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941.
The ratio of activities of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase (G6P DH/6PG DH), and the contents of glucose-6-phosphate (G6P), 6-phosphogluconate (6PG) and fructose-6-phosphate (F6P) were studied at various stages of potato virus Y (PVY) multiplication in Nicotiana tabacum cv. Samsun. G6P DH/6PG DH increased through the experiment from 0.42 to 0.53 in leaves of healthy tobacco, and up to 0.59 in PVY systemically infected leaves. However, these ratios in the ruptured protoplast preparations, and the chloroplast and cytosol fractions of healthy protoplasts were similar to that from infected ones. The ratio lower than 1, found in the healthy and/or PVY- infected leaf tissues and in the infected protoplasts as well, confirms the assumption that G6P DH is the control enzyme of oxidative pentosephosphate pathway not only in the healthy but also in the infected plants. The contents of G6P, 6PG and F6P in the period of the highest PVY multiplication were strongly decreased (to 30 – 50 % when compared with control healthy leaves) and were negatively correlated with the G6P DH and 6PG DH activities. 相似文献
942.
943.
Le Floch Gaétan Rey Patrice Benizri Emile Benhamou Nicole Tirilly Yves 《Plant and Soil》2003,257(2):459-470
Plant growth promotion induced by the antagonistic fungus, Pythium oligandrum, is the result of a complex interaction which includes an indirect effect through control of pathogens in the rhizosphere and/or a direct one mediated by plant-induced resistance. The present study shows an increased plant growth associated with direct interaction between P. oligandrum and roots, which is mediated by a fungus-produced auxin compound, tryptamine (TNH2). In vitro experiments provided evidence that P. oligandrum metabolised specifically indole derivatives, such as tryptophan and indole-3-acetaldehyde, to produce THN2 through the tryptamine pathway. When P. oligandrum grew in sterile root exudates, it also produced an auxin-like compound. Additional experiments on P. oligandrum–root interaction showed that, in amended nutrient solution of plants, the antagonist metabolised Trp into TNH2 and that root absorption of this newly formed auxin-compound in appropriate concentrations was associated with enhancement of plant growth. This phenomenon was observed only when nutrient solution was amended with low tryptophan (Trp) concentrations, i.e. 0.05 and 0.1 mM; higher concentration (0.5 and 1 mM Trp) induced abnormal root development. Similar experiments were performed with Pythium group F, a minor pathogen known for its ability to produce auxin-compounds through the tryptamine pathway. In this case, irregular root development was always noticed with all Trp concentrations added to the nutrient solution of plants. Moreover, Pythium group F colonization of roots was associated with leakage of auxin-compounds in the nutrient solution. Our results, therefore, highlight that the production of similar auxin-compounds by two Pythium species has contrary effects on plant development. 相似文献
944.
945.
It has been shown that the burst-phase (submillisecond) intermediate of barnase, if it exists, can be only marginally more stable than the fully unfolded state at pH 6.3 and 25 degrees C. In the study reported here, no stable burst-phase intermediate could be detected, even in the presence of stabilizing salt (0.4 M Na(2)SO(4)). These results suggest that a burst-phase intermediate with even marginal stability does not exist. The absence of such an intermediate in turn suggests the need for re-examination of the rate-limiting transition state (RLTS) under native conditions, which was previously characterized by using a three-state model with a stable intermediate and protein engineering. Surprisingly, mutations throughout the structure of barnase do not significantly affect the folding rate, suggesting a lack of specific favorable interactions among the side-chains in the RLTS. This RLTS is clearly different from that previously characterized under denaturing conditions, indicating that changes take place in the RLTS under native and denaturing conditions. The occurrence of such changes is further supported by the observation that the unfolding rate constants of barnase and its mutants were divergent or convergent as a function of denaturant concentrations. Consistent with changes in the RLTS, a re-analysis of data from native-state hydrogen exchange studies has shown that the logarithm of the unfolding rate constant inflects down under low concentrations of denaturant. Here, we discuss in detail the question of whether changes in the RLTS involve a kinetically silent intermediate that occurs after the initial RLTS. 相似文献
946.
947.
The activities of enzymes of pentose phosphate pathway (PPP) viz. glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and carbon metabolism viz. phosphoenol pyruvate carboxylase, NADP- isocitrate dehydrogenase and NADP-malic enzyme were measured in the plant and bacteroid
fractions of mungbean (ureide exporter) and lentil (amide exporter) nodules along with the developing roots for comparison.
The enzymes of pentose phosphate pathway in legume cytosol had higher activities at a stage of maximum nitrogenase activity
and higher sucrose metabolism. However, bacteroids had only limited capacity for this pathway. The specific activities of
these enzymes were greater in ureide than in amide exporter. CO2 fixation via higher activity of phosphoenolpyruvate carboxylase in the plant part of the nodules in lentil might have been due to the
greater synthesis of four carbon amino acids for amide export. The peak of NADP-isocitrate dehydrogenase in both legumes coincided
with the pentose phosphate pathway enzymes at the time of high rates of sucrose metabolism and nitrogen fixation. Higher activities
of NADP-malic enzyme were obtained in mungbean than in the lentil nodules. These findings are consistent with the role of
these enzymes in providing reductant (NADPH) and substrates for energy yielding metabolism of bacteroids and carbon skeletons
for ammonia assimilation. 相似文献
948.
Secondary metabolism in tobacco 总被引:1,自引:0,他引:1
Tobacco has been quite well studied phytochemically, more than 2500 compounds have been identified. Here, the secondary metabolism in tobacco will be reviewed in a biosynthetic perspective. Major groups of compounds which have extensively been studied are the isoprenoids, alkaloids, cinnamoylputrescines, flavonoids, and anthocyanins. Their biosynthetic pathways and its regulation, and their occurrence in cell cultures and in intact plants will be discussed. 相似文献
949.
Alternative pathway respiration is associated with ammonium ion sensitivity in spinach and pea plants 总被引:5,自引:0,他引:5
Berta Lasa Silvia Frechilla Pedro. M. Aparicio-Tejo Carmen Lamsfus 《Plant Growth Regulation》2002,37(1):49-55
Spinach and pea plants were grown in hydroponic culture with nitrate orammonium salts as the nitrogen source. Dry matter accumulation andphotosynthetic rate declined in spinach plants fed with ammonium salts, whereasthey did not change in pea plants compared with nitrate-fed plants. Measurementof organic nitrogen and free amino acid content showed that ammonium ions wereassimilated in shoots in spinach plants and in roots in pea plants. Ammoniumionnutrition led to a decline in starch content in both species. Organic acidsincreased in roots of pea plants fed with ammonium ions whereas they declinedinspinach plants. In both species ammonium ions increased root respiration ratebut the contribution of both routes (cytochromic and alternative pathway) tothis increase was different depending on the species. In spinach plants,ammonium ions increased the cytochromic path and decreased the alternativepathway, whereas in pea plants both routes were stimulated mainly through thealternative pathway. The differences in the sensitivity to ammonium ionsbetweenboth species are discussed in terms of differences in the availability of Cskeletons and energy, which could be due in part to differences in the capacityto stimulate the alternative pathway. 相似文献
950.
代谢网络定量分析研究进展 总被引:3,自引:0,他引:3
综述了代谢工程中代谢控制分析、代谢通量分析、生化系统理论、途径分析、控制论模型等定量分析方法的基本理论,以实例说明了这些方法的应用,并对代谢分析方法的发展进行了展望。 相似文献