Analysis And Localization of the Water-Deficit Stress-Induced Gene (lp3)

LP3 is a water-deficit-induced protein, which is highly homologous to ASR (ABA, stress and ripening) proteins. Homology was found in the C-terminal region of the putative LP3 protein while lower homologies were found in the N-terminal region. The goal of this study was to investigate the function of the LP3 protein and the mechanism of the lp3 promoter in response to water-deficit stress (WDS) and other stresses. In regenerated transgenic tobacco (T₀), expression of β-glucuronidase (GUS) from the lp3 promoter-GUS construct was observed in polyethylene glycol (PEG), abscisic acid (ABA), methyl-jasmonate (MeJa), and fluridone (Flu) treatments. GUS expression was not observed following gibberellin (GA₃), 2-methyl-4-dichlorophenoxy acetic acid (2,4-D), silver nitrate, or ethephon (ethylene releasing agent) treatments. Germinated T₁ seedlings containing the lp3 promoter-GUS construct exhibited GUS activity up to 40 days postgermination. Expression could be restored when 5-azacytidine was included in the culture media, indicative of a developmentally regulated silencing mechanism involving methylation. In transgenic tobacco, the LP3 protein localized in the cell nucleus was induced by WDS and appeared to be developmentally regulated.     

Crosstalk between ABA and auxin signaling pathways in roots of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> (L.) Heynh.

Studies of abscisic acid (ABA) and auxin have revealed that these pathways impinge on each other. The Daucus carota (L.) Dc3 promoter: uidA (-glucuronidase: GUS) chimaeric reporter (ProDc3:GUS) is induced by ABA, osmoticum, and the auxin indole-3-acetic acid (IAA) in vegetative tissues of transgenic Arabidopsis thaliana (L.) Heynh. Here, we describe the root tissue-specific expression of ProDc3:GUS in the ABA-insensitive-2 (abi2-1), auxin-insensitive-1 (aux1), auxin-resistant-4 (axr4), and rooty (rty1) mutants of Arabidopsis in response to ABA, IAA and synthetic auxins naphthalene acetic acid (NAA), and 2, 4-(dichlorophenoxy) acetic acid. Quantitative analysis of ProDc3:GUS expression showed that the abi2-1 mutant had reduced GUS activity in response to ABA, IAA, or 2, 4-d, but not to NAA. Similarly, chromogenic staining of ProDc3:GUS activity showed that the aux1 and axr4 mutants gave predictable hypomorphic ProDc3:GUS expression phenotypes in roots treated with IAA or 2, 4-d, but not the diffusible auxin NAA. Likewise the rty mutant, which accumulates auxin, showed elevated ProDc3:GUS expression in the absence or presence of hormones relative to wild type. Interestingly, the aux1 and axr4 mutants showed a hypomorphic effect on ABA-inducible ProDc3:GUS expression, demonstrating that ABA and IAA signaling pathways interact in roots. Possible mechanisms of crosstalk between ABA and auxin signaling are discussed.     

Determination of carbon-reduction-cycle intermediates in leaves of Arbutus unedo L. suffering depressions in photosynthesis after application of abscisic acid or exposure to dry air

Gas exchange and contents of photosynthetic intermediates of leaves of Arbutus unedo L. were determined with the aim of recognizing the mechanisms of inhibition that were responsible for the midday depression of photosynthesis following exposure to dry air, and the decline in photosynthetic capacity following application of abscisic acid (ABA). Rapidly killed (<0.1 s) leaf samples were taken when gas analysis showed reduced CO₂ assimilation. Determination of the contents of 3-phosphoglyceric acid (PGA), ribulose 1,5-bisphosphate (RuBP), triose phosphates, fructose 1,6-bisphosphate and hexose phosphates in the samples showed that significant variation occurred only in the level of PGA. As a result, the ratio PGA/RuBP decreased with increasing inhibition of photosynthesis, particularly when application of ABA had been the cause. A comparison of metabolite patterns did not bring out qualitative differences that would have indicated that effects of ABA and of dry air had been caused by separate mechanisms. Depression of photosynthesis occurred in the presence of sufficient RuBP which indicated that the carboxylation reaction of the carbon-reduction-cycle was inhibited after application of ABA or exposure to dry air.Abbreviations and symbols ABA abscisic acid - C _a partial pressure of CO₂ in the ambient air - C _i partial pressure of CO₂ in the intercellular spaces - I quantum flux - PGA 3-phosphoglyceric acid - RuBP ribulose 1,5-bisphosphate - I _L leaf temperature - w water-vapor pressure difference between leaf and air     

The role of cis-carotenoids in abscisic acid biosynthesis

Evidence has been obtained which is consistent with 9-cis-neoxanthin being a major precursor of abscisic acid (ABA) in higher plants. A mild, rapid procedure was developed for the extraction and analysis of carotenoids from a range of tissues. Once purified the carotenoids were identified from their light-absorbance properties, reactions with dilute acid, high-performance liquid chromatography R_ts, mass spectra and the quasiequilibria resulting from iodine-catalysed or chlorophyllsensitised photoisomerisation. Two possible ABA precursors, 9-cis-neoxanthin and 9-cis-violaxanthin, were identified in extracts of light-grown and etiolated leaves (of Lycopersicon esculentum, Phaseolus vulgaris, Vicia faba, Pisum sativum, Cicer arietinum, Zea mays, Nicotiana plumbaginifolia, Plantago lanceolata and Digitalis purpurea), and roots of light-grown and etiolated plants (Lycopersicon, Phaseolus and Zea). The 9,9-di-cisisomer of violaxanthin was synthesised but its presence was not detected in any extracts. Levels of 9-cis-neoxanthin and all-trans-violaxanthin were between 20- to 100-fold greater than those of ABA in light-grown leaves. The levels of 9-cis-violaxanthin were similar to those of ABA but unaffected by water stress. Etiolated Phaseolus leaves contained reduced amounts of carotenoids (15–20% compared with light-grown leaves) but retained the ability to synthesise large amounts of ABA. The amounts of ABA synthesised, measured as increases in ABA and its metabolites phaseic acid and dihydrophaseic acid, were closely matched by decreases in the levels of 9-cis-neoxanthin and all-trans-violaxanthin. In etiolated seedlings grown on 50% D₂O, deuterium incorporation into ABA was similar to that into the xanthophylls. Relative levels of carotenoids in roots and light-grown and etiolated leaves of the ABA-deficient mutants, notabilis, flacca and sitiens were the same as those found in wild-type tomato tissues.Abbreviations ABA abscisic acid - DPA dihydrophaseic acid - GC-MS gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - PA phaseic acid - t trans - Xan xanthoxin - flc flacca - not notabilis - sit sitiens The authors would like to thank the following for their help and advice: G. Britton (Department of Biochemistry, University of Liverpool, UK), B.H. Davies (Department of Biochemistry, University of Wales, Aberystwyth), P. Molnar, J. Szabolcs, D.C. Walton (Department of Biology, Suny, Syracuse, N.Y., USA), and Mr. J.K. Heald for his expert operation of the mass spectrometer. A.D.P. was supported initially by a Science and Engineering Research Council CASE award with Shell Biosciences, Sittingbourne, Kent, UK, and later by a Agricultural and Food Research Council (AFRC) grant. M.J.B. received a NATO fellowship. The mass spectrometer and HPLC-photodiode-array detector were purchased with funds provided by the AFRC.     

Evaluation of putative seed-specific promoters for Linum usitatissimum

The GUS reporter gene was used to test four different putativeseed-specific promoters in developing and mature seeds, leaves and roots fromlinseed flax (Linum usitatissimum). The promoters testedincluded the regulatory regions of the -ketoacyl-CoA synthase gene (KCS)and the napin protein gene from Brassica napus, thepromoter regions of the 'unknown seed protein' (USP), and a legumin proteingene(LeB4) from Vicia faba and the CaMV 35S promoter (positivecontrol). The promoter-GUS constructs were inserted into L.usitatissimum via Agrobacterium mediatedtransformation, and GUS activity evaluated using histochemical andfluorimetrical assays. All the promoters showed some activity, but only CaMV35S, LeB4 and USP exhibited an expression level high enough to be useful inlinseed flax. Plants with USP-GUS showed the earliest GUS activity at 5 to 6days after flowering (daf) and persisting until 40 daf. Expression of GUS underthe control of the LeB4 promoter was measurable 11 daf and was still detectableat 40 daf. The KCS-GUS construct showed a low level of GUS activity between 14daf and 40 daf. Plants transformed with USP-GUS or LeB4-GUS exhibited a lowlevel of GUS activity in leaves and roots of some of the transformants,indicating the need for generating large numbers of primary transformants,followed by careful evaluation and selection for ones with not only the desiredlevel of expression, but also the desired spatial and temporal expression.     

Intron position affects expression from thetpi promoter in rice

A series of promoter-GUS fusion constructs containing a portion of the rice triosephosphate isomerase (tpi) promoter, the firsttpi intron, and the gene encoding bacterial -glucuronidase (GUS) were made. These constructs were electroporated into rice protoplasts and transient expression was monitored. Inclusion of the first intron from the ricetpi gene enhanced expression of the GUS gene from thetpi promoter when it was placed 5 of the GUS gene. When thetpi intron was placed in the 3-untranslated region no enhancement of GUS gene expression was observed, indicating the importance of position in intron-mediated enhancement of gene expression.     

Simultaneous and independent effects of abscisic acid on stomata and the photosynthetic apparatus in whole leaves

(±)-Abscisic acid (ABA) at 10^-5 M was added to the transpiration stream of leaves of 16 species (C₃ and C₄, monocotyledons and dicotyledons). Stomatal responses followed one of three patterns: i) stomata that were wide and insensitive to CO₂ initially, closed partially and became sensitive to CO₂; ii) for stomata that were sensitive to CO₂ before the application of ABA, the range of highest sensitivity to CO₂ shifted from high to low intercellular partial pressures of CO₂, for instance in leaves of Zea mays from 170–350 to 70–140 bar; iii) when stomata responded strongly to ABA, their conductance was reduced to a small fraction of the initial conductance, and sensitivity to CO₂ was lost. The photosynthetic apparatus was affected by applications of ABA to various degrees, from no response at all (in agreement with several previous reports on the absence of effects of ABA on photosynthesis) through a temporary decrease of its activity to a lasting reduction. Saturation curves of photosynthesis with respect to the partial pressure of CO₂ in the intercellular spaces indicated that application of ABA could produce three phenomena: i) a reduction of the initial slope of the saturation curve (which indicates a diminished carboxylation efficiency); ii) a reduction of the level of the CO₂-saturated rate of assimilation (which indicates a reduction of the ribulose-1,5-bisphosphate regeneration capacity); and iii) an increase of the CO₂ compensation point. Photosynthesis of isolated mesophyll cells was not affected by ABA treatments. Responses of the stomatal and photosynthetic apparatus were usually synchronous and often proportional to each other, with the result that the partial pressure of CO₂ in the intercellular spaces frequently remained constant in spite of large changes in conductance and assimilation rate. Guard cells and the photosynthetic apparatus were able to recover from effects of ABA applications while the ABA supply continued. Recovery was usually partial, in the case of the photosynthetic apparatus occasionally complete. Abscisic acid did not cause stomatal closure or decreases in the rate of photosynthesis when it was applied during a phase of stomatal opening and induction of photosynthesis that followed a transition from darkness to light.Abbreviations and symbols A rate of CO₂ assimilation - ABA (±)-abscisic acid - c _a partial pressure of CO₂ in the ambient air or in the gas supplied to the leaf chambers - c _i partial pressure of CO₂ in the intercellular spaces of a leaf - e _a partial pressure of H₂O in the air - g conductance for water vapor - J quantum flux - T ₁ leaf temperature     

Effect of auxin and abscisic acid on cell wall extensibility in maize coleoptiles

Plastic and elastic in-vitro extensibilities (E _pland E _el ) of cell walls from growing maize (Zea mays L.) coleoptile segments were measured by stretching frozen-thawed tissue, pre-extended to its in-vivo length, at constant force (creep test) in a custom-buildt extensiometer, equipped with a linear-displacement transducer. The indole-3-acetic acid (IAA)-induced change of E _pl (E _pl ) is strictly correlated with the growth rate for a period of 3–4 h. Subsequently, E _plremains constant while the growth rate is slowing down. Since this discrepancy can be accounted for by a growth-dependent reduction of osmotic pressure, it is concluded that E _plrepresents quantitatively the relative increase of in-vivo extensibility (cell wall loosening) involved in IAA-mediated cell growth over a much longer time. On the other side it is argued that the growth rate may not be strictly correlated with wall extensibility during long-term growth. Abscisic acid (ABA) inhibits segment growth induced by auxin, fusicoccin, or exogenous acid, and this effect can be quantitatively attributed to an ABA-mediated reduction of cell wall extensibility as determined by the E _plmeasurement. Both, IAA and ABA have no effect on total protein synthesis, RNA synthesis, and amount of osmotic solutes. Fusicoccin-induced proton excretion is only slightly inhibited by ABA. In contrast to ABA, growth inhibition by cycloheximide (CHI) is always much larger than the concomitant reduction of E _pl , indicating that a further growth parameter is also involved in the inhibition of cell growth by CHI. E _el is not affected by either IAA, ABA, or CHI. It is concluded that E _pl as determined by the applied method, represents a relative measure of the actual in-vivo extensibility of the growing cell wall at the very moment when the tissue is killed, rather than an average extensibility accumulated over some immediate-past period of time as suggested by Cleland (1984, Planta 160, 514–520). Hence, we further draw the conclusion that IAA and ABA control of cell growth can entirely be attributed to a modulation of cell wall extensibility by these hormones in maize coleoptiles.Abbreviations ABA ±abscisic acid - CHI cycloheximide - E _el , E_pl elastic and plastic in vitro extensibilities, respectively (E _el+E_pl=E_tot>) - FC fusicoccin - IAA indole-3-acetic acid     

Analysis of an ABA-responsive rice gene promoter in transgenic tobacco

We have analyzed in transgenic tobacco the expression of a chimeric gene containing 5 sequences of the rice rab-16B gene fused to the -glucuronidase (GUS) reporter gene. This construct, a translational fusion (–482 to +184) including 14 amino acids of the RAB-16B protein, is expressed only in zygotic and pollen-derived embryos. In zygotic embryos, GUS activity begins to accumulate 10 days after flowering (daf), and increases until seed maturation at 25 daf. Immunological measurements of endogenous abscisic acid (ABA) accumulation in these seeds showed a close parallel between hormone levels and GUS activity. However, GUS activity could not be reproducibly induced by treatment of immature embryos with ABA (10 M). Neither GUS activity nor GUS mRNA could be detected in leaves of transgenic tobacco even after ABA treatment. In contrast, GUS activity could be induced to high levels in pollen-derived embryos by treatment with ABA. Our results show that 482 bp of 5 sequences of the rice rab-16B promoter can confer in transgenic tobacco developmentally regulated expression in embryos but not ABA-responsive expression in vegetative tissues.     

A stress-induced,developmentally regulated,highly polymorphic protein family in Pisum sativum L.

The expression of members of two closely related abscisic acid (ABA)-responsive pea protein families, ABR17 and ABR18 (ABA-responsive 17200-M_r and 18100-M_r, respectively), is developmentally, tissueand stress-specifically regulated. Two-dimensional polyacrylamide gel electrophoresis revealed a number of ABR polypeptides on fluorographs of immunoprecipitated translation products of mRNAs, depending on the tissue, stage of development or type of stress. High endogenous ABA, or added ABA, enhanced the accumulation of translatable mRNA for specific ABR members under certain conditions, but high endogenous ABA was not a pre-requisite for accumulation of translatable ABR mRNA. The accumulation of ABR polypeptides was examined by Western blot analysis of acetate-buffer-extracted proteins. In fully expanded, young unstressed leaves, the ABR17 polypeptides (ABR18 polypeptides not detectable) accumulated to markedly higher levels in the epidermis than in the mesophyll. Dehydration stress caused an increased (ABR17) and detectable (ABR18) polypeptide accumulation which occurred predominantly in the epidermis. Detached leaves were used further to characterise factors affecting ABR polypeptide accumulation. An enhanced (ABR17) and detectable (ABR18) polypeptide accumulation occurred in the presence of ABA (10^–4 M) but ABR18-polypeptide accumulation required light. The accumulation of both ABR polypeptides was stimulated in the presence of metabolisable and non-metabolisable carbohydrate sources but not in water or glutamine, indicating an osmotic rather than metabolic response. This carbohydrate-stimulated accumulation was markedly enhanced by light but unaffected by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosynthesis, indicating other photoreceptive processes besides photosynthesis were involved. The function of the ABR proteins remains unknown but their accumulation in aging tissues indicates a role in senescence. The results clearly demonstrate highly complex interactions between different environmental and developmental signals leading to the expression of these stressrelated proteins. In light of these results, the induction of protein expression of the newly-termed intracellular pathogenesis-related proteins, to which the ABR proteins are closely related, is discussed.Abbreviations ABA (±)cis, trans-abscisic acid - ABR17 M_r17200 ABA-responsive protein - ABR18 M_r-18100 ABA-responsive protein - 2-D two-dimensional - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - FW fresh weight - IgG immunoglobulin G - M_r apparent molecular mass - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis     

Dormancy in somatic embryos and seeds ofVitis: changes in endogenous abscisic acid during embryogeny and germination

Abscisic acid (ABA) in extracts of somatic embryos and seeds of Gloryvine (Vitis vinifera L.xV. rupestris Scheele) was measured by gas chromatography-mass spectrometry-selected ion monitoring using deuterated ABA, (±)-[C-3Me-²H₃]ABA, ([²H₃]ABA) as internal standard. The ABA content increased rapidly during embryogeny (0.035 ng/embryo at the globular stage to 0.22 ng/embryo at the mature stage). The level of ABA in the tissues of somatic embryos, expressed in ng/mg dry weight, decreased from the globular stage (0.76 ng/mg) to the mature stage (0.25 ng/mg). Chilling (4° C) induced normal germination of seeds and mature somatic embryos and precocious germination of globular, heart-shaped and torpedoshaped somatic embryos. In all cases chilling led to a marked reduction in endogenous ABA. Exogenous (±)-ABA inhibited the germination of chilled somatic embryos.Abbreviations ABA abscisic acid - [²H₃]ABA (±)-[C-3Me-²H₃]-abscisic acid - BHT 2,6-di-t-butyl-4-methylphenol - GC-MS gas chromatography-mass spectrometry - Me-ABA and Me-[²H₃]ABA methyl esters of ABA and [²H₃]ABA, respectively - SIM selected ion monitoring     

Developmental and pathogen-induced activation of an msr gene, str246C, from tobacco involves multiple regulatory elements

A family of genes, the so-called msr genes (multiple stimulus response), has recently been identified on the basis of sequence homology in various plant species. Members of this gene family are thought to be regulated by a number of environmental or developmental stimuli, although it is not known whether any one member responds more specifically to one stimulus, or whether each gene member responds to various environmental stimuli. In this report, we address this question by studying the tobacco msr gene str246C. Using transgenic tobacco plants containing 2.1 kb of 5 flanking DNA sequence from the str246C gene fused to the -glucuronidase (GUS) coding region, the complex expression pattern of the str246C promoter has been characterized. Expression of the str246C promoter is strongly and rapidly induced by bacterial, fungal and viral infection and this induction is systemic. Elicitor preparations from phytopathogenic bacteria and fungi activate the str246C promoter to high levels, as do wounding, the application of auxin, auxin and cytokinin, salicylic acid or copper sulfate, indicating the absence of gene specialization within the msr gene family, at least for str246C. In addition, GUS activity was visualized. histochemically in root meristematic tissues of tobacco seedlings and is restricted to roots and sepals of mature plants. Finally, analysis of a series of 5 deletions of the str246C promoter-GUS gene fusion in transgenic tobacco plants confirms the involvement of multiple regulatory elements. A region of 83 by was found to be necessary for induction of promoter activity in response to Pseudomonas solanacearum, while auxin inducibility and root expression are apparently not controlled by this element, since its removal does not abolish either response. An element of the promoter with a negative effect on promoter activation by P. solanacearum was also identified.Joint first authors     

Effect of nitrogen stress and abscisic acid on nitrate absorption and transport in barley and tomato

The potential of barley (Hordeum vulgare L.) and tomato (Lycopersicon esculentum Mill.) roots for net NO ₃ ^- absorption increased two-to five fold within 2 d of being deprived of NO ₃ ^- supply. Nitrogen-starved barley roots continued to maintain a high potential for NO ₃ ^- absorption, whereas NO ₃ ^- absorption by tomato roots declined below control levels after 10 d of N starvation. When placed in a 0.2 mM NO ₃ ^- solution, roots of both species transported more NO ₃ ^- and total solutes to the xylem after 2 d of N starvation than did N-sufficient controls. However, replenishment of root NO ₃ ^- stores took precedence over NO ₃ ^- transport to the xylem. Consequently, as N stress became more severe, transport of NO ₃ ^- and total solutes to the xylem declined, relative to controls. Nitrogen stress caused an increase in hydraulic conductance (L _p) and exudate volume (J _v) in barley but decrased these parameters in tomato. Nitrogen stress had no significant effect upon abscisic acid (ABA) levels in roots of barley or flacca (a low-ABA mutant) tomato, but prevented an agerelated decline in ABA in wild-type tomato roots. Applied ABA had the same effect upon barley and upon the wild type and flacca tomatoes: L _p and J _v were increased, but NO ₃ ^- absorption and NO ₃ ^- flux to the xylem were either unaffected or sometimes inhibited. We conclude that ABA is not directly involved in the normal changes in NO ₃ ^- absorption and transport that occur with N stress in barley and tomato, because (1) the root ABA level was either unaffected by N stress (barley and flacca tomato) or changed, after the greatest changes in NO ₃ ^- absorption and transport and L _p had been observed (wild-type tomato); (2) changes in NO ₃ ^- absorption/transport characteristics either did not respond to applied ABA, or, if they did, they changed in the direction opposite to that predicted from changes in root ABA with N stress; and (3) the flacca tomato (which produces very little ABA in response to N stress) responded to N stress with very similar changes in NO ₃ ^- transport to those observed in the wild type.Abbreviation and symbols ABA abscisic acid - J_v exudate volume - L_p root hydraulic conductance     

Abscisic acid-inducible nuclear proteins bind to bipartite promoter elements required for ABA response and embryo-regulated expression of the carrot<Emphasis Type="Italic"> Dc3</Emphasis> gene

The carrot (Daucus carota L.) lea-class gene Dc3 is expressed in developing seeds and in vegetative tissues subject to drought and treatment with exogenous abscisic acid (ABA). Cis regulatory elements involved in seed-specific expression and in response to ABA were identified in transgenic tobacco (Nicotiana tabacum L.) using -glucuronidase (GUS) reporter gene constructs containing a series of deletion and orientation mutants of the Dc3 promoter. These experiments demonstrated that the Dc3 promoter is comprised of a proximal promoter region (PPR) and a distal promoter region (DPR). TCGTGT motifs in the DPR in combination with the PPR comprise a novel, bipartite ABA module in the Dc3 gene promoter. The PPR contains cis-acting elements responsible for the developmental regulation of Dc3 expression in seeds. Five similar sequence motifs with the consensus ACACgtGCa were identified in the PPR. Both DPR and PPR interact with common nuclear proteins that are present in embryos and are inducible by ABA in vegetative tissues.     

Validation of a radioimmunoassay for (+)-abscisic acid in extracts of apple and sweet-pepper tissue using high-pressure liquid chromatography and combined gas chromatography-mass spectrometry

A radioimmunoassay for (+)-abscisic acid (ABA) was developed and applied to the analysis of free ABA in extracts of apple (Malus pumila Mill.) and sweet pepper (Capsicum annuum L.) leaves at various stages during extract purification. Conjugates of ABA, were quantified after alkaline hydrolysis. The validity of the radioimmunoassay was tested by comparison of immunoassay estimates of ABA at different levels of extract purity with high-pressure liquid chromatography (HPLC) and combined gas chromatography-mass spectrometry. The antiserum, raised against (+)-ABA, was almost equally sensitive to (-)-ABA. Serum cross-reactivity with the methyl ester of ABA was 160% and with the glycosyl ester of ABA was 34%. Cross-reactivity with protein-ABA conjugates was very slight for C₄-conjugated keyholelimpet haemocyanin, but about 1000% for C₁-conjugated alkaline phosphatase. Other compounds tested showed extremely low or undetectable cross-reactivities. Further evidence for the specificity of the assay came from the agreement between the results using different assay methods for both apple and pepper extracts, and from the observation that the only zone of immunoreactivity on HPLC elution profiles corresponded with authentic (+)-ABA. The use of polyvinylpyrrolidone in the assay minimised interference by other substances in plant extracts. In pepper, free ABA levels increased rapidly during water stress and recovered to pre-stress levels within two days after rewatering. Levels of ABA conjugates were significantly lowr than free ABA in unstressed plants, and also increased rapidly with stress, although not to the same extent as free ABA, and did not recover as rapidly as did free ABA. In apple, levels of free ABA and of ABA conjugates both increased more than twofold over a two-week period of water stress. In contrast to pepper, however, immunoreactivity of the conjugate fraction was increased by hydrolysis, indicating that different ABA conjugates predominate in the two species.Abbreviations ABA abscisic acid - GC-MS combined gas chromatography-mass spectrometry - HPLC high-pressure liquid chromatography - Me-ABA methyl ester of ABA - PVP polyvinylpyrrolidone - RIA radioimmunoassay     

中国沙棘克隆生长对灌水强度的响应规律及其激素调控机制

关于中国沙棘克隆生长调节研究目前局限于外在机制,旨在探讨其克隆生长对灌水强度的响应规律及其激素调控的内在机制。结果表明:随着灌水强度的增大,分株生长、克隆繁殖、克隆扩散能力先升后降,IAA(吲哚-3-乙酸)、ZR(玉米素核苷)、GA_3(赤霉酸)含量及其与ABA(脱落酸)的比值先升后降而ABA含量先降后升。同时,分株生长、克隆繁殖、克隆扩散能力与IAA、ZR、GA_3含量以及IAA/ABA、ZR/ABA、GA_3/ABA呈极显著或显著正相关,与ABA含量呈极显著负相关。灌水强度过小或过大,IAA、ZR、GA_3含量以及IAA/ABA、ZR/ABA、GA_3/ABA低而ABA含量高,克隆生长潜力受到抑制,种群以分株小、数量少(分布稀疏)、扩散(水平根延伸和分枝)能力弱为特征,克隆生长格局倾向于"游击型"、种群早衰概率高;灌水强度适宜,IAA、ZR、GA_3含量以及IAA/ABA、ZR/ABA、GA_3/ABA高而ABA含量低,克隆生长潜力得以充分发挥,种群以分株大、数量多(分布密集)、扩散能力强为特征,克隆生长格局倾向于"聚集型"、种群稳定性高。随着灌水强度过小-适宜-过大的连续变化,中国沙棘通过改变激素状况调控克隆生长,从而形成与灌水强度相适应的克隆生长格局连续体"游击型-聚集型-游击型",种群稳定性呈"低-高-低"的连续变化过程。由此可见:灌水强度诱导内源激素发生改变,激素特征调控克隆生长格局,克隆生长格局决定种群稳定性。