摘要:

Glutathione synthetase activity (EC 6.3.2.3) was analysed in ammonium sulfate precipitates of extracts l'rom photohetevotrophically grown cells ofNicotiana tabactmL. cv. Samsun by determination of glutathione as its monobromobimane derivative. Maximal enzyme activity was obtained at pH 8.0–9.0 in Tris‐HCl and CHES as buffer systems. The enzyme showed an absolute requirement for Mg2+ and was slightly stimulated by K+. When Mg2+ was replaced by Mn2+ less synthetase activity was observed, and above 30 mMMn2+ no activity was found. The enzyme was specific for glycine (KM = 0.308 mM). No product formation was observed withß‐alanine andγy‐aminobutyrate using substrate conccntrations of 10 mM. The apparent KM values forγ‐glutamylcysteine andγ‐glutamyl‐l‐α‐aminobutyrate were, respectively, 0.022 and 0.033 mM. By chloroplast Isolation ca 24% of the total glutathione synthetase activity of the cells could be shown to be localized in the chloroplasts, the rest being attributed to the cytoplas

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06624.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Spinach plunts (Spinacia oleraceaL. cv. Monosa) were exposed to air with and without 0.25μl l‐1H2S. Effects of H2S exposure for up to 18 days on photosynthesis, dark respiration and on chlorophyllafluorescence were studied. Dark respiration was not affected by H2S fumigation. Photosynthetic CO2fixation decreased linearly with time in both control and fumigated plants. The rate of decrease in CO2fixation was faster in the fumigated plants; after 14 days of exposure the fumigated plants showed a decrease in CO2fixation of 23%äs compared with the control plants. The H2S‐induced decrease in CO2fixation was accompanied by a decrease in quenching of the chlorophyll fluorescence. The most characteristic change in chlorophyll fluorescence was a decreased difference between maximum and steady‐state fluorescence [(P‐T)/P), suggesting a reduced efficiency in the use of photochemical energy in photosynthesis. Differences in CO2fixation were more pronounced whcn measured at high light intensity; the maximum rate of CO2fixation at light saturation decreased significantly with time in the H2S‐exposed plants; after 14 days of H2S exposure a decrease of more than 70% was noted. The decrease in CO2fixation could not be attributed to a decreased chlorophyll content; on the contrary, chlorophyll content even slightly increased during fumigation. The initial increase in CO2fixation rate with increasing light intensity was also reduced by prolonged H2S fumigation, indicating an effect of H2S fumigation on photosynthetic electron transport.Finally, the phytotoxicity of H2S is discusscd in relation to the H2S‐induced changes in photosynthetic CO2fixation and chlorophyllafluorescence, and the effect of H2S on leaf development observed in ea

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06625.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Root formation in vine (Vitis viniferaL. cv. Albariño) was accompanied by at first a rise and then a fall in total peroxidase (EC 1.11.1.7) activity in the explant. These variations ran parallel to similar changes in the amount of the three cathodic isope‐roxidases detected, the most abundant of which, C2, also exhibited IAA oxidase activity. The anodic isoperoxidase bands detected were very weak and underwent no variation during rooting. Changes in the opposite direction (a fall followed by a rise) were shown by certain endogenous phenolics, including monoferuloyl, monocaffeoyl and mono‐ρ‐coumaroyl tartaric acids, some of which may act as auxin pro

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06626.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Seeds of Norway maple (Acer platanoidesL.) differing in water content (10, 20 and 30%) were stored for 6 weeks at 20 to 30°C. During this period changes in phospholipids and fatty acids as well as in seed viability and germination capacity were studied. A considerable decrease in the phospholipid content was observed, which depended on the water content in the seeds and was related to the decrease of the seed germination capacity. The level of linoleic (18:2) and linolenic (18:3) acids in the phospholipid fraction decreased considerably in the course of the accelerated seed ageing. The results obtained suggest that phospholipid degradation and peroxidation of unsaturated fatty acids, followed by membrane destruction, play a considerable role in maple seed ageing

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06627.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Watermelon (Citrullus vulgarisSchrad. cv. Fairfax) cotyledons were excised from the embryo and grown in the dark for 4 days. They were then transferred to 10 μm benzyladenine (BA) solution or illuminated with white light. We have compared changes in ultrastructure of the plastids and of their polypeptide pattern induced by the two treatments.At the end of the 4‐day‐period in the dark the plastids differentiated to amyloplasts and had few polypeptides: only the two subunits of ribulose bisphosphate carboxylase (RuBP) were clearly observed. Both light and BA induced starch depletion and gratia formation after 12–24 h. BA was less efficient than light in inducing thylakoid formation and more efficient in inducing starch depletion. After 6 h both factors induced the appearance of the same new polypeptides in the 28–53 kDa range. Most prominent among them is a 32 kDa band. Light is much more effective in inducing the formation of a 29 kDa band than is BA. In mature chloroplasts this band stains very strongly, while the 32 kDa band disappears. We suggest that the 29 kDa polypeptide is the light harvesting complex (LHC), since a purified LHC preparation from cotyledons grown either on water in light or on BA in the dark migrates on the polyacrylamide gel as a single 29

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06628.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Xanthine dehydrogenase (XDH, EC 1.2.1.37) ofChlamydomonas reinhardtii(Sager) 6145c wild strain has been isolated and characterized for the first time in a unicellular green alga. The enzyme has an Mrof 330 kDa, and FAD, molybdenum and iron are cofactors required for its activity as deduced from results obtained using specific inhibitors,59Fe‐labelling experiments, activity protection by FAD, physiological responses in vivo to iron and molybdenum deficiencies in the culture medium and work with mutants lacking molybdenum cofactor. Xanthine dehydrogenase exhibited Mi‐chaelian kinetics typical for a bisubstrate enzyme with apparent Kmvalues for NAD+, hypoxanthine and xanthine of 35, 160 and 70 μM, respectively. Under phototrophic conditions enzyme activity was repressed by ammonium, but xanthine was not required for the enzyme to be induced, since high levels of enzyme activity were found in cells grown on ammonium and transferred to either N‐frec media or media containing either of the nitrogen sources adenine, urea, urate, xanthine, hypoxanthine and g

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06629.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

From pericarp tissue of ripening tomato (Lycopersicom esculentumMill. cv. Sonato), two isoenzymes of polygalacturonase, PGl and PG2, can be extracted. With water hardly any polygalaeturonase activity is extracted; with 0.5 M NaCl predominantly PG2 is found and subsequent extraction with 1.25 M NaCI delivers mainly PGl. A partly purified PGl solution gradually decomposes into PG2. Conversion of PG2 into an isoenzyme that resembles PGl, but differs from it, can be brought about by a faetor (eonvertor) that occurs at low levels in free form in unripe and early‐ripe fruits as well as in leaves. Convertor (CV) ean be set free from PGl by a short treatment at 100°C, at which temperature the convertor activity itself also decreases.The in vitro activities and several characteristics of the isoenzymes and CV as found by us differ from that found by others, probably because of carefully optimized methods. It is suggested that the CV anchors PG2 onto the cell wall, forming PGl. Thus PGl would constitute the form that depolymerizes the peetins in the middle lamell

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06630.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The effects of N‐phenyl‐N'‐l,2,3,‐thidiazol‐5‐ylurea (thidiazuron; Dropp; SN 49537) on fatty acids of membrane lipids and sterol content in apple (Malus domesticaBorkh cv. Golden Delicious) buds associated with bud break and bud development were determined. The predominant fatty acids in the membrane lipids of apple buds were palmitic acid (C16:0), linoleic acid (C18:2) and linolenic acid (C18:3).β‐Sitosterol and sitosteryl ester were the predominant sterols. An accumulation of unsaturated polar membrane fatty acids started after thidiazuron treatment. A decrease in the percentage of the sitosterol was accompanied by an increase in campesterol and stigmasterol at the beginning of rapid growth. An increase in the ratio of campesterol and stigmasterol to sitosterol and a decrease in the ratio of free sterols to membrane lipids upon breaking of dormancy also occurred in apple buds induced

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06631.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Six Argentinian wheat (Triticum aestivumL.) cultivars grown in nutrient solutions in controlled environment were compared for their nitrate uptake rates on a root dry weight basis. Up to 3‐fold differences were observed among the cultivars at 16, 20 and 24 days from germination, either when measured by depletion from the nutrient solution in short‐term experiments, or by total N accumulation in the tissue during 8 days.No differences in total N concentration in root or shoots were found among cultivars. Although the different cultivars showed significant differences in shoot/root ratio and nitrate reductase activity (EC 1.6.6.1) in the roots, none of these parameters was correlated with the nitrate uptake rate. However, nitrate uptake was found to be positively correlated (r = 0.99) with the shoot relative growth rate of the cultivars. The three cultivars with the highest nitrate uptake rates and relative growth rates showed a positive correlation between root nitrate concentration and uptake. However, this correlation was not found in the cultivars with the lowest growth and uptake rates.Our results indicate that the difference in nitrate uptake rate among these cultivars may only be a consequence of their differences in growth rate, and it is suggested that at least two mechanisms regulate nitrate uptake, one working when plant demand is low and another when plant demand is h

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06632.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A detailed study of lipoxygenase (EC 1.13.11.12) synthesis in cotyledons of soybean [Glycine max(L.) Merr. cv. Century] cultured in vitro for up to 40 h showed that synthesis of this protein, measured by in vivo [35S]‐methionine labelling in connection with immunological methods and cell‐free translation of mRNA, underwent a large transient reduction in the first 4 h of culturing and gradually increased in the following 36 h. Northern blot hybridizations with lipoxygenase cDNA clones showed that the decrease in translational activity was the consequence of a considerable reduction in lipoxygenase mRNA in the cotyledons. From these results we conclude that the transient decline in lipoxygenase synthesis in excised soybean cotyledons is regulated at the RNA level. Similarly judged from the analysis of patterns of uni‐dimensional gel electrophoresis, the synthesis of a few other polypeptides decreased during the first 4 h of culture as well, while several others increased; in cotyledons cultured for 20 to 40 h the protein‐synthesis pattern had returned to that in freshly excised cotyledons. An acclimation period of ca 1 day seems to be needed for isolated soybean cotyledons to stabilize and to resume regular RNA and protein sy

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb06633.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY