Plant Science Letters最新文献

Cell turgor pressure, volumetric elastic modulus (ϵ) and hydraulic conductivity (Lp) of the lower epidermal cells of the chill sensitive plant Rhoeo discolor (Commelinaceae) were measured at different temperatures between 7 and 24°C with a micro pressure-probe. Chilling at a rate of 1°C/2 min caused a small, gradual decrease in cell turgor, but turgor rapidly increased to the control level after 90 min at 8°C. In addition, chilling caused a decrease in Lp but did not influence ϵ. In cells chilled at 7°C there was an increase of relaxation half time which corresponded to a decreasing Lp.

Alcohol dehydrogenase (ADH) activity in roots and shoots of 8-day-old barley seedlings (Hordeum vulgare cv. Sundance) rose in response to periods of flooding. The increase was accompanied by changes in the amounts and proportions of ADH isoenzymes present in the tissues. Enzyme activity in excised shoots also rose in response to enclosed atmospheres; this increase was not inhibited by actinomycin D and only partially restricted by cycloheximide. The physiological significance of the observed changes in isoenzyme proportions is discussed with reference to the kinetic properties of the isoenzymes.

The RNA of the potyvirus, tobacco vein mottling virus (TVMV), was encapsulated in reverse-phase evaporation vesicle liposomes containing phosphatidylserine and cholesterol. The liposomes were used to inoculate tobacco mesophyll protoplasts. Analysis of extracts of protoplasts, by enzyme-linked immunosorbent assay (ELISA), hybridization with labeled cDNA, electron microscopy and infectivity assays, indicated that significant multiplication of the virus had occurred after incubation of the protoplasts for 2–3 days. It was estimated that approx. 15% of the protoplasts had become infected.

The metabolism of arachidonic acid (AA) and other selected fatty acids by potato (Solanum tuberosum) tuber slices was followed with the use of radioactive labeled substrates. The predominant metabolites observed were glyceries. Significant quantities of the unmetabolized acids were also recovered. None of the expected AA metabolites such as hydroperoxides or cyclopentenones that are produced by cell-free systems could be detected under the incubation conditions. The elicitor activity of the fatty acids could not be correlated with their rate of metabolism.

Protoplasts were isolated from leaves of field-grown grapevines (Vitas vinifera cv. Cabernet Sauvignon and Golden Muscat) by digestion with cellulase and driselase. The protoplasts were purified by floatation on a step gradient of Percoll. Purified protoplasts exhibited light-dependent oxygen evolution of 22–34 μmol O₂/mg chlorophyll per h, which was comparable to rates of photosynthesis reported for grapevine leaves and leaf discs. The protoplasts were 90% intact based on polarographic determination of penetration of glycolate. The results indicate that the grapevine leaf protoplasts retained their photosynthetic activities and were metabolically competent.

A restriction map of rice (Oryza sativa) rDNA was established for EcoRI, BamHI and Bg1II. The methylation pattern of these genes was studied using HpaII and MspI. Surprisingly, rice rDNA was found much more sensitive to these enzymes than the rDNA of the other plant species studied so far. No difference was observed between the methylation pattern of rDNA prepared from embryos grown in aerobic or anaerobic conditions although there is a marked difference between the rates of rRNA synthesis in these two situations.

The organization of 5 S rRNA genes was examined in the wheat, Triticum aestivum var. Hardi, and three size classes of repeated units were recognized. Digestion with micrococcal nuclease of nuclei from ungerminated embryos or from embryos germinated for 48 h revealed that these tissues have 5 S genes organized into nucleosomes with repeat lengths similar to those of bulk chromatin. No special arrangement of nucleosomes with respect to 5 S DNA sequences was found. The 5 S DNA methylation pattern was determined in genomic DNA at both developmental stages. The 410 bp unit family has significant undermethylation at CCGG sites, in both active and inactive tissues. This is in marked contrast to the situation with the 500 bp unit family, which has nearly all CCGG sites methylated at both developmental stages.

Glutamine synthetase was purified to apparent homogeneity from the leaves of light-grown tomato plants. The purification steps involved ammonium sulphate precipitation (40–60%), adsorption by hydroxyapatite, DEAE Sephadex ionic exchange chromatography, and Sephacryl S 300 gel filtration. Only one glutamine synthetase form was found, with K_m-values of 5.5 mM, 0.8 mM and 0.4 mM for glutamate, ATP and ammonium, respectively. The in vitro activity depended on Mg²⁺ or Mn²⁺ concentrations with positive cooperativity. Enzyme assay pH optima were 7.2 for synthetase, and 6.0 for transferase. The activation energy of the enzymatic reaction was 33.2 kJ/mol. ADP appeared to be a competitive inhibitor with a K_i-value of 0.4 mM. Enzyme inhibition was also produced by aspartate, alanine and phosphoserine.

Trichome densities of leaflets differed on plants of Lycopersicon esculentum, L. hirsutum, L. hirsutum f. globratum and two interspecific hybrids grown under an 8-h photophase with (long days (LD)) or without (short days (SD)) a 4-h night interruption. Response to the 2 photoperiods depended on the genotype of plant and the particular type of trichome. Generally, the densities of Type IV trichomes — short, glandular trichomes having a single tip cell — were greater under SD and densities of Type VI trichomes — short, glandular trichomes with a multicellular tip — were greater under LD. Densities of Type V trichomes — short, non-glandular trichomes — did not differ between LD and SD. Quantities of 2-tridecanone and two 15-carbon compounds were not significantly altered by the night interruption.