Effects of different factors on the production of cellulase byCurvularia lunata

A purified culture of the fungal pathogenCurvularia lunata causing leaf blight of pearl millet was used for studies on the production of cell-wall-degrading enzymes. Czapek-Dox medium was found to be the best medium of the five different nutrient media used for the production of cellulase and growth of the fungus. Pectolytic enzymes could not be detected under different cultural conditions. Two-week incubation period, pH 6.0 and temperature 25°C were found to be the most favorable conditions for good growth and maximum production of cellulase by the fungus in present studies. The results are presented and discussed in the light of the earlier findings onC. lunata.     

Interactions of Neotyphodium gansuense, Achnatherum inebrians, and plant-pathogenic fungi

Interactions of Neotyphodium gansuense, Achnatherum inebrians, and nine fungal pathogens were studied by tests of inhibition of four fungal pathogens by Neotyphodium endophytes in vitro and by inoculation of nine fungal pathogens on detached leaves of endophyte-infected (E+) and endophyte-free (E−) plants. Compared with the controls, most isolates of N. gansuense significantly inhibited the growth in vitro of, in decreasing order of inhibition, Bipolaris sorokiniana, Curvularia lunata, Fusarium acuminatum, and Alternaria alternata. Inhibition zones appeared between pathogens and some isolates of N. gansuense. Some isolates of N. gansuense significantly inhibited sporulation of B. sorokiniana, A. alternata, and C. lunata. However, there was no significant inhibition of F. acuminatum and a few isolates significantly increased sporulation. The leaf inoculation trial indicated that almost all fungal pathogens were able to cause lesions on detached leaves regardless of endophyte status. Both the number and size of disease lesions on E+ A. inebrians leaves caused by A. alternata, F. chlamydosporum, F. oxysporum, and F. solani were reduced compared with those on E− leaves. Only lesion numbers (not size) of Ascochyta leptospora leaf spots were significantly reduced on E+ leaves compared with E− leaves. Conversely, only the length of Ascochyta leptospora leaf spots were significantly smaller on E+ leaves than on E− leaves; numbers of lesions were not significantly affected. C. lunata was strongly pathogenic to both E+ and E− leaves and numerous lesions developed and merged into patches, the leaf surface was covered and the leaf rotted away.     

Understanding resistant germplasm‐induced virulence variation through analysis of proteomics and suppression subtractive hybridization in a maize pathogen Curvularia lunata

Curvularia lunata is an important pathogen causing Curvularia leaf spot in maize. Significant pathogenic variation has been found in C. lunata. To better understand the mechanism of this phenomenon, we consecutively put the selective pressures of resistant maize population on C. lunata strain WS18 (low virulence) artificially. As a result, the virulence of this strain was significantly enhanced. Using 2DE, 12 up‐regulated and four down‐regulated proteins were identified in virulence‐increased strain compared to WS18. Our analysis revealed that melanin synthesis‐related proteins (Brn1, Brn2, and scytalone dehydratase) and stress tolerance‐related proteins (HSP 70) directly involved in the potential virulence growth as crucial markers or factors in C. lunata. To validate 2DE results and screen differential genes at mRNA level, we constructed a subtracted cDNA library (tester: virulence‐increased strain; driver: WS18). A total of 188 unigenes were obtained this way, of which 14 were indicators for the evolution of pathogen virulence. Brn1 and hsp genes exhibited similar expression patterns corresponding to proteins detected by 2DE. Overall, our results indicated that differential proteins or genes, being involved with melanin synthesis or tolerance response to stress, could be considered as hallmarks of virulence increase in C. lunata.     

Studies on the biology of Botrytis species on overwintered salad onions

In the years 1973/4–1974/5, Botrytis cinerea was responsible for losses of 26% and 37% respectively in overwintered salad (green) onion crops grown at Wellesbourne. The fungus invaded the tips of cotyledonary and young true leaves and then grew downwards and inwards through the leaf axils to colonise the internal tissues and produce a collar rot which caused plants to collapse and die. More direct infection of the junction between an older and younger leaf produced a similar effect. Symptoms were rarely noticeable (except occasionally in the later stages of the disease) and affected plants disappeared unobtrusively. The incidence of collar rot increased as the rate of leaf production fell with the drop in temperatures in winter months but decreased as leaf growth resumed with increases in temperature in the spring. The fungus grew and sporulated well at low temperatures (5°C) and more inoculated seedlings developed collar rot when maintained at simulated winter temperatures (7°C) than when kept at simulated spring temperatures (15°C). B. squamosa occurred spasmodically producing white leaf lesions but caused no loss of plants. B. allii although present at a low incidence did not increase in the crops but in common with B. cinerea caused some damage to the bases of plants at harvest.     

Leaf age effects on solute accumulation in water-stressed grapevines

The effects of leaf age on water relations, organic solute, and total ion accumulation were studied in mature and immature leaves of two-year-old grapevines (Vitis vinifera L., cv. Savatiano) grown under water stress conditions. Osmotic potential at full turgor decreased significantly in leaves of stressed plants, irrespective of leaf age, indicating the occurrence of an active osmotic adjustment. The apoplastic water fraction (A) increased during leaf ontogeny in both control and stressed plants. However, the values of A were lower in stressed plants. Starch concentration decreased significantly in both mature and immature leaves during the drought cycle, while the relative proportion of monosaccharides and sucrose was markedly different in immature leaves compared to mature. The accumulation of total inorganic ions, induced by drought, was also age dependent, increasing significantly with leaf age, while there were no significant differences in total amino acids content. Inorganic ions and carbohydrates seem to be the major component of osmotic adjustment in mature and immature grapevine leaves, respectively.     

Juvenile Rhus glabra leaves have higher temperatures and lower gas exchange rates than mature leaves when compared in the field during periods of high irradiance

We sought to test the hypothesis that stomatal development determines the timing of gas exchange competency, which then influences leaf temperature through transpirationally driven leaf cooling. To test this idea, daily patterns of gas exchange and leaflet temperature were obtained from leaves of two distinctively different developmental stages of smooth sumac (Rhus glabra) grown in its native habitat. Juvenile and mature leaves were also sampled for ultrastructural studies of stomatal development. When plants were sampled in May-June, the hypothesis was supported: juvenile leaflets were (for part of the day) from 1.4 to 6.0 degrees C warmer than mature leaflets and as much as 2.0 degrees C above ambient air temperature with lower stomatal conductance and photosynthetic rates than mature leaflets. When measurements were taken from July to October, no significant differences were observed, although mature leaflet gas exchange rates declined to the levels of the juvenile leaves. The gas exchange data were supported by the observations that juvenile leaves had approximately half the number of functional stomata on a leaf surface area basis as did mature leaves. It was concluded that leaf temperature and stage of leaf development in sumac are strongly linked with the higher surface temperatures observed in juvenile leaflets in the early spring possibly being involved in promoting photosynthesis and leaf expansion when air temperatures are cooler.     

Plant transpiration at high elevations: Theory,field measurements,and comparisons with desert plants

Summary The influence of elevational changes on plant transpiration was evaluated using leaf energy balance equations and well-known elevational changes in the physical parameters that influence water vapor diffusion. Simulated transpirational fluxes for large leaves with low and high stomatal resistances to water vapor diffusion were compared to small leaves with identical stomatal resistances at elevations ranging from sea level to 4 km. The specific influence of various air temperature lapse rates was also tested. Validation of the simulated results was accomplished by comparing actual field measurements taken at a low elevation (300 m) desert site with similar measurements for a high elevation (2,560 m) mountain research site. Close agreement was observed between predicted and measured values of transpiration for the environmental and leaf parameters tested.Substantial increases in solar irradiation and the diffusion coefficient for water vapor in air (D _wv) occurred with increasing elevation, while air and leaf temperatures, the water vapor concentration difference between the leaf and air, longwave irradiation, and the thermal conductivity coefficient for heat in air decreased with increasing elevation. These changes resulted in temperatures for sunlit leaves that were further above air temperature at higher elevations, especially for large leaves. For large leaves with low stomatal resistances, transpirational fluxes for low-elevation desert plants were close to those predicted for high-elevation plants even though the sunlit leaf temperatures of these mountain plants were over 10°C cooler. Simulating conditions with a low air temperature lapse rate (0.003° C m^-1 and 0.004° C m^-1) resulted in predicted transpirational fluxes that were greater than those calculated for the desert site. Transpiration for smaller leaves decreased with elevation for all lapse rates tested (0.003° C m^-1 to 0.010° C m^-1). However, transpirational fluxes at higher elevations were considerably greater than expected for all leaves, especially larger leaves, due to the strong influence of increased solar heating and a greater D _wv. These results are discussed in terms of similarities in leaf structure and plant habit observed among low-elevation desert plants and high-elevation alpine and subalpine plants.     

A role for young leaves in vernalization of cauliflower: I. Analysis of leaf development during curd induction

Growth analysis techniques are used to test the hypothesis that chilling induces curd (flower) initiation in the cauliflower ( Brassica oleracea Botrytis L. cv. Perfection) through inhibiting leaf growth, thereby increasing the availability of growth factors to the stem apex and enabling differentiation of the curd. Effects of chilling on leaf growth and curd induction are compared in juvenile and mature, vegetative plants. Chilling at 5°C reduced dry matter accumulation in the total leaf complement by ca 60% in juvenile plants and 40% in mature plants, compared to control plants growth at 20°C. Juvenile plants showed slower rates of leaf initiation than mature plants. Leaf initiation was retarded by chilling in both plant types with the most marked effect seen in the juvenile plants. This was consistent with dry matter availability to the stem apex limiting differentiation more severely in juvenile plants than in mature plants. The rate of dry matter accumulation in existing leaves, however, was faster in juvenile plants than in mature plants at 20°C. Plants that were juvenile during chilling produced an average of 43 leaves below the curd whereas those that were mature produced 25.
Dry matter accumulation in younger leaves was more markedly inhibited by chilling than in older leaves. Chilling also reduced the rate at which enlarging leaves became positionally more remote from the stem apex. Possible roles for such leaves in regulating apical development are considered.     

Photosynthesis in Drought-Adapted Cassava

After 45 d of limited water supply, cassava (Manihot esculenta Crantz) exhibited pronounced reduction in shoot growth, high leaf fall, and decreased stomatal conductance. However, the water status of the remaining leaves was unaffected. This was combined with an amplified heliotropic response and drooping which minimises radiant energy interception at mid-day, suggesting that leaves are sensitive to high irradiance (I). In well-irrigated plants, CO₂-saturated oxygen evolution and net photosynthetic rate (P _N) in air were markedly higher (5-fold) in young (expanding) leaves than in mature leaves. Water limitation did not strongly modify CO₂-saturated oxygen evolution but it altered P _N in air for both types of leaves, although differently. The mature leaves of drought-adapted plants displayed residual rate of P _N and deteriorated photosystem 2 (PS2) photochemistry estimated from chlorophyll (Chl) a fluorescence measurements. In young leaves at moderate I, P _N was depressed by only 66 % in stressed plants. Moreover, the photochemical quenching of Chl a fluorescence and the quantum efficiency of PS2 photochemistry in young leaves were comparable in both control and stressed plants. In contrast at high I, P _N was almost null and marked decreases in the two fluorescence parameters were apparent. Hence the strong heliotropic response and drooping displayed by young leaves under water limitation is an important strategy for avoiding inactivation of P _N by high I and therefore for cassava tolerance to drought.     

Spectral Properties of Juvenile and Adult Leaves of Piper betle and Their Ecological Significance

Juvenile and adult leaves of Piper betle L. were shown to have different spectral properties. A computer model was used to calculate the temperature of these leaves taking the energy balance approach. At high values of solar radiation, juvenile leaves with lower absorptivity in the visible and the near infrared show markedly lower temperatures than mature leaves. There is an ecological effect of high and low leaf temperatures on heat load and water stress.     

Aggressiveness analysis of foliar fungi to leaves of wheat and rice crops

Abstract

The investigations were based on two surveys of wheat and one survey of rice. Alternaria alternata, Curvularia lunata, Helminthosporium tetramera and Bipolaris sorokiniana were isolated and identified from foliage and soil of both wheat and rice crops and their aggressiveness was studied by aggressiveness analysis screened out into different aggressiveness classes. The aggressiveness of isolated fungi was studied on wheat varieties (Inqalab-91 and Chakwal-86) and rice varieties (Basmati-385 and IRRI-6) under controlled conditions. In the foliar aggressiveness test of A. alternata, the overall number of aggressive isolates was higher on wheat varieties than rice. Bipolaris sorokiniana isolates showed foliar blight symptoms on wheat but not on rice varieties. In C. lunata, the overall number of aggressive isolates was higher on wheat. In the foliar aggressiveness test of H. tetramera, the number of non-aggressive isolates was almost the same on wheat and rice varieties. In the present study it became clear that A. alternate, B. sorokiniana, C. lunata and H. tetramera are common foliar pathogens in rice and wheat crops and can cause soil-borne and foliar diseases.     

Curvularia lunata in experimental phaeohyphomycosis

Curvularia lunata strain SP, isolated from a disseminated human infection, infected normal mice, but three other strains of C. lunata and one each of C. pallescens and C. spicifera did not. The SP strain was recovered in cultures from, and hyphal filaments were observed in, abscesses in the liver and spleen of experimentally infected mice. All strains of Curvularia infected mice treated with 400 rads X-irradiation and 10.0 mg cortisone, but at 400 rads and 5.0 mg only two strains of C. lunata (SP and Ghosh) and C. pallescens and C. spicifera infected mice. At 200 rads and 10.0 mg, C. lunata Sp, C. pallescens and C. spicifera; and at 200 rads and 5.0 mg, only C. lunata SP and C. pallescens caused infection. After X-irradiation (200 or 400 rads) or cortisone (5.0 or 10.0 mg) alone only C. lunata SP caused infections in mice.     

The influence of water stress preconditioning on dark respiration

The respiration rate of individual leaves of cotton (Gossypium hirsutum L. cv. Stoneville 213), beans (Phaseolus vulgaris L. cv. Bush Blue Lake), and sorghum (Sorghum vulgare Pers.) which had been fully expanded prior to a series of severe water stresses was compared with those of unstressed leaves of similar age. Measurements were made over a range of leaf temperatures. The respiration rate per unit area of the leaves of all rewatered plants were significantly lower than those of the plants which had not undergone water stress. During the stress periods, the leaves of all species suffered dry matter loss. The respiration rates per unit dry matter for cotton and beans were the same for the plants which had undergone stress as they were for the plants which had not undergone stress, thus for these two C3 plants the decrease in dark respiration due to water stress may be explained entirely by the loss of dry matter. Respiration rates of the water stressed sorghum leaves expressed on a per unit weight basis were significantly lower than those which had not undergone water stress preconditioning. The lower respiration rates of the stressed leaves when expressed on both a per unit area basis and a per unit weight basis for the C4 species indicate that water stress adaptation of C4 plants may include alterations in the respiratory mechanism or on the amount of residual respirable substrate. The light compensation points of all the species were not altered by the water stress preconditioning. This indicates that the mechanisms controlling the net photosynthetic exchange per unit leaf area underwent adaptations as a result of repeated water stress which decreased its efficiency.     

Antifungal metabolites (monorden, monocillins I, II, III) from Colletotrichum graminicola, a systemic vascular pathogen of maize

Colletotrichum graminicola is a systemic vascular pathogen that causes anthracnose stalk rot and leaf blight of maize. In the course of an effort to explore the potential presence and roles of C. graminicola metabolites in maize, ethyl acetate extracts of solid substrate fermentations of several C. graminicola isolates from Michigan and Illinois were found to be active against Aspergillus flavus and Fusarium verticillioides, both mycotoxin-producing seed-infecting fungal pathogens. Chemical investigations of the extract of one such isolate (NRRL 47511) led to the isolation of known metabolites monorden (also known as radicicol) and monocillins I–III as major components. Monorden and monocillin I displayed in vitro activity against the stalk- and ear-rot pathogen Stenocarpella maydis while only the most abundant metabolite (monorden) showed activity against foliar pathogens Alternaria alternata, Bipolaris zeicola, and Curvularia lunata. Using LC–HRESITOFMS, monorden was detected in steam-sterilized maize stalks and stalk residues inoculated with C. graminicola but not in the necrotic stalk tissues of wound-inoculated plants grown in an environmental chamber. Monorden and monocillin I can bind and inhibit plant Hsp90, a chaperone of R-proteins. It is hypothesized that monorden and monocillins could support the C. graminicola disease cycle by disrupting maize plant defenses and by excluding other fungi from necrotic tissues and crop residues. This is the first report of natural products from C. graminicola, as well as the production of monorden and monocillins by a pathogen of cereals.     

Physiological role of anthocyanin accumulation in common hazel juvenile leaves

Common hazel (Corylus avellana L., Fusca rubra Dipp.) juvenile leaves from the periphery of the canopy and thus subjected to high fluxes of solar radiation are characterized by red coloration due to anthocyanin accumulation disappearing in mature leaves. To elucidate the physiological role of anthocyanin accumulation, the interrelations between anthocyanin content, a degree of attenuation by the pigments of the light reaching the photosynthetic apparatus (PSA), and PSA tolerance to photoinhibition in C. avellana juvenile leaves were studied. Absorption spectra were calculated taking into account the light losses due to reflection by the leaf. The analysis of the spectra showed that, in red common hazel leaves accumulating high amounts of anthocyanins in the vacuoles of the upper and lower epidermal cells, up to 95% of visible radiation entering the leaf blade was absorbed by these pigments. The rate of the linear electron transport (ETR) in the chloroplast electron transport chain (ETC) was closely correlated with the anthocyanin content (r ² = 0.87). In red leaves, the saturation of ETR dependence on irradiance was observed at the higher values of PAR than in green leaves. In red juvenile leaves, this value was close to that in mature green leaves tolerant to high light. There were no differences between red and green leaves in the level of non-photochemical quenching, the content of violaxanthin cycle pigments, a degree of their de-epoxidation under natural illumination and at irradiation with high PAR fluxes. Basing on the data obtained, one may conclude that anthocyanins in C. avellana juvenile leaves serve PSA photoprotection, preventing injury of immature PSA with excessive fluxes of PAR.     

Photosynthetic responses and proline content of mature and young leaves of sunflower plants under water deficit

In mature and young leaves of sunflower (Helianthus annuus L. cv. Catissol-01) plants grown in the greenhouse, photosynthetic rate, stomatal conductance, and transpiration rate declined during water stress independently of leaf age and recovered after 24-h rehydration. The intercellular CO₂ concentration, chlorophyll (Chl) content, and photochemical activity were not affected by water stress. However, non-photochemical quenching increased in mature stressed leaves. Rehydration recovered the levels of non-photochemical quenching and increased the F_v/F_m in young leaves. Drought did not alter the total Chl content. However, the accumulation of proline under drought was dependent on leaf age: higher content of proline was found in young leaves. After 24 h of rehydration the content of proline returned to the same contents as in control plants.     

Microbial transformation of rifamycin B: A new extracellular oxidase fromCurvularia lunata

Summary A highly active extracellular rifamycin oxidase was isolated fromCurvularia lunata var.aeri. The enzyme has a pH optimum of 6.5 and temperature optimum of 50°C.     

Variation in potato microplant morphology in vitro and DNA methylation

Heterotrophic and autotrophic culture in agar and in polyurethane foam, the latter used as an alternative tissue support to agar, resulted in potato microplants with different in vitro morphologies. The microplants were visually characterised in terms of their relative developmental maturity, by comparing the respective leaf shapes in vitro with ontogenetic differences in leaf shape in glasshouse-grown potato plants. Cytosine methylation in the DNA of microplants of the different morphologies was determined using a method based on the AFLP technique but employing methylation-sensitive restriction enzymes (MSAP analysis) to test the hypothesis that DNA methylation could be used to characterise differences in microplant development in vitro. In three of the four treatments there was a good correlation between the visual assessment of relative morphological maturity and DNA base methylation levels. In these microplants there was increased DNA methylation in the leaves with mature leaf morphology represented by a decreased number of restriction fragments. The fourth in vitro morphology had the most juvenile leaf shape but did not have the predicted level of DNA methylation, having a relatively low number of restriction fragments. Subtraction analysis was used to discriminate the fragments that were unique to the juvenile and mature in vivo leaf morphologies. Comparison of the fragment patterns from the microplants with the latter reference profiles, confirmed the relationship with the total DNA methylation as detected by MSAP analysis, that is, the number of common fragments with the juvenile or mature in vivo leaf profiles, respectively. However, none of the fragment profiles, while sharing some common bands at random, was identical to any other; or to that of either the juvenile or mature in vivo leaf. The anomalous relationship of the microplants with most juvenile leaf shape and highest DNA methylation was confirmed. The measurement of DNA methylation in in vitro plants is discussed in the context of the development of a method to assess the quality of microplants produced by different in vitro protocols.     

Enhancement of emulsifier production by <Emphasis Type="Italic">Curvularia lunata</Emphasis> in cadmium,zinc and lead presence

The influence of cadmium, zinc and lead on fungal emulsifier synthesis and on the growth of filamentous fungus Curvularia lunata has been studied. Tolerance to heavy metals established for C. lunata was additionally compared with the sensitivity exhibited by strains of Curvularia tuberculata and Paecilomyces marquandii—fungi which do not secrete compounds of emulsifying activity. Although C. lunata, as the only one out of all studied fungi, exhibited the lowest tolerance to heavy metals when grown on a solid medium (in conditions preventing emulsifier synthesis), it manifested the highest tolerance in liquid culture - in conditions allowing exopolymer production. Cadmium, zinc and lead presented in liquid medium up to a concentration of 15 mM had no negative effect on C. lunata growth and stimulated emulsifier synthesis. In the presence of 15 mM of heavy metals, both the emulsifier and 24-h-old growing mycelium exhibited maximum sorption capacities, which were determined as 18.2 ± 2.67, 156.1 ± 10.32 mg g⁻¹ for Cd²⁺, 22.2 ± 3.40, 95.2 ± 14.21 mg g⁻¹ for Zn²⁺ and 51.1 ± 1.85, 230.0 ± 28.47 mg g⁻¹ for Pb²⁺ respectively. The results obtained by us in this work indicate that the emulsifier acts as a protective compound increasing the ability of C. lunata to survive in heavy metal polluted environment. Enhancement of exopolymer synthesis in the presence of Cd²⁺, Zn²⁺ and Pb²⁺ may also suggest, at least to some extent, a metal-specific nature of emulsifier production in C. lunata. Due to accumulation capability and tolerance to heavy metals, C. lunata mycelium surrounded by the emulsifier could be applied for toxic metal removal.     

夏季南亚热带森林演替中后期优势种幼叶花色素苷的光保护作用

为探讨夏季南亚热带森林演替过程中优势树种幼叶的光保护机制,以演替中期优势树种木荷(Schima superba)、黧蒴(Castanopsis fissa)、锥栗(C.chinensis)和演替后期优势种华润楠(Machilus chinensis)、厚壳桂(Cryptocarya chinensis)、黄果厚壳桂(C.concinna)为材料,分析了2种生长光强(全光照和30%全光照)下6种优势种幼叶和成熟叶的叶片表型、光合色素含量、花色素苷含量、抗氧化能力、类黄酮含量、总酚含量和最大量子产量(Fv/Fm)恢复效率间的差异。结果表明,两个演替阶段幼叶的叶绿素含量(Chl a+b)、Chl a/b比成熟叶低,但光保护物质比成熟叶多;演替中期幼叶的花色素苷含量和总抗氧化能力比演替后期的高,而类黄酮和总酚含量比演替后期的低;全光照下幼叶的总酚、类黄酮、总抗氧化能力及Fv/Fm恢复效率都要比30%全光照的高,并且含有花色素苷的幼叶恢复得更快。因此,植物的光合能力与自身的光保护潜力成反比关系,演替中期优势种幼叶的光保护在很大程度上是因为花色素苷的积累而演替后期优势种是因为自身抗氧化物质(类黄酮、总酚)的共同作用。