摘要:

Enhancement in the rates of photosystem (PS) II‐catalysed O2evolution was observed with thylakoids isolated from cotyledonary leaves ofBrassica junceaseedlings raised in medium containing 200 mMNaCl compared to controls. The nature of this enhancement in PS II activity by NaCl treatment has been investigated. The pH profile showed an optimal PS 11(H2O→FeCN) activity at pH 7.5 in thylakoids of both controls and NaCl‐raised seedlings. However, the thylakoids from NaCl‐raised plants showed significantly higher PS II activity at all the pHs (from 6.0 to 9.0) with maximal difference occurring at alkaline pHs. Besides the enhanced electron transport rates, light‐induced proton uptake was about 30% higher in the thylakoids from NaCl‐raised plants than in the control thylakoids. The 3‐(3,4‐dichlorophenyl)‐1, 1‐dimethylurea (DCMU)‐induced enhancement in the room temperature fluorescence was significantly higher in thylakoids from NaCl‐grown plants compared to controls, suggesting more efficient PS II photochemical reactions in thylakoids from NaCl‐raised seedlings. The analysis of the changes in the fluorescence yield of Chl also showed an enhancement in Fvlevel in NaCl‐raised plants, suggesting that NaCl treatment stimulates the photochemistry of PS II. Analysis of light saturation kinetics of PS II [H2O→2,6‐dichloro‐p‐benzoquinone (DCBQ) or phenylenediamine (PD)] activity showed that the extent of stimulation by NaCl under rate‐limiting light intensities was greater than at rate‐saturating intensities. This result indicates that NaCl treatment not only alters the electron transport rates but also the relative quantum yield. Incubation of thylakoids at pH 9.0 inhibited FeCN‐supported PS II activity more drastically in control than in NaCl‐treated thylakoids. Recovery from alkaline‐pH‐induced inhibition occurred when the thylakoids were resuspended at pH 7.5. Reversal in PS II activity was significantly higher in the thylakoids of NaCl‐raised plants than in the control thylakoids. These results suggest that the seedlings raised at moderately elevated levels of NaCl have thylakoids with enh

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860201.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

A novel biochemical assay system for detecting the early stage of flowering is reported. Peroxidase isozymes in shoot apices ofPharbitis nilplants that had been exposed to flower‐inducing or non‐inducing conditions were analyzed by isoelectric focusing in polyacrylamide gels and activity staining for peroxidase. Several isozymes with pH 8.5–8.8 appeared for the first time 7 days after the beginning of short‐day treatment, but not after nightbreak (non‐inducing) treatment. When shoot tips were cultured in vitro, these same isozymes also appeared after short‐day treatment but not after night‐break treatment. The extent of the appearance of these isozymes was reduced by exposure to high or low temperature during the inductive dark period and removal of cotyledons after the inductive dark period. Such treatments also reduced the extent of flowering. The appearance of an isozyme with pH 8.5 was more closely correlated with flowering than that of the other isozymes. From these results, the appearance of this peroxidase isozyme in shoot apices is discussed as a biochemical marker of flowering in intact plants and in cultur

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860202.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

Gibberellin A4/7(GA4/7) was applied twice weekly to 2‐year‐oldPinus sylvestris(L.) seedlings in each of two years, starting close to budbreak and ending after shoot elongation, but before cambial activity ceased. In 1988, the GA4/7was injected into the 1987 terminal shoot (0, 0.2 or 2 mg seedling−1application−1), while in 1990 it was applied as a soil drench (0, 10 or 50 mg seedling−1application−1). In the 1988 experiment, GA4/7treatment promoted diameter growth, and tended to increase both longitudinal growth and the indole‐3‐acetic acid (IAA) level in the 1988 terminal. In the 1990 experiment, GA4/7treatment increased tracheid production, longitudinal growth, and the cambial region IAA concentration in the 1990 terminal, but did not affect its pith diameter, needle number, needle dry weight, or needle IAA level. Tracheid production in the previous‐year's terminal was also promoted in both experiments. The 50 mg GA4/7soil drench markedly elevated the concentrations of GA4, GA7and GA9in the needles and cambial region of the 1990 terminal, while the 10 mg treatment raised the GA4level in the cambial region, providing evidence that GA4and GA7applied to the roots reaches the shoot system. The results support the hypothesis that the exogenous GA4/7‐induced stimulation of tracheid production in the terminal shoot of intact plants is mediated through an increase in the IAA level in the cambial region. However, per se activity of GA4, GA7or their metabolites

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860203.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

Light enhanced the abscisic acid‐induced accumulation of proline in barley (Hordeum vulgareL. cv. Georgie) and wheat (Triticum durumL. cv. Valnova). In wheat ABA is ineffective in the dark. In both barley and wheat, the accumulation of proline in the light showed the same characteristics as those of the process that occurs in barley in the dark, namely a synergistic interaction between the hormone and K(Na)Cl, an enhancing effect of Cl−anion in excess over K+cation in the incubation medium, and an inhibiting effect ofD‐mannose and monensine. In wheat, furthermore, light is needed during treatment with ABA if proline is to accumulate. Light was effective in both wheat and barley during the second or accumulation phase of the hormonal process, whereas the events occurring in the first (or lag) phase did not require light. The results suggest that in wheat light induces a putative factor(s) involved in the proline accumulation pathway that is lost in the dark, whereas in barley it is present in the

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860204.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

Although the inhibitory effects of high concentrations of mineral N (>1.0 mM) on nodule development and function have often been studied, the effects of low, static concentrations of NH4+(<1.0 mM) on nodulation are unknown. In the present experiments we examine the effects of static concentrations of NH4+at 0, 0.1 and 0.5 mMin flowing, hydroponic culture on nodule establishment and nitrogenase activity in field peas [Pisum sativumL. cv. Express (Svalöf AB)] for the initial 28 days after planting (DAP). Peas grown in the presence of low concentrations of NH4+had significantly greater nodule numbers (up to 4‐fold) than plants grown without NH4+. Nodule dry weight per plant was significantly higher at 14, 21 and 28 DAP in plants grown in the presence of NH4+, but individual nodule mass was lower than in plants grown without NH4+. The nodulation pattern of the plants supplied with NH4+was similar to that often reported for supernodulating mutants, however the plants did not express other growth habits associated with supernodulation. Estimates of N2fixation indicate that the plus‐NH4+peas fixed as much or more N2than the plants supplied with minus‐NH4+nutrient solution. There were no significant differences in nodule numbers, nodule mass or NH4+uptake between the plants grown at the two concentrations of NH4+. Nodulation appeared to autoregulate by 14 DAP in the minus‐NH4+treatment. Plant growth and N accumulation in the minus‐NH4+plants lagged behind those of the plus‐NH4+treatments prior to N2fixation becoming well established in the final week of the experiment. The plus‐NH4+treatments appeared not to elicit autoregulation and plants continued to initiate nodules throughout

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860205.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

We observed that guard cell protoplasts isolated from leaves collected at midday fromNicotiana glaucaGraham (tree tobacco) did not give the same physiological responses to light as those isolated from leaves collected in early morning. Based on that observation, we attempted to determine whether there were significant differences between the physiological responses of guard cell protoplasts isolated from leaves collected before dawn (with closed stomata) and those isolated from leaves collected at midday (with open stomata). We isolated guard cell protoplasts from leaves collected before dawn and at midday and compared (1) rates of red and blue light‐induced pH changes in weakly buffered media caused by changes in their metabolism, (2) their rates of oxygen consumption in darkness and oxygen evolution in light and (3) relative rates of decay of variable chlorophyllafluorescence in their chloroplasts. Studies with the vital stain fluorescein diacetate failed to reveal any significant differences in the viabilities of protoplast preparations from leaves collected before dawn and at midday. Furthermore, protoplasts from leaves collected at these times swelled to similar extents in an osmotic medium containing 10 µM fusicoccin and 5 mMKCI. Nevertheless, rates of light‐induced pH changes, rates of oxygen consumption and evolution and rates of decay of variable chlorophyllafluorescence were all lower in preparations of guard cell protoplasts from leaves collected at midday than in preparations from leaves collected before dawn. Initial volumes of guard cell protoplasts isolated from leaves collected at midday were 150% of those of guard cell protoplasts isolated from leaves collected before dawn. We suggest that the differences in responses of guard cell protoplasts isolated from leaves collected before dawn and at midday may be caused by (1) nonoptimal isolation conditions for guard cell protoplasts prepared from leaves collected at midday, (2) the lower surface‐to‐volume ratio of guard cell protoplasts isolated from leaves collected at midday or (3) diurnal and/or circadian regulation of guard cell metabolism over the course

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860206.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

The specific activity of NADH‐glutamate dehydrogenase (GDH, EC 1.4.1.2) in leaf protoplasts (Brassica napusL. cv. Bronowski) was initially low and progressively increased during culture in Murashige and Skoog (MS) medium and MS (−NH4) (ammonium nitrate‐free MS) medium in the dark. Native polyacrylamide gel electrophoresis (PAGE) and tetrazolium staining revealed that the high specific activity of NAD‐GDH (deamination) in leaves correlated with the cathodal isoenzymes, and the high specific activity of NADH‐GDH (amination) in leaf protoplasts to the anodal ones. Changes in isoenzyme pattern were correlated with an increase in the specific activity of NADH‐GDH but not with the NADH‐GDH/NAD‐GDH ratio. The increase in NADH‐GDH (amination) activity of leaf protoplasts was correlated with the occurrence of the isoenzyme GDH7, which was not d

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860207.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

The physiological response of cowpea (Vigna sinensisL.) epicotyl explants to far‐red light (FR) and its interaction with gibberellins (GAs) have been investigated. The effect of FR and GA1varied with the age of the seedlings from which the explants were made: for FR, it decreased progressively with age (though the sensitivity of the epicotyls to FR did not change significantly until at least day 11), whereas it remained essentially constant for applied GA1between days 5 and 9 after sowing. This indicates that the loss of response to FR may be due to a decrease in endogenous GA levels in the epicotyl. For a range of GA1and GA20(0.01–1 µg explant−1), both hormones were more active in FR than in R irradiated epicotyls, suggesting that phytochrome may affect GA sensitivity besides GA metabolism. The location of the epicotyl region most sensitive to FR (between 5 and 20 mm below the apex) was different from that to GAs (the upper 10 mm). Nevertheless, FR extended the region responsive to applied GAs, even in paclobutrazol‐treated epicotyls where elongation was due entirely to exogenous GAs. This means that modulation of epicotyl elongation by phytochrome, that occurs in a zone different from though overlapping with the GA‐sensitive subapical zone, is also mediated by GAs. Growth in the most FR‐sensitive region of the epicotyl stimulated by FR or GA1was due to cell elongation, and in the most GA‐sensitive region to both cell division and elongation. The effect of FR and GA1was negated by colchicine, indicating that microtubules may be involved in the response t

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860208.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

Screening of complementary DNA (cDNA) libraries constructed from poly(A) rich RNA isolated from young developing ovaries ofNarcissuscv. Fortune andHippeastrumhybr. resulted in the isolation of multiple lectin cDNA clones. Although the lectin clones show a high degree of overall homology within their coding region, they clearly differ from each other at some positions in their nucleotide sequence and deduced amino acid sequence. Moreover, since some differences in the sequence result in different charges along the lectin polypeptides, the different cDNA clones encode lectins with different isoelectric points, which explains the occurrence of multiple lectin isoforms inNarcissusandHippeastrumat the molecular level. Furthermore, Southern blot analysis of genomic DNA isolated fromNarcissusandHippeastrumyielded numerous restriction fragments hybridizing with lectin cDNA probes leaving no doubt that theNarcissusandHippeastrumlectins, like theGalanthus nivalislectin, are encoded by families of closely related lectin genes.

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860209.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY

摘要:

In many organisms, the synthesis of heat shock proteins during heat shock is concomitant with the cessation of at least a portion of normal cellular protein synthesis. Heat shocked barley aleurone layers selectively stop the synthesis and secretion of secretory proteins. Exposure to 40°C causes a disruption of endoplasmic reticulum (ER) lamellae, which we have hypothesized leads to the destabilization of otherwise stable mRNA previously associated with ER‐bound polyribosomes. We report here that this was also observed in wounded carrot (Daucus carotaL.) root parenchyma tissue which synthesizes and secretes cell wall proteins when mechanically wounded. Nondenaturing cationic polyacrylamide gel electrophoresis of radiolabeled proteins indicated that heat shock caused the cessation of the synthesis and secretion of extensin, a hydroxyproline‐rich cell wall glycoprotein. Northern blot analyses indicated that the mRNA levels for both extensin and another cell wall protein (p33) were rapidly diminished during heat shock. Under nonheat shock conditions extensin mRNA had a half‐life of greater than 4 h, but this appeared to be reduced to less than 30 min during heat shock. There was also a concomitant dissociation of ER lamellae in wounded, heat shocked carrot root tissue, as observed by transmission electron microscopy. These observations indicate that this response may be universal among plant secretory t

ISSN:0031-9317    

DOI:10.1034/j.1399-3054.1992.860210.x

出版商:Munksgaard International Publishers    

年代:1992

数据来源: WILEY