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91.
In an early-flowering line of pea (G2) apical senescence occurs only in long days (LD), while growth in short days (SD) is indeterminate. In SD, G2 plants are known to produce a graft-transmissible substance which delays apical senescence in related lines that are photoperiod-insensitive with regard to apical senescence. Gibberellic acid (GA3) applied to the apical bud of G2 plants in LD delayed apical senescence indefinitely, while N6-benzyladenine and -naphthaleneacetic acid were ineffective. Of the gibberellins native to pea, GA9 had no effect whereas GA20 had a moderate senescence-delaying effect. [3H]GA9 metabolism in intact leaves of G2 plants was inhibited by LD and was restored by placing the plants back in SD. Leaves of photoperiod-insensitive lines (I-types) metabolized GA9 readily regardless of photoperiod, but the metabolites differed qualitatively from those in G2 leaves. A polar GA9 metabolite, GAE, was found only in G2 plants in SD. The level of GA-like substances in methanol extracts from G2 plants dropped about 10-fold after the plants were moved from SD to LD; it was restored by transferring the plants back to SD. A polar zone of these GA-like materials co-chromatographed with GAE. It is suggested that a polar gibberellin is synthesized by G2 plants in SD; this gibberellin promotes shoot growth and meristematic activity in the shoot apex, preventing senescence.Abbreviations GA
gibberellin
- GA3
gibberellic acid
- SD
short days
- LD
long days 相似文献
92.
Testing the covarion hypothesis of molecular evolution 总被引:6,自引:8,他引:6
The covarion hypothesis of molecular evolution states that the fixation of
mutations may alter the probability that any given position will fix the
next change. Tests of this hypothesis using the divergence of real
sequences are compromised because models of rate variation among sites
(e.g., the gamma version of the one-parameter equation) predict sequence
divergence values similar to those for the covarion process. This study
therefore focuses on the extent to which the varied and unvaried codons of
two well-diverged taxa are the same, because fewer are expected by the
covarion hypothesis than by the gamma model. The data for these tests are
the protein sequences of Cu, Zn superoxide dismutase (SOD) for mammals and
plants. Simulation analyses show that the covarion hypothesis makes better
predictions about the frequencies of varied and unhit positions in common
between these two taxa than does the gamma version of the one-parameter
model. Furthermore, the analysis of SOD tertiary structure demonstrates
that mammal and plant variabilities are distributed differently on the
protein. These results support the conclusions that the variable and
invariable codons of mammal and plant SODs are different and that the
covarion model explains the evolution of this protein better than the gamma
version of the one-parameter process. Unlike other models, the covarion
hypothesis accounts for rate fluctuations among positions over time, which
is an important parameter of molecular evolution.
相似文献
93.
Taxol from fungal endophytes and the issue of biodiversity 总被引:7,自引:0,他引:7
GA Strobel WM Hess E. Ford RS Sidhu X Yang 《Journal of industrial microbiology & biotechnology》1996,17(5-6):417-423
Fungi represent one of the most understudied and diverse group of organisms. Commonly, these organisms make associations with higher life forms and may proceed to biochemically mimic the host organism. An excellent example of this is the anticancer drug, taxol, which had been previously supposed to occur only in the plant genusTaxus (yew). However, taxol has been reported in a novel endophytic fungus—Taxomyces andreanae, but also has been demonstrated to occur in a number of unrelated fungal endophytes includingPestalotia, Pestalotiopsis, Fusarium, Alternaria, Pithomyces, Monochaetia and others. Thus, this report presents information on the presence of taxol among disparate fungal genera, and uses these observations as an additional argument to support efforts to study fungal endophytes and preserve their associated host plants. 相似文献
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