摘要:

The uptake of [U-14C]threonine and of (α-14C]aminoisobutyrate (α-AIB) byVicia fabaleaf discs is strongly pH dependent (optimum: pH 4.0) and exhibits biphasic saturation kinetics. Kinetics ofα-AIB uptake at different pH values indicate that acidic pH values decrease theKmof the carriers while the maximal velocity remains nearly unaffected. Similar results were obtained for both system 1 (from 0.5 to 5 millimolar) and system 2 (from 20 to 100 millimolar).After addition of amino acids to a medium containing leaf fragments, alkalinizations depending both on the amino acid added and on its concentration have been recorded.The effects of compounds which increase (fusicoccin) or decrease (uncouplers, ATPase inhibitors, high KCl concentrations) the protonmotive force were studied both on the acidification of the medium and on amino acid uptake by the tissues. There is a close relationship between the time required for the effect of these compounds on the acidification and that needed for inhibition of uptake.Studies with thiol inhibitors show that 0.1 millimolarN-ethylmaleimide preferentially inhibits uptake by the mesophyll whereas 0.1 millimolar parachloromercuribenzenesulfonate affects rather uptake by the veins.New evidence was found which added to the electrophysiological data already supporting the occurrence of proton amino acid symport in leaf tissues, particularly in the vei

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

Translocation of nitrogen was measured in wheat (Triticum aestiviumL. cv SUN 9E) plants grown without an exogenous supply of nitrogen from the time that the flagleaf began to emerge, and a model of nitrogen translocation was constructed to describe translocation on one day during the linear period of grain growth. Nitrogen for grain development was derived entirely by the redistribution of nitrogen from vegetative organs. Leaves contributed 40%, glumes 23%, stem 23%, and roots 16% of the nitrogen incorporated by the grains on the fifteenth day after anthesis. Less than 50% of the nitrogen exported from leaves was translocated directly to the grain via the phloem, the rest was translocated to the roots and was cycled in the roots and exported to the shoot in the transpiration stream. Nitrogen imported by leaves and glumes via the xylem was not accumulated in these organs but was transferred to the phloem for reexport from the organs. A large proportion (60%) of the nitrogen in the transpiration stream was cycled in the glumes. The glumes were also a major source of nitrogen for grain development. It was considered likely that this organ always plays an important role in nitrogen metabolism in wheat.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

The fungusCercospora rosicolaproduces abscisic acid (ABA) as a secondary metabolite. We developed a convenient system using this fungus to determine the effects of compounds on the biosynthesis of ABA. Inasmuch as ABA and the gibberellins (GAs) both arise via the isoprenoid pathway, it was of interest to determine if inhibitors of GA biosynthesis affect ABA biosynthesis. All five putative inhibitors of GA biosynthesis tested inhibited ABA biosynthesis. Several plant growth retardants with poorly understood actions in plants were also tested; of these, six inhibited ABA biosynthesis to varying degrees and two had no effect. Effects of plant growth retardants on various branches of the isoprenoid biosynthetic pathway may help to explain some of the diverse and unexpected results reported for these compounds. Knowledge that certain inhibitors of GA biosynthesis also have the ability to inhibit ABA biosynthesis inC. rosicolaindicates the need for further studies in plants on the mode of action of these compounds.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

A new indole oxygenase from the leaves ofTecoma stanswas isolated and purified to homogenity. The purified enzyme system catalyzes the conversion of indole to anthranilic acid. It is optimally active at pH 5.2 and 30°C. Two moles of oxygen are consumed and one mole of anthranilic acid is formed for every mole of indole oxidized. Dialysis resulted in complete loss of the activity. The inactive enzyme could be reactivated by the addition of concentrated dialysate. The enzyme is not inhibited by copper-specific chelators, non-heme iron chelators or atebrin. It is not a cuproflavoprotein, unlike the other indole oxygenases and oxidases

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

A mechanical isolation procedure was developed to study the respiratory properties of mitochondria from the mesophyll and bundle sheath tissue ofPanicum miliaceum, a NAD-malic enzyme C4plant. A mesophyll fraction and a bundle sheath fraction were obtained from young leaves by differential mechanical treatment. The purity of both fractions was about 80%, based on analysis of the cross-contamination of ribulose bisphosphate carboxylase activity and phosphoenolpyruvate carboxylase activity.Mitochondria were isolated from the two fractions by differential centrifugation and Percoll density gradient centrifugation. The enrichment of mitochondria relative to chloroplast material was about 75-fold in both preparations.Both types of mitochondria oxidized NADH and succinate with respiratory control. Malate oxidation in mesophyll mitochondria was sensitive to KCN and showed good respiratory control. In bundle sheath mitochondria, malate oxidation was largely insensitive to KCN and showed no respiratory control. The oxidation was strongly inhibited by salicylhydroxamic acid, showing that the alternative oxidase was involved. The bundle sheath mitochondria of this type of C4species contribute to C4photosynthesis through decarboxylation of malate. Malate oxidation linked to an uncoupled, alternative pathway may allow decarboxylation to proceed without the restraints which might occur via coupled electron flow through the cytochrome chain.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

The ability of rice, wheat, and oat seedlings to germinate and grow as the O2concentration was lowered to zero was compared. The germination of rice was completely unaffected by O2supply, whereas that of oats and wheat was strongly retarded at levels below 5% O2. In contrast to the coleoptiles of oats and wheat and to roots of all three species where growth was progressively diminished as the O2concentration was lowered, that of the rice coleoptile was progressively increased. However, the dry weight and content of protein, sugars, and cellulose were all depressed in the rice coleoptile in anoxia, and the levels of several respiratory enzymes, particularly those of mitochondria, were also much lower than those of the coleoptiles grown in air. In 1% O2, the growth of the rice coleoptile was similar to that in air. The effect of ethanol concentration on germination and growth of rice was measured. Coleoptile growth was reduced when the ethanol concentration exceeded 40 millimolarity, and root growth was somewhat more sensitive. Coleoptiles of all three species grown in air were transferred to N2, and ethanol accumulation was measured over 24 hours. The rate of ethanol accumulation in oats was close to that in rice, and in all three species the amounts of ethanol lost to the surrounding medium were those expected from simple diffusion from the tissue. The ability of the rice coleoptile to grow in anoxia is apparently not due to a particularly low rate of ethanol formation or to unusual ethanol tolerance. Any explanation of the success of rice in anoxia must encompass the much lower rate of ATP synthesis than that in air and account for the biochemical deficiencies of the coleoptile.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

Several nuclear mutations were recovered that suppress the photosensitivity associated with theChamydomonas reinhardiichloroplast mutantrcl-u-1-10-6C, which is defective in ribulose-1,5-bisphosphate carboxylase/oxygenase. Two of the suppressor mutations affect other components of photosynthesis. These results show that suppressors of photosensitivity are sufficiently common to permit the recovery of photosensitive, photosynthesis-deficient mutants in bright light, and indicate that photosynthesis-deficient mutants selected and maintained in the light may accumulate suppressors which can confuse the biochemical analysis of lesions in photosynthesis. One of the suppressor mutations inhibits photosystem II activity, indicating that photosensitivity can be mediated by partial reactions of the photosynthetic electron transport chain.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

Ribonucleic acid and protein synthesis in developing wheat kernels have been studied throughin vivolabeling of wheat heads in culture. In INIA 66R wheat labeled with [5-3H]uridine for 24-hour periods between 9 and 33 days after flowering, the total rate of RNA accumulation in endosperm/testa pericarp tissues was highest in the youngest seeds, and declined with increasing seed age. In contrast, the rate of accumulation of poly(A)+RNA approximately doubled between 12 and 15 days after flowering, reached a maximum between 15 and 18 days, and declined to half the maximum rate by 24 days. Protein synthetic capacity, measured byin vitrotranslation of extracted seed RNA, increased in a developmental pattern similar to that of poly(A)+RNA accumulation, but remained near maximal through 24 days after flowering. Gliadins were prominent in thein vitrotranslation products. When seed protein was labeledin vivowithl-[3H]leucine, extracted, and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a significant change in the protein synthesis profile was apparent between 12 and 15 days after flowering, and was coincident with a marked increase in storage protein synthesis. Qualitatively similar characteristics were exhibited by the cultivar Cheyenne, although in a shorter developmental period. These results are consistent with a direct relation between levels of mRNA and rates of protein synthesis in developing wheat seeds, with a relatively long storage protein mRNA lifetime, and with control of storage protein gene expression primarily at the level of mRNA transcription.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

It was shown previously that when peas (Pisum sativumL.) are grown with suboptimal sulfur supply the level of legumin (the more S-rich of the two major seed storage proteins) in the mature seed is selectively reduced (Randall, Thomson, Schroeder, 1979 Aust J Plant Physiol 6: 11-24). This paper reports a study of the cellular mechanisms involved in regulating legumin synthesis under these conditions. Pulse and pulse-chase labeling experiments were carried out with excised, immature cotyledons from normal and S-deficient plants. Legumin was isolated from cotyledon extracts by immunochromatography, and the proportion of legumin synthesis relative to total protein synthesis was determined. Results showed that reduced legumin accumulation could largely be accounted for by a greatly reduced level of legumin synthesis (80-88% reduction) rather than by a major increase in legumin breakdown.Legumin mRNA levels were assayed by two methods.In vitrotranslation of polysomal RNA from cotyledons of normal and S-deficient plants indicated a reduction of 60 to 70% in synthesis of legumin-related products by preparations from S-deficient plants. A legumin cDNA clone was constructed, characterized, and used to measure the levels of legumin mRNA in polysomal and total RNA preparations from developing cotyledons. Legumin mRNA levels were reduced by 90% in preparations from S-deficient plants.When restored to an adequate S supply, S-deficient plants (or pods taken from such plants) recovered normal levels of legumin synthesis (in vivoandin vitro) and of legumin mRNA. These results indicate that reduced legumin accumulation under conditions of S deficiency is primarily a consequence of reduced levels of legumin mRNA.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB

摘要:

The ability of 19 structural analogs of propyl gallate to inhibit purified soybean seed (Glycine max[L.] Merr. var. Ransom) lipoxygenase-2 (EC1.13.11.12) was determined. The results indicate that theo-dihydroxy and not the ester function of propyl gallate is essential for inhibition of lipoxygenase. Catechol thus represents the minimum inhibitory structure. Among those compounds possessing ano-dihydroxy function, theKi′for inhibition of lipoxygenase is directly related to the lipophilicity of the inhibitor as measured by the octanol-water partition coefficient. The structural features of propyl gallate necessary for inhibition of lipoxygenase were found to differ from those required for inhibition of the plant mitochondrial alternative pathway. This further supports the concept that the alternative oxidase and lipoxygenase are functionally distinct specie

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1983

数据来源: ASPB