摘要:

Abstract.During the emergence of the eukaryotic line and the three classes of DNA‐dependent RNA polymerases with their specific transcriptional tasks, the subunit structure of these enzymes became more complex when compared with the prokaryotic enzyme. It is proposed, especially for the RNA polymerase I from higher plants, that the increase in the complexity of subunit structure during evolution was associated with an increase in the degree of co‐operativity of substrate binding sites. This multiplicity of substrate binding sites could be useful for fitting and proper base‐pairing between the incoming substrate molecules and the DNA tem

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1983.tb01249.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.In the preliminary purification ofCapsicumleaf nitrate reductase (EC 1.6.6.1), treatment of the crude extract on Sephadex G‐25 was necessary to prevent a gelling of the extract and sedimentation of the enzyme. Its Kmvalues for NADH and nitrate were estimated to be 9.3 and 105mmol m−3ADP and ATP gave hyperbolic competitive inhibition, with respect to NADH, while the inhibition by AMP was linear competitive. Kivalues calculated were: ADP and ATP approximately lmol m−3and AMP 2.3 mol m−3. Inhibition by ADP was not altered by reduced glutathione.TheCapsicumnitrate reduclase was very susceptible to inhibition by NADH (in the absence of nitrate) and anin vivoassay showed that the activity of the enzyme was limited by the supply of nitrate. NADH and adenine nucleotide levels measured in theCapsicumleaf were used to estimate inhibition of nitrate reductase and a prediction was made of the nitrate reductase activity at different times in the photoperiod. This was shown to follow the same trend as the measuredin vivoactivity of the enzyme. Changes in adenine nucleotide levels had little effect on nitrate reductase a

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11579979

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.Effects of paraquat were monitored by electron microscopic, cytochemical, andin vivospectrophotometric procedures. Electron microscopy of paraquat‐treated pea leaf discs indicates that the chloroplasts are affected primarily with both thylakoid dilation and apparent lamellar fusions, resulting in a ‘honeycomb’ of lamellae. No ultra‐structural effects were noted when leaf discs were incubated in both DCMU and paraquat. Paraquat‐induced peroxide was located cytochemically along the stroma lamellae, on the ends of the grana stack and in the dilated thylakoids. Less destruction was noted in those samples where peroxide was precipitated by cerium chloride, indicating that peroxide or one of its products is one of the major causes of paraquat toxicily. In C4plants mesophyll plastids exhibited much more peroxide deposition than was detected in bundle sheath plastids. No plastid peroxide depositions were noted in a photobleaching mutant that is resistant to paraquat.In situcytochromefoxidation‐reduction was followed during paraquat treatments and resulted in a hastening of the dark re‐reduction of cytochromefafter only 1 h of treatment. This effect was prevented by DCMU or CeCI3. Electron transport, as measured by cytochromefoxidation‐reduction, was completely obliterated by a 24 h paraquat treatment. Thesein situstudies on paraquat confirm previous studies that the primary effect in the light is on the plastid and involves peroxide or further products genera

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580509

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.Barley plants (Hordeum vulgareL. cv. Midas) raised under controlled environmental conditions were sprayed with either of the gametocides Ethrel and RH‐531. At various times after spraying the anthers were fixed for light and electron microscopy. Abortion of sporogenous cells occurred in plants sprayed at both pre‐ and post‐meiotic stages of microsporogenesis. In contrast, cells of the tapetum were insensitive to the immediate effects of gametocides. The cytological effects of the gametocides are similar to those induced by male sterile genes in a variety of plants. These range from the induction of additional mitotic divisions in the pollen mother cells to exine malformations on developing microspores. These observations are discussed in terms of the control mechanisms operating during microsporoge

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580515

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.In experiments withPisum sativumcv. Sleaford Orbiter in a controlled environment, the effect of fruit number and position, photon flux density and developmental stage on fruit growth was studied. During early development (up to 22 d from anthesis) growth of the first fruit was unaffected by the presence of one or two additional fruits irrespective of their position. When grown to maturity in competition with fruits at the same node a small decrease in weight of this fruit was observed. Where plants retained a full complement (20‐30) of fruits the growth of the first fruit was markedly decreased at all stages of development (6‐40 d). In all instances where competition was observed, the pericarp was more affected than the seeds. This was particularly so when photon flux was decreased 18‐22 d from anthesis compared with a decrease at an earlier stage. Partition of dry matter between fruits showed a progressively increasing allocation to the later‐formed fruits with time for all treatments. The actual proportions allocated to different fruits were not changed by the number of competing fruits. Decreasing photon flux by more than two‐thirds decreased fruit growth rates but had little effect on dry matter partitioning in most cases, although where all fruits were retained, there was a tendency for fruits at the lower reproductive nodes to be less affected. These findings are discussed in relation to known sources of assimilate for fruits, assimilate transport and sink demand. It is suggested that partition of dry matter between fruits can be estimated on the basis of fruit size and the developmental trend in relative growth rate of fruits grown in the absence of competition for assimilate from oth

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580520

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.Different morphological aspects of short tuberized roots initiated during drought stress in mesophytic species, such asSinapis albaL., were studied with the scanning electron microscopy technique of cryofixation. Specially adapted for direct and immediate observation of fresh living roots, this method has given precise information about rhizodermal organization and evolution during drought and rehydration.The main difference from a normal lateral root grown in a well‐watered soil appears in the basal enlarged zone of the short root where all the cells show the same round and turgid aspect. In the medium zone of the short root, rhizodermis differentiation into alternating rows of short (trichoblasts) and long (atrichoblasts) cells, which characterizes the typicalSinapisroot, remains clearly discernible, though not so regular as in normal lateral roots.The turgid state of rhizodermal cells all over the short tuberized root grown in a drying soil suggests an effective regulatory mechanism for water deficit avoidance.During the first hours of rehydration, immediate absorption of water is noticeable through the rapid swelling of some long cells which appear to protrude considerably among other rhizodermal cells. However, these protrusions will not give rise to hairs, as further observations of short roots after growth has resumed show very distinctly that progressive hair formation occurs in the medium zone of the root, and that their emergence originates from trichoblasts only.These observations may indicate that atrichoblasts, on account of their highly vacuolated condition, are the first cells to absorb water and that they may even be stimulated, in some environmental conditions, to initiate hair formation, although they are not so well adapted to do so as the short cells in this specie

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580525

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.Pre‐imbibed cocklebur (Xanthium penn‐sylvanicumWallr.) seeds displayed bimodal germination‐temperature responses with two optima at 8 and 33° C. Such germination responses occurred subsequent to bimodal respiration‐temperature upsurges at lower and higher temperature regions. At lower temperatures, cocklebur seeds respired predominantly through a cyanide‐sensitive cytochrome pathway. A rise in temperature resulted in a marked increase in flux via an alternative pathway, a propyl gallate‐ (PG) or benzohydroxamic‐acid‐ (BHAM) sensitive pathway, thus resulting in an increase in the ratio of this pathway relative to the cytochrome pathway. Both an increased capacity for the alternative pathway and an increase in the ratio of this pathway to the cytochrome pathway were obtained when pre‐imbibed seeds were exposed to either 8 or 33°C for a short period. The effects of low temperature were reduced as the exposure time was prolonged beyond 3d, resulting in a reduction in germination. Neither PG nor BHAM had an inhibitory effect on the chilling‐induced germination, but the germination‐stimulating effect of high temperatures was less pronounced in the presence of PG or BHAM. At high temperatures, on the other hand, KCN and NaN3were ineffective or, rather, slightly inhibited germination. It was thus concluded that low and high temperatures exert their germination‐stimulating effects by an essentially similar manner which increases fluxes both via the cytochrome pathway and, especially, via the alternative pathway and, as a result, raises the ratio of

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580530

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.The mechanism involved in a bimodal germination‐temperature response in pre‐soaked cocklebur (Xanthium pennsylvanicumWallr.) seeds was studied with special reference to adenylate metabolism. Exposure to either low (optimal at 8°C) or high (optimal at 34°C) temperature which was effective in inducing the germination of the seeds brought about the accumulation of ATP in them. The ATP level remained unchanged at temperatures around 23°C. Pretreatment with KCN, stimulating germination even at 23°C, subsequently increased the ATP content, total adenylate pool and energy charge (EC) in the axial tissue prior to germination above those of the untreated controls. The lower the treatment temperature, the greater the inhibitory effect of KCN on ATP formation. An increase in germination following an increasing duration of pre‐soaking at 8°C was comparable to increasing both the ATP content and total adenylate pool of axes, but not the EC value. Similarly, changes in germination following an increased exposure duration at 8°C correlated with changes in ATP content rather than EC value in the axes. Unlike the case of chilling, an increase in ATP level in response to 34°C was greater in the early period of water imbibition, during which times its germination‐stimulating effect appeared more striking than in the later period, and it occurred without a concomitant rise in EC value because of the increased supply of AMP. Such a supply of AMP was reduced in the presence of benzohydroxamic acid or propyl gallale, inhibitors of an alternative respiratory pathway. It was thus concluded that both low temperature, coupled with warm temperature, and high temperature, by itself, can induce seed germination by increasing the ATP level as well as the total adenylate pool, but not the EC value, in the axial tissue. Further, that increases in both the ATP level and the adenylate pool especially are required for seed germination to proceed, probably depending on the activities of the cytochrome and alternative respiration pathways

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580534

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.In four dicotyledonous species low levels of N strongly inhibited leaf expansion during the day but had little or no effect at night. In contrast, daytime and night‐time expansion were equally affected in four cereal species. The results support the general concept that in dicotyledons, N controls leaf expansion through its effects on hydraulic conductivity. In such N‐limited plants, water deficits generated by transpiration may inhibit daytime cell expansion. In cereals, cell expansion and transpiration occur in separate zones of the leaf and are apparently unrelated.Growth analysis showed that low levels of N inhibited leaf area growth more strongly in dicotyledons than in cereals, but had similar effects on net assimilation rates of plants in the two groups. As a result, dry matter production was more efficient in cereals than in dicotyledons when N was limit

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580537

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

Abstract.Changes in the bioelectric field potential at the apical end of dark‐grown soybean (Glycine max)hypocotyls after exposure to several wavelengths of light have been monitored with an electrometer. A small dose of 660 nm radiation brings about a rapid positive rise in the potential. A following small dose at 760 nm prevents the increase, suggesting a phytochrome action. Pre‐irradiation with 660 nm enables a subsequent larger dose of 760 nm, which by itself is without effect, to elicit a delayed rise in the potential.A large dose at 710 nm induces a delayed increase in the field potential. The increase is prevented by a following dose at 550 nm, but not at 660

ISSN:0140-7791    

DOI:10.1111/1365-3040.ep11580548

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY