摘要:

Foliar application of benzyladenine (BA) has been shown to enhance nitrate‐dependent induction of nitrate reductase (NR; EC 1.6.6.1) in etiolated wheat (Triticum aestivumL.) seedlings. Whether similar enhancement occurs in light‐grown plants, or whether endogenous cytokinin content affects this enhancement is unknown. Since the cytokinin content of etiolated plants probably differs from that of light‐grown seedlings, the NR response of each to exogenous root‐ or shoot‐applied BA in wheat (cv. Red Bob) was examined. Endogenous cytokinins present in untreated control tissues prior to BA application and changes that occurred after a 22 h (12 h dark followed by 10 h of light) period were determined using a combined HPLC‐immunoassay method. Shoot application of BA enhanced the induction of NR in etiolated seedlings in a concentration‐dependent manner but failed to enhance NR induction in light‐grown plants. Root‐applied BA enhanced NR induction in both etiolated and light‐grown seedlings. Endogenous root cytokinin levels were similar in both etiolated and light‐grown plants. In contrast, shoots of 6 day‐old light‐grown seedlings contained at least 20 times the amount of total cytokinins measured in shoots from etiolated plants of the same age. Total cytokinin content of the light‐grown plants diminished after the 22‐h period while that measured in etiolated seedlings increased. The responsiveness of seedlings to BA was correlated with endogenous cytokinin levels in that enhancement of NR induction by exogenous BA was low in tissues which contained high concentrations of cytokinin at the time of BA application. These results may prove useful in interpretation of gene responses to exog

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01329.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Plantlets of daylily (Hemerocalliscv. Autumn Blaze) regenerated from cell suspensions, and 4 clonal populations ofHaplopappus graciliswere aseptically cultivated aboard the Shuttle “Discovery’’ during a 5‐day mission within NASA's Plant Growth Unit (PGU) apparatus. Daylily was selected as a representative herbaceous perennial monocotyledon and the haplopappus clones represented an annual dicotyledon. The latter included 4 strains with different physiological and morphological characteristics: two aseptic seedling clones (each generated from a single seedling) and two tissue culture‐derived lines. Mean daily growth rates for the primary shoots of all plantlets averaged 4.13 mm day−1(sd = 2.20) for the flight experiment and 4.68 mm day−1(sd = 2.59) for the ground control. Comparable growth rates calculated by summing both the primary and secondary shoots for all plantlets were 5.94 mm day−1(sd = 2.89) for the flight experiment and 6.38 mm day−1(sd = 3.71) for the control. Statistically significant differences existed between: (1) flight vs control primary shoot growth (the controls growing more than plantlets subjected to spaceflight conditions), (2) the different populations (the daylily gaining more shoot material than any of the haplopappus populations and the haplopappus seedling clones outperforming the tissue culture‐derived haplopappus lines), and (3) the individual Plant Growth Chambers contained within the PGU. The data suggest that some spaceflight‐associated factor(s) increased the tendency for primary shoot apices to degrade or senesce, resulting in the release of apical dominance and permitting the emergence of axillary branches, which subsequently partially compensated for the reduced primary axis growth. In addition to spaceflight‐associated factors, the physiologically diverse nature of the experimental material as well as environmental heterogeneities within the culture apparatus contributed to the variation in growth results. The findings could explain some discrepancies reported from various plant culture experim

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01330.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The influence of nitrate and ammonium assimilation on glycogen metabolism has been determined in intactAnacystis nidulanscell actively fixing CO2. Assimilation of nitrate or ammonium resulted in significant decreases in both the incorporation into glycogen of newly fixed carbon and the accumulation of glycogen by the cells, the magnitude of these effects depending on the light intensity. The depression in glycogen synthesis induced by nitrogen assimilation was more marked at low light intensity, and especially when ammonium was the nitrogen source. Under these conditions, specific radioactivity of the glycogen pool was particularly high, indicating enhanced turnover of glycogen. Thus, in addition to a more general depressing effect of nitrogen assimilation on the carbon flow to glycogen, degradation of glycogen appears to be stimulated by ammonium assimilation at low (but not at high) light intensity.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01331.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Protein synthesis in dormant embryos of sugar maple (Acer saccharum) was investigated in seeds stratified at 4°C or incubated at 15°C. Seeds stratified at 4°C germinated after 27 days; seeds incubated at 15°C failed to germinate. Stratification increased the embryo's capacity for protein synthesis by day 11 as measured by in vivo incorporation of [35S]‐methionine into purified protein. At 4°C protein synthesis in the embryonic axis rose in a linear fashion prior to germination, whereas in cotyledons it increased until day 20 and then declined. Analysis of radiolabelled proteins by two‐dimensional gel electrophoresis revealed that the levels of specific proteins were altered by temperature, primarily in the cotyledons. Several proteins were expressed in the cotyledons at 15°C but were absent in unstratified embryos and in embryos stratified at 4°C. That is, the expression of these proteins was repressed during stratification and release from dormancy. Levels of other proteins in the cotyledons declined at 4°C during stratification. We suggest that one or more of these proteins may be associated with the inhibition of growth of the embryonic axis imposed by the

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01332.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Rates of photosynthesis and leaf conductance of the leaves of carob trees (Ceratonia siliquaL.) growing in natural conditions were measured during the course of the seasons to define the effects of the main climatic factors limiting growth in the region: temperature during the winter and water in the summer. The highest photosynthetic rates were measured in spring and autumn and could reach 25 μmol m−2s−1with optimal temperature and available water. Due to lower temperatures (4 to 6°C in the night) these values were frequently around 15 μmol m−2s−1during winter, but the strongest depression was due to prolonged drought in summer. However a reduction in photosynthesis rate down to 5 μmol m−2s−1occurred only after depletion of all the available water in the soil layer up to a depth of 50 cm. In the end of the summer, leaf conductance and water potential were in the order of 20 mmol m−2s−1and −3 MPa respectively. Compared to other trees that make up the Mediterranean sclerophyll forest, the photosynthetic activity of carob is high, and the tree tolerates a considerable de

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01333.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The cytokinin complex in tobacco leaves of various maturities was characterized by radioimmunoassay and mass spectrometry. Zeatin was the major base, whereas zeatin riboside was identified as the main riboside. in leaves of all maturities studied. Relative to upper younger leaves, the basal yellow leaves had reduced levels of both cytokinin bases and ribosides. Exogenous applications of dihydrozeatin and zeatin to detached tobacco leaves in amounts sufficient to delay senescence, elevated cytokinin base and riboside levels 2–5 fold. Presenescent and senescent leaves of intact plants showed quantitatively similar changes in cytokinin content. which therefore appear to be of significance in control of senescence. When supplied exogenously, the principal cytokinin bases found to occur in tobacco leaves (zeatin and dihydrozeatin) were markedly more effective than auxins and gibberellic acid in retarding senescence. Localised application of cytokinins to leaf blades of detopped plants was much less effective than application to intact plants. The cytokinin induced senescence retardation in tobacco leaves was independent of effects on directed metabolite transport. Evidence that endogenous levels of active cytokinins in intact tobacco leaves are involved in control of sequential leaf senescence is discusse

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01334.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Cytokinin bases (zeatin and dihydrozeatin) and ribosides (zeatin riboside and dihydrozeatin riboside) were identified as major cytokinins in tobacco xylem sap by radioimmunoassay. When3H‐labelled zeatin riboside or dihydrozeatin riboside were supplied to tobacco plants via the xylem, leaves of differing maturity did not differ appreciably in level of radioactivity or in metabolism of the cytokinin. The major metabolites of zeatin riboside in leaves were adenine, adenosine and adenine nucleotides, whereas that of dihydrozeatin riboside was dihydrozeatin 7‐glucoside. Incorporation of [14C]adenine into zeatin was evident in upper green leaves. indicating that young leaves have the capacity to synthesize cytokinins in situ. In contrast, fully expanded green leaves and senescing tobacco leaves exhibited little or no incorporation of [14C]adenine into cytokinins. This difference in cytokinin biosynthetic capacity may contribute to the differing cytokinin levels in leaves of different matirity, and may participate in control of sequential leaf senescence in toba

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01335.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The plasma membrane H+‐ATPase (EC 3.6.1.35) waspurified by washing redbeet (Beta vulgarisL.) plasma membranes with sodium deoxycholate and separating the ATPase, solubilized with lysophosphatidylcholine, by centrifugation in a glycerol gradient. The purified H+‐ATPase had a sedimentation coefficient of about 8S. In the absence of exogenous protein substrates, the purified ATPase preparation did not present protein kinase activity. Compared with the H+‐ATPase in the plasma membrane, the purified ATPase presented a higher affinity for adenosine 5′‐triphosphate (ATP) and a lower sensitivity to the inhibitors vanadate and inorganic phosphate. These changes in the kinetics of the ATPase could also be observed by treating the membranes with lysophosphatidylcholine, without purifying the enzyme. These results can be explained assuming that lysophosphatidylcholine interacts with the ATPase altering its kinetics probably by stimulating the transformation from the inhibitor‐binding conformation E2 into the ATP‐binding co

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01336.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Pubescence layers with their native structure and orientation were isolated from the leaves ofOlea europaeaL. andOlea chrysophyllaL. They were almost transparent in the visible, but considerable absorptance was evident in the ultraviolet‐B region (UV‐B), with maximum at 310 nm. Methanolic extracts of hairs fromOleaand a variety of other pubescent species consistently showed the existence of UV‐screening pigments. Absorptance of trichomes varied, but a trend towards more effective UV‐B radiation attenuation in the sub‐alpineVerbascumspecies may be claimed. In all cases, pigments were located within hair cells and inOleathey were characterized as phenolics with considerable flavonoid contribution. It is suggested that leaf hairs, besides other functions, may constitute a shield against UV‐

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01337.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The changes caused by NaCl− and CaCl2‐induced salinity on several leaf parameters have been measured in two cultivars of barley (Hordeum vulgareL.) growing in a growth chamber in nutrient solution. Salinity was induced by adding to the nutrient solution equal weights of NaCl and CaCl2, to obtain conductivities of 2, 6, 12, 19 and 26 dS m−1. Salinity induced decreases in the leaf water potential and in the osmotic potential. Salinity did not induce significant changes in the relative photosynthetic pigment composition of barley leaves, the photosynthetic pigment stoichiometry for neoxanthin:violaxanthin cycle pigments:lutein:β‐carotene:Chlb:Chlabeing close to 3:6:14:12:25:100 (mol:mol). Salinity per se did not induce interconversions in the carotenoids within the violaxanthin cycle in most barley leaves. The PSII photochemistry of most barley leaves was unchanged by salinity. However, some apparently healthy leaves growing in high salinity exhibited sudden decreases in PSII photochemistry and increases in zeaxanthin (at the expense of violaxanthin), that preceded rapid leaf drying. Salinity induced significant changes in the slow part of the chlorophyll fluorescence induction curve from barle

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1992.tb01338.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY