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Duniway JM 《Plant physiology》1971,48(1):69-72
Bean plants (Phaseolus vulgaris L.) infected with the rust Uromyces phaseoli became unusually susceptible to drought as sporulation occurred. Under the conditions used (1,300 ft-c, 27 C, and 55% relative humidity) such plants wilted at soil water potentials greater than −1 bar, whereas healthy plants did not wilt until the soil water potential fell below −3.4 bars. Determinations of leaf water and osmotic potentials showed that an alteration in leaf osmotic potential was not responsible for the wilting of diseased plants. When diffusive resistance was measured as a function of decreasing leaf water content, the resistance of healthy leaves increased to 50 sec cm−1 by the time relative water content decreased to 70%, whereas the resistance of diseased leaves remained less than 8 sec cm−1 down to 50% relative water content. Apparently, water vapor loss through cuticle damaged by the sporulation process, together with the reduction in root to shoot ratio which occurs in diseased plants, upset the water economy of the diseased plant under mild drought conditions. 相似文献
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Comparison of pressure chamber and thermocouple psychrometer determinations of leaf water status in tomato 总被引:1,自引:0,他引:1 下载免费PDF全文
Duniway JM 《Plant physiology》1971,48(1):106-107
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
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Two different DNA fragments, one of 2.9 kilobases and the other of 5.1 kilobases, were cloned from Phytophthora citrophthora and showed no homology with DNA from plants and other related fungi. These DNA probes hybridized with DNA from 12 different P. citrophthora isolates obtained from a variety of hosts but did not hybridize with DNA from 6 P. citrophthora isolates obtained from cacao. Southern blot analysis revealed that the probes contained repetitive DNA, and restriction fragment length polymorphisms were identified among several P. citrophthora isolates. Of the isolates tested, two major groups were observed whose genetic similarity correlated with geographical distribution. One of the DNA probes was used to detect P. citrophthora growing from infected citrus roots incubated on semiselective medium. P. citrophthora was not detected by a hybridization assay of total DNA extracted directly from infected roots. 相似文献