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1.
Impacts of chlorpyriphos (2, 4, 6 ppm) on the profiles of antioxidant (catalase) and anaerobic (lactate dehydrogenase) enzymes and other macromolecular contents (DNA, RNA, protein) of various tissues of the freshwater fish, Heteropneustes fossilis were studied. Chlorpyriphos significantly decreased the specific activity of catalase (CAT) and lactate dehydrogenase (LDH) in the brain, liver, gill and skeletal muscle of the fish. The reduction in specific activity might be due to the binding of chlorpyriphos or its metabolites with the enzyme molecules or affecting the synthesis and/or degradation of the enzymes. Like enzymes, the DNA, RNA and protein contents decreased in the brain, liver, gill and skeletal muscle of the fish as a function of increase in chlorpyriphos concentrations (2-6 ppm). The chlorpyriphos-induced reduction in these biochemical constituents might be because of alteration in their turnover (synthesis/degradation) in different tissues. The maximum effects on CAT, LDH, DNA, RNA and protein were obtained in response to 6 ppm chlorpyriphos. The present findings suggest chlorpyriphos concentration related impairment in antioxidative, anaerobic and protein synthesizing capacity of the fish. Therefore, the use of higher concentrations of chlorpyriphos should be avoided to protect the health of economically important freshwater food fish.  相似文献   

2.
Exposure of epigeic (Perionyx sansibaricus), anecic (Lampito mauritii) and endogeic (Metaphire posthuma) earthworms to four different concentrations (10 ppm, 20 ppm, 40 ppm and 80 ppm) of carbofuran for 16 days induced specific activities of cytoplasmic malate dehydrogenase (cMDH), mitochondrial malate dehydrogenase (mMDH) and lactate dehydrogenase (LDH). P. sansibaricus showed 33-52% increase in specific activities of aerobic (cMDH, mMDH) and anaerobic (LDH) enzymes and proteins (cytoplasmic and mitochondrial). In L. mauritii, the enhancement in enzyme and protein level was 30-46%. Similarly, M. posthuma indicated 29-43% increase in profile of enzymes and proteins. The significant increase was observed on 2nd or 3rd day and it was maximum on 16th day of carbofuran exposure. Maximum effect of carbofuran was on epigeic earthworm. The sensitivity of mitochondrial dehydrogenase and protein of different earthworm species to carbofuran appears to be associated with oxygen availability in different strata of soil habitats. Inductions in enzyme specific activity and protein content were concentration and time-dependent. The effect was more pronounced on aerobic enzymes (cMDH, mMDH) as compared to anaerobic (LDH) one. The increases in mitochondrial enzyme (47%) and protein (43%) were more than the cytoplasmic enzymes (35%) and protein (31%), which suggest a greater effect of carbofuran on respiratory metabolism of earthworms. The carbofuran-dependent increase in cytoplasmic and mitochondrial enzymes and proteins might be due to increased synthesis of metabolic enzymes and stress proteins.  相似文献   

3.
Chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesul-fonamide) is the active ingredient in DuPont “Glean” Weed Killer (formerly DPX-4189), a new herbicide for weed control in small grains as well as other uses. Continuous growth measurements of chlorsulfuron-sensitive seedlings demonstrated that the herbicide inhibits growth within 2 hr of application and by 8 hr reduces growth by 80%. This reduction in growth was closely associated with an inhibition of plant cell division. No significant effects were observed on auxin-, cytokinin-, or gibberellin-induced cell expansion. Photosynthesis, respiration, RNA synthesis, and protein synthesis were also initially unaffected under conditions where plant cell division is strongly inhibited.  相似文献   

4.
The effects of an organophosphate pesticide phorate on cytoplasmic malate dehydrogenase (cMDH), mitochondrial malate dehydrogenase (mMDH), lactate dehydrogenase (LDH), supernatant and mitochondrial proteins of an epigeic (Perionyx sansibaricus), anecic (Lampito mauritii) and endogeic (Metaphire posthuma) earthworms were studied. The treatment of different concentrations (20, 40, 80 and 160 ppm) of phorate for 16 days gradually decreased the specific activities of cMDH, mMDH and LDH as well as cytoplasmic and mitochondrial protein contents. This showed the inhibitory effect of phorate on metabolic enzymes and proteins in tropical earthworms. The inhibition was dose- and time-dependent. The inhibitory response in mitochondrial enzyme (mMDH) and protein was somewhat earlier and more as compared to the inhibitory effect of phorate on cytoplasmic enzymes (cMDH, LDH) and protein. This indicates a greater interference of phorate in cellular respiration of earthworms. The phorate related decreases in enzyme and protein profiles were about 60% and 58% in P. sansibaricus, 54% and 49% in L. mauritii and 47% and 42% in M. posthuma, respectively. It reflects phorate-induced substantial decline in protein synthesis and aerobic and anaerobic capacity of earthworms. The maximum effect of phorate was on epigeic earthworm followed by anecic and endogeic species. The present findings suggest the differential sensitivity of different earthworm species in enzymatic and protein responses to phorate and the sensitivity was associated with the ecophysiological categories of earthworms.  相似文献   

5.
Inhibition of growth of pith callus of tobacco (Nicotiana tabacum, var. S-73) by the herbicide trifluralin (α,α,α - trifluoro - 2,6 - dinitro - N,N- dipropyl - p - toluidine) was previously observed. Inhibition of cell division in callus tissue of varying age by this herbicide was investigated using the Feulgen reagent and light microscopy. Upon staining and counting the number of cells in each phase of mitosis, a decrease in the number of cells in metaphase, anaphase, and telophase in the treated tissues was found. In addition to this reduction, arrested metaphases and multinucleated cells were observed. Similar results were observed with 10?4M colchicine. The effects of trifluralin on incorporation of 14C-precursors into callus RNA, DNA, and protein were also investigated. Apparent RNA, DNA, and protein synthesis in callus were inhibited by trifluralin (5 × 10?6M) treatment. The inhibition, however, was not expressed until 5–7 days after initiating treatment. Colchicine also affected apparent RNA, DNA, and protein synthesis; however, these effects were different than those observed with trifluralin. Incorporation of 14C-amino acids into protein was most severely inhibited by colchicine.  相似文献   

6.
The sulfonylurea herbicides chlorsulfuron (CS) and sulfometuron methyl (SM) inhibit the growth of soybean cells (Glycine max L. var. Amsoy 71) in suspension culture with 50% inhibition at 170 and 62 ppb, respectively, relative to the initial cell dry weight, and CS is not rapidly metabolized in these cultures. In Glycine max L. cv Merrill var. Mandarin, CS inhibits the growth by 50% at 4 ppm on the basis of initial cell dry weight. This inhibition is partially reversed by valine, leucine, or 2-ketoisovalerate, but not by pyruvate, isoleucine, or any other single amino acid. CS drastically reduces the content of free valine and leucine in soybean cells without significant effect on the amount of other free amino acids. Deoxyribonucleosides alleviate a portion of the CS growth inhibition in soybean cells in vivo, though CS and SM do not inhibit ribonucleoside diphosphate reductase in vitro. CS and SM are bacteriostats for Escherichia coli and Salmonella typhimurium in minimal growth medium. E. coli growth is retarded at CS concentrations (100–300 μg/ml) that inhibit RNA and protein synthesis but not DNA synthesis. CS growth inhibition in E. coli is enhanced by cysteine and valine and partially alleviated by isoleucine and the aromatic amino acids, but not by leucine. The sulfonylureas appear to act in soybean by blocking the synthesis of valine and leucine between pyruvate and 2-ketoisovalerate and in E. coli by inhibiting isoleucine biosynthesis.  相似文献   

7.
The effects of the herbicides hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] and chlorsulfuron (2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl]benzenesulfonamide) on the metabolism of enzymatically isolated leaf cells from soybean [Glycine max (L.) Merr., cv. ‘Essex’] were examined. Photosynthesis, protein, ribonucleic acid (RNA), and lipid syntheses were assayed by the incorporation of specific radioactive substrates into the isolated soybean leaf cells. These specific substrates were NaH14CO3, [14C]leucine, [14C]uracil, and [14C]acetate, respectively. Time-course and concentration studies included incubation periods of 30, 60, and 120 min and concentrations of 0.1, 1, 10, and 100 μM of both herbicides. Photosynthesis was the most sensitive and first metabolic process inhibited by hexazinone. RNA and lipid syntheses were also inhibited significantly by hexazinone whereas the effect of this herbicide on protein synthesis was less. The most sensitive and first metabolic process inhibited by chlorsulfuron was lipid synthesis. Photosynthesis, RNA, and protein syntheses were affected significantly only by the highest concentration of this herbicide and longest exposure. Although these two herbicides may exert their herbicidal action by affecting other plant metabolic processes not examined in this study, hexazinone appears to be a strong photosynthetic inhibitor, while the herbicidal action of chlorsulfuron appeared to be related to its effects on lipid synthesis.  相似文献   

8.
The effect of asulam (methyl (4-aminobenzenesulphonyl) carbamate) on the synthesis of RNA and protein was investigated in bracken sporeling plants and excised rhizome bud tissue. Foliage application of asulam (4.4 kg/ha) reduced the RNA levels in frond buds and young fronds within 3 days, while protein levels were significantly reduced after 14 days. A significant reduction in respiratory activity of buds was observed after 2 weeks, the level of inhibition being 54% after 8 weeks. During a 3-h incubation period, O2 uptake by excised bud issue was stimulated by 5 and 10 ppm asulam and inhibited by higher concentrations; 32P uptake was inhibited at all concentrations. Asulam (5 ppm and above) inhibited bud growth and reduced RNA and protein levels in incubated buds (20 h at 30°C), and the incorporation of [14C]orotic acid into RNA and [14C]leucine into protein. Reduction of RNA levels and inhibition of [14C]ladenine incorporation into RNA in buds occurred entirely in the ribosomal and supernatant fractions of the cellular extract. Inhibition of RNA synthesis by asulam (50 ppm) as measured by [14C] orotic acid incorporation into RNA was completely antagonized by CEPA (3-chloroethylphosphonic acid) (50 ppm) and partially by 2,4-D (2,4-dichlorophenoxyacetic acid) (50 ppm) and GA (Gibberellic acid) (50 ppm). These results suggest that the interference of asulam with RNA and protein synthesis at the metabolically active sinks (rhizome buds) could be one of its major mechanisms of action in bracken.  相似文献   

9.
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10.
Time- and concentration-course studies were conducted to determine the effect of thirteen herbicides on photosynthesis, respiration, RNA synthesis, protein synthesis, and lipid synthesis using isolated single leaf cells. Each herbicide was from a different chemical class. Appropriate 14C-substrates and product purification procedures were used for each process prior to liquid scintillation counting. The most sensitive metabolic site of inhibition was photosynthesis for atrazine, bromacil, dichlobenil, monuron, and paraquat; RNA synthesis for dalapon and dinoseb; protein synthesis for chlorpropham; and lipid synthesis for CDAA, chloramben, 2,4-D, EPTC, and trifluralin. However, with several herbicides, one or more process was almost as sensitive as the one mentioned above. All herbicides inhibited more than one process, and the most sensitive site of inhibition may not be the same process that was inhibited the greatest at the maximum concentration and maximum exposure time used. Therefore, a concept of metabolic sites of action, rather than a primary site of action, appears to be more meaningful for herbicides.  相似文献   

11.
The growth of the root systems of 2-day-old wheat seedlings was more sensitive to the experimental herbicide WL 29226 than was the growth of the shoots. Inhibition of root growth was observed after 12 hr of exposure to the herbicide. The nuclear activity in these root systems, as estimated by RNA and DNA synthesis, was significantly inhibited before this time, ～30% after 4 hr increasing to ～55% after 8 hr. Nuclear activity was inhibited by ～80% after 24 hr and showed little increase in inhibition with any further increase in exposure to the herbicide. Protein synthesis was initially less inhibited, ～6% after 4 hr, rapidly increasing to ～40% after 8 hr. DNA polymerase activity was monitored as an indication of the nucleic acid biosynthetic capacity of herbicide-treated maize and barnyard grass chromatin. In both plants, the herbicide induced an inherent modification of this activity. In maize this was reflected by an inhibition of activity and in barnyard grass by a stimulation. The effect on barnyard grass chromatin is likely to be more complex than in maize because of the presence of a chromatin-bound DNase in the chromatin from control plants. There is no evidence for such an enzyme in the chromatin from either maize or glycerol ether-treated barnyard grass. The apparent stimulation of DNA polymerase activity may in some way be associated with the loss of this nuclease activity. In order to obtain an inhibition of chromatin DNA polymerase, the plants must be pretreated with the herbicide prior to chromatin extraction. The failure of the herbicide to induce an inhibition in vitro on isolated chromatin does not support a direct interaction between the herbicide and chromatin. The results suggest that, following herbicide application to the plant, chromatin integrity has been altered.  相似文献   

12.
The effects on DNA synthesis of the fungicide captan and several structurally related compounds were investigated in isolated bovine liver nuclei. Captan, folpet, captafol, and trichloromethanesulfenyl chloride inhibited DNA synthesis to the same degree with ID50 values of approximately 50 μM in a 40-min assay. The inhibition is concentration dependent and the degree of inhibition increases with time. Studies with structural analogs of captan indicated that inhibition of DNA synthesis by captan is mediated through the trichloromethylthio moiety of the captan molecule. In addition, the data indicate thiophosgene is probably not the toxic species involved in the inhibition of DNA synthesis. The isolated nuclei used in this study were shown to exhibit only a single DNA polymerase activity which was determined to be of the β or low-molecular-weight type. In addition to its inhibition in intact nuclei, captan inhibited the activity of the β polymerase in nuclear extracts as well as in partially purified enzyme preparations. These results indicate that captan inhibits DNA synthesis in our preparation of isolated nuclei by acting directly on the DNA polymerase-catalyzed reaction rather than by causing a nonspecific or indirect effect in the nuclear system such as alterations in the nuclear membrane or aggregation of the nuclei. The site of captan's inhibitory action is the DNA polymerase molecule. The interaction of captan with the polymerase results in irreversible inhibition of the enzyme. Interaction of captan with the template, if it occurs, does not appear to be involved in mediating the inhibition.  相似文献   

13.
The sublethal effect of a synthetic pyrethroid, cypermethrin on total protein, amino acids, ammonia, glycogen, and enzymes like aminotransaminases (AIAT, AAT), glutamate dehydrogenase, and glycogen phosphorylases (a and ab) was studied in physiological important tissues viz; liver and gill tissues of freshwater teleost air breathing fish, Clarias batrachus. The study was conducted during exposure of 1/3 (33%) of LC50 concentration and followed by cessation of exposure. Thirty-six fish were exposed to 0.07 mg/L cypermethrin for 10 days. After 10 days, 18 fish were released to freshwater and kept in the same for 10 days (recovery group). Thirty-six fish were kept in freshwater as control batch. Protein content in liver tissues decreased at the end of 1st and 5th day followed by slight increase at the end of 10th day. Gill tissue showed statistical significant decrease (P < 0.001) in protein content during exposure period of 10 days. Recovery in protein content was observed to a large extent in both the tissues. Total free amino acids were increased in liver and gill tissues throughout the treatment period, recovery response was seen after cessation of exposure. Ammonia level was decrease in both the tissues throughout the exposure period except in liver tissue at the end of 1st day of exposure. Recovery response was exhibited by both the tissues. A decreased in glycogen content of liver tissue was observed during exposure period, gill tissue also showed decrease in glycogen at the end of 1st and 5th day followed by increase at the end of 10th day of exposure period. When the fish were transferred to freshwater, recovery in glycogen content was noted. The activity level of alanine, aspartate aminotransaminase, glutamate dehydrogenase, and phosphorylases (a, ab) was increased in both the tissues, followed by recovery response after released of fish into freshwater. The present study showed that cypermethrin caused alterations in certain biochemical mechanisms of C. batrachus. This fish indicated recovery response when transferred to cypermethrin free water.  相似文献   

14.
Alterations in the levels of hemoglobin, total plasma proteins, glucose, and lactic acid in the blood; glycogen and lactic acid content of liver and white skeletal muscle; and the activities of lactate dehydrogenase, pyruvate dehydrogenase, and succinate dehydrogenase in liver, kidney, intestine, brain, gills, and muscles were examined in the fresh-water snake-head fish, Channa punctatus, after exposure to a sublethal concentration (25 μg/liter) of quinalphos for 60 and 120 days. Hemoglobin, plasma protein, glucose, and lactic acid decreased in pesticide-exposed fish. The glycogen content of the liver and muscles increased but lactic acid decreased. Lactate dehydrogenase activity decreased in all six tissues. Pyruvate dehydrogenase activity of liver, kidney, gill, and muscle decreased, but the enzyme activity was elevated in intestine and brain. In intestine, succinate dehydrogenase activity was elevated, and in the remaining five tissues the enzyme activity was significantly reduced. The present study showed that formation of glycogen and its breakdown was impaired in the liver, and aerobic oxidation of nutrients was adversely affected in quinalphos-exposed fish.  相似文献   

15.
Mutant strains of Aspergillus nidulans have been isolated which display a low level of resistance to imazalil, a recently developed systemic fungicide. Agar growth tests showed that A. nidulans is about three times as sensitive to imazalil when growing on supplemented minimal medium (SM) as compared with complete medium. This effect was reduced by adding glutamic acid to the SM.Imazalil resistance was found to be based on a multigenic system; 21 single gene mutations define 8 loci which were allocated to 6 different linkage groups. Mutations at different loci lead pleiotropically to one or more of the following properties: hypersensitivity or resistance to acriflavin, cycloheximide and neomycin, resistance to chloramphenicol and fenarimol, and to cold sensitivity. Of 120 cycloheximide-resistant strains isolated, 98 were also imazalil-resistant.Recombination analysis of different imazalil-resistant strains with mutations at three loci resulted in additive effects, giving strains with a high level of resistance to imazalil.The results indicate that imazalil may interfere either with protein synthesis like cycloheximide, chloramphenicol and neomycin or with synthesis or function of cell membranes. Interference with cell membrane synthesis might lead to altered sterol composition, resulting in selective permeability to different compounds.  相似文献   

16.
Thermal effluents discharged through cooling systems of nuclear power plants often contain chlorine (used to control bio-fouling), which may affect the metabolic status of fishes. In order to evaluate the hypothesis, we tested the effect of high temperature and a persistent sub-lethal chlorine exposure on stress responses in Cyprinus carpio advanced fingerlings. Fishes were acclimated to four different temperatures (26, 31, 33, and 36 °C) and maintained for 30 days in two different groups. Subsequently, one of the groups was exposed to persistent chlorine (0.1 mg L−1) for another 28 days and was compared with their respective temperature controls (without chlorine exposure). Sub-lethal doses of pollutants and increasing temperatures with in the tolerance range may not always register any morphological changes Therefore, we studied organ specific biochemical pathways viz. aspartate amino transferase, alanine amino transferase (enzymes of protein metabolism) in liver and muscle; fructose 1,6 diphosphatase (gluconeogenic pathway), in liver; pyruvate kinase, malate dehydrogenase, and lactate dehydrogenase (glycolytic pathway) in muscle; glucose-6-phosphate dehydrogenase (pentose phosphate pathway) in liver; alkaline phosphatase (phosphorus metabolism) in intestine, liver, and muscle; acetylcholine esterase (neurotransmitting enzyme) in brain, and adenosine triphosphate (for membrane transport) in gills at two different acclimation periods (14 and 28 days). The results indicate that C. carpio fingerlings demonstrated metabolic readjustments with increasing temperatures, in order to cope with energy demand of the cell. However, exposure to chlorine at higher temperatures affected protein metabolism, gluconeogenic pathway and subsequently glycolytic pathway, leading to an energy-limited condition. In addition, alteration of membrane transport and neurotransmission might be an early indication of cellular damage. Overall results indicate that persistent sub-lethal chlorine exposure elicits temperature induced stress response in C. carpio early fingerlings.  相似文献   

17.
Recovery study was performed at regular intervals to establish the time course of 50% and 100% recovery in neurotransmitter enzyme (acetylcholinesterase, AChE, EC 3.1.1.7) and locomotor behaviour response of mosquito fish, Gambusia affinis exposed to lethal concentration (20.49 mg L−1) of an organophosphorous pesticide, monocrotophos (MCP) for 96 h. In vitro AChE activity studies indicated that MCP could cause 50% inhibition (I50) at 10.2 × 10−5 M. A positive correlation was observed between brain AChE activity and swimming speed during the recovery study. Also, the recovery response of the antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6) and glutathione reductase (GR, EC 1.6.4.2) as well as lipid peroxidation (LPO) as biomarkers of oxidative stress were assessed in viscera of G. affinis. The results showed that the MCP besides its inhibitory effect on target enzyme AChE activity and induction in antioxidant enzyme activities as a characteristic of oxidative stress, which can be used as biomarkers in the pesticide contaminated aquatic streams.  相似文献   

18.
Changes in glucose metabolism were studied in hepatopancreas and gill of freshwater mussel, Lamellidens marginalis, exposed to a sublethal concentration (8 ppm) of methyl parathion. A slight decrease in glycogen and pyruvate and an increase in lactate levels were observed. An increase in phosphorylase and aldolase suggested increased formation of trioses during methyl parathion toxicity. The decrease in lactate dehydrogenase activity and increase in lactate content indicated reduced mobilization of pyruvate into the citric acid cycle. Glucose-6-phosphate dehydrogenase activity was increased, suggesting enhanced oxidation of glucose by the HMP shunt pathway. Citric acid cycle enzymes such as isocitrate, succinate, and malate dehydrogenases were found to be decreased, suggesting abnormality in mitochondrial oxidative metabolism as a consequence of methyl parathion toxicity. The decreased cytochrome c oxidase and Mg2+-ATPase, apart from citric acid cycle enzymes, indicated impaired energy synthesis as a result of reduced aerobic oxidation of glycose. The increase in acid and alkaline phosphatase activities suggested enhanced breakdown of phosphate to release energy in view of inhibition of the ATPase system during methyl parathion stress. The changes were more pronounced in hepatopancreas as compared to gill of mussel exposed to methyl parathion.  相似文献   

19.
Heptachlor metabolism was determined in young male rats fed for 10 days diets containing 18% protein supplied either by gluten or casein. Rats on the casein diet were either pair-fed on an individual basis to the gluten-fed animals or they were fed ad lib. Saline, sodium phenobarbital (80 mg/kg) or diethylaminoethyl 2,2-diphenylvalerate HCl (SKF 525-A, 50 mg/kg) was administered ip to the animals before sacrifice. Weight gain, liver microsomal protein, and heptachlor metabolism (nmole of product/g liver/10 min), assayed in 9000g rat liver supernatants, were found to be significantly reduced in the gluten-fed animals. Animals pair-fed the casein diet had higher heptachlor epoxidase activity than those fed ad lib. Phenobarbital pretreatment significantly enhanced the metabolism of heptachlor in animals in all groups to varying magnitudes. Heptachlor epoxidase activity (units/g liver) was increased 11-fold in the gluten-fed animals, 6-fold in the pair-fed animals on casein diet, and 7-fold in the animals fed casein ad lib. Heptachlor metabolism was less inhibited by SKF 525-A in the rats fed gluten compared to the rats on casein diet, either pair-fed or ad lib. The degree of induction or inhibition of enzyme activity was not influenced by restriction of food intake (pair-fed vs ad lib). The results of these studies suggest an interaction of protein inadequacy with drug metabolism and its induction or inhibition.  相似文献   

20.
S-ethyl dipropylthiocarbamate (EPTC) inhibited gibberellic acid (GA) precursor biosynthesis in a cell-free enzyme preparation from unruptured, etiolated sorghum (Sorghum bicolor L. cv. G522 DR) coleoptiles. EPTC, 1 μM, inhibited incorporation of [14C]mevalonic acid into kaurene 60%, while 10 μM EPTC inhibited 14C incorporation into kaurene 90%. The precursor of kaurene cyclization (GGPP) increased in 14C content at both EPTC concentrations. R-25788 reversed the EPTC inhibition of kaurene synthesis. Kaurene oxidation was modified by both EPTC and R-25788. Hypothesized modes of action for EPTC and R-25788 are (a) inhibition of GA synthesis, (b) increased peroxidase activity resulting in increased lignification, (c) increased detoxification by sulfoxidation and carbamoylation, and (d) inhibition of fatty acid synthesis and/or desaturation. These hypotheses are discussed with three of them being incorporated into one working unit which correlates with EPTC and R-25788 symptom phenology. The fourth hypothesis could also fit into this general pattern.  相似文献   

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