Stem Tissues Of Plants Research Articles

Water source utilization by Pinus jeffreyi and Arctostaphylos patula on thin soils over bedrock.

Stable isotopes were used to evaluate water sources for co-occurring Jeffrey pine (Pinus jeffreyi Grev & Balf.) and greenleaf manzanita (Arctostaphylos patula Greene) in the southern Sierra Nevada, California, where soils averaged only 75 cm thick but were underlain by up to 5 m of weathered granitic bedrock. Soils and underlying weathered bedrock were sampled three times during both the 1997 and 1998 growing seasons, in 25 cm increments, from 0 to 400 cm or until hard bedrock was reached, and plant stem tissue was sampled simultaneously. Extracted water from the soil/bedrock substrate and plant tissue was analyzed for delta(18)O and/or deltaD, and depth of water source was determined by inference in conjunction with moisture status of the substrate. Water source utilization over the growing seasons for both plants generally followed a pattern similar to that observed for water depletion. Predominant water use was initially from the surface soils. Progressively deeper water sources, including weathered bedrock to a depth of several meters, were exploited as the season progressed and the overlying substrate was depleted of moisture. Early in the growing season, stable isotope values were slightly lower for pine than for manzanita (e.g., average deltaD in June 1997 was -81 per thousand for pine and -77 per thousand for manzanita), and suggest that the functional rooting depth for pine may have been slightly greater than for manzanita. In September 1997, manzanita deltaD values averaged -57 per thousand while pine values averaged -85 per thousand, indicating that manzanita opportunistically utilized summer precipitation while pine used more dependable bedrock water. In 1998, soils remained moist through July due to a late snowfall. Unlike the previous year, pine and manzanita deltaD values were not significantly different in mid- and late-growing season, and both plants exploited bedrock-derived water as soil water was depleted. Water held within bedrock was essential for meeting plant transpirational requirements over the summer drought.

Accurate and high resolution in situ hybridization analysis of gene expression in secondary stem tissues.

Accurate in situ hybridization analysis in secondary stem tissues of plants has been hindered by specific characteristics of these tissues. First, secondary cell walls non-specifically bind probes used for in situ hybridization thus preventing gene expression analysis in the lignified regions of the stem, such as the xylem. Second, the mRNA in the cambial meristem and its recent derivatives are prone to inadequate fixation when conventional techniques are used. Here we describe an in situ hybridization technique which uses fast freezing and freeze substitution to cryoimmobilize the mRNA followed by embedding in a methacrylate resin for high-resolution analysis of gene expression. By using a transgenic poplar line harbouring rolC:uidA, rolC:iaaM, the gene expression pattern could be compared with histochemical GUS staining. This in situ hybridization technique results in superior preservation of cellular contents, retention of mRNA in all cell types in the poplar stem, a significant reduction of non-specific binding to secondary cell walls and a resolution not previously possible in secondary tissues. This technique will be particularly valuable for the expression analysis of genes involved in xylogenesis and wood formation.

Determination of Nitrogen Status in Winter Wheat by Measuring Basal Stem Tissue Sap Nitrate Concentration

The aim of this study was to assess a quick-test method determining nitrate in basal stem tissue sap for the prediction of nitrogen status in winter wheat (Triticum aestivum L.). The nitrate content in plant stem tissue sap collected at Zadoks growth stages GS 31 and GS 49 of winter wheat in 11 annual field trials in south-east Norway in the years 1993-96 was measured with Merckoquant test strips with a Nitracheck Meter. Relationships between NO3 - concentrations and final yields were good within individual trials, but when the results from all trials were pooled, the NO3 - concentration was a poor predictor of final yields. This study suggests that the critical nitrate values required in plant stem sap for sufficient grain protein content for bread-baking quality are 4000 ppm NO3 - at GS 31 and 2000 ppm at GS 49 in situations with a single N application in the spring. In situations with split N applications (25 kg N ha-1 at GS 31 and 25 kg N ha-1 at GS 49 in addition to spring application), 1000 and 500 ppm were found to be the critical values at GS 31 and 49, respectively. Because of the large between-site and between-year variability, this study does not indicate that the method can be recommended for extended practical use.

Role of Extracellular Polysaccharide and Endoglucanase in Root Invasion and Colonization of Tomato Plants by Ralstonia solanacearum

ABSTRACT Ralstonia solanacearum is a soilborne plant pathogen that normally invades hosts through their roots and then systemically colonizes aerial tissues. Previous research using wounded stem infection found that the major factor in causing wilt symptoms was the high-molecular-mass acidic extracellular polysaccharide (EPS I), but the beta-1,4-endoglucanase (EG) also contributes to virulence. We investigated the importance of EPS I and EG for invasion and colonization of tomato by infesting soil of 4-week-old potted plants with either a wild-type derivative or genetically well-defined mutants lacking EPS I, EG, or EPS I and EG. Bacteria of all strains were recovered from surface-disinfested roots and hypocotyls as soon as 4 h after inoculation; that bacteria were present internally was confirmed using immunofluorescence microscopy. However, the EPS-minus mutants did not colonize stems as rapidly as the wild type and the EG-minus mutant. Inoculations of wounded petioles also showed that, even though the mutants multiplied as well as the wild type in planta, EPS-minus strains did not spread as well throughout the plant stem. We conclude that poor colonization of stems by EPS-minus strains after petiole inoculation or soil infestation is due to reduced bacterial movement within plant stem tissues.

On the Strength of Herbaceous Vascular Plant Stems

Abstract During the past 120 years researchers have tried to provide an understanding of the relationship between the arrangement of stiffening tissue in the cross-section of plant stems and their mechanical integrity. The mechanical analysis of vertical stems of self-supporting plants has traditionally been concerned with issues involving global and local stability of the stem, and with stresses developed due to wind loads. Plant stem tissue, considered as a material, is both heterogeneous and highly anisotropic, and this must be reflected in any characterization of its mechanical behaviour. This fact strongly influences the type of failure criterion which should be applied for compressive failure of the stem subjected to loads causing bending. It is shown, here, that applying modern ideas as to the appropriate criteria for compressive failure of fibre-reinforced composite materials can influence how we assess the efficacy of various stelar arrangements concerning their ability to fulfill their mechanical function. Specifically, it is demonstrated that peripheral arrangements of supporting tissue are, in some circumstances, less advantageous than more uniform distributions of this tissue.

Growth of micropropagated lowbush blueberry with defined fungi in irradiated peat mix

There is an interest in vegetative multiplication of high-yielding clones of Vaccinium angustifolium Ait. to establish or enhance blueberry production. This study evaluates mycorrhizal inoculation as an aid in such propagation from microcuttings. Shoots of Vaccinium angustifolium (clone 7062) generated in vitro were rooted in a peat–vermiculite–perlite substrate with or without ericoid mycorrhizal fungi fortification by Hymenoscyphus ericae or Scytalidium vaccinii and with or without peat sterilization by γ irradiation. Both in irradiated peat mix inoculated with S. vaccinii and in unirradiated peat mix with H. ericae, microcuttings grew taller and branched more than with the four other treatments. The profusely rooted plantlets available from all treatments of the cuttings put on significantly more total length of stems and branches after 167 days in the greenhouse when growing with either inoculant in unirradiated peat than in the unirradiated peat without inoculation. However, the magnitude of difference might be of borderline importance in commercial nursery operations. A higher level of copper and zinc in stem tissue was observed in stem tissue of plants grown with H. ericae with or without irradiation but not with S. vaccinii. Key words: ericoid mycorrhizae, micropropagation, Hymenoscyphus ericae, Scytalidium vaccinii, Vaccinium angustifolium.

Fusicoccin‐induced membrane depolarization, K+ efflux and extracellular alkalinization in leaves of Vigna unguiculata

Abstract. In leaves of three different cultivars of cowpeas (Vigna unguiculata), the fungal toxin fusi‐coccin (FC) induced a plasmalemma depolarization from ‐175 to ‐100mV, a value slightly below the N2‐determined diffusion potential in the dark, and to a lesser extent in the light. The depolarization was preceded by the usual initial membrane hyperpolarization (up to 18mV). The membrane depolarization was accompanied by considerable K+ efflux and extracellular alkalinization. Primary and secondary leaves as well as stem tissue of plants, grown under long‐day conditions or in the dark responded similarly. Dark O2 uptake in leaves and hypocotyls was stimulated by FC by up to 77 and 87%, respectively. In contrast, FC caused a typical Em hyperpolarization, K+ influx, extracellular acidification and smaller stimulation of respiration (50%) in leaves of other legumes such as mungbean (Vigna radiata), or soybean (Glycine max). Leaves of navy beans (Phaseolus vulgaris) revealed an intermediate response to FC. The unusual effect of FC in Vigna might be related to the production of toxic catabolites during degradation and fermentation of storage products necessary to meet the strong energy requirement of the pm‐H+ ATPase.

Staining of the Stem Tissue of Plants by Triphenyltetrazolium Chloride

Staining of the Stem Tissue of Plants by Triphenyltetrazolium Chloride