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1.
Summary Alanine-rich peptides serve as models for exploring the factors that control helix structure in peptides and proteins. Scalar CH-NH couplings (3JHN) are an extremely useful measure of local helix content; however, the large alanine content in these peptides leads to significant signal overlap in the CH region of 1H 2D NMR spectra. Quantitative determination of all possible 3JHN values is, therefore, very challenging. Szyperski and co-workers [(1992) J. Magn. Reson., 99, 552–560] have recently developed a method for determining 3JHN from NOESY spectra. Because 3JHN may be determined from 2D peaks outside of the CH region, there is a much greater likelihood of identifying resolved resonances and measuring the associated coupling constants. It is demonstrated here that 3JHN can be obtained for every residue in the helical peptide Ac-(AAAAK)3A-NH2. The resulting 3JHN profile clearly identifies a helical structure in the middle of the peptide and further suggests that the respective helix termini unfold via distinct pathways.Abbreviations 3JHN three-bond CH-NH scalar coupling constant - NOE nuclear Overhauser enhancement - NOESY two-dimensional nuclear Overhauser spectroscopy - COSY two-dimensional correlated spectroscopy - DQF-COSY two-dimensional double-quantum-filtered correlated spectroscopy - TOCSY two-dimensional total correlation spectroscopy To whom correspondence should be addressed.Deceased March 5, 1996.  相似文献   

2.
Summary Thirteen spontaneously occurring chlorophyll deficient phenotypes have been described and their genetic basis was established. Ten of these — white, white tipped green, patchy white, white virescent, white striping 1, white striping 2, white striping 4, fine striping, chlorina and yellow virescent showed monogenic recessive inheritance and the remaining three — yellow striping, yellow green and light green seedling phenotypes showed digenic recessive inheritance. The genes for (i) white tipped green (wr) and yellow virescent (yv) and (ii) patchy white (pw) and white striping 1 (wst 1) showed independent assortment. Further, the genes for white (w), white tipped green (wr) and yellow virescent (yv) were inherited independently of the gene for hairy leaf margin (Hm).In the mutants — white tipped green, patchy white, white striping 1, white striping 2, fine striping, chlorina, yellow virescent, yellow striping, yellow green and light green phenotypes total quantity of chlorophyll was significantly less than that in the corresponding controls, while in white virescent there was no reduction in the mature stage. For nine of the mutants the quantity of chlorophyll was also estimated in F1's (mutant x control green). In F1's of six of the mutants — white tip, patchy white, chlorina, yellow virescent, fine striping and yellow striping the quantity of chlorophyll was almost equal to the wild type. In the F1's of three of the mutants — white striping 1, white striping 2 and light green an intermediate value between the mutant and wild types was observed. In yellow virescent retarded synthesis of chlorophyll, particularly chlorophyll a was observed in the juvenile stage. Reduced quantity of chlorophyll was associated with defective chloroplasts. In the mutants — white tipped green, white virescent, fine striping, chlorina, yellow striping, yellow green and light green defective plastids were also observed. In patchy white secondary destruction of chlorophylls and the presence of defective plastids were found to be associated with reduced chlorophyll quantity at maturity.Paper chromatographic studies of leaf flavonoids revealed some variation between the inbreds, but there were three common spots, 7, 8 and 9, except for PDP in which the spot 8 was absent. Chlorophyll deficient mutants differed from their respective controls in the absence of one or more of the spots present in the controls and in the presence of new spots in some of the mutants.Most of the chlorophyll mutants showed higher survival rate in the Kharif season than in Rabi season which was attributed to the higher mean day temperature and longer day light period in the Kharif season than in Rabi season.  相似文献   

3.
Neurosteroids are endogenous Central Nervous System (CNS) compounds which act mainly by allosteric modulation of the GABAA receptor complex. The presence of a 3-hydroxyl group and a 5-hydrogen atom have been found to be essential structural requirements for biological activity in mammals. In the present work we report the enhancing activity on [3H]GABA binding to its receptor sites in chick optic lobe produced by progesterone metabolites 3-hydroxy,5-pregnan-20-one (3,5-P) and 3-hydroxy,5-pregnan-20-one (3,5-P). Both steroids were found able to enhance [3H]GABA binding along ontogeny, displaying a similar profile at early developmental stages, while in adulthood 3,5-P had greater potency (EC50 0.22 M) and enhancing effect (Emax: 122%). In adult synaptic membranes, the two compounds displayed a complex interaction with the GABAA receptor, disclosed by a Schild plot with slope below one and an incomplete displacement of 3,5-P by its 3,5 isomer. Such complexity could be related to the steroidogenic profile in avian CNS, with 5-reduced progesterone metabolites present since early development, while 3,5-P is found only in adulthood. Bearing in mind differences between avian and mammalian steroidogenic profiles and the relevance of 5-steroids in early avian development, we propose that 3,5-P, instead of the classical potent 3,5-steroids, may be the endogenous modulator of GABAergic activity in developing avian brain.  相似文献   

4.
Summary We have synthesized 2(3)-O-(glycyl)-adenosine-5-(O-methylphos-phate), an analogue of the 3-terminus of aminoacylated tRNA. A 0.4M solution of this compound maintained at pH 8.2, yields 5.5% of diglycine and 11.5% of diketopiperazine, in addition to the hydrolysis products glycine and adenosine-5-(O-methylphosphate). Under the same conditions, glycine ethyl ester reacts much more slowly, but ultimately gives similar yields of diglycine and diketopiperazine.The aminolysis of 2(3)-O-(glycyl)-adenosine-5-(O-methylphosphate) by free glycine is relatively inefficient, but serine reacts 20 times more rapidly and yields up to 50% of N-glycylserine. The prebiotic significance of these reactions is discussed.Abbreviations MepA adenosine-5-(O-methylphosphate) - MepA-gly 2(3)-O-(glycyl)-adenosine-5-(O-methylphosphate) - MepA-bis-gly 2,3-O-(bis-glycyl)-adenosine-5-(O-methylphosphate) - DKP diketopiperazine - gly Et glycine ethyl ester - gly-ser N-glycylserine - O-gly-ser O-glycylserine - O-(gly)-gly-ser O-(glycyl)-glycylserine - Boc-gly N-tert-butyloxycarbonylglycine - MepA-Boc-gly 2(3)-O-(Boc-glycyl)-adenosine-5-(O-methylphosphate) - MepA-bis-Boc-gly 2,3-O-(bis-Boc-glycyl)-adenosine-5(O-methylphosphate) - (gly)2 diglycine - (gly)3 triglycine  相似文献   

5.
Summary Organic pyrophosphates such as UppA and NAD are formed when a solution containing a nucleotide, a nucleoside 5-polyphosphate, Mg2+ and imidazole are allowed to dry out. We suggest that this synthesis may have occured concurrently with oligonucleotide formation.Abbreviations Im Imidazole - CDI 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride - EDTA ethylenediaminetetraacetic acid - A adenosine - U uridine - pnA adenosine 5-poly-phosphate containing n phosphate residues - pU uridine 5-phosphate - AppA P1,P2-diadenosine 5-pyrophosphate - UppA P1-(uridine 5)-P2-(adenosine 5)-pyrophosphate - ImpA adenosine 5-phosphorimidazolide - NMN nicotinamide mononucleotide - NAD nicotinamide-adenine dinucleotide  相似文献   

6.
We have designed protein molecules based on an -helical coiled-coil structure. These proteins can be tailored to complement nutritionally unbalanced seed meals. In particular, these proteins may contain up to 43% mol/mol of the essential amino acid lysine. Genes encoding such proteins were constructed using synthetic oligonucleotides and the protein stability was tested for in vivo by expression in an Escherichia coli model system. A protein containing 31% lysine and 20% methionine (CP 3-5) was expressed in transgenic tobacco seeds utilizing the seed specific bean phaseolin and soybean -conglycinin promoters. Both promoters provided a level of expression in the mature transgenic tobacco seeds which resulted in a significant increase in the total lysine content of the seeds. Several of these transgenic lines were analyzed for three generations to determine the stability of gene expression. Plants transformed with the soybean -conglycinin promoter/CP 3-5 gene consistently expressed the high-lysine phenotype through three generations. However, expression of the high-lysine phenotype in plants transformed with the bean phaseolin/CP 3-5 was variable. This is the first report of a significant increase in seed lysine content due to the seed-specific expression of a de novo protein sequence.  相似文献   

7.
Summary The angular dependence of1JC,H in model compounds related to -linked oligosaccharides has been established by FPT INDO quantum chemical calculations. Values calculated for models of (1 1)-, (1 2)-, (1 3)- and (1 4)-linked disaccharides were compared, and the effect of the orientation of HO-2 elucidated. The angular dependence of1JC,H on the torsional angles H and H and the solvent dielectric constant (s) was characterized in the form:1JC,H = A cos2+B cos + C sin2 + D since + E + Fe. The1JC,H values, measured by DEPT methods for C-1-H-1 and C-X-H-X in cellobiose, cyclic trisaccharide and hexopyranoses were used to adjust the calculated angular dependences. Based on the occurrence of the conformers for agarobiose, neoagarobiose, mannobiose and methyl -xylobioside, the thermodynamically averaged <1JC,H > values were calculated. The results obtained (<1JC-1,H-1 > 162.4, <1JC-4, H-4 > 147.6 Hz for methyl -xylobioside; <1JC-1,H-1 > 162.4 and <1JC-4,H-4] > 147.6 Hz for mannobiose; <1JC-1,H-1 > 162.8 Hz for neo agarobiose and <1JC-1,H-1 > 163.2 Hz for agarobiose) agree well with the experimental values of 162.7, 147.5, 160.4, 147.2, 160.9 and 165.7 Hz, respectively.  相似文献   

8.
The purified isopropylmalate synthase of Alcaligenes eutrophus H 16 reacted with the following -keto acids and acyl-coenzyme A derivatives (in the sequence of decreasing affinities): -ketoisovalerate, -keto-n-valerate, -ketobutyrate and pyruvate; acetyl-CoA, propionyl-CoA, butyryl-CoA. malonyl-CoA, valeryl-CoA, and crotonyl-CoA. -Ketoisocaproate, however, is a strong inhibitor of the enzyme. All reactions catalyzed by isopropylmalate synthase were inhibited to the same extent by the endproduct l-leucine. the substrate saturation curves of -ketoisovalerate or other -keto acids and of acetyl-coenzyme A or other acyl-CoA derivatives had intermediary plateau regions; the Hill coefficient alternated between n H -values higher and lower than 1.0, indicating changes from positive to negative and from negative to positive cooperativity for the substrates. The products, isopropylmalate and free coenzyme A, showed competitive inhibition patterns against both substrates (-ketoisovalerate and acetyl-CoA). Free coenzyme A (1 M) inactivated the enzyme irreversibly. The 3-phosphate of coenzyme A and the free carboxyl group of -ketoisovalerate were involved in optimal binding of these substrates, but 3-dephospho-acetyl-coenzyme A and the methylester of -ketoisovalerate were also converted by this enzyme. A CH3–CH2-grouping of the -keto acids seemed to be necessary for binding this substrate.Abbreviations Used CoA Coenzyme A - Tris Tris(hydroxymethyl)aminomethane hydrochloride - DTNB 5,5-dithiobis-(2-nitrobenzoic acid) - IPM -Isopropylmalate - KIV -Ketoisovalerate Prepared from doctoral thesis of the University of Göttingen 1973  相似文献   

9.
Summary The fluorescent intercalation complex of ethidium bromide (ETB) with DNA was used as a probe to compare the effects of various radicals with respect to impairment of the DNA base-pair region.OH radicals inhibit up to 0.7 dye intercalations perOH at low salt concentration, and for various oxidizing species the effect decreases in the orderOH > Br 2 > N 3 > $$ " align="middle" border="0"> (SCN) 2 . DNA impairment by theOH product of Met-Gly is comparable to that of N 3 , but no effect was found due to the interaction between DNA and Lys-Tyr-Lys phenoxyl radicals. The reducing speciese aq , H, O 2 , and CO 2 hardly affect the DNA-ETB intercalation.  相似文献   

10.
Ni  Zhang-Lin  Wang  Da-Fu  Wei  Jia-Mian 《Photosynthetica》2002,40(4):517-522
The conserved residue Thr42 of -subunit of the chloroplast ATP synthase of maize (Zea mays L.) was substituted with Cys, Arg, and Ile, respectively, through site-directed mutagenesis. The over-expressed and refolded -proteins were purified by chromatography on DEAE-cellulose and FPLC on mono-Q column, which were as biologically active (inhibiting Ca2+-ATPase activity and blocking proton gate) as the native subunit isolated from chloroplasts. The T42C and T42R showed higher inhibitory activities on the soluble CF1(–) Ca2+-ATPase than the WT. The T42I inhibited the Ca2+-ATPase activity of soluble CF1 and restored photophosphorylation activity of membrane-bound CF1 deficient in the most efficiently. Far-ultraviolet CD spectra showed that the portions of -helix and -sheet structures of the three mutants were somewhat different from WT. Thus the conserved residue Thr42 may be important for maintaining the structure and function of the -subunit and the basic functions of the -subunit as far as an inhibitor of Ca2+-ATPase and the proton gate are related.  相似文献   

11.
Summary Insulin binding to human placenta membranes treated at pH 7.6 or 8.5 in the presence or absence of 2.0mm DTT for 5 min, followed by the simultaneous removal of the DTT and pH adjustment to pH 7.6, displayed curvilinear (heterogeneous) insulin binding plots when analyzed by the method of Scatchard. However, Triton X-100 solubilization followed by Bio-Gel A-1.5m gel filtration chromatography of the placenta membranes previously treated with DTT at pH 8.5 generated a nearly straight line (homogeneous) Scatchard plot.125I-insulin affinity crosslinking studies coupled with Bio-Gel A-1.5m gel filtration chromatography demonstrated that the alkaline pH and DTT treatment of placenta membranes followed by detergent solubilization generated an heterodimeric insulin receptor complex from the 22 heterotetrameric disulfide-linked state. The ability of alkaline pH and DTT to produce a functional heterodimeric insulin receptor complex was found to be time dependent with maximal formation and preservation of tracer insulin binding occurring at 5 min. These data demonstrate that (i) a combination of alkaline pH and DTT treatment of placenta membranes can result in the formation of a functional heterodimeric insulin receptor complex. (ii) the heterodimeric complex displays homogeneous insulin binding. (iii) the insulin receptor membrane environment maintains the 22 association state, which displays heterogeneous insulin binding, despite reduction of the critical domains that are responsible for the covalent interaction between the heterodimers.Abbreviations used are ATP adenosine 5-triphosphate - DTT dithiothreitol - SDS sodium dodecyl sulfate - DSS disuccinimidyl suberate - NEM N-ethylmaleimide - IGF-I insulin-like growth factor-I - EDTA ethylenediaminetetraacetic acid - HEPES 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid  相似文献   

12.
To examine the influence of the spectral characteristics of underwater light on spectral sensitivity of the ON and OFF visual pathways, compound action potential recordings were made from retinal ganglion cells of threespine stickleback from different photic regimes. In fish from a red-shifted photic regime (P50 680 nm for downwelling light at 1m), peak sensitivity of both the ON and OFF pathways was limited to long wavelength light (max 600–620). In contrast, the ON pathway of fish from a comparatively blue-shifted (P50 566 nm) photic regime exhibited sensitivity to medium (max 540–560) and long (max 600 nm) wavelengths, while the OFF pathway exhibited peak sensitivity to only medium (max 540 nm) wavelength light. In a third population, where the the ambient light is moderately red-shifted (P50 629 nm), the ON pathway once again exhibited only a long wavelength sensitivity peak at 620 nm, while the OFF pathway exhibited sensitivity to both medium (max 560 nm) and long (max 600–620 nm) wavelength light. These findings suggest that the photic environment plays an integral role in shaping spectral sensitivity of the ON and OFF pathways.  相似文献   

13.
Four methods for classifying cultivated rices (Oryza sativa L.) (including IR varieties) into indica and japonica types — waxy gene product in endosperm starch, glutelin 3 molecular weight in milled rice, RFLP polymorphism at the Wx locus and Glaszmann's isozyme method — were compared. On the basis of the two endosperm traits and the RFLP method Glaszmann's group 1 (indica) was classified as mainly indica and intermediate groups 2, 3 and 4 as exclusively indica. However, the endosperm traits classified Glaszmann's group 5 as mainly indica, while the RFLP method classified it as japonica. The RFLP waxy gene probe was closest to the isozyme method in classifying group 6 as japonicas; the waxy gene product gave mainly indica reaction even in group 6, and the glutelin 3 method was intermediate. All IR rices were classified as being indica on the basis of Wx gene product and by Glaszmann's method, but a few were classified as japonica by the glutelin 3 method and by the RFLP waxy gene probe.  相似文献   

14.
Rat liver mitochondria were examined for their ability to reduce dehydroascorbic acid to ascorbic acid in an -lipoic acid dependent or independent manner. The a-lipoic acid dependent reduction was stimulated by factors that increased the NADH dependent reduction of -lipoic acid to dihydrolipoic acid in coupled reactions. Optimal conditions for dehydroascorbic acid reduction to ascorbic acid were achieved in the presence of pyruvate, -lipoic acid, and ATP. Electron transport inhibitors, rotenone and antimycin A, further enhanced the dehydroascorbic acid reduction. The reactions were strongly inhibited by 1 mM iodoacetamide or sodium arsenite. Mitoplasts were qualitatively similar to intact mitochondria in dehydroascorbate reduction activity. Pyruvate dehydrogenase and -ketoglutarate dehydrogenase reduced dehydroascorbic acid to ascorbic acid in an -lipoic acid, coenzyme A, and pyruvate or -ketoglutarate dependent fashion. Dehydroascorbic acid was also catalytically reduced to ascorbic acid by purified lipoamide dehydrogenase in an -lipoic acid (K 0.5=1.4±0.8 mM) and lipoamide (K 0.5=0.9±0.3 mM) dependent manner.  相似文献   

15.
Summary The genomes of the phylogenetically related but morphologically distinct bacteriophages LP52 and theta () were compared by electron microscopic heteroduplex analysis. The heteroduplex maps were aligned with known restriction maps. In the heteroduplices of LP52 DNA (63.8 kb) with the DNA of the lytic phage c (65.9 kb) the tracts of homologous DNA cover about 50% of the genome length and are interspaced by four large and ten smaller non-base-paired regions. The largest block of non-homologous DNA (18.9 kb), represents the right-hand end and there is an unmatched piece of DNA at the left-hand end as well. Most of the heterology is due to substitution resulting in the conservation of the total length of DNA; the three insertions/deletions amount to less than 3.2% of the genome length. Heteroduplices between the DNAs of phage LP52 and the temperate phage 1 (65.0 kb) resembled those of LP52: c except for the absence of minor loops. Heteroduplex c:1 displayed about 9% heterology in seven separate loops which coincided with sections of diversity on the restriction maps; 4.8% of 1 DNA did not hybridize with either c or LP52 DNA.  相似文献   

16.
The regulation of total creatine content in a myoblast cell line   总被引:5,自引:0,他引:5  
Total cellular creatine content is an important bioenergetic parameter in skeletal muscle. To understand its regulation we investigated creatine transport and accumulation in the G8 cultured skeletal myoblast line. Like other cell types, these contain a creatine transporter, whose activity, measured using a radiolabelling technique, was saturable (Km = 110 ± 25 M) and largely dependent on extracellular [Na+]. To study sustained influences on steady state creatine concentration we measured total cellular creatine content using a fluorimetric method in 48 h incubations. We found that the total cellular creatine content was relatively independent of extracellular creatine concentration, consistent with high affinity sodium-dependent uptake balanced by slow passive efflux. Accordingly, in creatine-free incubations net creatine efflux was slow ( 5 ± 1 % of basal creatine content per day over 6 days), while creatine content in 48 h incubations was reduced by 28 ± 13% of control by the Na+,K+-ATPase inhibitor ouabain. Creatine accumulation after 48 h was stimulated by treatment with the mixed - and -adrenergic agonist noradrenaline, the -adrenergic agonist isoproterenol, the 2-agonist clenbuterol and the cAMP analogue N6,2-O-dibutyryladenosine 3,5-cyclic monophosphate, but was unaffected by the 1 adrenergic agonist methoxamine. The noradrenaline enhancement of creatine accumulation at 48 h was inhibited by the mixed - and -antagonist labetalol and by the -antagonist propranolol, but was unaffected by the 2 antagonist phentolamine; greater inhibition was caused by the 2 antagonist butoxamine than the 1 antagonist atenolol. Creatine accumulation at 48 h was increased to 230 ± 6% of control by insulin and by 140 ± 13% by IGF-I (both at 3 nM). Creatine accumulation at 48 h was also increased to 280 ± 40% of control by 3,3,5-triiodothyronine (at 70 M) and to 220 ± 35% of control by amylin (60 nM). As 3,3,5-triiodothyronine, amylin and isoproterenol all stimulate the Na+,K+-ATPase, we suggest that they stimulate Na+-creatine cotransport indirectly by increasing the transmembrane [Na+] concentration gradient and membrane potential.Abbreviations IGF-I insulin-like growth factor I - IGF-II insulin-like growth factor II - T3 3,3,5-triiodothyronine - CGRP calcitonin gene-related peptide  相似文献   

17.
Summary 13C NMR relaxation data have been used to determine dipolar auto- and cross-correlation times for the di- and tripeptides GK, KG and GKG, primarily to analyze lysine side-chain motional dynamics. In general, correlation times are largest for backbone positions and decrease on going through the lysine side chain, consistent with the idea of increased mobility at C and C methylenes. Correlation times, however, vary with the peptide ionization state. In the zwitterionic state of GK, for example, both auto-and cross-correlation times are at their maximum values, indicating reduced internal motions probably resulting from intramolecular electrostatic interactions. Modifying the charge state increases motional fluctuations. Activation energies determined from the temperature dependence of CH rotational autocorrelation times at neutral pH are approximately equal for glycine and lysine C and lysine C and C positions (4.1±0.2 to 4.5±0.2 kcal/mol) and tend to decrease slightly for lysine C and C (3.8±0.2 to 4.3±0.2 kcal/mol). The sign of lysine side-chain cross-correlations could not be explained by using any available rotational model, including one parameterized for multiple internally restricted rotations and anisotropic overall tumbling. Molecular and stochastic dynamics calculations were performed to obtain insight into correlated internal rotations and coupled overall tumbling and internal motions. Relatively strong correlations were found for i,i+1 backbone and lysine side-chain internal bond rotations. Stochastic dynamics calculations were more successful at explaining experimentally observed correlation times. In the fully charged state, a preferred conformation was detected with an all-trans lysine side chain.Abbreviations rf radio frequency - GK dipeptide glycine-lysine - KG dipeptide lysine-glycine - GKG tripeptide glycine-lysine-glycine  相似文献   

18.
Summary Collagen and fibronectin synthesis by trisomic and triploid fibroblasts derived from human spontaneous abortuses was studied. It was demonstrated that the level of fibronectin and collagen production in fibroblasts with trisomy 7, trisomy 9, and triploidy was reduced as compared with diploid cells. A correlation between this observation and an increased rate of intracellular 14C-procollagen degradation was also established for the anomalous strains. No difference in hydroxylation of 14C-proline residues in 1() and 2() collagen chains and no fluctuation in the collagen type (): type ratio was found in the strains with the abnormal karyotypes. It was concluded that differentiation of the abnormal fibroblasts was impaired. The data also favour the hypothesis that the deficiency of the fibroblasts in producing proteins may account for a variety of anatomic abnormalities of embryos.  相似文献   

19.
Summary The ratio of deuterium to hydrogen (expressed as D) in hydrogen released as water during the combustion of dried plant material was examined. The D value (metabolic hydrogen) determined on plant materials grown under controlled conditions is correlated with pathways of photosynthetic carbon metabolism. C3 plants show mean D values of-132 for shoots and -117 for roots; C4 plants show mean D values of -91 for shoots and-77 for roots and CAM plants a D value of-75 for roots and shoots. The difference between the D value of shoot material from C3 and C4 plants was confirmed in species growing under a range of glasshouse conditions. This difference in D value between C3 and C4 species does not appear to be due to differences in the D value (tissue water) in the plants as a result of physical fractionation of hydrogen isotopes during transpiration. In C3 and C4 plants the hydrogen isotope discrimination is in the same direction as the carbon isotope discrimination and factors contributing to the difference in D values are discussed. In CAM plants grown in the laboratory or collected from the field D values range from-75 to +50 and are correlated with 13C values. When deprived of water, the D value (metabolic hydrogen) in both soluble and insoluble material in leaves of Kalanchoe daigremontiana Hamet et Perr., becomes less negative. These changes may reflect the deuterium enrichment of tissue water during transpiration, or in field conditions, may reflect the different D value of available water in areas of increasing aridity. Whatever the origin of the variable D value in CAM plants, this parameter may be a useful index of the water relations of these plants under natural conditions.  相似文献   

20.
As part of our investigation of the mode of action of plant hormones in barley (Hordeum vulgare L.) aleurone layers, we have studied the expression of five identified and three unidentified mRNA species in the presence of exogenous gibberellic acid (GA3) and abscisic acid. Three of the mRNAs are GA3-inducible, three are suppressed by GA3, and two are constitutive. The extent of the GA3 effect differs considerably for both inducible and suppressible mRNAs. For example, a ten-fold higher concentration of GA3 (10-8 M) is required for full induction of the high-pl group -amylase mRNA than is required for the low-pI -amylase mRNA (10-9 M). Temporal regulation of mRNA abundance also varies between the two -amylase isoenzyme groups. The three GA3-suppressible mRNA species studied, alcohol dehydrogenase (ADH1), a probable amylase and protease inhibitor, and an unidentified barley mRNA species also varied in response to GA3. The ADH1 mRNA decreased drastically within 8 h of GA3 treatment, whereas the other two began to decrease in abundance only after 12–16 h of GA3 treatment. Abscisic-acid treatment counteracted the GA3 effects for both the inducible and suppressible mRNA species. Comparison of -amylase-mRNA levels and -amylase-synthesis rates showed a strong correlation between the two parameters, the only exception being a lack of -amylase synthesis in the presence of -amylase mRNA at low GA3 concentrations. Therefore, the expression of -amylase seems to be regulated primarily by its mRNA levels.Abbreviations ABA abscisic acid - ADH1 alcohol dehydrogenase 1 - cDNA copy DNA - GA3 gibberellic acid - PAPI probable amylase/protease inhibitor  相似文献   

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