Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Xylem”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,081 records · Page 60Linked to original sources
PubMed2000

Some compartmental models of the root: steady-state behavior.

Plots of the pressure difference (DeltaP) applied to plant roots vs. the resulting volume flow rate (Q(v)) often exhibit an anomalous offset that has been difficult to explain. The present analysis suggests that solute build-up in two- and three-compartment models of the root cannot account for this offset. The Ginsburg-Newman three-compartment model explains the offset in terms of differing reflection coefficients for the membranes bounding the intermediate compartment. This model appears more promising, but it predicts a minimum in the plot of xylem-sap osmotic pressure vs. Q(v)which is not observed in practice. Fiscus hypothesized that an internal asymmetric distribution of non-mobile solutes is responsible for the offset. In the present study, this hypothesis is incorporated into a four-compartment model of the root that is conceptually related to the three-compartment model of Miller. But according to the four-compartment model, the asymmetric solute distribution does not arise because of solvent drag. Rather the anomalous offset is associated with a concentration gradient of photoassimilates (the non-mobile solutes) that exists in the absence of volume flow, and which drives the diffusive transport of these solutes from the stele to the cortex via endodermal plasmodesmata. This model is consistent with the existence of radial symplastic osmotic-pressure gradients, and it appears to have greater explanatory power than the Ginsburg-Newman model. In particular, it suggests explanations for diurnal variations in DeltaP-Q(v)curves, as well as the effects of changing external solute concentrations. It also shows how the overall root reflection coefficient can be less than unity, even when the cell membranes are effectively ideally semipermeable, and there is negligible extracellular transport of water and solutes. The model makes a number of experimentally testable predictions.

Biological Transport↗
PubMed2002

Stability of rice yellow mottle virus and cellular compartmentalization during the infection process in Oryza sativa (L.).

Rice yellow mottle virus (RYMV) is icosahedral in morphology and known to swell in vitro, but the biological function of swollen particles remains unknown. Anion-exchange chromatography was used to identify three markedly stable forms of RYMV particles from infected plants: (1) an unstable swollen form lacking Ca2+ and dependent upon basic pH; (2) a more stable transitional form lacking Ca2+ but dependent upon acidic pH; and (3) a pH-independent, stable, compact form containing Ca2+. Particle stability increased over the time course of infection in rice plants: transitional and swollen forms were abundant during early infection (2 weeks postinfection), whereas compact forms increased during later stages of infection. Electron microscopy of infected tissue revealed virus particles in vacuoles of xylem parenchyma and mesophyll cells early in the time course of infection and suggested that vacuoles and other vesicles were the major storage compartments for virus particles. We propose a model in which virus maturation is associated with the virus accumulation in vacuoles. In this acidic compartment, virus particles may bind Ca2+ to produce a highly stable, compact form of the virus. The localization of subcellular RYMV isoforms in infected cells and the corresponding biological properties of the virus are discussed.

Calcium↗
PubMed1993

Activity of the promoter of the Lhca3.St.1 gene, encoding the potato apoprotein 2 of the light-harvesting complex of Photosystem I, in transgenic potato and tobacco plants.

We have isolated cDNA and genomic clones for the potato (Solanum tuberosum) apoprotein 2 of the light harvesting complex of Photosystem I, designated Lhca3.St.1. The protein shows all characteristics of the family of chlorophyll a/b-binding proteins. Potato Lhca3.1 gene expression occurs predominantly in leaves, and is transcriptionally regulated by light. One gene copy is present per haploid genome. The sequence of the 5' upstream region was determined. Most boxes identified in the promoter sequences of genes whose expression is light-regulated recur in the Lhca3.St.1 sequence. Functional analyses of the Lhca3.St.1 promoter and two deletion derivatives in transgenic potato transformed with a promoter-GUS fusion show high promoter activity in leaves and other green parts of the plant, which depends on light. Activity is absent in roots and potato tubers. The 500 bp promoter fragment is as active as the full 2.0 kb sequence, showing that all regulatory elements are present on the smallest deletion derivative. In transgenic tobacco (Nicotiana tabacum) plants carrying the largest promoter derivative a similar distribution of activity is found. Promoter activity is not restricted to the phloem, but also prominent in the xylem of the young stem, which contrasts with promoters of other photosynthesis-associated genes.

Amino Acid Sequence↗
PubMed1995

Expression patterns of three genes in the stem of lucerne (Medicago sativa).

We have identified three stem abundantly expressed genes in lucerne (alfalfa, Medicago sativa). A cDNA library, constructed from lucerne stem polyadenylated RNA, was screened by differential hybridization. From this screening, cDNA clones that correspond to genes which are preferentially, or specifically, expressed in the stem were isolated. MsaS1 encodes an unidentified protein, MsaS2 encodes an S-adenosyl-homocysteine hydrolase and MsaS3 encodes an extensin-like protein. Northern blot analysis of RNA isolated from individual stem internodes indicated that the three corresponding genes show differing developmental patterns of expression. The expression of MsaS1 was confined to the youngest stem tissue and may be regulated by sucrose. In stem tissue the level of RNA for the three genes decreased in response to wounding. Tissue print hybridization analysis was used to localize the expression of the genes to the xylem side of vascular bundles in lucerne stems.

Adenosylhomocysteinase↗
PubMed1996

Expression of two heterologous promoters, Agrobacterium rhizogenes rolC and cauliflower mosaic virus 35S, in the stem of transgenic hybrid aspen plants during the annual cycle of growth and dormancy.

We monitored, for the first time, the activity of two model heterologous promoters, the Agrobacterium rhizogenes rolC and the cauliflower mosaic virus (CaMV) 35S, throughout the annual cycle of growth and dormancy in a perennial species, hybrid aspen. Each promoter was fused to the uidA beta-glucuronidase (GUS) reporter gene and the constructs were introduced into the hybrid aspen genome by Agrobacterium-mediated transformation. Both wild-type and transgenic plants were cultivated under different regimes of photoperiod and temperature to induce passage through one growth-dormancy-reactivation cycle, and at intervals GUS staining was assessed in stem sections. In rolC::uidA transformants, GUS activity in rapidly growing current-year shoots was not only tissue-specific, being localized to the phloem, but also cell-specific at the shoot base, where it was present only in the companion cells. However, during the onset of dormancy induced by short photoperiod, GUS activity shifted laterally from the phloem to include the cortex and pith. After subsequent exposure to chilling temperatures to induce the transition between the dormancy stages of rest and quiescence, GUS activity almost disappeared from all stem tissues, but regained its original phloem specificity and intensity after the shoots were reactivated by exposing them to long photoperiod and high temperatures. In contrast, GUS activity in the stem of 35S::uidA transformants was strong in all tissues except for the vascular cambium and xylem, and did not vary in intensity during the growth-dormancy-reactivation cycle. The lateral shift and increased intensity of GUS activity in the stem of rolC::uidA transformants during dormancy induction was shown to be associated with the accumulation of starch, and to be mimicked by incubating stem sections in sucrose, as well as glucose and fructose, but not sorbitol, prior to the GUS assay. Our results demonstrate that the activities of the rolC and 35S promoters varied in very different, unpredictable ways during the annual cycle of growth and dormancy in a perennial species, and indicate that the spatial and temporal variation in rolC promoter activity that we observed in the stem of transgenic hybrid aspen plants is attributable to cellular and seasonal changes in sucrose content.

Bacterial Proteins↗
PubMed1995

Anion channels as central mechanisms for signal transduction in guard cells and putative functions in roots for plant-soil interactions.

In higher plants anion channels have recently been suggested to play key roles in controlling cellular functions, including turgor- and osmoregulation, stomatal movements, anion transport, signal transduction and possibly also signal propagation. In guard cells and roots, physiological functions of anion channels have been proposed which will be discussed here. In initial investigations it was proposed that anion channels in the plasma membrane of guard cells provide a prominent control mechanism for stomatal closing. The proposed model suggests that anion channel activation and the resulting anion efflux from guard cells cause membrane depolarization, thereby driving K+ efflux through outward-rectifying K+ channels required for stomatal closing. This article provides a brief review of new and recent insights into the molecular properties and cell biological functions of anion channels in guard cells. Furthermore, recently implicated putative functions of anion channels in roots during salt stress, xylem loading and Al3+ tolerance are addressed.

Anions↗
PubMed1996

Molecular cloning and characterisation of asparagine synthetase from Lotus japonicus: dynamics of asparagine synthesis in N-sufficient conditions.

Two cDNA clones, LJAS1 and LJAS2, encoding different asparagine synthetases (AS) have been identified and sequenced and their expression in Lotus japonicus characterised. Analysis of predicted amino acid sequences indicted a high level of identity with other plant AS sequences. No other AS genes were detected in the L. japonicus genome. LJAS1 gene expression was found to be root-enhanced and lower levels of transcript were also identified in photosynthetic tissues. In contrast, LJAS2 gene expression was root-specific. These patterns of AS gene expression are different from those seen in pea. AS gene expression was monitored throughout a 16 h light/8 h dark day, under nitrate-sufficient conditions. Neither transcript showed the dark-enhanced accumulation patterns previously reported for other plant AS genes. To evaluate AS activity, the molecular dynamics of asparagine synthesis were examined in vivo using 15N-ammonium labelling. A constant rate of asparagine synthesis in the roots was observed. Asparagine was the most predominant amino-component of the xylem sap and became labelled at a slightly slower rate than the asparagine in the roots, indicating that most root asparagine was located in a cytoplasmic 'transport' pool rather than in a vacuolar 'storage' pool. The steady-state mRNA levels and the 15N-labelling data suggest that light regulation of AS gene expression is not a factor controlling N-assimilation in L. japonicus roots during stable growth in N-sufficient conditions.

Amino Acid Sequence↗
PubMed1996

The maize caffeic acid O-methyltransferase gene promoter is active in transgenic tobacco and maize plant tissues.

The pattern of expression directed by the promoter of the maize caffeic acid O-methyltransferase (COMT) gene was studied by histochemical and fluorometric beta-glucuronidase (GUS) analysis in transgenic maize and tobacco plants. The COMT promoter directs GUS expression to the xylem and the other tissues undergoing lignification, and it responds to wounding and to elicitors. In transgenic maize plants, expression of GUS corresponds to the pattern of expression of the endogenous COMT gene as determined by northern analysis and in situ hybridization. The pattern in transgenic tobacco plants clearly shows that the maize promoter sequence is recognized by tobacco transcriptional factors, in spite of the anatomical differences and the evolutionary distance between these two species. The results suggest that the most significant promoter signals that induce the specific expression of the lignin COMT are conserved in different species.

Gene Expression Regulation, Enzymologic↗
PubMed1993

Molecular cloning and expression of a Eucalyptus gunnii cDNA clone encoding cinnamyl alcohol dehydrogenase.

Cinnamyl alcohol dehydrogenase (CAD) catalyses the reduction of hydroxycinnamyl aldehydes (sinapyl, paracoumaryl, coniferyl aldehydes) to the corresponding alcohols which are the direct monomeric precursors of lignins. Recently, we have purified from Eucalyptus gunnii two isoforms of CAD (CAD1 and CAD2), distinct in their biochemical and functional properties. In this paper, we report the cloning of a CAD cDNA (pEuCAD2) isolated by screening a lambda gt11 library generated from cell suspension culture of Eucalyptus gunnii, using a tobacco CAD cDNA as a probe. This full-length clone (1392 bp) encodes a protein of 356 amino acids which corresponds to the subunit molecular weight of the CAD2 isoform. Sequence analysis revealed that CAD2 is very well conserved among species (78% homology with CAD from tobacco, a herbaceous angiosperm, and 81% with the partial sequence from a gymnosperm, loblolly pine). The identity of this clone was unambiguously demonstrated (1) by comparison with peptide sequence data from purified CAD2 and (2) by functional expression of the recombinant enzyme in Escherichia coli. Recombinant CAD showed the same properties as the natural isoform CAD2, in terms of electrophoretic mobility, polypeptide structure, substrate specificity and antigenicity. The CAD2 transcript is equally abundant in stems and leaves and at the limit of detection in roots. At the tissue level the CAD2 gene is highly expressed in xylem and virtually undetectable in phloem.

Alcohol Oxidoreductases↗
PubMed1993

Expression of the Arabidopsis AtAux2-11 auxin-responsive gene in transgenic plants.

Five constructions containing deletions of the promoter from an auxin-inducible gene of Arabidopsis thaliana, AtAux2-11, were fused to the coding region of the reporter gene LacZ, which encodes beta-galactosidase, and a polyadenylation 3'-untranslated nopaline synthase sequence from Agrobacterium. These chimeric genes were introduced into Arabidopsis by Agrobacterium tumefaciens-mediated transformation, and expression of the gene was examined by spectrophotometric and histochemical analyses. A 600 bp fragment from the AtAux2-11 promoter conferred histochemical patterns of staining similar to the longest 5' promoter tested, a 3.0 kb fragment. Localization of AtAux2-11/LacZ activity in the transgenic plants revealed spatial and temporal expression patterns that correlated with tissues and cells undergoing physiological processes modulated by auxin. LacZ activity was expressed in the elongating region of roots, etiolated hypocotyls, and anther filaments. Expression was detected in the vascular cylinder of the root and the vascular tissue, epidermis, and cortex of the hypocotyl, and filament. The AtAux2-11/LacZ gene was preferentially expressed in cells on the elongating side of hypocotyls undergoing gravitropic curvature. Expression of the chimeric gene in the hypocotyls of light-grown seedlings was less than that in etiolated seedling hypocotyls. The AtAux2-11/LacZ gene was active in the root cap, and expression in the root stele increased at sites of lateral root initiation. Staining was evident in cell types that develop lignified cell walls, e.g. trichomes, anther endothecial cells, and especially developing xylem. The chimeric gene was not expressed in primary meristems. While the magnitude of expression increased after application of exogenous auxin (2,4-D), the histochemical localization of AtAux2-11/LacZ remained unchanged. Transgenic plants with a 600 bp promoter construct (-0.6 kb AtAux2-11/LacZ) had higher levels of basal and auxin-inducible expression than plants with a 3.0 kb promoter construct. Transgenic plants with a -500 bp promoter had levels of expression similar to the -3.0 kb construct. The -0.6 kb AtAux2-11/LacZ gene responded maximally to a concentration of 5 x 10(-6) to 5 x 10(-5) M 2,4-D and was responsive to as little as 5 x 10(-8) M. The evidence presented here suggests that this gene may play a role in several auxin-mediated developmental and physiological processes.

Amino Acid Oxidoreductases↗
PubMed1994

Cloning of a lectin cDNA and seasonal changes in levels of the lectin and its mRNA in the inner bark of Robinia pseudoacacia.

A cDNA clone encoding a lectin was isolated by immunological screening of an expression library prepared from poly(A)+ RNA from the inner bark of Robinia pseudoacacia. The cDNA clone (RBL104) had an open reading frame of 858 bp that encoded a polypeptide with a predicted molecular weight of 31210. This molecular weight corresponded closely to that of a polypeptide immunoprecipitated from products of translation in vitro of the poly(A)+ RNA. Thus, RBL104 appeared to be a full-length cDNA. The N-terminal amino acid sequence of the purified lectin protein matched a portion of the predicted amino acid sequence. It appeared that the lectin was synthesized as a precursor that consisted of a putative signal peptide of 31 amino acids and a mature polypeptide of 255 amino acids. Southern blot analysis of the genomic DNA revealed that the lectin was encoded by a small multigene family. The lectin was mostly localized in the axial and ray parenchymal cells of the inner bark. A small amount of lectin was also found in the axial and ray parenchymal cells of the xylem. The lectin accumulated in the inner bark in September, remained at high levels during the winter and disappeared in May. The mRNA for the lectin was detected from August to the following March. The appearance and disappearance of the mRNA were observed prior to those of the lectin protein.

Amino Acid Sequence↗
PubMed1995

Characterization of the structure and determination of mRNA levels of the phenylalanine ammonia-lyase gene family from Populus kitakamiensis.

We isolated two new PAL genes, palg2b and palg4, from Populus kitakamiensis, palg2a and palg2b are clustered and palg2b encodes a polypeptide of 710 amino acids. The nucleotide sequence in the coding region of palg2b was 94.6% identical to that of palg2a. The promoter regions of palg1, palg2a and palg2b have several elements conserved among many phenylpropanoid biosynthetic genes. We measured the mRNA levels of the four PAL genes by S1 mapping using total RNA from stem tissues developing secondary xylem. Results showed that the transcript level of palg2b was higher than that of the other PAL genes.

Amino Acid Sequence↗
PubMed1992

Reduced PAL gene suppression in Verticillium-infected resistant tomatoes.

In tomato, resistance to the wilt fungus Verticillium albo-atrum is determined primarily by the Ve locus. When two tomato near-isolines which differ at this locus and in their susceptibility to the pathogen were compared, more rapid suberin coating in the xylem of resistant plants correlated closely with a more rapid increase in the activity of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), an enzyme which is essential to the suberization process. In contrast, levels of mRNA did not increase proportionally to the measured enzyme activities; rather, there was a substantial suppression of mRNA levels in the susceptible tomato line, consistent with a much lower elevation of PAL activity and significantly less vascular coating. The suppression was absent or substantially reduced in the resistant line. The results indicate that the pathogen can suppress defense genes in susceptible plants but suggest that their expression is altered in resistant hosts and that post-transcriptional regulation plays a significant role.

Amino Acid Sequence↗
PubMed1996

Immunocytochemical localization of phenylalanine ammonia-lyase in tissues of Populus kitakamiensis.

The polypeptide encoded by the partial fragment of cDNA of phenylalanine ammonia-lyase (PAL; EC 4.3.1.5), PALcDNA1 (Osakabe et al., 1995, Plant Sci. 105: 217-226), isolated from Populus kitakamiensis (P. sieboldii x P. grandidentata), was expressed in Escherichia coli cells. The polypeptide was purified and an antiserum raised against it. The antiserum recognized a protein of 77 kDa on nitrocellulose blots after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total protein and the partially purified PAL protein from P. kitakamiensis. Moreover, the antiserum recognized a protein on the blot after non-denaturing polyacrylamide gel electrophoresis of P. kitakamiensis proteins and this protein had PAL activity. Furthermore, the antibody inhibited PAL activity of extracts from stem tissues. These results showed that the antiserum against the partial PAL peptide recognized only the PAL subunits in extracts of P. kitakamiensis. Immunolocalization studies of P. kitakamiensis tissues revealed that the PAL protein was specifically localized in the xylem and the phloem fibers and no immunogold signal was found in the epidermis, the cortex, the pith, or the cambium of either stems or leaves.

Animals↗
PubMed1992

Rapid alterations in growth rate and electrical potentials upon stem excision in pea seedlings.

Excision of the epicotyl base of pea (Pisum sativum L.) seedlings in air results in a fast drop in the growth rate and rapid transient membrane depolarization of the surface cells near the cut. Subsequent immersion of the cut end into solution leads to a rapid, transient rise in the epicotyl growth rate and an acropetally propagating depolarization with an amplitude of about 35 mV and a speed of approx. 1 mm s-1. The same result can be achieved directly by excision of the pea epicotyl under water. Shape, amplitude and velocity of the depolarization characterize it as a "slow-wave potential". These results indicate that the propagating depolarization is caused by a surge in water uptake. Neither a second surge in water uptake (measured as a rapid increase in growth rate when the cut end was placed in air and then back into solution) nor another cut can produce the depolarization a second time. Cyanide suppresses the electrical signal at the treated position without inhibiting its transmission through this area and its development in untreated parts of the epicotyl. The large depolarization and repolarization which occur in the epidermal and subepidermal cells are not associated with changes in cell input resistance. Both results indicate that it is a transient shut-down of the plasma-membrane proton pump rather than large ion fluxes which is causing the depolarization. We conclude that the slow wave potential is spread in the stem via a hydraulic surge occurring upon relief of the negative xylem pressure after the hydraulic resistance of the root has been removed by excision.

Membrane Potentials↗
PubMed1996

Induction and ionic basis of slow wave potentials in seedlings of Pisum sativum L.

Slow wave potentials (SWPs) are transient depolarizations which propagate substantial distances from their point of origin. They were induced in the epidermal cells of pea epicotyls by injurious methods such as root excision and heat treatment, as well as by externally applied defined steps in xylem pressure (Px) in the absence of wounding. The common principle of induction was a rapid increase in Px. Such a stimulus appeared under natural conditions after (i) bending of the epicotyl, (ii) wounding of the epidermis, (iii) rewatering of dehydrated roots, and (iv) embolism. The induced depolarization was not associated with a change in cell input resistance. This result and the ineffectiveness of ion channel blockers point to H(+)-pumps rather than ion channels as the ionic basis of the SWP. Stimuli such as excision, heat treatment and pressure steps, which generate SWPs, caused a transient increase in the fluorescence intensity of epicotyls loaded with the pH-indicator DM-NERF, a 2',7'-dimethyl derivative of rhodol, but not of those loaded with the pH indicator 2',7'bis(2-carboxyethyl)-5-(and-6)-carboxyfluorescein (BCECF). Matching kinetics of depolarization and pH response identify a transient inactivation of proton pumps in the plasma membrane as the causal mechanism of the SWP. Feeding pump inhibitors to the cut surface of excised epicotyls failed to chemically simulate a SWP; cyanide, azide and 2,4-dinitrophenol caused sustained, local depolarizations which did not propagate. Of all tested substances, only sodium cholate caused a transient and propagating depolarization whose arrival in the growing region of the epicotyl coincided with a transient growth rate reduction.

Cholic Acids↗
PubMed1983

Quantitative changes in the degree of chromatin condensation during the cell cycle in differentiating Pisum sativum vascular tissue.

Fixed tissue from the base of the fourth internode above the cotyledons of Pisum sativum plants were Feulgen-stained for DNA. In squash preparations three cell types: xylem vessel elements, phloem fibres and phloem sieve tube elements were identified. Measurement of Feulgen absorbance values in 0.5 X 0.5 microns measuring points across each nucleus were obtained with a scanning cytophotometer. Condensed chromatin was defined as any measuring point having an absorbance value greater than 0.32. Calculating 'percent condensed chromatin' as the percentage of the total nuclear DNA contained in those densely stained points, the pattern of change in this parameter during interphase in each cell type was observed. A generally similar pattern occurs in all three cell types. Percent condensed chromatin decreased from about 45% to 12% during G1, increased rapidly to the end of S, decreased during G2 and the following G1 to increase again during the subsequent S phase.

Cell Cycle↗
PubMed1983

The role of plant hormones in higher plant cellular differentiation. II. Experiments with the vascular cambium, and sclereid and tracheid differentiation in the pine, Pinus contorta.

In sterile-cultured explants of stems of the pine Pinus contorta Dougl., fusiform cambial cells differentiated entirely into axial parenchyma cells when exogenous indol-3yl-acetic acid (IAA) was omitted. The normal appearance of the cambial zone was maintained when IAA was included in the medium. The IAA-maintained stability of cambial structure suggests physiological rather than epigenetic control over vascular cambium structure. IAA was essential for the occurrence of callus growth in stem explants. Callus growth was similar in appearance and extent in winter- and summer-explanted material. Tracheids differentiated in explants only when actively differentiating tracheids were already present at the moment of explanting, suggesting the absence of factors necessary for tracheid differentiation in over-wintering tissues. Sclereid differentiation, which normally does not occur in phloem or xylem development in P. contorta, occurred in callus derived from active cambial explants. The sclereids were identical to sclereids which differentiated in pith of intact stems. The possibility that sclereid and tracheid differentiation may be fundamentally similar types of gene expression is discussed. Growth of P. contorta trees in continuous darkness resulted in extensive compression-wood tracheid differentiation in the upright main stem. Normal-wood tracheids differentiated in similar trees grown in light. More tracheids differentiated in light than in darkness. This apparently is the first report of induction of compression-wood tracheid differentiation in the absence of hormone treatment or tilting of trees. Different types and numbers of tracheids differentiated at different position in two-year-old disbudded defoliated stem cuttings of P. contorta in response to apically supplied IAA. No evidence for new tracheid differentiation was seen in control cuttings; however, the results suggest that neither cambial cell division nor tracheid differentiation were actually initiated by IAA. Directed transport of additional regulatory factors toward areas of high IAA concentration is formulated as a hypothesis to explain these observations. Gibberellic acid, (S)-abscisic acid and IAA inhibited tracheid differentiation when individually supplied to basal ends of P. contorta cuttings predisposed to differentiate new tracheids. Experiments with single intact needles on Pinus cembroides var. monophylla cuttings confirmed a previous interpretation that the mature pine needle, rather than the short-shoot apical meristem at its base, promotes tracheid differentiation in the stem.

Abscisic Acid↗