown (C) of two mature Quercus robur L. trees were subjected to rooting experiments to relate rooting with shoot topophysical origin. The BS shoots exhibited morphologically juvenile characteristics and rooted more easily after indole-3-butyric acid (IBA) treatment than C shoots. When naphthylphthalamic acid (NPA) was applied to BS shoots, rooting capacity decreased and root emergence was delayed at least 2 days compared with shoots treated with IBA only. During the first days of the rooting process, endogenous indole-3-acetic acid (IAA) concentration was higher in C shoots than in BS shoots, regardless of whether the shoots were treated with NPA. Mitotic figures were observed in cells from the basal part of both BS and C shoots 24 h after IBA treatment. After 4 days of IBA treatment, the occurrence of histological events differed between BS shoots and C shoots. Cells of BS shoots became meristematic, giving rise to meristemoids and root primordia, whereas no differentiation of root meristemoids occurred in cells of C shoots. Thus, although adult oak material (C shoots) is capable of responding to the initial stimulus of auxin during the adventitious rooting process, the endogenous IAA concentration is not the factor limiting rooting in adult material.

Indoleacetic Acids↗