Antimicrobial agents from higher plants: two dimethylbenzisochromans from Karwinskia humboldtiana

Two new antimicrobial dimethylbenzisochromans were isolated from the roots of Karwinskia humboldtiana together with the known 7-acetyl-6,8-dimethoxy-3-methyl-l-naphthol. The structures and absolute configurations were determined by spectroscopic examination and by chemical transformation to the known quinones eleutherin and 7-methoxyeleutherin.     

Effect of auxins on <Emphasis Type="Italic">Karwinskia humboldtiana</Emphasis> root cultures

Effects of auxins (IAA, IBA and NAA) on K. humboldtiana root culture cultivated in 16-h photoperiod or in dark have been observed. Light affected positively the production of biomass when cultivated on medium supplemented with NAA in 10 and 25 mol ^–1 concentrations. In the presence of IAA and IBA these values were significantly lower. The growth dynamics of root cultures depended on the auxin used. The best adventitious roots elongation and lateral roots induction on media supplemented with IBA has been ascertained. Morphological and anatomical differences in dependence on auxin used were observed. NAA supported the formation of huge callus-like mass besides mostly very short roots, especially under the light. Similarly IAA induced short roots, and IBA seems to be the most effective substance for the root elongation in this model system. NAA induced roots with larger diameter under the light compared with the other two auxins used. The reason is in the different anatomical structure of roots which was characterized by higher number of cell layers and large intercellulars in the cortex. The shape of cortical cells in the presence of IBA depended on the light conditions. Isodiametric cortical cells were present in roots cultivated in 16-h photoperiod, irregularly-shaped cells in the dark. The effect of light conditions was the smallest in the case of roots grown on IAA enriched media.     

Thermoperiodic control of stem elongation and endogenous gibberellins in Campanula isophylla

The effect of day/night temperature regimes on stem elongation and on the content of endogenous gibberellins (GAs) in vegetatively propagated plants of Campanula isophylla cv. Hvit have been studied. Compared with a constant temperature regime at 18°C (18/18°C), stem and internode elongation was enhanced significantly by a combination of high day/low night temperature (21/15°C) and inhibited by an opposite regime (15/21°C). Gibberellins A₁, A₁₉, A₄₄, A₅₃, and A₉₇ were identified as endogenous components in Campanula. (GA₉₇ was earlier referred to as 2-OH-GA₅₃.) Quantitative analysis of the endogenous GAs indicates that temperature regimes that stimulate elongation growth are accompanied by an increase in the level of GA₁, GA₁₉, and GA₄₄. On the other hand, in plants grown under conditions that reduced stem elongation growth, there was an increased level of GA₉₇.Abbreviations DIF difference between day temperature and night temperature - GA gibberellin - HPLC high performance liquid chromatography - GC-MS gas chromatography-mass chromatography - SPE solid phase extraction - TMS trimethylsilyl - MSTFA N-methyl-N-TMS-trifluoroacetamide - KRI Kovats retention index - SIM selected ion monitoring - D2 deuterated     

Effect of four fluctuating temperature regimes on cui-ui,Chasmistes cujus,survival from egg fertilization to swim-up,and size of larvae produced

Synopsis We evaluated cui-ui,Chasmistes cujus, swim-up success, time of hatching and swim-up, and size of larvae at swim-up under four fluctuating temperature regimes (8.9–15.0, 12.2–18.3, 15.0–21.1, and 17.8–23.9° C). The greatest swim-up success was at the 8.9–15.0° C regime and the lowest at the 15.0–21.1° C regime. Hatching and swim-up time varied inversely with incubation temperature. The largest (and presumably the most fit) larvae were in the 8.9–15.0° C treatment, whereas the smallest were in the 17.8–23.9° C treatment. Cui-ui appeared best adapted to the coolest of the four temperature regimes.     

Low temperature effect on selective fertilization by pollen mixtures of wild and cultivated tomato species

Summary In vitro pollen germination of cultivated tomato, Lycopersicon esculentum Mill., is inhibited by an ambient temperature of 5°C, more so than pollen from a Peruvian ecotype of Lycopersicon hirsutum Humb. & Bonpl. originating from an altitude of 3200 m. The frequency of L. hirsutum gametes contributing to hybrid zygote formation is more than doubled when controlled fertilizations with pollen mixtures of the two species occurs at 12/6°C as compared to crosses with the same mixtures at 24/19°C. The results suggest that differential selection at the gametophytic level occurs in response to low temperature regimes. To our knowledge this is the first time in higher plants that alteration of an environmental factor has been demonstrated to change selection values of male gametophytes in a fashion predicted by the ecology of the parental sporophytes.     

Influence of root temperature on the potassium requirements of young tomato plants

The effect of low root temperature on the growth and K requirements of young tomato (Lycopersicon esculentum Mill. cv Sonatine) plants was investigated. When K was supplied in solution at high concentration (5 mM), lowering the temperature of the root system from 25° to 15°C reduced the relative growth rate so that after ten days plant dry weight was 60% and leaf area 44% of that of controls maintained at 25°C. Shoot: root dry weight ratio was initially increased by cooling, but declined to 84% of controls after ten days. In spite of these changes in shoot: root ratio the concentration of K in whole plants, expressed on the basis of tissue water, was stable throughout the experiment and was significantly higher than that of controls. Further, the critical concentration of K for shoots (the concentration in the shoot associated with 90% maximum growth) was also increased at root temperatures of 15° and 30°C compared with 24°C. It is suggested that the higher concentration of K at low root temperature may reflect a real increase in requirement for the element at the physiological level. Preliminary measurements of the solute potential demonstrated a less osmotically active sap in leaves of root-cooled plants, thus there may be a greater reliance on K as an osmoticum in these individuals. When supplies of K limited growth, root-cooling had no effect on any of the parameters determining the efficiency of its use; the minimum concentration to which roots could deplete the solution of K was identical for cooled and control plants and at the same stage of visible deficiency there was no significant difference in the efficiency ratio (mg DW, mg^-1 K) or utilization efficiency (mg DW mM ^-1 K), in spite of large differences in the partitioning of dry matter.     

Influence of Thermoperiod on Growth and Development in Cucumber

We studied the influence of gradient temperature regimes on various parameters of the formation of shoots and roots of cucumber plants, such as rate of leaf appearance, rate of growth, duration of growth and length of leaves, and the rate of growth shoots organs and roots. The plants were grown under the controlled conditions: at different combinations of day and night temperature, illumination 100 W/m², and 12 h photoperiod. The comparison of constant and fluctuating diurnal temperature regimes has shown that in the optimal area for all studied indices, the highest values were recorded at the constant daily temperature (25°C for all growth indices of shoots and 20°C for growth of roots), while all gradient regimes either did not affect, or exerted inhibitory effects on the plant. Outside the optimum area, the effects of gradient temperatures differed. The main acting fluctuating temperatures, that exerted stimulating effects, combined low hardening (15°C) and optimal temperatures (25°C), which was earlier described for animals. The 15/35 and 35/15°C combinations were unambiguously inhibitory, since both temperatures are hardening for the cucumber. A lesser stimulating effect of gradient temperatures on the developmental rate in a plant, as compared to poikilothermic animals, could be due to a greater autonomy of plant ontogenesis because of autotrophy and, correspondingly, a greater degree of homeostasis. The mechanisms accounting for the responses to temperature gradients are similar in different groups of ectotherms.     

Effects of supplemental nitrate and thermal regime on the nitrogen nutrition of chickpea (Cicer arietinum L.)

Summary Nodulated chickpea plants were grown in pots in a glasshouse programmed to simulate either hot (32.5°C day/18°C night) or warm (25°/18°C) thermal regimes characteristic of those experienced by crops grown in different seasons or locations in the semi-arid tropics. The plants were irrigated with nutrient solution either devoid of inorganic nitrogen or containing 0.71, 1.43 or 2.86 mM nitrate. Increasing concentrations of supplemental nitrate stimulated the rate of dry matter production by vegetative plants in both thermal regimes. Differences between vegetative dry weight of plants given nitrate and those relying exclusively on symbiotic dinitrogen fixation were greatest in the hot regime where the durations of vegetative growth were shorter. However, symbiotically-dependent plants and those given 0.71 mM nitrate continued to produce branches throughout the reproductive period, particularly in the warm regime. As they matured, these plants became more comparable in vegetative stature to those which had received greater concentrations of nitrate and had established final branch numbers earlier (i.e prior to main pod-fill). Potential seed yields were determined primarily by the number of potential reproductive sites (nodes) available (i.e. by the extent of branching) which largely determined the number of seeds harvested. Since final branch numbers in all nitrate treatments were greatest in the warm regime, yields were also larger than those at 32.5°C. The implications of these data for the nitrogen economy of chickpea crops is discussed.One of a series of papers resulting from a collaborative project with the International Crops Research Institute for the Semi-Arid Tropics, India; sponsored by the UK Overseas Development Administration.     

Seasonal variation in the competence of the buds of three cultivars from different Citrus species to flower

The role of bud competence in the determination of flowering seasonality was studied in three Citrus cultivars, Bearss lime (Citrus latifolia Tan.), Fino lemon (C. limon [L.] Burm. f.) and Owari satsuma (C. unshiu (Mak.) Marc.), which differ in their adaptation to hot climates and their propensity to produce off-season blooms. Potted plants were kept in a greenhouse under non-inductive conditions (minimum temperature higher than 20°C), and periodically the flowering response was determined of a group of trees exposed for 30 days to an inductive temperature regime (15/8°C). A seasonal change in bud competence was demonstrated, and both bud sprouting and flower formation were highest when the low temperature regime was imposed during February and March. During the summer months, the low temperature regime resulted in a small increase in bud sprouting as compared to non-chilled trees, but only vegetative buds developed and no flowers were formed. The influence of environmental factors on the determination of bud competence was further studied. No effect of photoperiod was found, but raising the minimum air temperature above 25°C during 60 days, eliminated bud competence in Owari satsuma. In Bearss lime trees, the buds reacquired the competence after 4 months at 25/20°C, a temperature regime that does not induce flower formation. The reacquisition of competence was much faster at a lower temperature (15/8°C). A consistent relationship between the flowering response and DNA methylation in buds could not be demonstrated in all cultivars.     

Thermal tolerance,net CO2 exchange and growth of a tropical tree species, Ficus insipida, cultivated at elevated daytime and nighttime temperatures

Global warming and associated increases in the frequency and amplitude of extreme weather events, such as heat waves, may adversely affect tropical rainforest plants via significantly increased tissue temperatures. In this study, the response to two temperature regimes was assessed in seedlings of the neotropical pioneer tree species, Ficus insipida. Plants were cultivated in growth chambers at strongly elevated daytime temperature (39 °C), combined with either close to natural (22 °C) or elevated (32 °C) nighttime temperatures. Under both growth regimes, the critical temperature for irreversible leaf damage, determined by changes in chlorophyll a fluorescence, was approximately 51 °C. This is comparable to values found in F. insipida growing under natural ambient conditions and indicates a limited potential for heat tolerance acclimation of this tropical forest tree species. Yet, under high nighttime temperature, growth was strongly enhanced, accompanied by increased rates of net photosynthetic CO₂ uptake and diminished temperature dependence of leaf-level dark respiration, consistent with thermal acclimation of these key physiological parameters.     

Microsporogenesis in a normal line and in the ogu cytoplasmic male-sterile line of Brassica napus

Summary Under an intermediate temperature regime (23° C/18° C; day/night), microsporogenesis in stamens of the ogu cytoplasmic male-sterile (CMS) line of Brassica napus terminated by the tetrad stage, although in some cases degeneration of the sporogenous tissue occurred prior to meiosis. In most cases the tetrads were collapsed and bounded by a sparse exine, but contained many organelles. Also, the tapetum in CMS anthers was abnormal and often highly vacuolated by the tetrad stage. Under low temperature conditions (18° C/15° C; day/night), neither microsporogenous nor tapetal tissues were observed. In the normal stamens, no differences were observed under different temperature regimes. In conjunction with the adjoining paper, this study demonstrates that temperature conditions strongly affect the cytological processes associated with microsporogenesis in the CMS anthers.     

Effect of temperature on rice growth in nutrient solution and in acid sulphate soils from Vietnam

Climatic and soil factors are limiting rice growth in many countries. In Vietnam, a steep gradient of temperature is observed from the North to the South, and acid sulphate soils are frequently devoted to rice production. We have therefore attempted to understand how temperature affects rice growth in these problem soils, by comparison with rice grown in nutrient solution. Two varieties of rice, IR64 and X2, were cultivated in phytotrons at 19/21°C and 28/32°C (day/night) for 56 days, after 3 weeks preculture in optimal conditions. Two soils from the Mekong Delta were tested. Parallel with the growing experiments, these two soils were incubated in order to monitor redox potential (E _h ), pH, soluble Al and Fe, soluble, and available P. Tillering retardation at 20°C compared to 30°C was similar in nutrient solutions and in soils. The effect of temperature on increasing plant biomass was more marked in solutions than in soils. The P concentrations in roots and shoots were higher at 20°C than at 30°C, to such an extent that detrimental effect was suspected in plants grown in solution at the lowest temperature. The translocation of Fe from roots to shoots was stimulated upon rising temperature, both in solutions and in soils. This led to plant death on the most acid soil at 30°C. Indeed, the accumulation of Fe in plants grown on soils was enhanced by the release of Fe²⁺ due to reduction of Fe(III)-oxihydroxides. Severe reducing conditions were created at 30°C: redox potential (E _h ) dropped rapidly down to about 0 V. At 20°C, E _h did not drop below about 0.2 V, which is a value well in the range of Fe(III)/Fe(II) buffering. Parallel to E _h drop, pH increased up to about 6–6.5 at 30°C, which prevented plants from Al toxicity, even in the most acid soil. Phosphate behavior was obviously related to Fe-dynamics: more reducing conditions at 30°C have resulted in enhancement of available P, especially in the most acid soil.     

Effects of temperature and CO2 enrichment on kinetic properties of phospho-enol-pyruvate carboxylase in two ecotypes of Echinochloa crus-galli (L.) Beauv., a C4 weed grass species

Summary Two populations of Echinochloa crus-galli (Québec, Mississippi) were grown at the Duke University Phytotron under 2 thermoperiods (28°/22°C, 21°/15°C day/night) and 2 CO₂ regimes (350 and 675 l l^-1). Thermostability, energy of activation (E _a ),K _m (PEP), K _m (Mg⁺⁺), and specific activity of phospho-enol-pyruvate carboxylase (PEP_c) were analyzed in partially purified enzyme preparations of plants grown for 5 weeks. Thermostability of PEP_c from extracts (in vitro) and leaves (in situ) was significantly higher in Mississippi plants. In vitro denaturation was not appreciably modified by thermal acclimation but CO₂ enrichment elicited higher thermostability of PEP_c. In situ thermostability was significantly higher than that of in vitro assays and was higher in Mississippi plants acclimated at 28°/22°C and in plants of the two ecotypes grown at 675 l l^-1 CO₂. E _a (Q ₁₀ 30°/20°C) for PEP_c was significantly lower in Québec plants as compared to Mississippi and no acclimatory shifts were observed. Significantly higher K _m's (PEP) in 20°C assays were obtained for Mississippi as compared to Québec plants but values were similar at 30°C and 40°C assays. K _m (Mg⁺⁺) decreased at higher assay temperatures and were significantly lower for PEP_c of the Québec ecotype. No significant changes in K _m (Mg⁺⁺) values were associated with modifications in temperature on CO₂ regimes. PEP_c activity measured at 30°C was significantly higher for Québec plants when measured on a leaf fresh weight, leaf area or protein basis but not on a chlorophyll basis. Significantly higher PEP_c activity for both genotypes was observed for plants acclimated at 21°/15°C or grown at 675 l l^-1 CO₂. Net photosynthesis (Ps) and net assimilation rates (NAR) were higher in Québec plants and were enhanced by CO₂ enrichment. NAR was higher in plants acclimated at low temperature, while an opposite trend was observed for Ps. PEP_c activities were always in excess of the amounts required to support observed rates of CO₂ assimilation.     

Ectomycorrhizae,arbuscular mycorrhizae,and dark-septate fungi on <Emphasis Type="Italic">Salix humboldtiana</Emphasis> in two riparian populations from central Argentina

Colonization of Salix humboldtiana (Salicaceae) by ectomycorrhizae (ECM), arbuscular mycorrhizae (AM), and dark-septate endophytic (DSE) fungi was studied throughout autumn on two riparian populations in central Argentina. AM and DSE infection on roots ranged from 0% to 17% and from 2% to 20% respectively, whereas ECM colonization was higher, varying between 33% and 99% for both sites. Seven ECM morphotypes were found on S. humboldtiana roots. The nuclear rDNA internal transcriber spacer (ITS) region from the ectomycorrhizal root tips was amplified using ITS-1F and ITS-4 primers. Two of the seven ECM types were identified by searching GenBank blasts: one attributed to the genus Tomentella (Thelephoraceae) and the second most closely matched to Inocybe sp. (Cortinariaceae). The ECM colonization varied among sampling dates and sites, whereas AM and DSE colonization varied only among sampling dates. Diversity values for the ECM morphotype were not significantly different for autumn months or among the two sites. Positive correlations were found between Inocybe sp. and sites and between Inocybe sp., Tomentella sp., morphotypes III, IV, and VI, and sampling dates. This article provides the first documented evidence of co-occurrence of ECM, AM, and DSE in S. humboldtiana.     

放牧管理模式对高原鼢鼠(Eospalax baileyi)鼠丘形态特征的影响

为明晰放牧对高原鼢鼠（Eospalax baileyi）造丘活动的影响,于2019年5月、8月和10月分别对禁牧（No grazing,NG）、生长季休牧（Rest grazing in growing season,RG）、传统放牧（Traditional grazing,TG）和连续放牧（Continuous grazing,CG）4种放牧管理模式样地下高原鼢鼠的新鼠丘（2个月内形成）半径、高度、表面积和体积等进行测定,并分析其表面积、体积与土壤和植被生物量间的关系。结果发现：放牧管理模式显著影响了高原鼢鼠鼠丘形态特征,且具有季节性差异。NG下鼠丘的半径、表面积和体积最大,而CG下鼠丘的体积和表面积显著变小（P<0.05）,在8月和10月,鼠丘半径在CG样地显著小于其他3种放牧模式样地（P<0.05）;8月TG下鼠丘高度最高,而5月和10月NG下鼠丘高度最高,鼠丘高度在CG样地显著小于NG样地（P<0.05）。冗余分析2个排序轴几乎全部解释了土壤因子及地下生物量与鼠丘特征之间的关系,但各放牧管理模式下影响因子不同,NG样地的土壤容重（P<0.05）、土壤紧实度（P<0.01）和莎草科植物的地上生物量（P<0.01）,RG样地的地下生物量（P<0.01）、土壤紧实度（P<0.01）和豆科植物的地上生物量（P<0.01）,TG样地的禾本科和豆科植物的地上生物量（P<0.01）,CG样地的土壤水分、地下生生物量、土壤紧实度（P<0.05）和莎草科植物的地上生物量（P<0.01）均显著影响了鼠丘的形态特征。可见,放牧会影响高原鼢鼠的鼠丘形态特征,进而对草地的演替产生不同的影响。     

Root cooling strongly affects diel leaf growth dynamics,water and carbohydrate relations in Ricinus communis

In laboratory and greenhouse experiments with potted plants, shoots and roots are exposed to temperature regimes throughout a 24 h (diel) cycle that can differ strongly from the regime under which these plants have evolved. In the field, roots are often exposed to lower temperatures than shoots. When the root‐zone temperature in Ricinus communis was decreased below a threshold value, leaf growth occurred preferentially at night and was strongly inhibited during the day. Overall, leaf expansion, shoot biomass growth, root elongation and ramification decreased rapidly, carbon fluxes from shoot to root were diminished and carbohydrate contents of both root and shoot increased. Further, transpiration rate was not affected, yet hydrostatic tensions in shoot xylem increased. When root temperature was increased again, xylem tension reduced, leaf growth recovered rapidly, carbon fluxes from shoot to root increased, and carbohydrate pools were depleted. We hypothesize that the decreased uptake of water in cool roots diminishes the growth potential of the entire plant – especially diurnally, when the growing leaf loses water via transpiration. As a consequence, leaf growth and metabolite concentrations can vary enormously, depending on root‐zone temperature and its heterogeneity inside pots.     

The Effect of Ventilation on in vitro Response of Seedlings of the Cultivated Tomato and its Wild Salt-tolerant Relative Lycopersicon pennellii to Salt Stress

Organs or plants grown in vitro do not always exhibit the same responses to salinity as the whole plant of same species grown ex vitro. The response to salinity (100 mM NaCl) of seedlings of the wild tomato species Lycopersicon pennellii acc. Atico (Lpa) and of the cultivated tomato L. esculentum cv. M82 (Lem), the former is known as salt tolerant and the second as relatively salt sensitive under ex vitro conditions, was compared under in vitro conditions with three different ventilation regimes. It was found that under salinity shoots of the wild species accumulated the same or even more dry biomass than the control (roots somewhat less) under all ventilation levels. Growth of shoots and roots of the cultivated species was inhibited under the same conditions especially under the high ventilation. Ventilation reduced some abnormalities of leaf development related to hyperhydricity and consequently ventilated leaves exhibited a more compounded structure, increased area, increased resistance to water loss and stomata functioning. Ventilation increased K⁺, Na⁺ and Cl⁻ accumulation in shoots of both tomato species. This was more pronounced under salinity and in Lpa. This work indicates that differences that characterize whole plants of these species in response to salinity under ex vitro conditions are exhibited also in whole plants grown in vitro under high ventilation. It is suggested that ventilation is needed to evaluate well the response of whole plants to salt stress applied in vitro.     

Adaptation and acclimation of higher plants at the enzyme level: Latitudinal variations of thermal properties of NAD malate dehydrogenase in Lathyrus japonicus Willd. (Leguminosae)

Summary Thermal properties of NAD malate dehydrogenase were investigated in 8 clonal populations of Lathyrus japonicus Willd. collected over a 16° latitudinal gradient in eastern North America. Clones from warmer summer sites had higher activation energies (E _a) and enhanced thermostability for the enzyme under three contrasting growth temperature regimes. A strong component of acclimation was associated with E _a, but not with thermostability. Activity levels of the enzyme were higher in warm-adapted genotypes but cold-acclimated plants had similar low levels of specific activity. The clones were differentiated by ordination in a pattern related to climatic origin.     

Effects of a fluctuating temperature regime experienced by Daphnia during diel vertical migration on Daphnia life history parameters

Many freshwater zooplankton species perform a diel vertical migration (DVM) and spend the day within the lower, colder hypolimnion of stratified lakes. Trade-offs that arise from this migration have already attracted much attention and the cold temperature in the hypolimnion is thought to be the main cost of this behaviour. In this study we additionally looked at the extra costs daphnids have from being exposed to a fluctuating temperature regime (cold during the day and warm during the night) which is less well studied until today. In our experiment Daphnia hyalina Leydig and Daphnia magna Straus either spent 24 h in constant warm water (19 °C), 24 h in constant cold water (12 °C), or spent 12 h in warm and 12 h in cold water in an alternating way (fluctuating temperature regime). We expected the values of the life history parameters of Daphnia in the fluctuating temperature regime to be exactly halfway between the values of the life history parameters in the warm and cold treatments because the daphnids spent exactly half of the time in warm water, and half of the time in cold water. Concordant with earlier studies our results showed that age at first reproduction and egg development time were reduced at higher temperatures. In the fluctuating temperature regime the values of both parameters were exactly halfway between the values at permanently warm and cold temperature regimes. In contrast, somatic growth was higher at higher temperatures but was lower in the fluctuating temperature regime than expected from the mean somatic growth rate. This suggests that a fluctuating temperature regime experienced by migrating daphnids in stratified lakes involves additional costs for the daphnids.