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PubMed2001

A theoretical analysis of the influence of heterogeneity in chlorophyll distribution on leaf reflectance.

Attempts to determine the vitality of vegetation and to detect vegetation stress from remotely sensed data have focused on chlorophyll concentration, because it influences the reflectance of vegetation and tends to correlate with vegetation health and stress. Pollution, pathogens and pests can cause localized regions of chlorosis and necrosis across a leaf surface, but the extent to which these patches influence the overall reflectance and spectral signature of the leaf and canopy has not been tested. A conifer leaf model (LIBERTY), which simulates the influence of leaf biochemical concentrations of chlorophyll, water, lignin, cellulose and protein on the reflectance of leaves from 400 to 2500 nm, was used to determine the effect of patches of chlorosis on leaf reflectance. A fraction of the leaf f is assumed to be chlorotic with a chlorophyll concentration C(1). The remainder of the leaf has chlorophyll concentration C(2) such that mean leaf chlorophyll concentration, C(mean) = fC(1) + (1 - f)C(2), is constant for a range of f and C(1) values. LIBERTY can be used to estimate the reflectance of a leaf with a particular chlorophyll concentration at a particular wavelength R(lambda,C) (assuming other leaf properties remain constant), thus we can estimate the reflectance of the chlorotic leaf as fR(lambda,C(1))+ (1 - f)R(lambda,C(2)). The model indicated that small areas of chlorosis have a disproportionately large influence on overall leaf reflectance. For example, a leaf with 25% of its area chlorotic can have the same reflectance (400-700 nm) as a homogeneous leaf with 60% less chlorophyll. Thus, determination of chlorophyll concentration from remotely sensed data is prone to underestimation when chlorophyll is nonuniformly distributed. Hence, attempts to model leaf and canopy reflectance using radiative transfer models will need to consider how to incorporate nonuniform chlorophyll distribution.

Chlorophyll↗

PubMed2001

A method for estimating light interception by a conifer shoot.

We present an operational method for estimating the amount of PAR intercepted by a coniferous shoot. Interception of PAR by a shoot is divided into three components: the amount of radiation coming from the sky, the transmission of radiation through the surrounding vegetation, and the shoot' s silhouette area facing the direction of the incoming radiation. All three components usually vary with direction. Radiation incident from the sky consists of direct and diffuse radiation. The well-known equation of motion for the sun and Beer' s Law for atmospheric transmittance are used to simulate the directional distribution of direct sunlight for any given period of time. The diffuse component is assumed to be uniform. Meteorological field measurements are used to calibrate the absolute amounts of the direct and diffuse components. The gap fraction (proportion of visible sky) in different directions around a shoot is measured by analyzing a hemispherical fish-eye photograph, taken at the location of the shoot, with an image processing program. Similarly, the shoot silhouette area (SSA) is measured by photographing the shoot from many different directions. The measurements of SSA are interpolated by a method called trigonometric interpolation to obtain the directional distribution of SSA over the entire hemisphere. This distribution is then rotated according to the shoot' s position in the canopy. Multiplying incoming PAR, canopy gap fraction and SSA in different directions, and summing over all directions, gives an estimate of PAR intercepted by the shoot during the chosen period of time. The method is described step by step, and applied, as an example, to a shoot from a Scots pine (Pinus sylvestris L.) stand in central Finland. Differences in radiation interception properties between sun and shade shoots and their relevance to canopy-scale models are discussed.

Cycadopsida↗

PubMed2002

Age-related variations in delta(13)C of ecosystem respiration across a coniferous forest chronosequence in the Pacific Northwest.

We tested the hypothesis that forest age influences the carbon isotope ratio (delta13C) of carbon reservoirs and CO2 at local and regional levels. Carbon isotope ratios of ecosystem respiration (delta13C(R)), soil respiration (delta13C(R-soil)), bulk needle tissue (delta13C(P)) and soil organic carbon (delta(13)C(SOC)) were measured in > 450-, 40- and 20-year-old temperate, mixed coniferous forests in southern Washington, USA. Values of delta13C(R), delta13C(R-soil), delta13C(P) and delta13C(SOC) showed consistent enrichment with increasing stand age. Between the youngest and oldest forests there was an approximately 1 per thousand enrichment in delta13C(P) (at similar canopy levels), delta13C(SOC) (throughout the soil column), delta13C(R-soil) (during the wet season) and delta13C(R) (during the dry season). Mean values of delta13C(R) were -25.9, -26.5 and -27.0 per thousand for the 450-, 40- and 20-year-old forests, respectively. Both delta13C(R-soil) and the difference between delta13C(R) and delta13C(R-soil) were more 13C enriched in older forests than in young forest: delta13C(R) - delta13C(R-soil) = 2.3, 1.1 and 0.5 per thousand for the 450-, 40- and 20-year-old forests, respectively. Values of delta(13)C(P) were proportionally more depleted relative to delta13C(R): delta13C(R) - delta13C(P) = 0.5, 2.2 and 2.5 per thousand for the 450-, 40- and 20-year-old forests, respectively. Values of delta13C(P) were most 13C-enriched at the top of the canopy and in the oldest forest regardless of season (overall values were -26.9, -28.7 and -29.4 per thousand for the 450-, 40- and 20-year-old forests, respectively). Values of delta13C(SOC) from shallow soil depths were similar to delta13C(P) values of upper- and mid-canopy needles. All delta13C data are consistent with the hypothesis that a decrease in stomatal conductance associated with decreased hydraulic conductance leads to increased CO2 diffusional limitations in older coniferous trees. The strong associations between delta13C(P) in needles with delta13C(R) and delta13C(R-soil) at the forest level suggest that 13C observations scale between leaf and ecosystem levels.

Carbon Dioxide↗

PubMed2003

Incorporation of transfer resistance between tracheary elements into hydraulic resistance models for tapered conduits.

The model of West, Brown and Enquist (1999) shows that hydraulic resistance in trees can be independent of path length, provided that vascular conduits widen sufficiently from tree top to base. We demonstrate that this result does not depend theoretically on branching architecture or cross-sectional conductive area of the stem. Previous studies have shown that pit membrane resistance, encountered when water moves between either tracheids or vessels, accounts for up to 60% of the total resistance in stem segments. When pit membrane resistance, which is neglected by most whole-tree hydraulic models, was incorporated in hydraulic models in three different ways, the near invariance of hydraulic resistance was preserved. If relative pit resistance was independent of tracheid size or if tracheid dimensions were scaled to minimize wood resistivity, the minimum conduit taper required for path length independence equaled that in the original model of West et al. (1999). Under the most realistic model, in which relative pit resistance increased with tracheid radius, this value was doubled. Such taper is not possible within the typical size range of tracheids over the entire length of moderately tall trees, but it might be possible for vessel-bearing trees. Preliminary results indicated that although tracheid radius in the outer growth ring initially increased basipetally from the top of an 18-m tall Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), it stabilized at mid-trunk. Also, conduit taper was not constant in this species, violating a key assumption of the model of West et al. (1999), on which the invariance of hydraulic resistance depends.

Cycadopsida↗

PubMed2004

Variation in transcript abundance during somatic embryogenesis in gymnosperms.

Somatic embryogenesis of Norway spruce (Picea abies L.) is a versatile model system to study molecular mechanisms regulating embryo development because it proceeds through defined developmental stages corresponding to specific culture treatments. Normal embryonic development involves early differentiation of proembryogenic masses (PEMs) into somatic embryos, followed by early and late embryogeny leading to the formation of mature cotyledonary embryos. In some cell lines there is a developmental arrest at the PEM-somatic embryo transition. To learn more about the molecular mechanisms regulating embryogenesis, we compared the transcript profiles of two normal lines and one developmentally arrested line. Ribonucleic acid, extracted from these cell lines at successive developmental stages, was analyzed on DNA microarrays containing 2178 expressed sequence tags (ESTs) (corresponding to 2110 unique cDNAs) from loblolly pine (Pinus taeda L.). Hybridization between spruce and pine species on microarrays has been shown to be effective (van Zyl et al. 2002, Stasolla et al. 2003). In contrast to the developmentally arrested line, the early phases of normal embryo development are characterized by a precise pattern of gene expression, i.e., repression followed by induction. Comparison of transcript levels between successive stages of embryogenesis allowed us to identify several genes that showed unique expression responses during normal development. Several of these genes encode proteins involved in detoxification processes, methionine synthesis and utilization, and carbohydrate metabolism. The potential role of these genes in embryo development is discussed.

Cycadopsida↗

PubMed2006

Contrasting seasonal leaf habits of canopy trees between tropical dry-deciduous and evergreen forests in Thailand.

We compared differences in leaf properties, leaf gas exchange and photochemical properties between drought-deciduous and evergreen trees in tropical dry forests, where soil nutrients differed but rainfall was similar. Three canopy trees (Shorea siamensis Miq., Xylia xylocarpa (Roxb.) W. Theob. and Vitex peduncularis Wall. ex Schauer) in a drought-deciduous forest and a canopy tree (Hopea ferrea Lanessan) in an evergreen forest were selected. Soil nutrient availability is lower in the evergreen forest than in the deciduous forest. Compared with the evergreen tree, the deciduous trees had shorter leaf life spans, lower leaf masses per area, higher leaf mass-based nitrogen (N) contents, higher leaf mass-based photosynthetic rates (mass-based P(n)), higher leaf N-based P(n), higher daily maximum stomatal conductance (g(s)) and wider conduits in wood xylem. Mass-based P(n) decreased from the wet to the dry season for all species. Following onset of the dry season, daily maximum g(s) and sensitivity of g(s) to leaf-to-air vapor pressure deficit remained relatively unchanged in the deciduous trees, whereas both properties decreased in the evergreen tree during the dry season. Photochemical capacity and non-photochemical quenching (NPQ) of photosystem II (PSII) also remained relatively unchanged in the deciduous trees even after the onset of the dry season. In contrast, photochemical capacity decreased and NPQ increased in the evergreen tree during the dry season, indicating that the leaves coped with prolonged drought by down-regulating PSII. Thus, the drought-avoidant deciduous species were characterized by high N allocation for leaf carbon assimilation, high water use and photoinhibition avoidance, whereas the drought-tolerant evergreen was characterized by low N allocation for leaf carbon assimilation, conservative water use and photoinhibition tolerance.

Biomass↗

PubMed2006

Seasonal patterns of leaf gas exchange and water relations in dry rain forest trees of contrasting leaf phenology.

Diurnal and seasonal patterns of leaf gas exchange and water relations were examined in tree species of contrasting leaf phenology growing in a seasonally dry tropical rain forest in north-eastern Australia. Two drought-deciduous species, Brachychiton australis (Schott and Endl.) A. Terracc. and Cochlospermum gillivraei Benth., and two evergreen species, Alphitonia excelsa (Fenzal) Benth. and Austromyrtus bidwillii (Benth.) Burret. were studied. The deciduous species had higher specific leaf areas and maximum photosynthetic rates per leaf dry mass in the wet season than the evergreens. During the transition from wet season to dry season, total canopy area was reduced by 70-90% in the deciduous species and stomatal conductance (g(s)) and assimilation rate (A) were markedly lower in the remaining leaves. Deciduous species maintained daytime leaf water potentials (Psi(L)) at close to or above wet season values by a combination of stomatal regulation and reduction in leaf area. Thus, the timing of leaf drop in deciduous species was not associated with large negative values of daytime Psi(L) (greater than -1.6 MPa) or predawn Psi(L) (greater than -1.0 MPa). The deciduous species appeared sensitive to small perturbations in soil and leaf water status that signalled the onset of drought. The evergreen species were less sensitive to the onset of drought and g(s) values were not significantly lower during the transitional period. In the dry season, the evergreen species maintained their canopies despite increasing water-stress; however, unlike Eucalyptus species from northern Australian savannas, A and g(s) were significantly lower than wet season values.

Australia↗

PubMed2001

Isolation and characterization of a symbiosis-regulated ras from the ectomycorrhizal fungus Laccaria bicolor.

Ectomycorrhizae formed by the symbiotic interaction between ectomycorrhizal fungi and plant roots play a key role in maintaining and improving the health of a wide range of plants. Mycorrhizal initiation, development, and functional maintenance involve morphological changes that are mediated by activation and suppression of several fungal and plant genes. We identified a gene, Lbras, in the ectomycorrhizal fungus Laccaria bicolor that belongs to the ras family of genes, which has been shown in other systems to be associated with signaling pathways controlling cell growth and proliferation. The Lbras cDNA complemented ras2 function in Saccharomyces cerevisiae and had the ability to transform mammalian cells. Expression of Lbras, present as a single copy in the genome, was dependent upon interaction with host roots. Northern analysis showed that expression was detectable in L bicolor 48 h after interaction as well as in the established mycorrhizal tissue. Phylogenetic analysis with other Ras proteins showed that Lbras is related most closely to Aras of Aspergillus nidulans.

Agaricales↗

PubMed2006

Latitudinal and longitudinal barriers in global biogeography.

Due to changes in climate and continental arrangement, plant and animal assemblages faced different dispersal barriers at different moments in Earth's history. It is generally accepted that groups which diversified during times of Gondwanan-Laurasian separation show different distribution patterns from those of more recent origin. Here I present principal component-derived maps for two globally distributed groups, with ca 1000 species each. Gymnosperm assemblages perfectly illustrate the existence of southern and northern components, corresponding to the Gondwanan and Laurasian temperate floras at the time when angiosperms started becoming dominant in the tropics, thus imposing a latitudinal barrier. Bat (chiropteran) assemblages indicate that the major biogeographical barrier in their Cenozoic dispersal was the longitudinal separation between the Old and New World.

Animals↗

PubMed2000

Hot spots, indicator taxa, complementarity and optimal networks of taiga.

If hot spots for different taxa coincide, priority-setting surveys in a region could be carried out more cheaply by focusing on indicator taxa. Several previous studies show that hot spots of different taxa rarely coincide. However, in tropical areas indicator taxa may be used in selecting complementary networks to represent biodiversity as a whole. We studied beetles (Coleoptera), Heteroptera, polypores or bracket fungi (Polyporaceae) and vascular plants of old growth boreal taiga forests. Optimal networks for Heteroptera maximized the high overall species richness of beetles and vascular plants, but these networks were least favourable options for polypores. Polypores are an important group indicating the conservation value of old growth taiga forests. Random selection provided a better option. Thus, certain groups may function as good indicators for maximizing the overall species richness of some taxonomic groups, but all taxa should be examined separately.

Animals↗

PubMed2000

Evolutionary assembly of the conifer fauna: distinguishing ancient from recent associations in bark beetles.

Several shifts from ancestral conifer feeding to angiosperm feeding have been implicated in the unparalleled diversification of beetle species. The single largest angiosperm-feeding beetle clade occurs in the weevils, and comprises the family Curculionidae and relatives. Most authorities confidently place the bark beetles (Scolytidae) within this radiation of angiosperm feeders. However, some clues indicate that the association between conifers and some scolytids, particularly in the tribe Tomicini, is a very ancient one. For instance, several fragments of Gondwanaland (South America, New Caledonia, Australia and New Guinea) harbour endemic Tomicini specialized on members of the formerly widespread and abundant conifer family Araucariaceae. As a first step towards resolving this seeming paradox, we present a phylogenetic analysis of the beetle family Scolytidae with particularly intensive sampling of conifer-feeding Tomicini and allies. We sequenced and analysed elongation factor 1alpha and nuclear rDNAs 18S and 28S for 45 taxa, using members of the weevil family Cossoninae as an out-group. Our results indicate that conifer feeding is the ancestral host association of scolytids, and that the most basal lineages of scolytids feed on Aramucaria. If scolytids are indeed nested within a great angiosperm-feeding clade, as many authorities have held, then a reversion to conifer feeding in ancestral scolytids appears to have occurred in the Mesozoic, when Araucaria still formed a major component of the woody flora.

Animals↗

PubMed2001

Competition between Eurasian red and introduced Eastern grey squirrels: the energetic significance of body-mass differences.

Daily energy expenditure (DEE) was measured in sympatric populations of red and grey squirrels using the doubly labelled water technique. Grey squirrels had significantly higher DEEs than red squirrels. However, the difference between the species was not separable from the effects of body mass on DEE. The DEEs of both species were in accordance with published allometric predictions incorporating body mass and ambient temperature. The differences in energetic requirements and social dominance, both consequences of body size, may represent means by which grey squirrels exert more interspecific competition on red squirrels than do conspecifics, potentially driving populations below viable levels in some sites.

Analysis of Variance↗

PubMed2006

Widespread genome duplications throughout the history of flowering plants.

Genomic comparisons provide evidence for ancient genome-wide duplications in a diverse array of animals and plants. We developed a birth-death model to identify evidence for genome duplication in EST data, and applied a mixture model to estimate the age distribution of paralogous pairs identified in EST sets for species representing the basal-most extant flowering plant lineages. We found evidence for episodes of ancient genome-wide duplications in the basal angiosperm lineages including Nuphar advena (yellow water lily: Nymphaeaceae) and the magnoliids Persea americana (avocado: Lauraceae), Liriodendron tulipifera (tulip poplar: Magnoliaceae), and Saruma henryi (Aristolochiaceae). In addition, we detected independent genome duplications in the basal eudicot Eschscholzia californica (California poppy: Papaveraceae) and the basal monocot Acorus americanus (Acoraceae), both of which were distinct from duplications documented for ancestral grass (Poaceae) and core eudicot lineages. Among gymnosperms, we found equivocal evidence for ancient polyploidy in Welwitschia mirabilis (Gnetales) and no evidence for polyploidy in pine, although gymnosperms generally have much larger genomes than the angiosperms investigated. Cross-species sequence divergence estimates suggest that synonymous substitution rates in the basal angiosperms are less than half those previously reported for core eudicots and members of Poaceae. These lower substitution rates permit inference of older duplication events. We hypothesize that evidence of an ancient duplication observed in the Nuphar data may represent a genome duplication in the common ancestor of all or most extant angiosperms, except Amborella.

Cycadopsida↗

PubMed2004

Functional characterization of nine Norway Spruce TPS genes and evolution of gymnosperm terpene synthases of the TPS-d subfamily.

Constitutive and induced terpenoids are important defense compounds for many plants against potential herbivores and pathogens. In Norway spruce (Picea abies L. Karst), treatment with methyl jasmonate induces complex chemical and biochemical terpenoid defense responses associated with traumatic resin duct development in stems and volatile terpenoid emissions in needles. The cloning of (+)-3-carene synthase was the first step in characterizing this system at the molecular genetic level. Here we report the isolation and functional characterization of nine additional terpene synthase (TPS) cDNAs from Norway spruce. These cDNAs encode four monoterpene synthases, myrcene synthase, (-)-limonene synthase, (-)-alpha/beta-pinene synthase, and (-)-linalool synthase; three sesquiterpene synthases, longifolene synthase, E,E-alpha-farnesene synthase, and E-alpha-bisabolene synthase; and two diterpene synthases, isopimara-7,15-diene synthase and levopimaradiene/abietadiene synthase, each with a unique product profile. To our knowledge, genes encoding isopimara-7,15-diene synthase and longifolene synthase have not been previously described, and this linalool synthase is the first described from a gymnosperm. These functionally diverse TPS account for much of the structural diversity of constitutive and methyl jasmonate-induced terpenoids in foliage, xylem, bark, and volatile emissions from needles of Norway spruce. Phylogenetic analyses based on the inclusion of these TPS into the TPS-d subfamily revealed that functional specialization of conifer TPS occurred before speciation of Pinaceae. Furthermore, based on TPS enclaves created by distinct branching patterns, the TPS-d subfamily is divided into three groups according to sequence similarities and functional assessment. Similarities of TPS evolution in angiosperms and modeling of TPS protein structures are discussed.

Alkyl and Aryl Transferases↗

PubMed1999

Genes expressed in Pinus radiata male cones include homologs to anther-specific and pathogenesis response genes.

We describe the isolation and characterization of 13 cDNA clones that are differentially expressed in male cones of Pinus radiata (D. Don). The transcripts of the 13 genes are expressed at different times between meiosis and microspore mitosis, timing that corresponds to a burst in tapetal activity in the developing anthers. In situ hybridization showed that four of the genes are expressed in the tapetum, while a fifth is expressed in tetrads during a brief developmental window. Six of the seven cDNAs identified in database searches have striking similarity to genes expressed in angiosperm anthers. Seven cDNAs are homologs of defense and pathogen response genes. The cDNAs identified are predicted to encode a chalcone-synthase-like protein, a thaumatin-like protein, a serine hydrolase thought to be a putative regulator of programmed cell death, two lipid-transfer proteins, and two homologs of the anther-specific A9 genes from Brassica napus and Arabidopsis. Overall, our results support the hypothesis that many of the reproductive processes in the angiosperms and gymnosperms were inherited from a common ancestor.

Acyltransferases↗

PubMed2000

Compression wood-responsive proteins in developing xylem of maritime pine (Pinus pinaster ait.).

When a conifer shoot is displaced from its vertical position, compression wood (CW) is formed on the under side and can eventually return the shoot to its original position. Changes in cell wall structure and chemistry associated with CW are likely to result from differential gene/protein expression. Two-dimensional polyacrylamide gel electrophoresis of differentiating xylem proteins was combined with the physical characterization of wooden samples to identify and characterize CW-responsive proteins. Differentiating xylem was harvested from a 22-year-old crooked maritime pine (Pinus pinaster Ait.) tree. Protein extracted from different samples were revealed by high-resolution silver stained two-dimensional polyacrylamide gel electrophoresis and analyzed with a computer-assisted system for single spot quantification. Growth strain (GS) measurements allowed xylem samples to be classified quantitatively from normal wood to CW. Regression of lignin and cellulose content on GS showed that an increase in the percentage of lignin and a decrease of the percentage of cellulose corresponded to increasing GS values, i.e. CW. Of the 137 studied spots, 19% were significantly associated with GS effect. Up-regulated proteins included 1-aminocyclopropane-1-carboxylate oxidase (an ethylene forming enzyme), a putative transcription factor, two lignification genes (caffeic O-methyltransferase and caffeoyl CoA-O-methyltransferase), members of the S-adenosyl-L-methionine-synthase gene family, and enzymes involved in nitrogen and carbon assimilation (glutamine synthetase and fructokinase). A clustered correlation analysis was performed to study simultaneously protein expression along a gradient of gravistimulated stressed xylem tissue. Proteins were found to form "expression clusters" that could identify: (a) Gene product under similar control mechanisms, (b) partner proteins, or (c) functional groups corresponding to specialized pathways. The possibility of obtaining regulatory correlations and anticorrelations between proteins provide us with a new category of homology (regulatory homology) in tracing functional relationships.

Cellulose↗

PubMed2000

Multisite inhibition of Pinus pinea isocitrate lyase by phosphate.

Our results show that the phosphate ion is a nonlinear competitive inhibitor of Pinus pinea isocitrate lyase. In addition, this compound induces a sigmoidal response of the enzyme, which usually exhibits standard Michaelis-Menten kinetics. This peculiar behavior of P. pinea isocitrate lyase could be explained by a dimer (two-site) model, in which phosphate binds cooperatively, but the affinity of the vacant site for substrate (the magnesium-isocitrate complex) remains the same. As a result, the interaction of phosphate with free enzyme produces an inhibitor-enzyme-inhibitor species that is of significant importance in determining reaction rate; a possible regulatory role of the glyoxylate cycle by inorganic phosphate is suggested. The mode of phosphate inhibition is consistent with both the mechanism for magnesium ion activation of P. pinea isocitrate lyase and its site heterogeneity. Our results explain the cooperative effects observed by some authors in kinetic studies of isocitrate lyase carried out in phosphate buffers and also account for the higher K(m) values determined by using such assay systems. Phosphate buffer should be avoided in performing isocitrate lyase kinetics.

Buffers↗

PubMed2001

Function and dynamics of auxin and carbohydrates during earlywood/latewood transition in scots pine.

In temperate regions the annual pattern of wood development is characterized by the formation of radially narrow and thick walled latewood cells. This takes place at the later part of the growing season when cambial cell division declines. To gain new insight into the regulation of this process, micro-analytical techniques were used to visualize the distribution of indole-3-acetic acid (IAA), soluble carbohydrates, and activities of sucrose (Suc)-metabolizing enzymes across the cambial region tissues in Scots pine (Pinus sylvestris). The total amount of IAA in the cambial region did not change with latewood initiation. But its radial distribution pattern was altered, resulting in an increased concentration in the cambial meristem and its recent derivatives. Thus, initiation of latewood formation and cessation of cambial cell division is not a consequence of decreased IAA concentrations in dividing and expanding cells. Rather, IAA most likely has a role in defining the altered developmental pattern associated with latewood formation. Carbohydrates and enzyme activities showed distinctive radial distribution patterns. Suc peaked in the phloem and decreased sharply to low levels across the cambial zone, whereas fructose and glucose reached their highest levels in the maturing tracheids. Suc synthase was the dominating Suc cleaving enzyme with a peak in the secondary wall-forming tracheids and in the phloem. Soluble acid invertase peaked in dividing and expanding cells. Suc-phosphate synthase had its highest activities in the phloem. Activities of cell wall bound invertase were low. The absence of major seasonal variations indicates that carbohydrate availability is not a trigger for latewood initiation. However, steep concentration gradients of the sugars suggest a role for sugar signaling in vascular development.

Carbohydrate Metabolism↗