摘要:

The number of isoperoxidases and the intensity of certain isozymes increased with increasing periods of stratification of pear (Pyrus communiscv. Bartlett) embryos. The presence of GA3or kinetin during stratification enhanced the activity of certain isoperoxidases, and these enhancements were blocked in the presence of ABA which by itself had an inhibitory effect. Enhancement in isoperoxidases of pear embryos during stratification was inhibited by 6-methylpurine and cycloheximide; and in the presence of either of these two inhibitors, stratification failed to release the dormancy. Pear embryos germinated for 3 days showed changes in the pattern of isoperoxidases depending on the length of stratification.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

A procedure was developed for extracting polysomes from tobacco (Nicotianasp) leaves. Unexpanded leaves ground in a medium consisting of 200 mmtris-HCl, pH 9, 400 mmKCl, 200 mmsucrose, and 35 mmMgCl2yielded larger amounts of polysomes with less degradation than polysomes from leaves extracted with buffers of lower ionic strength or pH. Extraction of polysomes from expanded leaves required the inclusion of ethyleneglycol-bis(2-aminoethyl ether)tetraacetic acid (EGTA, a divalent cation chelator with a high affinity for Ca2+, Cu2+, and Zn2+). EGTA also improved isolation of polysomes from unexpanded leaves. Addition of 25 mmCa2+, Cu2+, or Zn2+to extracts from young leaves precipitated polysomes, and density gradient profiles of polysome preparations from the cation treatments mimicked profiles from expanded leaves which were extracted without EGTA. Polysome precipitation by Ca2+was prevented by EGTA. Endogenous Ca2+was present in unexpanded leaves in sufficient concentrations (25 mm) to cause some precipitation of polysomes during extraction, and this cation increased by 60% in expanded leaves. Cu2+and Zn2+were not present in amounts sufficient to cause polysome precipitation. The results show that recovery of polyribosomes may be reduced by divalent cations in leaf tissue, and this can be overcome by chelation of these ions with EGTA.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

The subcellular changes which occurred in sorghum leaves during increasing water stress and subsequent rewatering are described. Stomata were closed, abscisic acid levels were elevated, and the amounts of starch in the bundle sheath chloroplasts were much reduced by - 14 bars leaf water potential. Swelling of the outer chloroplast membrane, and reorganization of the tonoplast to form small vesicles from the large central vacuole, occurred by a leaf water potential of - 37 bars. Complete structural disruption of the tonoplast, as previously described for maize was not found. On rewatering, large amounts of starch reappeared within three hours. These findings strengthen the hypothesis that maintenance of tonoplast integrity is an important factor in the ability of plants to withstand drought.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

The incorporation of the cytokinin N6-benzyladenine into tobacco (Nicotiana tabacum) callus tRNA and rRNA preparations isolated from tissue grown on medium containing either N6-benzyladenine-8-14C or N6-benzyladenine-8-14C: benzene-3H(G) has been examined. N6-benzyladenine was incorporated into both the tRNA and rRNA preparations as the intact base. Over 90% of the radioactive N6-benzyladenosine recovered from the RNA preparations was associated with the rRNA. Purification of the crude rRNA by either MAK chromatography or Sephadex G-200 gel filtration had no effect on the N6-benzyladenosine content of the RNA preparation. The distribution of N6-benzyladenosine moieties in tobacco callus tRNA fractionated by BD-cellulose chromatography did not correspond to the distribution of ribosylzeatin activity. N6-benzyladenosine was released from the rRNA preparation by treatment with venom phosphodiesterase and phosphatase, ribonuclease T2and phosphatase, or ribonuclease T2and a 3′-nucleotidase. N6-benzyladenosine was not released from the RNA preparation by treatment with either ribonuclease T2or phosphatase alone or by successive treatment with ribonuclease T2and a 5′-nucleotidase. Brief treatment of the rRNA preparation with ribonuclease T1and pancreatic ribonuclease converted the N6-benzyladenosine moieties into an ethyl alcohol soluble form. On the basis of these and earlier results, the N6-benzyladenosine recovered from the tobacco callus RNA preparations appears to be present as a constituent of RNA and not as a nonpolynucleotide contamin

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

Carbamoyl phosphate synthetase of pea shoots (Pisum sativum L.) was purified 101-fold. Its stability was greatly increased by the addition of substrates and activators. The enzyme was strongly inhibited by micromolar amounts of UMP (Kiless than 2μm). UDP, UTP, TMP, and ADP were also inhibitory. AMP caused either slight activation (under certain conditions) or was inhibitory. Uridine nucleotides were competitive inhibitors, as was AMP, while ADP was a noncompetitive inhibitor. Enzyme activity was increased manyfold by the activator ornithine. Ornithine acted by increasing the affinity for Mg·ATP by a factor of 8 or more. Other activators were IMP, GMP, ITP, and GTP, IMP, like ornithine, increased the Michaelis constant for Mg·ATP. The activators ornithine, GMP, and IMP (but not GTP and ITP) completely reversed inhibition caused by pyrimidine nucleotides while increasing the inhibition caused by ADP and A

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

Endogenous levels of cyclic adenosine-3′:5′-monophosphate in coleoptile first leaf segments of oat (Avena sativaL.), potato (Solanum tuberosumL.) tubers, tobacco (Nicotiana tabacumL.) callus, and germinating seeds of lettuce (Lactuca sativaL.) were measured with a modified Gilman binding assay and a protein kinase activation assay. The incorporation of adenosine-8-14C into compounds with properties similar to those of cyclic AMP was also measured in studies with germinating lettuce seeds. The binding assay proved reliable for mouse and rat liver analyses, but was nonspecific for plant tissues. It responded to various components from lettuce and potato tissues chromatographically similar to but not identical with cyclic AMP. The protein kinase activation assay was much more specific, but it also exhibited positive responses in the presence of compounds not chromatographically identical to cyclic AMP. The concentrations of cyclic AMP in the plant tissues tested were at the lower limits of detection and characterization obtainable with these assays. The estimates of maximal levels were much lower than reported in many previous stud

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

The fatty acid composition of the major lipids of the chloroplast membranes, the mono- and digalactosyl diglycerides, can be definably altered with various substituted pyridazinones. Galactolipid fatty acid composition of wheat (Triticum aestivumL.) can be altered so that there is a decrease in linolenic acid accompanied by an increase in linoleic acid without a shift in the relative proportion of saturated to unsaturated fatty acids; the fatty acid composition can be shifted toward a higher proportion of saturated fatty acids; or the fatty acid composition of the monogalactosyl diglycerides can be altered in preference to the digalactosyl diglycerides. Also, the light-mediated parallel accumulation of chlorophyll and linolenic acid can be separated with a substituted pyridazinone. The substituted pyridazinones may be useful tools in clarifying the role the galactolipids and their component fatty acids play in the structure and function of chloroplast membranes in higher plants.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

Spinach seeds (Spinacia oleracea L.) given massive doses ofγ-irradiation (500 krad) germinate and form a seedling with two green cotyledons and a radicle, but develop no further. Irradiated cotyledons show no increase in cell number or total DNA over a 7-day period in the light, while in control cotyledons there is a small increase in cell number and large increases in total DNA and chloroplast number. The chloroplasts of irradiated cotyledons are delayed in their division, become greatly enlarged and contain large amounts of starch. The whole population of chloroplasts subsequently undergoes a wave of division. The daughter chloroplasts show normal thylakoid development, but have some abnormal structural features caused by the radiation stress. Information on the effect of X-irradiation, ultraviolet irradiation, and 5-fluorodeoxyuridine on chloroplast replication and on chloroplast and nuclear DNA synthesis was obtained from cultured spinach leaf discs. It appears that chloroplast replication is more resistant to ionizing radiation than cell division and can proceed in the absence of nuclear DNA synthesis and greatly reduced chloroplast DNA synthesis

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

The molecular organization of chlorophyll inChlamydomonas reinhardiihas been shown to be essentially similar to that in higher plants. Some 50% of the chlorophyll inChlamydomonas reinhardiichloroplast membranes has been shown to be located in a chlorophylla/b-protein complex. The complex was isolated in a homogeneous form by hydroxylapatite chromatography of sodium dodecyl sulfate extracts of the chloroplast membranes. Its absorption spectrum exhibits two maxima in the red region at 670 and 652 nm due to the presence of equimolar quantities of chlorophyllsaandbin the complex. Preparations of the chlorophyll-protein also contain some of each of the carotenoids observed in the intact chloroplast membrane, but not in the same proportions. The native complex (S value = 2.3S) exhibits a molecular weight of 28,000±2,000 on calibrated sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, on the basis of its amino acid composition and other data a more probable molecular weight of about 35,000 was calculated. Each 35,000 dalton unit contains three chlorophyllaand three chlorophyllbmolecules, and on the average one carotenoid molecule conjugated with probably a single polypeptide of 29,000 daltons. Comparison of spectral and biochemical characteristics demonstrates that this algal chlorophyll-protein is homologous to the previously described major light-harvesting chlorophylla/b-protein of higher plants. It is anticipated that theChlamydomonascomplex functions solely in a light-harvesting capacity in analogy to the function determined for the higher plant component

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB

摘要:

Intact chloroplasts of spinach (Spinacia oleraceaL.), sunflower (Helianthus annuusL.), and maize (Zea maysL.) mesophyll cells contained 0.33, 0.50, and 0.14% of bound hexosamine on a protein basis, respectively. Undifferentiated maize chloroplasts contained 0.19%. Values for chloroplast lamellae were, respectively, 0.16, 0.18, 0.12, and 0.06% and for envelope membranes they were 1.6, 2.5, 3.8, and 2.7%. Thus most of the hexosamine of chloroplasts is located in the envelope membrane.

ISSN:0032-0889    

出版商:American Society of Plant Biologists    

年代:1976

数据来源: ASPB