Speculations on carbon dioxide starvation, Late Tertiary evolution of stomatal regulation and floristic modernization

Ambient atmospheric CO₂ concentration ([CO₂]_a) has apparently declined from values above 200μmol mol⁻¹ to values below 200μmol mol⁻¹ within the last several million years. The lower end of this range is marginal for C₃ plants. I hypothesize that: (1) declining [CO₂]_a imposed a physiological strain on plants, and plant taxa evolving under declining [CO₂]_a tended to develop compensating mechanisms, including increased stomatal efficiency; (2) angiosperms were better able to adjust to declining [CO₂]_a than were gymnosperms and pteridophytes; and (3) angiosperm adjustment has been uneven. Fast-evolving taxa (e.g. grasses and herbs) have been better able to adapt to CO₂ starvation. If these propositions are true, stomatal adjustment mechanisms should show patterned variation, and a single pattern of stomatal regulation cannot be assumed.     

A new,pathogen-inducible gene of Arabidopsis is expressed in an ecotype-specific manner

In this study we describe a novel gene, which was isolated in an attempt to search for specific plant resistance genes of Arabidopsis against isolates of the phytopathogenic bacterium Xanthomonas campestris pv. campestris. The gene was cloned by differential screening of a genomic library of the Xcc 750-resistant ecotype Col-0, using cDNA populations derived from ecotype Col-0 and the Xcc 750-susceptible ecotype Oy-0. The isolated gene, CXc750, is differentially expressed in ecotypes of Arabidopsis thaliana. In addition, although highly expressed in uninfected plants, gene expression increases in response to pathogen attack. CXc750 potentially codes for a small, basic protein of about 10 kDa. The predicted protein product contains a potential signal leader peptide at the amino-terminal end but no ER retention sequence and no further transmembrane domain. This indicates that the gene product is transported to other compartments or out of the cell.The possible function of CXc750 as a member of the plant defense response system is discussed.     

A simple classification of the complex parts of vascular plants

Four operational morphological units are defined to characterize 'typical' stems, leaves, roots and hairS. Any complex part can be classified among these OMUs by a graphical representation or by a quadruplet suitable for computer-aided analyses. Thirty-nine examples are given, suggesting a continuous view of plant morphology.     

Analysis of DNA polymerase activity in Petunia protoplasts treated with clastogenic agents

Clastogenic agents, i.e. agents that can induce chromosome or DNA breakage, have been shown to enhance the rale of direct gene transfer to protoplasts. The effect was analysed at the enzymatic level using protoplast homogenates as well as intact protoplasts. For that purpose existing procedures were modified to enable measurement of DNA polymerase in vivo. In the system used, external DNA was able to enter the cells without the addition of membrane-permeabilizing compounds. When comparing total DNA polymerase activity of protoplasts irradiated with X-rays or UV-light with that of untreated cells we did not observe significant differences. Incubation of protoplasts with high doses of bleomycin affected total DNA polymerase activity negatively. but dideoxythymidine triphosphate-sensitive activity was not influenced. We conclude that the DNA strand-breaks induced by low doses of X-rays. UV-light or bleomycin do not increase the total or the repair-DNA polymerase activity and. therefore. that the increase in the transformation rates after DNA strand-breaking is not preceded by enhanced DNA polymerase activity.     

Genetic manipulation of 6-phosphofructokinase in potato tubers

The aim of this work was to discover whether genetic manipulation of 6-phosphofructokinase [EC 2.7.1.11; PFK(ATP)] influenced the rate of respiration of tuber tissue of Solanum tuberosum L. Transgenic plants were produced that contained the coding sequence of the Escherichia coli pfkA gene linked to a patatin promoter. Expression of this chimaeric gene in tubers resulted in a 14to 21-fold increase in the maximum catalytic activity of PFK(ATP) without affecting the activities of the other glycolytic enzymes. Tubers, and aged disks of tuber tissue, from transformed plants showed no more than a 30% fall in the content of hexose 6-monophosphates; the other intermediates of glycolysis increased threeto eightfold. Fructose-2,6-bisphosphate was barely detectable in aged disks of transformed tubers. The relative rates of ¹⁴CO₂ production from [1-¹⁴C]-and [6-¹⁴C]-glucose supplied to disks of transformed and control tubers were similar. Oxygen uptake and CO₂ production by aged disks of transformed tubers did not differ significantly from those from control tubers. The same was true of CO₂ production, in air, and in nitrogen, for tuber tissue. It is concluded that PFK(ATP) does not dominate the control of respiration in potato tubers.Abbreviations Fru2,6bisP fructose-2,6-bisphosphate - FW freshweight - GUS -glucuronidase - PFK(ATP) 6-phosphofructokinase - PFK(PPi) pyrophosphate: fructose-6-phosphate 1-phosphotransferase     

Assessing the risks of transgene escape through time and crop-wild hybrid persistence

Transgenes introduced into crops can escape in time, as well as space, via the seed bank. For annual plants, especially ruderals, seed bank behaviour may be the most important factor determining population persistence. Crop seeds may exhibit some dormancy and germination cueing in the soil but are expected to be less able to persist than their wild relatives, which often have considerable dormancy and longevity, as well as effective germination cueing responses. Crop-wild hybrids may have seed bank characteristics more suited to persistence, and maternal effects may favour persistence of hybrids having wild plants for their female parent. Escape of transgenes via crop-wild hybrids presents unique concerns not present for crops. Hybrids can undergo natural selection and may back-cross with wild plants. We suggest methods that can be used in conjunction with evaluation of the relative fitness of crop-wild hybrids that will determine the likelihood of back-crossing. Accurate assessment of escape in time and transgene persistence via crop-wild hybrids requires proper plant materials. We emphasize the use of null segregants as controls for transgenic crops and for generating crop-wild hybrid controls for transgenic hybrids. Since good empirical and theoretical understanding of how individual genes influence the fate of plants in different environments is lacking, evaluation of escape in time and the persistence of transgenes via crop-wild hybrids should be on a case-by-case basis.     

Studies on plant regeneration from cotyledonary protoplasts in Brassica campestris

Protoplasts isolated from both 7-day-old light-grown and 4-day-old dark/dim light-grown cotyledons of four Brassica campestris varieties (Arlo, Sonja, Bunyip and Wonk Bok) were cultured in three liquid media: modified K8P, modified MS and modified Pelletier's B to compare the capacities for cell division and plant regeneration. Following cell wall regeneration the cultured protoplasts from dark/dim light-grown cotyledons of four varieties showed rapid division and high frequency of cell division compared with those isolated from light-grown cotyledons. The frequencies of cell division were significantly influenced by varieties and culture media but only in cultured protoplasts isolated from dark/dim light-grown cotyledons. The interaction between varieties and media was also significant. Cell colonies formed within 7–14 days in protoplast cultures from dark/dim light-grown cotyledons, and calli subsequently grown on a solid medium developed shoots when transferred onto a regeneration medium. Three of four tested varieties (Arlo, Sonja and Bunyip) showed shoot regeneration within 2–3 months after protoplast isolation, with a high degree of reproducibility in Arlo and Bunyip. Regenerated shoots, which were induced to root on half-strength MS medium with 0.1 mg.l^–1 IBA, survived in soil and grew to produce siliques and set viable seeds in the greenhouse. The present report is the first to document the production of regenerated plants that set seeds in Brassica campestris from cotyledonary protoplasts.Abbreviations BAP benzylaminopurine - CPW Composition of Protoplast Washing-solution - 2,4-D 2,4-dichlorophenoxyacetic acid - EDTA ethylenediamine-tetraacetic acid - GA₃ gibberellic acid - IBA indole-3-butyric acid - IAA indole-3-acetic acid - MS Murashige and Skoog medium - NAA -naphthaleneacetic acid - KT kinetin - FDA fluorescein diacetate - SDS sodium dodecyl sulfate     

The structure of feeding behavior in the colorado potato beetle,Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Feeding behavior, in an ad libitum situation on potato plants in the laboratory, was continuously observed for approximately 7 h/day on 2 successive days for 18 adult femaleLeptinotarsa decemlineata. Additional behaviors were also recorded including resting, walking, biting, local movements, grooming, defecating, and regurgitating. These data were used to calculate a time budget for the various behaviors. The feeding data were analyzed to describe the structure of feeding for young adult females on their normal host plant. The criterion for a meal (minimum intermeal interval) was determined to be 286 s. This criterion was used to distinguish between intra- and intermeal interruptions in feeding for all subsequent analyses. Meals taken from leaves that were young, medium aged, or old did not differ, but on average beetles took 60% of their meals from young leaves. Meal size and meal duration were equally good predictors of when a meal would end. Feeding from stems was a prominent feature for most beetles. The stem meals had much longer durations than leaf meals, but stem feeding did not affect subsequent leaf feeding. The structure of feeding by these beetles is compared with that found in other insects, especiallyLocusta migratoria.     

植物肌动蛋白研究的过去及现状

肌动蛋白作为一种骨架蛋白广泛存在于植物细胞,有重要的生理功能.综述了植物肌动蛋白的发现及研究现状,着重介绍了植物肌动蛋白的性质、结构和生理功能.