Concentration of virus and ultrastructural changes in oats at various stages of barley yellow dwarf virus infection

Enzyme-linked immunosorbent assay was used to monitor the concentration of barley yellow dwarf virus (BYDV) in roots and leaves of oats inoculated at the 1 - 2 leaf stage and at the 4 - 5 leaf stage, respectively. Virus was detectable 20 h after inoculation in the roots and after 48 h in the leaves of plants inoculated at the 1 - 2 leaf stage. The virus concentration reached a plateau in the roots after 7–8 days, and was 3–4 times higher than in the leaves. In plants inoculated at the 4 - 5 leaf stage virus was detectable in roots and leaves after 3 and 5 days, respectively. The concentration reached a maximum after 10 days in the roots and after 18 days in the leaves; the concentration in the leaves was 2–3 times higher than in the roots. Virus was readily detectable in seeds from infected plants, both fresh and old dried seeds. However, seed transmission could not be demonstrated. Virus-like particles were first observed in phloem cells of roots 4 days after inoculation, but no ultrastructural changes were detected at this stage. After 5–6 days, disintegrated nuclei and virus-induced vesicles were observed in many cells and abnormal production of callose was found after 10 days. Necrotic phloem cells were observed from day 13, shortly after the appearance of external symptoms.     

Changes in specific activities of peroxidase, chitinase and phenylalanine ammonia-lyase and phenolic content in cucumber leaves inoculated with Podosphaera fusca, the causal agent of powdery mildew

In this investigation, the effects of powdery mildew disease [caused by Podosphaera fusca (syn. Sphaerotheca fuliginea)] on specific activities of several defense-related enzymes and phenolic content were studied in cucumber leaves. Spore suspension of the fungus was sprayed on cucumber (cv. Super Dominus) plants in greenhouse and leaves from both inoculated and non-inoculated control plants were sampled at 0, 24, 48, 72 and 144 hours after inoculation (HAI). Spore germination and tissue colonization of P. fusca were microscopically studied on the inoculated surface of leaf samples. Further, Phenolic content (PHE) and specific activities of peroxidase (POX), chitinase (CHI) and phenylalanine ammonia-lyase (PAL) were spectrophotometrically measured in leaf extracts. Time-course of disease progress on the leaf surface showed that maximum spore germination occurred within 24 HAI and host penetration and disease development process began during 24-48 HAI. Evaluation of enzyme activities showed that POX specific activity in inoculated plants significantly increased at 72 HAI onwards and reached 2.5 times of that of control at 144 HAI. CHI specific activity showed a transient reduction in inoculated plants between 48-72 HAI and thereafter increased significantly in relation to control. PAL specific activity in inoculated plants was not significantly different from that of control. PHE in inoculated plants showed a significant increase compared to control at 48 HAI and thereafter. Comparison of time-course of disease progress with changes in enzyme activities indicated that POX activity had an increasing trend during disease progress whereas CHI activity showed a transient decrease at the early stages and then increased during the later stages of infection: PAL activity did not show any changes during the infection and PHE increased at the early stages of infection process and remained constant at rest of the time.     

Changes in Ribonuclease and Glucose-6-Phosphate Dehydrogenase Activities Induced by Beet Necrotic Yellow Vein Virus in Sugar Beet

Activities of host ribonucleases and glucose-6-phosphate dehydrogenase were studied in three cultivars (Monosvalof, Steffi and Rimini) of sugar beet differing in their resistance to beet necrotic yellow vein virus (BNYVV). No differences were found in the susceptibility of cultivars to BNYVV between mechanically inoculated and Polymyxa betae (a natural fungal vector of the virus) infected plants, but the culmination of reproduction curves of BNYVV in mechanically inoculated plants was observed one week earlier than in plants inoculated by means of P. betae. The activities of ribonucleases corresponded with virus multiplication. In roots, activities of ribonucleases reached a maximum at day 7; in leaves, maximum activity was found at day 21 in cv. Monosvalof, and at day 14 in cv. Steffi. The relatively resistant cultivar Rimini showed much lower activities. The activity of glucose-6-phosphate dehydrogenase was only slightly increased at the time of culmination of the BNYVV reproduction curve in cvs. Monosvalof and Steffi. This revised version was published online in June 2006 with corrections to the Cover Date.     

黄连木雌、雄株内源植物激素和POD同工酶的比较

为揭示黄连木（Pistacia chinensis Bunge）不同性别植株的生理差异,以雌株和雄株叶片为试材,对叶片赤霉素（GA3）、脱落酸（ABA）、吲哚-3-乙酸（IAA）、亚精胺（Spd）、精胺（Spm）和腐胺（Put）含量变化及过氧化物酶同工酶进行了测定。结果表明,黄连木雌、雄株叶片GA3含量在6至9月均达到极显著差异,含量均在10月8日达到最大值,分别为100.9μg/g FW和92.9μg/g FW;雄株叶片ABA含量均高于雌株,雌、雄株叶片ABA含量在5月21日和7月8日达到极显著差异,5月21日均为最小值,含量分别为222.0 ng/g FW和340.1 ng/g FW;雄株叶片IAA含量均高于雌株,雌、雄植株叶片中IAA含量在8月8日达到极显著差异,9月8日达到最大值,分别为984.8 ng/g FW和1000.6 ng/g FW;雌株GA3/ABA的比值在7月至9月极显著高于雄株,9月8日差异值最大,为42.8;雌、雄株叶片IAA/ABA在5月21日差异值最大,为0.54;雌、雄株叶片Spd含量存在显著或极显著差异,均在7月8日达到最大值,分别为47.9μg/g FW和42.8μg/g FW;雄株叶片Spm含量均大于雌株,雌、雄株叶片Spm含量在10月8日达到极显著差异,均在7月8日出现最大值,分别为24.3μg/g FW和34.5μg/g FW;雄株叶片Put含量在各个时期均低于雌株,雌、雄株叶片Put含量除5月21日外,存在显著或极显著差异,在9月8日均达到最大值,分别为156.0μg/g FW和135.1μg/g FW。雌、雄株叶片、叶柄过氧化物酶同工酶有显著差异,雌株叶片过氧化物酶同工酶有5条带,分别为POD-1、POD-2、POD-3、POD-4、POD-5;雄株叶片只有4条带,分别为POD-2、POD-3、POD-4、POD-5;雌株叶柄内的过氧化物酶同工酶有4条带,分别为POD-1’、POD-3’、POD-4’、POD-5’,雄株叶柄内的过氧化物酶同工酶有3条带,分别为POD-2’、POD-4’、POD-5’。POD-1为雌株叶片特有条带,POD-1’、POD-3’为雌株叶柄特有条带,POD-2’为雄株叶柄特有条带。通过试验得出,黄连木叶片中ABA、IAA、Spd、Spm和Put含量与性别有关,叶片和叶柄的POD同工酶条带也是鉴别黄连木性别的有效指标。     

Role of leaf surface sugars in colonization of plants by bacterial epiphytes

The relationship between nutrients leached onto the leaf surface and the colonization of plants by bacteria was studied by measuring both the abundance of simple sugars and the growth of Pseudomonas fluorescens on individual bean leaves. Data obtained in this study indicate that the population size of epiphytic bacteria on plants under environmentally favorable conditions is limited by the abundance of carbon sources on the leaf surface. Sugars were depleted during the course of bacterial colonization of the leaf surface. However, about 20% of readily utilizable sugar, such as glucose, present initially remained on fully colonized leaves. The amounts of sugars on a population of apparently identical individual bean leaves before and after microbial colonization exhibited a similar right-hand-skewed distribution and varied by about 25-fold from leaf to leaf. Total bacterial population sizes on inoculated leaves under conditions favorable for bacterial growth also varied by about 29-fold and exhibited a right-hand-skewed distribution. The amounts of sugars on leaves of different plant species were directly correlated with the maximum bacterial population sizes that could be attained on those species. The capacity of bacteria to deplete leaf surface sugars varied greatly among plant species. Plants capable of supporting high bacterial population sizes were proportionally more depleted of leaf surface nutrients than plants with low epiphytic populations. Even in species with a high epiphytic bacterial population, a substantial amount of sugar remained after bacterial colonization. It is hypothesized that residual sugars on colonized leaves may not be physically accessible to the bacteria due to limitations in wettability and/or diffusion of nutrients across the leaf surface.     

Bromovirus movement protein conditions for the host specificity of virus movement through the vascular system and affects pathogenicity in cowpea

Previously, we reported that CCMV(B3a), a hybrid of bromovirus Cowpea chlorotic mottle virus (CCMV) with the 3a cell-to-cell movement protein (MP) gene replaced by that of cowpea-nonadapted bromovirus Brome mosaic virus (BMV), can form small infection foci in inoculated cowpea leaves, but that expansion of the foci stops between 1 and 2 days postinoculation. To determine whether the lack of systemic movement of CCMV(B3a) is due to restriction of local spread at specific leaf tissue interfaces, we conducted more detailed analyses of infection in inoculated leaves. Tissue-printing and leaf press-blotting analyses revealed that CCMV(B3a) was confined to the inoculated cowpea leaves and exhibited constrained movement into leaf veins. Immunocytochemical analyses to examine the infected cell types in inoculated leaves indicated that CCMV(B3a) was able to reach the bundle sheath cells through the mesophyll cells and successfully infected the phloem cells of 50% of the examined veins. Thus, these data demonstrate that the lack of long-distance movement of CCMV(B3a) is not due to an inability to reach the vasculature, but results from failure of the virus to move through the vascular system of cowpea plants. Further, a previously identified 3a coding change (A776C), which is required for CCMV(B3a) systemic infection of cowpea plants, suppressed formation of reddish spots, mediated faster spread of infection, and enabled the virus to move into the veins of inoculated cowpea leaves. From these data, and the fact that CCMV(B3a) directs systemic infection in Nicotiana benthamiana, a permissive systemic host for both BMV and CCMV, we conclude that the bromovirus 3a MP engages in multiple activities that contribute substantially to host-specific long-distance movement through the phloem.     

Spatial Distribution of Lectin Activity in Perilesional Areas of Tobacco Leaves Inoculated with Tobacco Mosaic Virus

The activities of lectins and peroxidase and lignin content were studied in the perilesional area of leaves in two tobacco species (Nicotiana tabacumL., cultivar Samsun NN, and N. glutinosa L.) inoculated with tobacco mosaic virus. The development of hypersensitivity response proved to be accompanied by a complex spatial and temporal distribution of lectin activity. The area 5–9 mm away from the lesion center was characterized by the highest activity of loosely bound membrane lectins eluted with 0.05% Triton X-100. In the fraction of tightly bound membrane lectins (eluted with 0.5% detergent), lectin activity decreased during the first two days but increased on day 4 after inoculation. The activity of loosely bound membrane lectins increased in the leaf areas distant from the lesion. Two-phase dynamics in the interlesional area were also observed for lectin activity in the tightly bound membrane fraction (decrease on day 2 days and increase on day 4 after inoculation) and for peroxidase activity (increase on day 2 days and decrease on day 4). The relationship between the dynamics and spatial distribution of lectins in the perilesional area and the possible involvement of these proteins in pathogen-induced changes in photosynthesis are discussed.     

Changes in leaf gas exchange,chlorophyll a fluorescence and antioxidant metabolism within wheat leaves infected by Bipolaris sorokiniana

The photosynthetic performance (leaf gas exchange and chlorophyll a (Chla) fluorescence), activities of antioxidant enzymes [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX)] and the concentrations of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) in the flag leaves of plants from two wheat cultivars with contrasting levels of resistance to spot blotch was assessed. Spot blotch severity was significantly lower in plants from cv. BR‐18 compared to cv. Guamirim. Net carbon assimilation rate, stomatal conductance and concentrations of Chla, Chlab and carotenoids were significantly decreased from fungal infection. In contrast, internal CO₂ concentration was significantly increased from fungal infection in comparison to their non‐inoculated counterparts. Similarly, inoculation significantly reduced photochemical performance in the inoculated flag leaves in comparison to their non‐inoculated counterparts. However, plants from cv. BR‐18 were able to sustain greater functionality of the photosynthetic apparatus during fungal infection process compared to cv. Guamirim. The activities of SOD, POX, APX and CAT increased in inoculated flag leaves from both cultivars compared to non‐inoculated plants, and the highest increases were measured in cv. BR‐18. The greater activities of these enzymes were associated with a reduced H₂O₂ concentration in the inoculated flag leaves from cv. BR‐18, resulting, therefore, in a lower MDA concentration. Thus, a more efficient antioxidative system in flag leaves from cv. BR‐18 plays a pivotal role in removing the excess reactive oxygen species that were generated during the infection process of Bipolaris sorokiniana, therefore limiting cellular damage and largely preserving the photosynthetic efficiency of the infected flag leaves.     

Active Oxygen-producing and -scavenging Enzymes in Pepper Leaves Infected with Xanthomonas campestris pv. vesicatoria

Lipoxygenase (LOX), peroxidase (POX), superoxide dismutase (SOD) and catalase (CAT) activities were determined in pepper (Capsicum annuum) leaves infected with Xanthomonas campestris pv. uesicatoria, from 3 to 15 days after inoculation, before symptom appearance and during the development of the disease. Strong Stimulation of LOX and POX activities was observed in infected leaves at an advanced stage of the disease (12–15 days after inoculation), when bacterial water-soaked spots and a slight chlorosis of the inoculated leaf areas were evident and a decrease in chlorophyll content of infected tissue was detected. The infection also induced a significant increase in CAT activity at the day 9 and a decrease in SOD and CAT activities at the day 12. On the basis of the changes observed, uncontrolled production of active oxygen species at advanced stages of infection is hypothesized.     

Exogenous salicylic acid alleviates effects of long term drought stress and delays leaf rolling by inducing antioxidant system

Salicylic acid (SA) is one of the important signal molecules modulating plant responses to environmental stress. In this study, the effects of exogenous SA on leaf rolling, one of drought avoidance mechanisms, and antioxidant system were investigated in Ctenanthe setosa during long term drought stress. The plants were subjected to 38-day drought period and they were treated with or without SA (10⁻⁶ M) on the 25th, 27th and 29th days of the period. Leaf samples were harvested on the 30th, 34th and 38th days. Some antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase), reactive oxygen species (hydrogen peroxide and superoxide) and lipid peroxidation were determined during the drought period. Treatment with SA prevented water loss and delayed leaf rolling in comparison with control leaves. Exogenous SA induced all antioxidant enzyme activities more than control leaves during the drought. Ascorbate and glutathione, α-tocopherol, carotenoid and endogenous SA level were induced by the SA treatment. Levels of reactive oxygen species were higher in SA treated plants than control ones on the 34th day. Their levels on the 38th day, however, fastly decreased in SA treated plants. SA treatment prevented lipid peroxidation while the peroxidation increased in control plants. The results showed that exogenous SA can alleviate the damaging effect of long term drought stress by decreasing water loss and inducing the antioxidant system in the plant having leaf rolling, alternative protection mechanism to drought.     

Arbuscular mycorrhiza‐mediated resistance in tomato against Cladosporium fulvum‐induced mould disease

Root colonization with arbuscular mycorrhizal fungi (AMF) enhances plant resistance particularly against soil‐borne pathogenic fungi. In this study, mycorrhizal inoculation with Glomus mosseae (Gm) significantly alleviated tomato mould disease caused by the air‐borne fungal pathogen, Cladosporium fulvum (Cf). The disease index (DI) in local leaves (receiving pathogen inoculation) and systemic leaves (just above the local leaf without pathogen inoculation) was 36.4% and 11.7% in mycorrhizal plants, respectively, whereas DI was 59.6% and 36.4% in the corresponding leaves of AMF non‐inoculated plants, after 50 days of Gm inoculation, corresponding to 15 days after Cf inoculation by leaf infiltration. Foliar spray inoculation with Cf also revealed that AMF pre‐inoculated plants had a higher resistance against subsequent pathogen infection, where the DI was 41.3% in mycorrhizal plants vs. 64.4% in AMF non‐inoculated plants. AMF‐inoculated plants showed significantly higher fresh and dry weight than non‐inoculated plants under both control (without pathogen) and pathogen treatments. AMF‐inoculated plants exhibited significant increases in activities of superoxide dismutase and peroxidase, along with decreases in levels of H₂O₂ and malondialdehyde, compared with non‐inoculated plants after pathogen inoculation. AMF inoculation led to increases in total chlorophyll contents and net photosynthesis rate as compared with non‐inoculated plants under control and pathogen infection. Pathogen infection on AMF non‐inoculated plants led to decreases in chlorophyll fluorescence parameters. However, pathogen infection did not affect these parameters in mycorrhizal plants. Taken together, these results indicate that AMF colonization may play an important role in plant resistance against air‐borne pathogen infection by maintaining redox poise and photosynthetic activity.     

土壤pH值对烤烟叶片生理生化特性的影响

烟草生长初期,超氧化物歧化酶(SOD)活性及丙二醛(MDA)含量与pH增长呈正相关,而过氧化氢酶(CAT)和过氧化物酶(POD)活性则随着pH的增加而下降,pH值6.5和7.5时叶绿素含量和净光合速率(Pn)较高,旺长期达到高峰;生长后期,各处理的MDA含量和POD活性最高,SOD、CAT活性最低.各pH值处理的叶片中,叶绿素含量、Pn下降,比叶重达到高峰,但pH 8.5下的烟叶中叶绿素含量高,Pn大,比叶重较小.pH 6.5和7.5下的烟叶中蛋白质和可溶性糖总体含量高于其它pH的.烟碱含量在pH 5.5时最高,pH 8.5时最低.     

Detection of maize streak virus antigens over time in different parts of maize plants of a sensitive and a so-called tolerant cultivar by ELISA

Maize streak virus (MSV) capsid antigens were detected over time in different parts of maize plants of a sensitive (INRA508) and a so-called tolerant (“tolerant”) cultivar (IRAT297) using a direct or an indirect double antibody sandwich ELISA. Based on three types of experiments, it was shown that the antigens were distributed in the plant according to the age of the tissues. When the virus was inoculated on a particular leaf of 18-day old plants with infective Cicadulina mbila, only the young leaves above the inoculated one were positive by ELISA but not the older ones below. The antigens could not be detected in the inoculated leaf. At day 3 after inoculation, the antigens were detected in the sheath and/or in the whorl of the third leaf above the inoculated one but not in the oldest part of the leaf, the unfolded lamina. Plants of the sensitive cultivar were inoculated at 9 days with C. mbila deposited in the whorl. At 23 h after inoculation, the antigens were detected in the sheath but not in the whorl which was found to be positive only at 32 h. On the basis of these results, a hypothesis of the mode of virus infection is proposed. Our results contribute to a better understanding of the relationship between the age of the plant at inoculation and yield loss as well as secondary infection. By transmission tests with C. mbila, it was shown that virus could only be acquired from leaves exhibiting symptoms. Virus concentrations were measured in plant samples by ELISA using a range of dilutions of purified virus. The virus concentrations were higher in the sensitive than in the “tolerant” cultivar, but no difference in antigen distribution was observed between the two cultivars. The “tolerant” cultivar appeared to be resistant to virus multiplication.     

Development of cytosol and chloroplast aldolases during germination of spinach seeds

The total activity of aldolase (EC 4.1.2.13) and the activities of cytosol and chloroplast aldolase were determined in seeds, cotyledons, primary leaves and secondary leaves of spinach (Spinacia oleracea L., cv. Monopa) during germination. Total aldolase activity in cotyledons increased from low levels to a low maximum in the dark after one week and to a high maximum in white light after three to four weeks and declined thereafter. The activity in primary and secondary leaves started to rise strongly from the 18th and 26th days, respectively, up to the 42nd day of germination. The levels of aldolase activity paralleled the development of leaf area, chlorophyll content and protein content per leaf except that the leaf area of cotyledons continued to increase steadily up to the 42nd day after the maximum of aldolase activity was reached. Resolution of cytosol- and chloroplast-specific isoenzymes by chromatography on diethylaminoethylcellulose indicated that in the light the cytosol enzyme represented approx. 8% of the total activity in cotyledons, primary and secondary leaves throughout germination, and the chloroplast enzyme represented the remaining 92%. Only in cotyledons of dark-grown seedlings was the cytosol aldolase between 25 and 50% of the total activity. Seeds contained almost exclusively a cytosol aldolase. In cotyledons the increase of total activity in the light was specifically the consequence of an increase in chloroplast aldolase while the cytosol aldolase was little affected by light. The light effect was mediated by phytochrome as demonstrated by classical induction and reversion experiments with red and far-red light and by continuous far-red light treatment.Abbreviation DEAE-cellulose diethylaminoethylcellulose     

Role of Leaf Surface Sugars in Colonization of Plants by Bacterial Epiphytes

The relationship between nutrients leached onto the leaf surface and the colonization of plants by bacteria was studied by measuring both the abundance of simple sugars and the growth of Pseudomonas fluorescens on individual bean leaves. Data obtained in this study indicate that the population size of epiphytic bacteria on plants under environmentally favorable conditions is limited by the abundance of carbon sources on the leaf surface. Sugars were depleted during the course of bacterial colonization of the leaf surface. However, about 20% of readily utilizable sugar, such as glucose, present initially remained on fully colonized leaves. The amounts of sugars on a population of apparently identical individual bean leaves before and after microbial colonization exhibited a similar right-hand-skewed distribution and varied by about 25-fold from leaf to leaf. Total bacterial population sizes on inoculated leaves under conditions favorable for bacterial growth also varied by about 29-fold and exhibited a right-hand-skewed distribution. The amounts of sugars on leaves of different plant species were directly correlated with the maximum bacterial population sizes that could be attained on those species. The capacity of bacteria to deplete leaf surface sugars varied greatly among plant species. Plants capable of supporting high bacterial population sizes were proportionally more depleted of leaf surface nutrients than plants with low epiphytic populations. Even in species with a high epiphytic bacterial population, a substantial amount of sugar remained after bacterial colonization. It is hypothesized that residual sugars on colonized leaves may not be physically accessible to the bacteria due to limitations in wettability and/or diffusion of nutrients across the leaf surface.     

Induction of porphobilinogen oxygenase and porphobilinogen deaminase in rat blood under conditions of erythropoietic stress

Porphobilinogen is the substrate of two enzymes: porphobilinogen deaminase and porphobilinogen-oxygenase. The first one transforms it into the metabolic precursors of heme and the second diverts it from this metabolic pathway by oxidizing porphobilinogen to 5-oxopyrrolinones. Rat blood is devoid of porphobilinogen-oxygenase under normal conditions while it carries porphobilinogen-deaminase activity. When the rats were submitted to hypoxia (p_O2 = 0.42 atm) for 18 days, the activity of porphobilinogen-oxygenase appeared at the tenth day of hypoxia and reached the maximum at the 14–16th day. It decreased to a half after 2 days (half-life of the enzyme) and disappeared after 4 days of return to normal oxygen pressure. Porphobilinogen-deaminase activity increased after the first day of hypoxia, reached a maximum at the 14–16th day and did not decrease to normal values until the 15th day after return to normal oxygen pressure. The activities of both prophobilinogen-oxygenase and porphobilinogen-deaminase were induced by administration of erythropoietin. When rats were made anaemic with phenylhydrazine, porphobilinogen-oxygenase activity also appeared in the blood cells. Although the reticulocyte concentration was higher when compared to that obtained under hypoxia, the activities of the oxygenase obtained under both conditions were comparable. Porphobilinogen-deaminase activity was always closely related to the reticulocyte content. The appearance of porphobilinogen-oxygenase under the described erythropoietic conditions was due to a de novo induction of the enzyme, as shown by its inhibition with actinomycin D and cycloheximide. Porphobilinogen-oxygenase as well as porphobilinogen-deaminase were present in the rat bone marrow under normal conditions. Their activities increased in phenylhydrazine treated rats. The properties and kinetics of porphobilinogen-oxygenase from the rat blood and bone marrow were determined and found to differ in several aspects.     

Endophytic Pseudomonas fluorescens Endo2 and Endo35 induce resistance in black gram (Vigna mungo L. Hepper) to the pathogen Macrophomina phaseolina

Abstract

The effect of endophytic Pseudomonas fluorescens isolates Endo2 and Endo35 on induced systemic disease protection against dry root rot of black gram (Vigna mungo L. Hepper) caused by Macrophomina phaseolina was investigated under glasshouse conditions. When the bacterized black gram plants were inoculated with dry root rot pathogen, the activities of peroxidase (PO), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL) were stimulated in addition to accumulation of phenolics and lignin. Activity of phenylalanine ammonia-lyase (PAL) reached the maximum 24 h after pathogen challenge inoculation, whereas the activities of PO and PPO reached the maximum at 72 h and 48 h, respectively. Isoform analysis revealed that a unique PPO3 isozyme was induced in bacterized black gram tissues inoculated with the pathogen. Phenolics were found to accumulate in bacterized black gram tissues challenged with M. phaseolina one day after pathogen challenge. The accumulation of phenolics reached maximum at the third day after pathogen inoculation. Similar observation was found in the lignin content of black gram plants. In untreated control plants, the accumulation of defence enzymes and chemicals started at the first day and drastically decreased 3 days after pathogen inoculation. These results suggest that induction of defense enzymes involved in phenylpropanoid pathway and accumulation of phenolics and PR-proteins might have contributed to restricting invasion of Macrophomina phaseolina in black gram roots.     

Effects of temperature and gibberellin on the activity of endogenous cytokinin-like substances in leaves of Begonia x cheimantha

Changes in activity of endogenous cytokinin-like substances were examined in intact plants and excised leaves of Begonia x chemantha Everett cv. Prinsesse Astrid (Christimas Begonia) by means of the tobacco callus bioassay. Cytokinin activity in the leaves of intact plants was higher in plants grown at 18°C than in those grown at 21° or 24°C. In excised leaves, an increase in cytokinin activity was observed during the first 4 days following leaf detachment. However, after the seventh day cylokinin activity decreased again. This decrease was more profound in leaves exposed to 24°C than in those exposed to 18°C.
Treatment of detached leaves with gibberellic acid (2.8 m M ) caused an increase in measurable cytokinin activity. This increase was more profound in the zones of activity which correspond with zeatin glucosides on paper and Sephadex LH-20 chromatography. Additional zones of activity appeared after Sephadex chromatography. These were of a more slow moving nature with elution volumes corresponding to N^b-(Δ²-isopentenyl)adenine and its derivaties. Water-treated control leaves had higher activity in the regions corresponding to zeatin and zeatin riboside.     

THE EFFECT OF INFECTION WITH TOBACCO MOSAIC VIRUS ON THE RESPIRATION OF TOBACCO LEAVES OF VARYING AGES IN THE PERIOD BETWEEN INOCULATION AND SYSTEMIC INFECTION

Leaves of tobacco plants inoculated with tobacco mosaic virus were divided into three groups: ( a ) inoculated leaves; ( b ) younger non-inoculated leaves present at the time of inoculation; ( c ) leaves formed since inoculation. The respiration rate of each group was compared with that of similar leaves from healthy plants. The respiration rate of inoculated leaves was increased by a constant amount for 3 weeks after inoculation, when it decreased. The respiration rate of group ( b ) leaves was not affected at any time, and that of group ( c ) leaves was decreased by 10% when they showed symptoms. The increased respiration in the inoculated leaves occurred too soon to reflect virus formation, and it is suggested that it reflects an initial change in infected cells preparatory to virus synthesis. The subsequent decrease in respiration may be due to the accumulation of virus which does not contribute to the total leaf respiration.     

CMV抑制PVYN CP基因沉默及其介导的抗病性

以前曾报道用RNA介导的抗病毒策略,获得了高度抗病的表达马铃薯Y病毒坏死株系外壳蛋白基因(PVY^N CP)的转基因烟草,并对T1、T2代转基因植株进行了遗传和抗病性分析。此次以T,代转基因植株为试验材料,在筛选高度抗病植株并证明其抗病性是基于转基因沉默的基础上,采用Northern杂交的方法,证明CMV侵染抑制了转基因植株中PVY^N CP基因的沉默,而且CMV对PVY^N CP基因沉默的抑制部位是发生在接种后的新生叶上,接种叶及其下部叶片中PVY^N CP基因沉默则未受到影响。采用ELISA方法对CMV PVY^N复合接种的转基因植株进行PVY^N检测,结果表明,接种叶及下部叶没有检测到PVY^N,植株叶片对PVY^N表现为抗病。而在CMV接种后植株新生叶中则检测出了高滴度的PVY^N,植株叶片对PVY^N表现为感病。该文报道了在表达PVY^N CP基因的RNA介导抗性转基因植株中,异源病毒侵染抑制了转基因的沉默,并导致转基因植株的抗病性丧失。