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PubMed1999

Mineral nutrition, resin flow and phloem phytochemistry in loblolly pine.

Southern pine beetles and associated pathogenic fungi represent the largest biotic threat to pine forests in the southeastern USA. The two primary defensive mechanisms of the tree to the beetle-fungal complex are the primary oleoresin flow and the concentrations of preformed and induced secondary compounds. We compared oleoresin flow and concentrations of phloem nutrients, soluble sugars, starch, total phenolics and proanthocyanidins in Pinus taeda L. trees in fertilized and control plots in the Sandhills region of North Carolina. Four blocks of 10 trees per treatment were sampled on five dates from May to November 1995. Phloem nitrogen and potassium concentrations were elevated in trees on fertilized plots, whereas phloem calcium concentrations were decreased. Fertilization significantly enhanced (10-20%) concentrations of phloem phenolics and proanthocyanidins. In contrast, phloem soluble sugars and starch concentrations were up to 30% lower in fertilized trees than in control trees. Increased phenolic concentrations and lower nonstructural carbohydrates should correlate with reduced tissue palatability and decreased pathogen susceptibility in fertilized trees; however, resin flows were significantly lower (30-100%) in fertilized trees compared with control trees, which may facilitate pine bark beetle establishment. Furthermore, fertilization-induced increases in phloem nitrogen concentration may be more important than tissue carbohydrate or phenolic content in determining tissue palatability.

Journal Article↗
PubMed1999

Effects of CO2 enrichment on the photosynthetic light response of sun and shade leaves of canopy sweetgum (Liquidambar styraciflua) in a forest ecosystem.

To investigate whether sun and shade leaves respond differently to CO2 enrichment, we examined photosynthetic light response of sun and shade leaves in canopy sweetgum (Liquidambar styraciflua L.) trees growing at ambient and elevated (ambient + 200 microliters per liter) atmospheric CO2 in the Brookhaven National Laboratory/Duke University Free Air CO2 Enrichment (FACE) experiment. The sweetgum trees were naturally established in a 15-year-old forest dominated by loblolly pine (Pinus taeda L.). Measurements were made in early June and late August 1997 during the first full year of CO2 fumigation in the Duke Forest FACE experiment. Sun leaves had a 68% greater leaf mass per unit area, 63% more leaf N per unit leaf area, 27% more chlorophyll per unit leaf area and 77% greater light-saturated photosynthetic rates than shade leaves. Elevated CO2 strongly stimulated light-saturated photosynthetic rates of sun and shade leaves in June and August; however, the relative photosynthetic enhancement by elevated CO2 for sun leaves was more than double the relative enhancement of shade leaves. Elevated CO2 stimulated apparent quantum yield by 30%, but there was no interaction between CO2 and leaf position. Daytime leaf-level carbon gain extrapolated from photosynthetic light response curves indicated that sun leaves were enhanced 98% by elevated CO2, whereas shade leaves were enhanced 41%. Elevated CO2 did not significantly affect leaf N per unit area in sun or shade leaves during either measurement period. Thus, the greater CO2 enhancement of light-saturated photosynthesis in sun leaves than in shade leaves was probably a result of a greater amount of nitrogen per unit leaf area in sun leaves. A full understanding of the effects of increasing atmospheric CO2 concentrations on forest ecosystems must take account of the complex nature of the light environment through the canopy and how light interacts with CO2 to affect photosynthesis.

Journal Article↗
PubMed1999

Thinning, fertilization, and crown position interact to control physiological responses of loblolly pine.

To examine physiological responses to thinning, fertilization, and crown position, we measured net photosynthesis (P(n)), transpiration (E), vapor pressure difference (VPD), stomatal conductance (g(s)), and xylem pressure potential (Psi(1)) between 0930 and 1130 h under ambient conditions in the upper and lower crowns of a 13-year-old loblolly pine (Pinus taeda L.) plantation six years (1994) after the treatments were applied. Photosynthetic photon flux density (PPFD) and air temperature (T(a)) within the canopy were also recorded. Needle P(n) of thinned trees was significantly enhanced by 22-54% in the lower crown, because canopy PPFD increased by 28-52%. Lower crown foliage of thinned plots also had higher E and g(s) than foliage of unthinned plots, but thinning had no effect on needle Psi(1) and predawn xylem pressure potential (0430-0530 h; Psi(pd)). Tree water status did not limit P(n), E and g(s) during the late-morning measurements. Fertilization significantly decreased within-canopy PPFD and T(a). Needle Psi(1) was increased in fertilized stands, whereas P(n), E and g(s) were not significantly altered. Upper crown foliage had significantly greater PPFD, P(n), VPD, g(s), E, and more negative Psi(1) than lower crown foliage. In both crown positions, needle P(n) was closely related to g(s), PPFD and T(a) (R(2) = 0.77 for the upper crown and 0.82 for the lower crown). We conclude that (1) silvicultural manipulation causes microclimate changes within the crowns of large trees, and (2) needle physiology adjusts to the within-crown environmental conditions.

Journal Article↗
PubMed2000

Oxidase activity in lignifying xylem of a taxonomically diverse range of trees: identification of a conifer laccase.

In a diverse taxonomic range of tree species, including representative species of ancient families of angiosperms (Magnolia x soulangiana Soul.-Bod.) and gymnosperms (Ginkgo biloba L.), oxidase activity was associated with cell walls of developing xylem and was enriched in extracts of cell wall-associated glycoproteins. In all species where oxidase activity was detected histochemically, it was expressed in cell walls of lignifying, differentiating xylem cells and was absent from old wood, cambium and phloem, suggesting that oxidases have a conservative role in lignification of tree xylem. An oxidase from the developing xylem of Picea sitchensis (Bong) Carr. (Sitka spruce) was partially purified by a combination of lectin affinity and immobilized metal ion affinity chromatography. A portion of the total oxidase activity had high affinity for immobilized zinc ions and this feature allowed it to be separated from the bulk of oxidase activity. Two polypeptides that could have been responsible for the bound oxidase activity were enriched by this procedure. The smaller polypeptide of Mr approximately 73 kDa yielded an N-terminal amino-acid sequence that was homologous to laccase-like polyphenol oxidases (E.C. 1.10.3.2) from loblolly pine (Pinus taeda L.), poplar (Populus euramericana (Dode) Guinier) and Arabidopsis. The larger polypeptide (Mr approximately 77 kDa) yielded an N-terminal amino-acid sequence that was homologous with a range of plant subtilisin-like serine proteinases. The roles of oxidase and proteinase activities in developing xylem are discussed.

Cycadopsida↗
PubMed2000

Differential expression of genes encoding cell wall proteins in vascular tissues from vertical and bent loblolly pine trees.

Differential expression of cell wall proteins during plant development and in response to biotic or abiotic stress suggests that these proteins may contribute in different ways to plant cell wall architecture. Because the wood of loblolly pine (Pinus taeda L.) is highly specialized in the formation of secondary cell walls, it is an ideal tissue for studying these proteins. The cDNAs coding for six novel cell wall associated proteins, as well as a homologue for a phytocyanin, were identified and characterized from differentiating xylem of loblolly pine. Three of these cDNAs encoded new putative loblolly pine arabinogalactan proteins, based on their structural similarity to classical arabinogalactan proteins (AGPs). In addition, one clone was related to the proline-rich protein group and the other two to the glycine-rich protein group and the mussel adhesive protein. Relative expression of these genes was examined in different tissues and organs from normal trees (needles, phloem and vertical wood), the underside of bent trees (compression wood) and the lateral sides of the bent stems (side wood). All clones, except one, were highly expressed in vascular tissues with noticeable differences among the three types of wood. Their relationships and diversity provide the first insights into concerted expression and related function for this important group of proteins in cell wall formation of wood.

Journal Article↗
PubMed2000

Analyses of assumptions and errors in the calculation of stomatal conductance from sap flux measurements.

We analyzed assumptions and measurement errors in estimating canopy transpiration (E(L)) from sap flux (J(S)) measured with Granier-type sensors, and in calculating canopy stomatal conductance (G(S)) from E(L) and vapor pressure deficit (D). The study was performed in 12-year-old Pinus taeda L. stands with a wide range in leaf area index (L) and growth rate. No systematic differences in J(S) were found between the north and south sides of trees. However, J(S) in xylem between 20 and 40 mm from the cambium was 50 and 39% of J(S) in the outer 20-mm band of xylem in slow- and fast-growing trees, respectively. Sap flux measured in stems did not lag J(S) measured in branches, and time and frequency domain analyses of time series indicated that variability in J(S) in stems and branches is mostly explained by variation in D. Therefore, J(S) was used to estimate transpiration, after accounting for radial patterns. There was no difference between D and leaf-to-air vapor pressure gradient, and D did not have a vertical profile in stands of either low or high L suggesting a strong canopy-atmosphere coupling. Therefore, D estimated at one point in the canopy can be used to calculate G(S) in such stands. Given the uncertainties in J(S), relative humidity, and temperature measurements, to keep errors in G(S) estimates to less than 10%, estimates of G(S) should be limited to conditions in which D >/= 0.6 kPa.

Journal Article↗
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↗
PubMed1988

Inhibition of protein synthesis in loblolly pine hypocotyls by mannitol-induced water stress.

The relationship between mannitol-induced water stress and protein synthesis was investigated in hypocotyl slices of loblolly pine (Pinus taeda L.). Mannitol-induced water stress inhibited the incorporation of L-[(35)S]methionine into protein. As the water potential decreased, incorporation of label into protein decreased in both the soluble- and membrane-protein fractions. There were no significant differences in response to water stress among seed sources from four different geographical regions.

Journal Article↗
PubMed1989

Seasonal changes in intensity of bud dormancy in loblolly pine seedlings.

The terminal buds of six-month-old loblolly pine (Pinus taeda L.) seedlings remained closed for approximately six months, although bud dormancy, as measured by rate of bud break in a standard greenhouse environment, was only exhibited for about one month. The peak of bud dormancy was in December for seedlings grown near Auburn, Alabama. However, the timing and intensity varied with seed source and may have been affected by the warm fall temperatures. Seedlings from the more northern provenances entered dormancy first and reached a deeper state of dormancy than seedlings from southern provenances. The rate of shoot elongation was not consistently related to the rate of bud break.

Journal Article↗
PubMed1989

Pine needle holders for use in gas exchange measurements.

Simple holders for positioning pine needles in a gas exchange cuvette are described. The holders make it easy to enclose a standard length of needles in the cuvette in a single plane without mutual shading. The holders also make it possible, following gas exchange measurements, to harvest for further analysis just those needle portions that were enclosed in the leaf chamber. Field observations, which were made with a gas exchange cuvette incorporating the needle holders, on the relationship between carbon exchange rate and photon flux density in loblolly pine (Pinus taeda L.) needles are reported.

Journal Article↗
PubMed1991

Net photosynthesis and leaf conductance of loblolly pine seedlings in 2 and 21% oxygen as influenced by irradiance, temperature and provenance.

Carbon dioxide assimilation and transpiration by secondary needles of two-year-old loblolly pines (Pinus taeda L.) were measured at 2 and 21% (ambient) oxygen. Measurements were made with a Georgia provenance at irradiances (photosynthetic photon flux density) of 150, 300, 700 and 1200 micromol m(-2) s(-1) and a constant temperature of 25 degrees C, and at temperatures of 15, 25 and 35 degrees C and a constant irradiance of 1200 micromol m(-2) s(-1). Measurements were made with provenances from North Carolina, Florida, Arkansas, and Georgia at 25 degrees C and an irradiance of 1200 micromol m(-2) s(-1). There was no significant interaction between the effects of irradiance and oxygen on either net photosynthesis or leaf conductance. Taking all irradiances together, photosynthesis was 16% less and leaf conductance 28% less in 2% oxygen than in 21% oxygen. There was a significant interaction between the effects of temperature and oxygen concentration on both net assimilation and leaf conductance. Net photosynthesis at 21% oxygen relative to that at 2% was significantly reduced at 25 and 35 degrees C, but not at 15 degrees C, whereas leaf conductance at 21% oxygen relative to that at 2% was significantly increased at 15 and 25 degrees C, but not at 35 degrees C. In the provenance study, net photosynthesis was 11% higher and leaf conductance 36% lower in 2% oxygen than in 21% oxygen. There was no significant interaction between the effects of provenance and oxygen on either net photosynthesis or leaf conductance.

Journal Article↗
PubMed1997

Amino Acid Utilization in Seeds of Loblolly Pine during Germination and Early Seedling Growth (I. Arginine and Arginase Activity).

The mobilization and utilization of the major storage proteins in loblolly pine (Pinus taeda L.) seeds following imbibition were investigated. Most of the seed protein reserves were contained within the megagametophyte. Breakdown of these proteins occurred primarily following radicle emergence and correlated with a substantial increase in the free amino acid pool in the seedling; the majority of this increase appeared to be the result of export from the megagametophyte. The megagametophyte was able to break down storage proteins and export free amino acids in the absence of the seedling. Arginine (Arg) was the most abundant amino acid among the principal storage proteins of the megagametophyte and was a major component of the free amino acid pools in both the seedling and the megagametophyte. The increase in free Arg coincided with a marked increase in arginase activity, mainly localized within the cotyledons and epicotyl of the seedling. Arginase activity was negligible in isolated seedlings. Experiments with phenylphosphorodiamidate, a urease inhibitor, supported the hypothesis that arginase participates in Arg metabolism in the seedling. The results of this study indicate that Arg could play an important role in the nutrition of loblolly pine during early seedling growth.

Journal Article↗
PubMed1999

Expansins are conserved in conifers and expressed in hypocotyls in response to exogenous auxin.

Differential display reverse transcription-polymerase chain reaction was used to detect the induction of gene expression during adventitious root formation in loblolly pine (Pinus taeda) after treatment with the exogenous auxin indole-3-butyric acid. A BLAST search of the GenBank database using one of the clones obtained revealed very strong similarity to the alpha-expansin gene family in angiosperms. A near-full-length loblolly pine alpha-expansin sequence was obtained using 5'- and 3'-rapid amplification of cDNA end cloning, and the deduced amino acid sequence was highly conserved relative to those of angiosperm expansins. Northern analysis indicates that alpha-expansin mRNA expression increases 50- to 100-fold in the base of hypocotyl stem cuttings from loblolly pine seedlings in response to indole-3-butyric acid, with peak expression occurring 24 to 48 h after induction.

Amino Acid Sequence↗
PubMed1999

Does free-Air carbon dioxide enrichment affect photochemical energy use by evergreen trees in different Seasons? A chlorophyll fluorescence study of mature loblolly pine

Previous studies of the effects of growth at elevated CO(2) on energy partitioning in the photosynthetic apparatus have produced conflicting results. The hypothesis was developed and tested that elevated CO(2) increases photochemical energy use when there is a high demand for assimilates and decreases usage when demand is low. Modulated chlorophyll a fluorescence and leaf gas exchange were measured on needles at the top of a mature, 12-m loblolly pine (Pinus taeda L.) forest. Trees were exposed to ambient CO(2) or ambient plus 20 Pa CO(2) using free-air CO(2) enrichment. During April and August, periods of shoot growth, light-saturated photosynthesis and linear electron transport were increased by elevated CO(2). In November, when growth had ceased but temperatures were still moderate, CO(2) treatment had no significant effect on linear electron transport. In February, when low temperatures were likely to inhibit translocation, CO(2) treatment caused a significant decrease in linear electron transport. This coincided with a slower recovery of the maximum photosystem II efficiency on transfer of needles to the shade, indicating that growth in elevated CO(2) induced a more persistent photoinhibition. Both the summer increase and the winter decrease in linear electron transport in elevated CO(2) resulted from a change in photochemical quenching, not in the efficiency of energy transfer within the photosystem II antenna. There was no evidence of any effect of CO(2) on photochemical energy sinks other than carbon metabolism. Our results suggest that elevated CO(2) may increase the effects of winter stress on evergreen foliage.

Journal Article↗
PubMed1992

Phenylalanine ammonia-lyase from loblolly pine : purification of the enzyme and isolation of complementary DNA clones.

Phenylalanine ammonia-lyase (EC 4.3.1.5) has been purified from differentiating secondary xylem of loblolly pine (Pinus taeda L.). Native molecular weight of the enzyme was estimated to be 280,000, with a subunit molecular weight of 74,000; isoelectric point, 5.8; and Michaelis constant for i-phenylalanine, 27 micromolar. No evidence was obtained for the existence of isoforms of the enzyme, nor for negative cooperativity of substrate binding. Polyclonal antibodies were raised against the phenylalanine ammonia-lyase subunit and used to identify a pal clone in an expression library of xylem complementary DNA (cDNA). Polymerase chain reaction, using oligonucleotide primers made from N-terminal amino acid sequence and from the 5' end of the clone isolated from the expression library, was also used to isolate cDNA clones. These methods yielded cDNA clones covering the protein coding region of the pal messenger RNA. Comparisons of nucleotide sequence of pal cDNAs from pine, bean, sweet potato, and rice showed 60 to 62% identity between the pine clone and the angiosperm clones.

Journal Article↗
PubMed2001

Rising CO2 levels and the fecundity of forest trees.

We determined the reproductive response of 19-year-old loblolly pine (Pinus taeda) to 4 years of carbon dioxide (CO2) enrichment (ambient concentration plus 200 microliters per liter) in an intact forest. After 3 years of CO2 fumigation, trees were twice as likely to be reproductively mature and produced three times as many cones and seeds as trees at ambient CO2 concentration. A disproportionate carbon allocation to reproduction under CO2 enrichment results in trees reaching maturity sooner and at a smaller size. This reproductive response to future increases in atmospheric CO2 concentration is expected to change loblolly dispersal and recruitment patterns.

Atmosphere↗
PubMed1997

Survey of microsatellite DNA in pine.

A large insert genomic library from eastern white pine (Pinus strobus) was probed for the microsatellite motifs (AC)n and (AG)n, all 10 trinucleotide motifs, and 22 of the 33 possible tetranucleotide motifs. For comparison with a species from a different subgenus, a loblolly pine (Pinus taeda) genomic library was also probed with the same set of di- and tri-nucleotide repeats and 11 of the tetranucleotide repeats. The four most abundant microsatellite motifs in both species were (AC)n, (AG)n, (AAT)n, and (ATC)n, which as a group accounted for over half the microsatellite sites investigated. The two dinucleotide repeats were the most abundant microsatellite motifs tested in both species, each at 2-4.5 sites/megabase pair (Mbp), but the two trinucleotide motifs were nearly as abundant and are considered good candidates for pine microsatellite marker development efforts. Eastern white pine had more than twice as many (AC)n as (AG)n loci, in contrast with loblolly pine and most other plant species in which (AG)n is more abundant. In both pine species the minimum estimated genome density for all microsatellites, excluding (AT)n repeats, was 16 sites/Mbp.

DNA, Plant↗
PubMed2004

Comparative mapping in the Pinaceae.

A comparative genetic map was constructed between two important genera of the family Pinaceae. Ten homologous linkage groups in loblolly pine (Pinus taeda L.) and Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) were identified using orthologous expressed sequence tag polymorphism (ESTP) and restriction fragment length polymorphism (RFLP) markers. The comparative mapping revealed extensive synteny and colinearity between genomes of the Pinaceae, consistent with the hypothesis of conservative chromosomal evolution in this important plant family. This study reports the first comparative map in forest trees at the family taxonomic level and establishes a framework for comparative genomics in Pinaceae.

Base Sequence↗