摘要:

In suspension cultures ofPhytolacca americana, betacyanin accumulation was reduced when cell division was inhibited by treatment with various inhibitors of DNA synthesis or anti‐microtubule drugs. Aphidicolin (APC), an inhibitor of DNA synthesis, reduced the incorporation of radioactivity from labeled tyrosine into betacyanin, but the incorporation of radioactivity from labeled 3,4‐dihydroxyphenylalanine (DOPA) into betacyanin was not affected by similar treatments. Propyzamide, another anti‐microtubule drug, reduced incorporation of radioactivity from tyrosine and DOPA into betacyanin. However, the rate of incorporation from DOPA was higher than that from tyrosine. The results suggest that inhibition of betacyanin accumulation inPhytolacca americanacells by APC and propyzamide is due to suppression of the reaction converting tyrosine to DOPA, which may be closely related to cell div

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Embryos from the mature unstratified loblolly pine (Pinus taedaL.) seeds used in this study were nondormant: however, they failed to germinate in situ because of constraints imposed by the surrounding tissues. During a stratification period of 35 days of moist chilling at 2°C, seed germinability increased from 19 to 76%. The total lipid content of the megagametophyte did not change during stratification, whereas the total protein content of both megagametophyte and embryo was more variable. The rate of synthesis of buffer soluble proteins in these two tissues increased and electrophoretic analysis showed that while similar proteins were synthesized during the stratification period, changes in the patterns of synthesis of some proteins did occur. In both the embryo and megagametophyte the synthesis of a set of proteins with molecular masses below 46 kDa decreased markedly after 14 days of chilling (DOC). In the megagametophyte, the synthesis of a more diverse set of proteins with molecular masses ranging from 16 to 78 kDa increased after 14 DOC. It is noteworthy that these changes in the patterns of protein synthesis coincided with the greatest relative increase in seed germinability of 35%

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Cellular injury resulting from partially reduced oxygen species (superoxide, peroxides and/or hydroxyl radicals) or singlet oxygen frequently increases during environmental stress. Because protein methionine residues are susceptible to oxidation, we investigated the effects of water‐deficit stress and high temperature stress on the content of oxidized methionyl residues [Met(O)] in leaves. Leaf proteins from water‐deficit‐stressed cotton (Gossypium hirsutumL. cv. Paymaster HS‐26). pea (Pisum sativumL. cv. Progress No. 9). wheat (Triticum aestivumL. em. Thell. cv. Len) and potato (Solanum tuberosumL. cv. Norgold M) and from the leaves of high‐temperature‐stressed pea seedlings were evaluated. The activity of protein methionine‐S‐oxide reductase (PrMSR). an enzyme responsible for re‐reducing oxidized methionyl residues, was also determined. Protein Met(O) content did not change in response to either water‐deficit or high temperature stress. PrMSR activity decreased in pea and cotton leaves, remained unchanged in potato leaves and significantly increased in leaves of water‐deficit‐stressed wheat. The findings demonstrate that these plants have developed protection systems that effectively maintain stable levels of oxidized methionyl residues in leaf proteins despite exposure to severe water and high temperature stress. The findings also suggest that changes in PrMSR activity do not fully account for the observed maintenance of protein methionyl sulfoxide con

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

To address the questions of whether allocation of carbohydrates to roots is influenced by ionic form of nitrogen absorbed and whether allocation of carbohydrates to roots in turn influences proportionality between NH4+and NO3−uptake from mixed sources, NH4+and NO3−were supplied separately to halves of a split‐root hydroponic system and were supplied in combination to a whole‐root system. Dry matter accumulation in the split‐root system was 18% less in the NH4+‐fed axis than in the NO3−‐fed axis. This, however, does not indicate that partitioning of carbohydrate between the two axes was different. Most of the reduction in dry matter accumulation in the NH4+‐fed axis can be accounted for by the retransport of CH2O equivalents from the root back to the shoot with amino acids produced by NH4+assimilation. Uptake of NH4+or NO3−by the respective halves of the split‐root system was proportional to the estimated allocation of carbohydrate to that half.When NH4+and NO3−were supplied to separate halves of the split‐root system, the cumulative NH4+to NO3−uptake ratio was 0.81. When supplied in combination to the whole‐root system, the cumulative NH4+to NO3−uptake ratio was 1.67. Thus, while the shoot may affect total nitrogen uptake through the export of carbohydrates to roots, the shoot (common for halves of the split‐root system) apparently does not exert a direct effect on proportionality of NH4+and NO3−uptake by roots. For whole roots supplied with both NH4+and NO3−, the restriction in uptake of NO3−may involve a stimulation of NO3−efflux rather than an inhibition of NO3−influx. While only the net uptake of NH4+and NO3−was measured by ion chromatography, monitoring at approximately hourly intervals during the first 3 days of treatment revealed irregularly occurring intervals of both depletion (net influx) and enrichment (net efflux) in solutions. In the case of NH4+, numbers of net efflux events were similar (21 to 24 out of 65 sequential sampling intervals) whether NH4+was supplied with NO3−to whole‐root systems or separately to an axis of the split‐root system. In the case of NO3−, however, the number of net efflux events increased from 8 when NO3−was supplied to a separate axis of the split‐root system to between 19 an

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

InCathuranthus roseus(L.) G. Don cells the cyanide‐resistant pathway is engaged after phosphate or nitrogen starvation. Re‐addition of these nutrients disengaged it again. Re‐addition of phosphate leads to a transient disengagement which becomes onlypermanent after a second addition of phosphate. Disengagement after re‐addition of nitrogen is slow: it takes 9 days before the activity has disappeared. In this system the mechanism of engagement of the cyanide‐resistant pathway was studied. Addition of phosphate to phosphate‐starved cells induced cell division within 24 h. The disengagement of the cyanide‐resistant pathway was probably only an indirect effect of phosphate because the cellular P, content, which increased rapidly after addition, was low again before the cyanide‐resistant pathway was disengaged. A better correlation was observed between high ADP and adenylate content of the cells and disengagement of the cyanide‐resistant pathway. In addition it appeared that the engagement of the cyanide‐resistant pathway was not the result of a limited carrier capacity of the cytochrome pathway. It is tentatively concluded that the engagement of the cyanide‐resistant pathway in phosphate‐starved cells was the result of a limited adenylate content.After nitrogen addition to N‐starved cells, it took 5 days until the first growth occurred. Before the cyanide‐resistant pathway was disengaged, its activity increased with the increased respiration rate which preceded growth. Within 72 h a higher ADP content was observed, which was still high after 10 days. The stimulation of the cytochrome pathway by uncoupler was small and more or less the same with and without added nitrogen, as long as the cyanide‐resistant pathway was engaged. After disengagement the stimulation by uncoupler was significantly larger. It is suggested that the engagement during N‐starvation was the result of a limited carrier capacity of the cytochrome pathway.Stimulation of the metabolism by re‐addition of phosphate, nitrogen or sucrose resulted in a rapid increase in the levels of uracil nucleotides and uridine diphosphoglucose (UDPG) which a

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00387.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The specific activities of 6 enzymes, which are involved in the synthesis and catabolism of membrane lipids, were monitored in plasma membranes isolated from petunia petals during senescence. These included phosphatidylinositol (PI) kinase (EC 2.7.1.67), phosphatidylinositol monophosphate (PIP) kinase (EC 2.7.1.68). diacylglycerol (DAG) kinase (EC 2.7.1.107), phospholipase A (EC 3.1.1.4) and PIP‐ and PIP2‐phospholipase C˙(EC 3.1.4.3). Using endogenous substrate, the [32P]PA and [32P]PIP2formation increased to 140 and 200%, respectively, of the day 1 value by 4 days after harvest. There was no significant change in [32P]PIP formation during the same time period. On the fifth day the petals wilted and the [32P]PA and [32P]PIP formation declined significantly. In contrast, the [32P]PIP2formation remained high in the day 5 petals. When the lipid kinase activities were assayed in the membranes in the presence of exogenous substrate the specific activity of all of the enzymes increased. and the changes in [32P]PA production over the 5‐day period were similar to those observed with endogenous substrate. When exogenous PI and PIP were added, however, there was no longer an increase in [32P]PIP2formation by plasma membranes of day 4 petals and [32P]PIP formation significantly decreased. The relative decrease in PIP and PIP2formation by day 4 membranes when exogenous substrate was added may have resulted from differences in the lipase activities in the day 1 and day 4 membranes. The plasma membrane A‐type phospholipase activity increased throughout the 5 day period, and phospholipase C activity increased two‐fold between day 1 and day 4. Such changes in the metabolism of the plasma membrane lipids during flower senescence would affect the ability of the petals to use inositol phospholipid‐based signal transduct

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00388.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

In using an efficient and synchronised in vitro tuberisation system the transition of axillary buds from stolons to tubers inSolanum tuberosumL. cv. Bintje was followed. After 5 or 6 days on tuber‐inducing medium all axillary buds had formed tubers which increased in size until the experiment was ended at day 10. Concomitantly with the visible appearance of tubers the fresh weight of the axillary buds increased as well as their starch content. Soluble sugar content, notably glucose, increased until tuberisation occurred and dropped after that. In the daily sampled explants gene expression was studied at several levels. RNA was isolated from the different explants during the whole tuberisation experiment and northern blots were probed with cDNAs encoding genes involved in starch‐ and patatin‐biosynthesis. It was shown that in the very early stages of development hardly any transcript could be detected. Only one day before visible swelling occurred were clear signals obtained for all the genes investigated. Although it was evident that coordinate expression of starch biosynthetic genes did occur, it was not in a similar fashion for all the genes. Sucrose synthase and ADPG‐pyrophosphorylase B were expressed in an identical fashion which was different from ADPG‐pyrophosphorylase S, granule‐bound starch synthase and branching enzyme. The RNA levels of these three latter genes reached a maximum at day 5, remaining constant until the experiment was finished. The transcript levels of sucrose synthase and ADPG‐pyrophosphorylase B reached their highest level at day 5 after which they dropped to a lower level at day 10. Patatin gene expression was clearly different from that of the starch biosynthetic genes: it steadily increased from day 4 until the end of the experiment. Enzyme activities of sucrose synthase. ADPG‐pyrophosphorylase and branching enzyme confirmed the RNA expression data and showed that ADPG‐pyrophosphorylase enzyme activity reached a maximum at day 4 after which it dropped. The other two enzyme activities could be detected at or one day after tuberisation occurred and increased until the exp

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00389.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The functioning of the photosynthetic apparatus during leaf senescence was investigated in alstroemeria cut flowers by a combination of gas‐exchange measurements and analysis of in vivo chlorophyll fluorescence. Chlorophyll loss in leaves of alstroemeria cut flowers is delayed by light and by a treatment of the cut flowers with gibberellic acid (GA3). The maximal photosynthesis of the leaves was approximately 6 μmol CO2m−2s−1at I 350 μmol m−2s−1(PAR) which is relatively low for intact C3leaves. Qualitatively the gas‐exchange rates followed the decline in chlorophyll content for the various treatments, i.e. light and GA3‐treatment delayed the decline in photosynthetic rates. However, when chlorophyll loss could not yet be observed in the leaves, photosynthetic rates were already strongly decreased. In vivo fluorescence measurements revealed that the decrease in CO2uptake is (partly) due to a decreased electron flow through photosystem II. Furthermore, analysis of the fluorescence data showed a high nonphotochemical quenching under all experimental conditions, indicating that the consumption of reducing power in the Calvin cycle is very low. The chlorophyll, remaining after 9 days incubation of leaves with GA3in the dark should be considered as a ‘cosmetic’ pigment without any function in the supply of assimil

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00390.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

In lyophilized needles of Norway spruce (Picea abies[L.] Karsten) and starting from bud break, we determined enzyme activities (sucrose phosphate synthase [SPS; EC 2.4,1.14]. sucrose synthase [SS; EC 2.4,1.13]. acid invertase [AI; EC 3.2,1.26]) and intermediates (starch, sucrose, glucose, fructose; fructose 6‐phosphate, fructose 2.6‐bisphosphate [F26BP]) of carbohydrate metabolism together with needle weight, shoot length, chlorophyll and protein. For up to 110 days after bud break, samples were taken twice a week from about 25‐year‐old trees under field conditions. At least three periods can be distinguished during needle maturation. During the first period (up to 45 days after bud break) Al showed the highest extractable activity. This coincided with very high levels of F26BP (up to 11 pmol [mg dry weight]−1) and a transient increase of starch in parallel to a decrease of sucrose. The interval between 45 and 70 days after bud break was characterized by high SS activity (ratio of fructose/glucose>1), much decreased levels of F26BP (down to below 1 pmol [mg dry weight]−1), and a pronounced increase in the dry weight/fresh weight ratio. In parallel, starch declined and soluble carbohydrates increased. Finally, needle maturation was characterized by decreasing SS and continuously increasing SPS activities, so that the ratio of SPS/SS increased more than 6‐fold. AI. however, did not decline with maturation. Changes in pool sizes of metabolites and enzyme activities (AI. SPS) are consistent with current concepts on sink/source transition. SS is obviously important with regard to the synthesis of structural po

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00391.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The effects of ionizing radiation, used in post‐harvest treatment of fruit and vegetables. were investigated on cultured apple cells (Pyrus malusL. cv. Royal Red) on a short‐term period. Irradiation (2 kGy) induced an increase of passive ion effluxes from cells and a decrease of cell capacity to regulate external pH. These alterations are likely due to effects on plasma membrane structure and function and were further investigated by studying the effects of irradiation on plasma membrane H+‐ATPase activity. Plasma membrane‐enriched vesicles were prepared and the H+‐ATPase activity was characterized. Irradiation of the vesicles induced a dose dependent inhibition of H+‐ATPase activity. The loss of enzyme activity was immediate, even at low doses (0.5 kGy), and was not reversed by the addition of 2mMdithiothreitol. This inhibition may be the result of an irreversible oxidation of enzyme sulfhydryl moieties and/or the result of changes induced within the lipid bilayer affecting the membrane‐enzyme interactions. Further analysis of the H+‐ATPase activity was carried out on vesicles obtained from irradiated cells confirming the previous results. In vivo recovery of activity was not observed within 5 h following the treatment, thus explaining the decrease of cell capacity to regulate external pH.This rapid irreversible inhibition of the plasma membrane H+‐ATPase must be considered as one of the most important primary biochemical events occurring in irradiat

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb00392.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY