Hydraulic properties of individual xylem vessels of Fraxinus americana.
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Studies of the hydraulic properties of xylem vessels have been limited to measurements of whole plant or whole stem segments. This approach allows the longitudinal transport properties of the ensemble of vessels within a stem to be determined, but provides little information on radial transport. Here the xylem of Fraxinus americana L. has been examined using a new method that allows the transport properties of individual vessels to be examined. One goal of this study was to quantify transport parameters relevant to embolism repair. The longitudinal conductivity of vessel segments open at both ends (i.e. no end walls) agreed with values predicted by the Poiseuille equation. Radial specific conductance (conductance per unit area) was approximately six orders of magnitude lower than the longitudinal conductance of the vessel segment normalized by the cross-sectional area of the vessel lumen. There was a step increase in the radial specific conductance of previously gas-filled vessels when the delivery pressure exceeded 0.4 MPa. This is consistent with the idea that positive pressure, required for embolism repair, can be compartmentalized within a vessel if the bordered pit chambers are gas-filled. The diffusion coefficient for the movement of gas from a pressurized air-filled vessel was of the same order of magnitude as that for air diffusing through water (1.95 e(-9) m(2) s(-1)). Estimates of the time needed to displace all of the gas from an air-filled vessel were in the order of 20 min, suggesting that gas removal may not be a major limitation in embolism repair. (+info)
Xylem hydraulic conductivity related to conduit dimensions along chrysanthemum stems.
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The stem xylem conduit dimensions and hydraulic conductivity of chrysanthemum plants (Dendranthema x grandiflorum Tzvelev cv. Cassa) were analysed and quantified. Simple exponential relations describe conduit length distribution, height dependency of conduit length distribution, and height dependency of stem hydraulic conductivity. These mathematical descriptions can be used to model the xylem water transport system. Within a chrysanthemum stem of 1.0 m, the conduit half-length (the length within which 50% of the conduits have their end) was 0.029 m at soil surface and decreased by half at a height of 0.6 m. With each 0.34 m increase in height up the stem, the hydraulic conductivity decreased by 50%. The resistance calculated from conduit lumen characteristics was 70% of the measured resistance. The remaining unexplained part of the hydraulic resistance is at least partly caused by inter-conduit connections. (+info)
Cloning of a cDNA encoding EIN3-like protein (DC-EIL1) and decrease in its mRNA level during senescence in carnation flower tissues.
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A cDNA clone encoding a putative EIN3-like protein (DC-EIL1) was obtained from total RNA isolated from senescing carnation (Dianthus caryophyllus L.) petals using RT-PCR and RACE techniques. The cDNA (2382 bp) contained an open reading frame of 1986 bp corresponding to 662 amino acids. The amino acid sequence of the N-terminal half of the protein, ranging from 80-300 amino acid residues, had 84% identity with that of the corresponding regions of Arabidopsis EIN3 and tobacco TEIL, although the overall identity was 49% and 52%, respectively. Northern blot analysis revealed that the amount of mRNA corresponding to DC-EIL1 decreased in flower tissues, especially in petals, during natural senescence and senescence induced by exogenously applied ethylene or ABA. (+info)
Cell-type-specific expression of plant cytochrome c mRNA in developing flowers and roots.
(68/1585)
We have used RNA in situ hybridization to analyze the expression of transcripts encoding cytochrome c in different tissues and organs of sunflower (Helianthus annuus). Although northern-blot hybridization experiments indicate that the relative abundance of transcripts does not vary greatly, we have detected important changes in localization during flower development. Enhanced expression is observed in floral meristems as soon as they are discernible from the central portion of the capitulum containing the inflorescence meristem. As flowers develop, labeling is observed in all developing floral organ primordia. Later in development, expression in petals is reduced, and only the central portion of the flower becomes labeled. During the process of stamen formation, hybridization signals were obtained mainly in anthers. Less developed flowers at this stage showed expression through the archesporial tissue. During meiosis, the label was observed mainly in tapetal cells. Specific expression patterns, similar to those obtained for sunflower, were observed when Arabidopsis flowers were analyzed with a homologous cytochrome c probe. Specific patterns of expression were also observed in young sunflower roots. In this case, enhanced expression was detected in developing endodermis and pericycle and in protoxylem initials. We conclude that cell-specific mechanisms operate to regulate the abundance of cytochrome c encoding transcripts in different plant tissues. The overlap between the expression patterns of the nuclear encoded cytochrome c gene and some mitochondrial genes suggests the existence of coordinated mechanisms of expression. (+info)
Xylem cavitation in the leaf of Prunus laurocerasus and its impact on leaf hydraulics.
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This paper reports how water stress correlates with changes in hydraulic conductivity of stems, leaf midrib, and whole leaves of Prunus laurocerasus. Water stress caused cavitation-induced dysfunction in vessels of P. laurocerasus. Cavitation was detected acoustically by counts of ultrasonic acoustic emissions and by the loss of hydraulic conductivity measured by a vacuum chamber method. Stems and midribs were approximately equally vulnerable to cavitations. Although midribs suffered a 70% loss of hydraulic conductance at leaf water potentials of -1.5 MPa, there was less than a 10% loss of hydraulic conductance in whole leaves. Cutting and sealing the midrib 20 mm from the leaf base caused only a 30% loss of conduction of the whole leaf. A high-pressure flow meter was used to measure conductance of whole leaves and as the leaf was progressively cut back from tip to base. These data were fitted to a model of hydraulic conductance of leaves that explained the above results, i.e. redundancy in hydraulic pathways whereby water can flow around embolized regions in the leaf, makes whole leaves relatively insensitive to significant changes in conductance of the midrib. The onset of cavitation events in P. laurocerasus leaves correlated with the onset of stomatal closure as found recently in studies of other species in our laboratory. (+info)
Evolution of floral meristem identity genes. Analysis of Lolium temulentum genes related to APETALA1 and LEAFY of Arabidopsis.
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Flowering (inflorescence formation) of the grass Lolium temulentum is strictly regulated, occurring rapidly on exposure to a single long day (LD). During floral induction, L. temulentum differs significantly from dicot species such as Arabidopsis in the expression, at the shoot apex, of two APETALA1 (AP1)-like genes, LtMADS1 and LtMADS2, and of L. temulentum LEAFY (LtLFY). As shown by in situ hybridization, LtMADS1 and LtMADS2 are expressed in the vegetative shoot apical meristem, but expression increases strongly within 30 h of LD floral induction. Later in floral development, LtMADS1 and LtMADS2 are expressed within spikelet and floret meristems and in the glume and lemma primordia. It is interesting that LtLFY is detected quite late (about 12 d after LD induction) within the spikelet meristems, glumes, and lemma primordia. These patterns contrast with Arabidopsis, where LFY and AP1 are consecutively activated early during flower formation. LtMADS2, when expressed in transgenic Arabidopsis plants under the control of the AP1 promoter, could partially complement the organ number defect of the severe ap1-15 mutant allele, confirming a close relationship between LtMADS2 and AP1. (+info)
Isolation of a CONSTANS ortholog from Pharbitis nil and its role in flowering.
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The short-day plant Pharbitis nil is a model plant for the study of photoperiodic control of floral initiation. Flower formation can be induced at the cotyledon stage by a single long night of at least 14 h in duration. Using differential display of mRNA we identified a P. nil ortholog of the Arabidopsis CONSTANS (CO) gene, which will be referred to as PnCO. Expression of PnCO was high after a 14-h night, but low when the dark period was 12 h or less. Our results indicate that the level of the PnCO transcript is photoperiodically regulated. After transfer from continuous light to darkness, PnCO showed a circadian pattern of expression. Expression of the CAB gene, which is a molecular marker for the circadian clock, exhibited a different pattern of expression than did PnCO and was not subject to the same photoperiodic control. A major portion of the PnCO transcripts contained an unspliced intron. Only the intron-free PnCO was able to complement the co mutant of Arabidopsis by shortening the time to flower. (+info)
Light-dependent osmoregulation in pea stem protoplasts. photoreceptors, tissue specificity, ion relationships, and physiological implications.
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Light-induced changes in the volume of protoplasts bathed in a medium of constant osmolarity are useful indications of light-dependent cellular osmoregulation. With this in mind, we investigated the effect of light on the volume of protoplasts isolated from the elongating stems of pea (Pisum sativum) seedlings raised under red light. The protoplasts were isolated separately from epidermal peels and the remaining peeled stems. Under continuous red light, the protoplasts of peeled stems swelled steadily, but those of epidermal peels maintained a constant volume. Experiments employing far-red light and phytochrome-deficient mutants revealed that the observed swelling is a light-induced response mediated mainly by phytochromes A and B with a little greater contribution by phytochrome A. Protoplasts of epidermal peels and peeled stems shrank transiently in response to a pulse of blue light. The blue light responsiveness in this shrinking response, which itself is probably mediated by cryptochrome, is under the strict control of phytochromes A and B with equal contributions by these phytochromes. We suggest that the swelling response participates in the maintenance of high tissue tension of elongating stems and that the shrinking response is involved in stem growth inhibition. Other findings include the following: The swelling is caused by uptake of K+ and Cl-. The presence of Ca2+ in the bathing medium is required for phytochrome signaling in the swelling response, but not in the response establishing blue light responsiveness. Phytochrome A mediates the two responses in a totally red/far-red light reversible manner, as does phytochrome B. (+info)