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H. Kvaalen 《Physiologia plantarum》1994,92(1):109-117
Ethylene production from an embryogenic culture of Norway spruce ( Picea abies L.) was generally low. ca 2.5 nl g−1 h−1 , whereas 1-aminocyclopropane-1 -carboxylic acid (ACC) concentration was high, fluctuating between 50 and 500 nmol g−1 during the 11-day incubation period. Hypoxia (2.5 and 5 kPa O2 ) rapidly inhibited ethylene production without subsequent accumulation of ACC. Exogenous ACC (1, 10 and 100 μ M ) did not increase ethylene production, but the highest concentrations inhibited tissue growth. Ethylene (7 μl I−1 ) did not inhibit growth either when supplied as ethephon in the medium or in a continuous flow system. Benzyladenine (BA) had little effect on ethylene production, although it was necessary for sustaining the ACC level. Omission of 2.4-dichloro-phenoxyacetic acid (2.4-D) from the medium caused ethylene production to increase from about 2.5 to 7 nl g−1 h−1 within the 11-day incubation period. Although 2.4-D did not specifically alter the endogenous level of ACC, the lowest ACC level, 33 nmol g−1 , was observed in tissue treated with 2.4-D (22.5 μ M ) and no BA for 11 days. Data from this treatment were used to estimate the kinetic constants for ACC oxidase, the apparent Km was 50 μ M and Vmax 2.7 nl g−1 h−1 . Growth of the tissue was strongly inhibited by 2.4-D in the absence of BA, but weakly in the presence of BA (4.4 μ M ). The results suggest that ethylene or ACC may be involved in the induction of embryogenic tissue and in the early stages of embryo maturation. 相似文献
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The mitochondrial fraction isolated from plumular hooks of etiolated pea seedlings ( Pisum sativum L. cv. Kelvedon Wonder) displayed a ten-fold higher rate of ethylene formation from 1-aminocyclopropane-1-carboxylic acid [ACC; 3.2 nmol C2 H4 (mg protein −1 )h−1 ], than the tissue from which it was isolated. When the ionophores valinomycin or nigericin were added, a 60- to 70-fold increase in activity in intact mitochondria over the activity in plumular hooks was obtained for ethylene formation under the same conditions, and a 20-fold increase was obtained upon addition of gramicidin. The addition of ionophores did not affect the rate of ethylene formation in submitochondrial particles (55% inside-out as determined by cytochrome oxidase latency) which already exhibited a 2–3-fold higher specific activity than intact mitochondria. Low concentrations of the detergents cholate and deoxycholate increased mitochondrial ethylene formation activity and had no effect on the rate of the reaction in submitochondrial particles. These results support the suggestion that ACC conversion to ethylene is associated with the inner side of the inner mitochondrial membrane and that transport across the intact mitochondrial membrane is rate-limiting in the reaction. 相似文献
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Salicylic acid (SA), a common plant phenolic compound, influences diverse physiological and biochemical processes in plants.
To gain insight into the mode of interaction between auxin, ethylene, and SA, the effect of SA on auxininduced ethylene production
in mung bean hypocotyls was investigated. Auxin markedly induced ethylene production, while SA inhibited the auxin-induced
ethylene synthesis in a dose-dependent manner. At 1 mM of SA, auxininduced ethylene production decreased more than 60% in
hypocotyls. Results showed that the accumulation of ACC was not affected by SA during the entire period of auxin treatment,
indicating that the inhibition of auxin-induced ethylene production by SA was not due to the decrease in ACC synthase activity,
the rate-limiting step for ethylene biosynthesis. By contrast, SA effectively reduced not only the basal level of ACC oxidase
activity but also the wound-and ethylene-induced ACC oxidase activity, the last step of ethylene production, in a dose-dependent
manner. Northern and immuno blot analyses indicate that SA does not exert any inhibitory effect on the ACC oxidase gene expression,
whereas it effectively inhibits both the in vivo and in vitro ACC oxidase enzyme activity, thereby abolishing auxin-induced
ethylene production in mung bean hypocotyl tissue. It appears that SA inhibits ACC oxidase enzyme activity through the reversible
interaction with Fe2+, an essential cofactor of this enzyme. These results are consistent with the notion that ethylene production is controlled
by an intimate regulatory interaction between auxin and SA in mung bean hypocotyl tissue. 相似文献
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Ethylene production was measured from excised 10-mm apical and subapical root segments from 50 cultivars in 19 species of 7 families. Monocotyledonous species tended to have much lower rates of ethylene production than dicotyledonous species. Ethylene production was generally higher in apical root segments than in subapical segments within 1 h of wounding. However, cultivars of Cucumis melo , C. sativus , Helianthus annuus , Hibiscus esculentus , and Zea mays had higher rates of ethylene production from subapical segments. In apical root segments, Phaseolus aureus cv. Berken had the highest ethylene production rate (76.7 ηl g−1 h−1 ), while Zea mays cv. Silver Queen had the lowest rate (0.6 ηl g−1 h−1 ). In subapical root segments, Cucumis sativus cv. Armenian had the highest rate (55.7 ηl g−1 h−1 ), while Zea mays cv. Silver Queen again had the lowest rate (0.6 ηl g−1 h−1 ). The many different responses in magnitude and kinetics of wound-induced ethylene production among the species, cultivars and tissues should provide interesting and useful systems with which to study wound responses and induced ethylene production. 相似文献
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Mohamed Benichou Gracia Martinez-Reina Felix Romojaro Jean-Claude Pech Alain Latché 《Physiologia plantarum》1995,94(4):629-634
A 36-kDa 1-aminocyclopropane-1-carboxylate (ACC) N-malonyltransferase, which converts the ethylene precursor ACC into the conjugated derivative malonyl-ACC (MACC), has been isolated from etiolated mung bean ( Vigna radiata ) hypocotyls, and partially purified in a four-step procedure. The enzyme is stimulated about 7-fold by 100 m M K+ salts or 0.5 m M Co2+ salts, and is inhibited competitively by D-phenylalanine (Ki = 1.3 m M ) and non competitively by CoASH (0.3 m M ). Beside malonyl-CoA, it is capable to use succinyl-CoA as an acyl donor. The 36-kDa enzyme described here exhibits a lower optimum temperature (40°C) and a 7- or 3-fold lower apparent Km for ACC (68 μ M ) and malonyl-CoA (74 μ M ), respectively, when compared with its 55 kDa isoform already isolated from the same plant material. This data support the idea that several isoforms of ACC N-malonyltransferase exist in plants. These isoforms may play a differential role in regulating the availability of ACC, and consequently the rate of ethylene production, as well as detoxifying cells from D-amino acids. 相似文献
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Lack of ethylene involvement in tulip tepal abscission 总被引:4,自引:0,他引:4
The tepals of cut flowers of Tulipa hybrida cv. Golden Apeldoorn and Tulipa kaufmanniana cv. Shakespeare abscise 3–4 days after harvest. The weakening of the abscission zones is accompanied by cell wall breakdown and the separation of 3–4 rows of intact cells at the base of the tepal. During senescence, there is no ethylene climacteric and ethylene production rates remain low, between 0.07 and 0.4 nl g−1 fresh weight h−1 . Adding 3–5 μl l−1 ethylene slightly accelerated the weakening of the abscission zones but had no effect on the time of first abscission. Neither 0.5 m M silver thiosulphate nor 5 m M aminoethoxyvinylglycine delayed the time to abscission. It is concluded that tulip tepal fall does not involve primary regulation by ethylene, unlike the majority of other abscission systems that have been studied. 相似文献
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The respiration of coho salmon, Oncorhynchus kisutch , weighing between 15 and 50 g was measured at gradually declining oxygen levels and at temperatures ranging between 14 and 17°C. The maximum and minimum oxygen concentrations tested were 250 and 40 μmol L−1 , respectively. Respiration rates were measured for 1 h periods before oxygen concentration was lowered by 12.5 or 25.0 μmol oxygen L−1 . At the end of these endurance tests the oxygen level was returned to normoxic conditions and respiration rates were determined for the recovery period. Under normoxic conditions (> 200 μmol L−1 ) the respiration of coho levelled around 5.1 μmol g−1 wet weight h−1 . At intermediate levels between 150 and 200 μmol oxygen L−1 , the average rate increased to 5.8 μmol g−1 h−1 , which could be attributed to higher spontaneous activity of the test animals. At low oxygen levels (< 150 μmol−1 ) average respiration rates dropped to values between 5.5 and 5.7 μmol g−1 h−1 , reaching a minimum of 3.8 μmol g−1 h−1 at oxygen levels below 50 μmol Lμ . First mortality was observed in this range. After exposure to reduced oxygen levels the fish maintained a higher respiration rate when again exposed to normoxic oxygen levels above 200 μmol L−1 . Increased respiration rates were observed for a recovery period of 6 h. 相似文献
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The effects of water hardness (9 and 220 mgl−1 as CaCO3 ) upon zinc exchange in brown trout exposed to 0.77 μmol Zn 1−1 have been investigated using artificial soft water (<49.9 μmol Ca l-1 , <40.1 μmol Mg 1−1 ) and mains hard water (1671.7 μmol Ca 1−1 , 493.6 μmol Mg 1−1 ) of known composition. Both hard and soft water-adapted fish exhibited a bimodal pattern of net zinc influx. Net zinc influxes during both fast and slow uptake phases were significantly greater ( P <0.001) in soft (82.9 and 6.2 μmol Zn 100 g−1 h−1 ) than in hard water (46.3 and 2.4 μmol Zn 100 g h−1 ). Zinc efflux (- 0.2 μmol Zn 100 g−1 h−1 ) was enhanced only in hard water during the slow net influx phase.
Brown trout exposed to zinc in hard water and placed in metal-free media exhibited a greater net efflux (- 25.6 μmol Zn 100 g−1 h−1 ) of the metal than did fish in soft water (-4.2 μmol Zn 100 g−1 h−1 ) treated in the same manner. Tissue 65 Zn activities reflected both the differences in uptake and excretion rates of the metal between hard and soft water fish. During zinc exposure (0.77 μmol Zn 1−1 ) high water hardness reduced tissue burdens of the metal by reducing net branchial influx, and enhancing efflux of the metal in hard water fish. 相似文献
Brown trout exposed to zinc in hard water and placed in metal-free media exhibited a greater net efflux (- 25.6 μmol Zn 100 g
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Ammonium ion affecting tylosin production by Streptomyces fradiae NRRL 2702 in continuous culture 总被引:1,自引:0,他引:1
S.H. Lee 《Letters in applied microbiology》1997,25(5):349-352
Nitrogen regulation in tylosin production by Streptomyces fradiae NRRL 2702 was studied in chemostat culture using a soluble synthetic medium. The maximum value of specific tylosin formation rate ( q TYL ) was 1·13 mg g−1 h−1 at the specific growth rate (μ) of 0·05 h−1 , and q TYL decreased with increasing levels of the specific growth rate after reaching a rate of 0·1 h−1 . The optimum conditions for tylosin formation were that the specific ammonium ion uptake rate ( q N ) and μ were 0·13 mmol g−1 h−1 and 0·05 h−1 , respectively. The specific formation rates of threonine dehydratase (TDT) and tylosin were repressed by high levels of specific ammonium ion uptake rate. This study showed the adaptation to chemostat cultures of the nitrogen regulation of tylosin fermentations. 相似文献
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The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine ( Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO3 − , no such increase could be detected in the needles. Detached seedlings placed in NO3 − solution showed increasing NR activities with increasing NO3 − concentrations. Exposure of seedlings to NOx (70–80 ppb NO2 and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO2 − (g fresh weight)−1 h−1 to about 400 nmol NO2 − (g fresh weight)−1 h−1 . This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO2 − (g fresh weight)−1 h−1 . Analyses of free amino acids showed low concentrations of arginine and glutamine in NOx -fumigated seedlings compared to corresponding controls. 相似文献