摘要:

Ascorbic acid is a strong inhibitor of indole‐3‐acetic oxidation catalyzed by commercial horse‐radish peroxidase. In the presence of excess ascorbic acid, the indole‐acetic acid oxidation catalysis is apparently blocked. The activity of peroxidase for indoleacetic acid at pH 3.7 and 33°C, in the presence of 2,4‐dichlorophenol and MnCl2as promotors was measured by polarographic technique. The Kmwas 0.27 mMand the maximum velocity was 1.02 mmol O2(mg protein)−1min−1. Dixon plots lead to an apparent Kiof 1.25 (μMfor ascorbic acid and the inhibition was apparently competitive. Ascorbic acid, besides appearing to be a strong inhibitor of the IAA oxidase activity of peroxidase, seemed to protect IAA from total degradation. Addition of more than 5 μMascorbic acid produced both an exponential increase in the lag time before the onset of reaction and, at the end, an oxidation protection of 26 μMIAA when 111 μMIAA was present at the stawrt. The possibility of ascorbic acid‐IAA auxin from endogenous oxidation in

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04890.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Abscission in styles of excisedCitrus limon(cv. Lisbon) pistils was stimulated by addition of 70 μM2‐chloroethylphosphonic acid (ethephon) or 0.1 mM1‐aminocyclopropane‐1‐carboxylic acid (ACC) to the defined medium of cultures. To study the relationship between ethylene and abscission, we used gas chromatography to analyze ethylene in cultures containing a test medium plus or minus abscission‐active chemicals. In the presence of ethephon or ACC, ethylene levels in sealed tubes increased rapidly, suggesting that these compounds stimulated abscission because they were converted to ethylene. In the presence of test medium or the inhibitor of abscission 2 μMpicloram, the low ethylene levels found in sealed tubes did not differ strikingly in the two treatments. Ethylene production rates measured prior to abscission with test medium or in the presence of picloram were not markedly different either, although picloram completely inhibited abscission. Stylar abscission was delayed but not prevented by 50 μMaminoethoxyvinylglycine, an inhibitor of ethylene biosynthesis, and by hypobaric conditions (280 mm Hg) which removed ethylene from cultures. We concluded that ethylene is an important factor regulating stylar abscission in vitro and suggest that the inhibitory effect of picloram involves a process other than detectable ethylene production. Our results do not exclude the possibility that picloram affects enodgenous ethylene biosynthesis and/or metabolism and/or tiss

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04891.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The translocation of nitrogen was studied in vegetative wheat plants (Triticum aestivumL. cv. SUN 9E) grown with a limited supply of nitrogen. The concentration of nitrogen in xylem sap exuding from the excised roots was the same as the nitrogen concentration in the transpiration stream. Translocation of nitrogen to the shoot was, therefore, calculated as the product of the transpiration rate and the concentration of nitrogen in xylem exudates. On the 22nd day from sowing more nitrogen was translo‐cated to the shoot than it incorporated, and 56% of the nitrogen translocated to the shoot was retranslocated to the roots. The nitrogen retranslocated to the roots was more than adequate to supply the requirements of the roots for growth, and the balance of the retranslocated nitrogen was reloaded into the xylem stream. Expressed as a proportion of the total increment of nitrogen in the plant on day 22, between 79 and 100% of the nitrogen absorbed by the plant was “cycled'’ in the plant (root → shoot → root → shoot). It is suggested that the size of this mobile reserve of nitrogen may vary depending on the growth requirement of the plant, its nitrogen‐uptake capacity and the contribution of nitrogen from mobilisation of leaf protein duri

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04892.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Wheat (Triticum aestivumL. cv. SUN 9E) was grown in a growth chamber under conditions of low soil nitrogen. Translocation of carbon to the roots and the subsequent utilization of these carbohydrates was determined. In vegetative plants (22 days old), 21.5 mg C day−1were translocated to the roots. 29% of this was incorporated into dry matter, 32% was respired (28% via the cytochrome and 4% via a SHAM‐sensitive, presumably the alternative nonphosphorylating, pathway) and 39% was translocated back to the shoots, mainly in the form of amino acids. – The rote of root maintenance respiration during the vegetative phase was estimated to be 0.7 mg O2h−1(g dry weight of roots)−1and the root growth respiration to be 0.41 g O2(g dry weight of roots)−1. Total carbohydrate utilization due to root respiration via the alternative, nonphosphorylating pathway during the major part of the growth period was calculated to be only ca 6% of carbohydrate utilization for grain growth. The rate of specific mass transfer (SMT) of sugars in the sieve tubes was estimated from the data on C‐translocation and data on the total area occupied by sieve tubes in a cross section of the root system. SMT was calculated to be 0.8 mg sucrose s−1cm−2, which is very similar to the published value on SMT for other org

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04893.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The photosynthetic rate ofLemna gibbawas measured as14CO2uptake at the beginning of and after 1 h DCMU treatment during the separate excitation of PS I (703 nm), mainly PS II (662 nm) and the combined excitation of both photosystems (662 + 703 nm) in 2 and 21% oxygen. The results show the Warburg effect. Photosynthesis was significantly reduced by DCMU whenever PS II was excited, at 662 nm and 662 + 703 nm. Photosynthetic enhancement was greater in 21 than in 2% oxygen in both the treated and untreated plants.Photorespiratory14CO2release was only affected by DCMU treatment at 662 + 703 nm. It was significantly decreased in 21% O2and significantly increased in 2% O2as compared to the controls without DCMU. The14C‐glycolate remaining in the plant after photosynthesis/photorespiration measurements was reduced whenever the electron supply to PS I was low.These data support the hypothesis that a relationship exists between glycolate metabolism and photosynthesis via the electron transport chain where electrons from the oxidation of glycolate are donated to PS I when the electron supply from water is lo

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04894.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

In contrast to previous work, the distribution of cholinesterase was found to be ubiquitous in plant leaves. Cholinesterase activity was detected in 91% of the 70 species surveyed from 50 higher plants and three families of ferns. A radiometric assay was used to determine the hydrolysis of acetylcholine by leaf tissue slices in the presence and absence of 29 μMdiisopropyl phosphofluoridate. The results obtained using this inhibitor as a criterion for cholinesterase activity were found to be consistent with previous studies using neostigmine as the inhibitor although there were some quantitative differences between the inhibitors. With some of the tested plants acetyl‐β‐methylcholine was also hydrolyzed, indicating that acetylcholinesterase rather than pseudocholinesterase was present at least in these cases. These findings demonstrate that the relative activity of cholinesterase in leaves can serve as an indicator of organophosphorous anticholinesterase contamination of the enviro

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04895.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The long and short term metabolic effects of a shift in root temperature was investigated inPlantago lanceolataL. with special reference to the role of the cyanide resistant alternative pathway in root respiration. After a 10‐day period of growth at a 13°C root temperature, a decrease in root as well as shoot growth was observed, compared to control plants grown continuously at 21°C. Apart from an increase in shoot soluble and insoluble sugar level, no changes in metabolism were found, neither in root respiration, shoot photosynthesis, nor in root sugar and plant protein level.Decreasing the root temperature from 21 to 13°C gave several clear short term changes in metabolism. Within one hour a decrease in cytochrome chain activity of the roots was found together with an increase in activity of the alternative chain. After 24 h a recovery to the initial level of both chains was observed. An increase in root temperature from 13 to 21°C gave an immediate increase in activity of both respiratory chains that was still present 24 h after the switch.It is concluded that the activity of the alternative respiratory pathway in the root is strongly affected by a sudden temperature change in the root environment. This pathway acts in a way which is described by ‘the energy overflow model'. The presence of the alternative electron transport pathway should be taken into account in determinations of the respiratory Q10. Moreover, the length of time between the temperature change and respiration measurements is an important

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04896.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

The effects of auxin and gibberellic acid on cell wall composition in various regions of epicotyls of azuki bean (Vigna angularisOhwi and Ohashi cv. Takara) were investigated with the following results. (1) Young segments excised from apical regions of the epicotyl elongated in response to added 10−4Mindole‐3‐acetic acid (IAA). When the segments were supplied with 50 mMsucrose, the IAA‐induced segment growth was accompanied by enhanced overall synthesis of cell wall polysaccharides, such as xyloglucans, polyuronides and cellulose. This IAA effect on the cell wall synthesis is a consequence of extension growth induced by IAA. Gibberellic acid (GA) at 10−4Msynergistically enhanced the IAA‐induced cell wall synthesis as well as IAA‐induced extension growth, although GA by itself neither stimulated the cell wall synthesis nor extension growth. In the absence of sucrose, cell wall synthesis was not induced by IAA or GA. (2) In mature segments excised from basal regions of the epicotyl, no extension growth was induced by IAA or GA. GA enhanced the synthesis of xylans and cellulose when the segments were supplied with 50 mMsucrose. IAA had no effect on the cell wall synthesis. These findings indicate that synthesis of polyuronides, xyloglucans and cellulose, which occurs during extension growth of the apical region of the epicotyl, is regulated chiefly by auxin whereas synthesis of xylans and cellulose during cell maturation in the basal region of the epicotyl is re

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04897.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

A method based on simultaneous short‐term exposure to14CO2and15N2is described for studying nitrogen fixation and distribution in legumes relative to carbon assimilation and use. Equipment designed to accomodate experiments under natural conditions with very little disturbance of the N2fixing association is used. It permits continuous measurement and regulation of variables such as air temperature, humidity and CO2concentration as well as soil aeration. Measurements of distribution and use of assimilates, respiration of nodulated roots, quantitative N2fixation and the distribution and fate of fixed N as a function of time lead to a precise estimation of C and N budgets for each labelling period. When experiments are done at several phenological stages they give a new insight into the complex C and N interrelations in legume symbiosis.A series of trials throughout the growth period ofGlycine max(L.) Merr. cv. Hodgson demonstrated the sensitivity of the method. The development of the plants from vegetative to reproductive stages was accompanied by a complete change in the distribution patterns of current assimilates and products of nitrogen fixation. Maximum sink strength moved from the leaves to the pods and seeds which ended up receiving 70% of the incoming C and 35% of the fixed N. The fact that up to 85% of fixed N in the plants was in the reproductive organs at maturity can be accounted for by remobilisation from vegetative parts.The respiration of nodulated roots utilized 33% of carbon translocated to below‐ground plant parts before nitrogen fixation started, but as much as 50% during the period of optimal fixation. The advantages and limitations of the isotopic method described are critically discussed as a prelude to future investigati

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04898.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Low temperature (77°K) fluorescence emission and excitation spectra were recorded for wet and desiccated thalli ofPorphyra perforata. The photosystem I (F730) and photosystem II (F695) fluorescence emission kinetics during photosystem II trap closure were also recorded at 77°K. Desiccation induced a lowering of the fluorescence yield over the whole emission spectrum but the decrease was most pronounced for the photosystem II fluorescence bands, F688 and F695. It was shown that the desiccation‐induced changes of the phycoerythrin sensitized emission spectrum were due to 1) a decrease in the fluorescence yield of the photosystem I antenna, 2) an even stronger decrease in the fluorescence of photosystem II, which was mediated by an increased spillover (kT(II→I)) of excitation to photosystem I and an increase in the absorption cross section, α, for photosystem I. We hypothesize that the increase of both kT(II→I)and α are part of a mechanism by which the desiccation‐tolerant, high light exposed,Porphyracan avoid photodynamic damage to photosystem II, when photosynthesis becomes inhibited as a result of desiccation during periods

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1982.tb04899.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY