Impact of <Emphasis Type="Italic">Erysiphe alphitoides</Emphasis> on transpiration and photosynthesis in <Emphasis Type="Italic">Quercus robur</Emphasis> leaves

Oak powdery mildew, (Erysiphe alphitoides) causes one of the most common diseases of oaks. We assessed the impact of this pathogen on photosynthesis and water relations of infected leaves using greenhouse-grown oak seedlings. Transpiration of seedlings infected by oak powdery mildew was also investigated. Altogether, E. alphitoides had a low impact on host gas exchange whether at the leaf or whole plant scale. Maximal stomatal conductance of infected leaves was reduced by 20–30% compared to healthy controls. Severely infected seedlings did not experience any detectable change of whole plant transpiration. The reduction in net CO₂ assimilation, A_n, was less than proportional to the fraction of leaf area infected. Powdery mildew reduced both the maximal light-driven electron flux (J_max) and the apparent maximal carboxylation velocity (Vc_max) although Vc_max was slightly more impacted than J_max. No compensation for the infection occurred in healthy leaves of partly infected seedlings as the reduced photosynthesis in the infected leaves was not paralleled by increased A_n levels in the healthy leaves of the seedlings. However, E. alphitoides had a strong impact on the leaf life-span of infected leaves. It is concluded that the moderate effect of E. alphitoides on oak might be related to the small impact on net CO₂ assimilation rates and on tree transpiration; nevertheless, the severe reduction in leaf life-span of heavily infected leaves may lead to decreased carbon uptake over the growth season.     

Biochemical and physiological responses to long‐term Citrus tristeza virus infection in Mexican lime plants

Reactions that occur when a plant is subjected to Citrus tristeza virus (CTV) infection often result in triggering of numerous defence mechanisms to fight the infection. The reactions vary according to virus strain, host genotype, time of exposure to the infection and environmental conditions. To date, no study has examined in detail the consequences of 10‐year exposure to CTV infection on the biochemical and physiological status of susceptible Mexican lime plants (Citrus aurantifolia). To understand the reaction of such plants, changes in nutrient status, total proteins, enzyme activity involved in scavenging of reactive oxygen species, photosynthetic and transpiration rates, chlorophyll content, membrane permeability and water content were analysed in plants infected with different CTV isolates and in healthy plants. The activity of superoxide dismutase and polyphenol oxidase significantly decreased in the infected leaves, and membrane permeability was lower in the infected plants. Macro‐ and micronutrient elements were significantly changed: concentrations of leaf nitrogen, zinc, magnesium and iron were elevated but potassium concentration depressed in comparison to noninfected control leaves. Levels of other analysed nutrient elements, enzymes, photosynthesis and stomatal conductance, chlorophyll content and relative water content were unchanged. Clear physiological changes were found among infected and noninfected control plants but none between plants infected with different CTV isolates. The data suggest that some of the defence mechanisms investigated here were suppressed due to the continuous and long‐term pressure of biotic stress.     

Synergism of Pratylenchus penetrans and Verticillium dahliae Manifested by Reduced Gas Exchange in Potato

ABSTRACT The effects of solitary and concurrent infection by Pratylenchus pene-trans and Verticillium dahliae on gas exchange of Russet Burbank potato (Solanum tuberosum) were studied in growth chamber experiments. Treatments were P. penetrans at low, medium, and high density; V. dahliae alone at one initial density; the combination of the nematode at these three densities and V. dahliae; and a noninfested control. Gas exchange parameters of leaf cohorts of different ages in the different treatments were repeatedly measured with a Li-Cor LI-6200 portable photosynthesis system. At 45 days after planting, joint infection significantly reduced net photosynthesis, stomatal conductance, and transpiration of 1- to 25-day-old leaf cohorts. Intercellular CO(2) levels were significantly increased by co-infection, especially in older leaves. The synergistic effect of co-infection on gas exchange parameters was greater in the oldest cohort than in the youngest cohort. No consistent effects on leaf gas exchange parameters were observed in plants infected by the nematode or the fungus alone. The relationship between the assimilation rate and stomatal conductance remained linear regardless of solitary or concomitant infection, indicating that stomatal factors are primarily responsible for regulating photosynthesis. The significant reduction of gas exchange in leaves of co-infected plants without reduction in intercellular CO(2) concentrations suggests that nonstomatal factors also play a role when both organisms are present.     

The influence of Verticillium dahliae and drought on potato crop growth. 1. effects on gas exchange and stomatal behaviour of individual leaves and crop canopies

Potato (Solanum tuberosum L.) plants cv.Saturna were subjected to infection withVerticillium dahliae and drought stress. At the early stages of growth, stomatal conductance, transpiration and net photosynthesis were measured at light saturation (PAR>300 m^–2) on individual leaves and with mobile field equipment with the aid of field enclosures. No significant changes in stomatal conductance and gas exchange characteristics occurred as a result ofV. dahliae instomatal conductance, transpiration and and photosynthetic rates, especially on older leaves and on plants exposed to direct sunlight for a longer period of time. In combination with drought,V. dahliae only occasionally showed interaction; their effects being less than additive. High values of coefficients of variatoon necessitated a high number of measurements per treatment; the more so in the inoculated plants which shows thatV. dahliae seems to affect certain leaves while not affecting others early in growth. Crop photosynthesis was less reduced byV. dahliae than individual leaf photosynthesis due to the levelling effect of integration over the whole canopy and possibly through a stimulation of the top leaves. The upper non-affected leaves are responsible for the bulk of photosynthetic crop activity. The results indicate that following an infection withV. dahliae photosynthesis is reduced early in growth as a result of drought stress in the leaves.Samenvatting Aardappelplanten (Solanum tuberosum L.) cv.Saturna werden onderworpen aan stress als gevolg vanVerticillium dahliae en droogte. In vroege stadia van de groei werden stomataire geleiding, transpiratie en netto fotosynthese bij lichtverzadiging (PAR>300 W m^–2) gemeten aan individuele bladeren en met een mobiel instrumentarium met behulp van gewaskappen. Er werden geen significante verschillen gevonden in de waarden van de stomataire geleiding en de gasuitwisslingskarakteristieken als gevolg vanV. dahliae-besmetting tot een maand na opkomst. Daarna leidde infectie metV. dahliae tot een afname van de stomataire geleiding, transpiratie en netto fotosynthese, speciaal bij oudere bladeren en bij planten die meer aan zonlicht waren blootgesteld. Soms vertoondeV. dahliae interactie met droogte en bleken beide effecten minder dan optelbaar. De hoge waarden van de variatiecoëfficiënten maakten een groot aantal metingen per behandeling noodzakelijk; dit was vooral het geval bij metV. dahliae geïnfecteerde planten hetgeen aantoont datV. dahliae vooral in het begin van de groei niet alle bladeren in gelijke mate aantast. Door de matigende invloed van de integratie van alle bladlagen en mogelijk doordat de bovenste bladeren werden gestimuleerd, werd de totale gewasfotosynthese in mindere mate beïnvloed doorV. dahliae dan de individuele bladfotosynthese. De bovenste niet geïnfecteerde bladeren bleken verantwoordelijk voor het grootste gedeelte van de gewas-fotosynthese. De resultaten tonen aan, dat volgend op een infectie metV. dahliae, de fotosynthese reeds in een vroeg stadium van de groei wordt verminderd als een gevolg van droogtestress in de bladeren.     

祁连山高海拔雨养农业区油菜、小麦光合特性比较研究

在作物生长旺盛期,采用LI-6400便携式光合仪测定了祁连山高海拔雨养农业区环境因子和油菜、小麦叶片光合生理指标,比较了油菜、小麦及低海拔地区作物光合参数的差异性。结果表明:光合有效辐射和空气温度均呈单峰型日变化曲线,而空气湿度呈"S"型日变化曲线,大气CO2浓度为早晚较低,下午高。油菜和小麦的叶片净光合速率日变化均呈双峰型曲线,存在"午休"现象,且上午光合速率高于下午。油菜的蒸腾速率日变化呈双峰型曲线,小麦的蒸腾速率却呈单峰型曲线。气孔导度日变化大体呈"S"型曲线。光合有效辐射是影响叶片净光合速率和蒸腾速率的主要环境因子之一,空气湿度是气孔导度的主要影响因子。大气CO2浓度与小麦叶片的净光合速率、蒸腾速率和气孔导度呈显著正相关关系。     

植物对土壤水分变化的响应与控制性分根交替灌溉

在土壤水分减少的情况下,植物可以感知并利用脱落酸(ABA)作物信号传递物质,将水分胁迫信号传至叶片,进而调节气孔导度,减少蒸腾耗水。同时,植物蒸腾耗水与气孔导度为线性关系,而光合作用与气孔导度为渐趋饱和关系,如果适当降低气孔导度,可以在显著降低蒸腾耗水的基础上,对光合没有影响或影响很小。在此理论基础上,提出了一种新的灌溉技术——控制性分根交替灌溉。其核心是通过一定的灌溉措施,形成土壤水分的不均匀分布,使作物的根系处于不同的水分状态：处于湿润部分的根系吸收水分,保证作物光合,处于干燥土壤的根系产生ARA,调节叶片气孔导度。这样,在不降低或少量降低光合作用的前提下,更多地减少作物的蒸腾耗水,提高作物的水分利用率。它是一种以内涵为主的节水灌溉技术,具有坚实的理论基础和良好的应用前景。     

Effects of Infection by Mycosphaerella graminicola on Translocation of Fluquinconazole in Wheat Seedlings

ABSTRACT Translocation of (14)C-labeled fluquinconazole was measured using combustion analysis and radio thin-layer-chromatographic analysis in seedling wheat leaves uninfected and infected with Mycosphaerella graminicola. Two isolates were used with differing sensitivity to demethylation inhibitor fungicides. Fluquinconazole was translocated acropetally, but not basipetally. Fluquinconazole accumulated around infection sites within 6 days after treatment. Accumulation occurred before M. graminicola hyphae had colonized the host mesophyll further than one host cell around the invasion site. This suggested that the accumulation was caused by a host response to infection. Infrared gas analysis showed that rates of transpiration and stomatal conductance in inoculated leaves were significantly increased very soon after inoculation but net photosynthesis was decreased. The actual mechanism of fungicide accumulation was not determined.     

北方寒区日光温室冬季基质袋培番茄蒸腾量模拟

北方寒区日光温室冬季生产基本无通风,为了探寻室内弱光、高湿、低温及低风速环境下的番茄蒸腾量模拟模型,基于Penman-Monteith（P-M）方程及适应此特定环境的边界层空气动力学阻力、气孔平均阻力、土壤热通量等参数模拟了温室长季节栽培番茄（Lycopersicon esculentum Mill）单株的蒸腾速率并进行了试验验证,揭示了蒸腾速率与净辐射、饱和水汽压差的日变化规律,确定了蒸腾速率与植株上方净辐射的定量关系,检验了土壤热通量取值对蒸腾速率的影响。结果显示：2017-12-11—2018-01-03室内太阳总辐射最大值367 W·m^-2、夜晚及阴天相对湿度接近100%、室内风速接近0 m·s^-1的情况下,单株植株边界层空气动力学阻力变化范围晴天为147~438 s·m^-1,阴天为 211~365 s·m^-1;气孔平均阻力晴天69~1 506 s·m^-1,阴天132~1 151 s·m^-1;P-M方程模拟的单株番茄逐时蒸腾速率在晴天、阴天中午的平均值分别为0.06、0.02 mm·h^-1,模拟值与实测值比较,平均相对误差约为10%。研究还表明,单株番茄上方净辐射量的43.5%通过蒸腾作用转化为潜热;试验环境下,土壤热通量的取值变化对蒸腾速率影响不大。研究确定的蒸腾速率估算模型可为北方寒区冬季日光温室基质袋培番茄蒸腾量估算以及水分管理提供参考。     

云杉矮槲寄生的侵染对青杄光合与蒸腾作用的影响

 云杉矮槲寄生(Arceuthobium sichuanense)属半寄生性多年生种子植物,是青海省云杉天然林毁灭性生物灾害之一。本研究首次报道了云杉矮槲寄生在自然条件下可以侵染青杄,并对健康与染病青杄(Picea wilsonii)针叶形态及其光合日变化进行了测定。结果表明:1)染病青杄的针叶长度和宽度显著小于健康青杄(P＜0.001),而染病青杄的针叶比叶面积(SLA)显著大于健康青杄(P＜0.001);2)云杉矮槲寄生的侵染显著降低了青杄叶片的净光合速率、蒸腾速率以及气孔导度(P＜0.05),但不影响其胞间CO₂浓度(P =0.32);3)冗余分析(RDA)表明,云杉矮槲寄生的侵染导致青杄对不同环境因子的依赖程度发生变化,健康青杄表现为环境CO₂浓度(CO₂)＞空气温度(T_air)＞叶片温度(T_l)＞蒸汽压亏缺(Vpd)＞空气相对湿度(RH)＞光合有效辐射(PAR),而染病青杄则出现T_l＞RH＞T_air＞PAR＞Vpd＞CO₂,且T_l成为影响染病青杄叶片光合与蒸腾作用(P_n、T_r)的主要环境因子,且染病青杄对RH和PAR变化的响应更加敏感。此外,染病青杄叶片的水分利用率(WUE)显著低于健康寄主(P＜0.05)。因此,云杉矮槲寄生的侵染可降低青杄对环境的适应能力,从而加速寄主的衰老死亡。     

Photosynthesis,transpiration and plant growth characters of different potato cultivars at various densities of Globodera pallida

Plants of four potato (Solanum tuberosum L.) cultivars were grown in pots in a greenhouse at five densities ofGlobodera pallida between 0 and 300 eggs per gram of soil. Photosynthesis and transpiration of selected leaves were measured at 30, 37, 49 and 60 days after planting. Stem length was recorded at weekly intervals. Plants were harvested 70 days afteer planting and various plant variables were determined.At 30 days after planting, when second and third stage juveniles were present in roots, both photosynthesis and transpiration rates were severely reduced byG. pallida. In the course of time these effects became less pronounced. Water use efficiency was reduced byG. pallida between 30 and 49 days, but not at 60 days after planting. The results suggest independent effects ofG. pallida on stomatal opening and on photosynthesis reactions. There were no consistent differences among cultivars in the response of leaf gas exchange rates and water use efficiency to nematode infection. Reduction of photosynthesis byG. pallida appeared additive to photosynthesis reduction due to leaf senescence.Total dry weight was reduced by 60% at the highestG. pallida density. Weights of all plant organs were about proportionally affected. Shoot/root ratio was not affected and dry matter content was reduced. Stem length and leaf area were most strongly reduced during early stages of plant-nematode interaction. The number of leaves formed was only slightly reduced byG. pallida, but flowering was delayed or inhibited. Reduction of total dry weight correlated with reduction of both leaf area and photosynthesis rate. Leaf area reduction seems the main cause of reduction of dry matter production. Tolerance differences among cultivars were evident at 100 eggs per gram of soil only, where total dry weight of the intolerant partially resistant cv. Darwina was lower than that of the tolerant partially resistant cv. Elles and of the tolerant susceptible cv. Multa. The tolerance differences were not correlated with leaf photosynthesis and transpiration. Apparently these processes are not part of tolerance of plants.     

Strobilurin fungicides induce changes in photosynthetic gas exchange that do not improve water use efficiency of plants grown under conditions of water stress

The effects of five strobilurin (beta-methoxyacrylate) fungicides and one triazole fungicide on the physiological parameters of well-watered or water-stressed wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and soya (Glycine max Merr.) plants were compared. Water use efficiency (WUE) (the ratio of rate of transpiration, E, to net rate of photosynthesis, A(n)) of well-watered wheat plants was improved slightly by strobilurin fungicides, but was reduced in water-stressed plants, so there is limited scope for using strobilurins to improve the water status of crops grown under conditions of drought. The different strobilurin fungicides had similar effects on plant physiology but differed in persistence and potency. When applied to whole plants using a spray gun, they reduced the conductance of water through the epidermis (stomatal and cuticular transpiration), g(sw), of leaves. Concomitantly, leaves of treated plants had a lower rate of transpiration, E, a lower intercellular carbon dioxide concentration, c(i), and a lower net rate of photosynthesis, A(n), compared with leaves of control plants or plants treated with the triazole. The mechanism for the photosynthetic effects is not known, but it is hypothesised that they are caused either by strobilurin fungicides acting directly on ATP production in guard cell mitochondria or by stomata responding to strobilurin-induced changes in mesophyll photosynthesis. The latter may be important since, for leaves of soya plants, the chlorophyll fluorescence parameter F(v)/F(m) (an indication of the potential quantum efficiency of PSII photochemistry) was reduced by strobilurin fungicides. It is likely that the response of stomata to strobilurin fungicides is complex, and further research is required to elucidate the different biochemical pathways involved.     

Carbon dioxide assimilation by virus-free sugarcane plants and by plants which were infected by Sugarcane Yellow Leaf Virus

Infection of sugarcane by Sugarcane Yellow Leaf Virus (SCYLV) remains mostly asymptomatic. The assimilation rates and the water relations parameters were measured to test whether the plants are already inflicted by the infection. The assimilation rate and the stomatal conductance were 10–30% higher in virus-free plants than in infected plants. The observed differences were significant in young potted plants, not in older field plants. Virus-free leaves had a higher bundle sheath leakiness and a lower ¹³C discrimination rate than infected leaves. The water relations parameters of SCYLV-infected asymptomatic plants showed resemblance to those of salinity- and drought-stressed plants.     

Impact of Cuscuta australis infection on the photosynthesis of the invasive host,Mikania micrantha,under drought condition

Cuscuta species (dodders) are widespread stem holoparasites that depend on host plants for their entire mineral and water and most carbohydrate requirements. Dodders negatively affect host photosynthesis but precise information on their impact on hosts in the presence of environmental stress factors (i.e. drought) is little known. In a pot experiment, the leaf traits, gas exchange and chlorophyll a fluorescence of the invasive climber, Mikania micrantha, parasitized by Cuscuta australis, were investigated in order to study variations of host photosynthesis in response to parasitism and drought. The results showed that the concomitant presence of C. australis infection and drought significantly impacted the leaf traits (i.e. increased leaf dry mass content), gas exchange (i.e. decreased stomatal conductance and transpiration rates and increased water‐use efficiency) and quantum yield of chlorophyll a fluorescence of M. micrantha. The presence of a single stress factor (C. australis infection or drought), however, only significantly affected the leaf traits and gas exchange of M. micrantha. These results suggested that the combined additive effects of C. australis parasitism and drought significantly suppressed the photosynthesis of M. micrantha in relation to both stomatal and non‐stomatal limitation of host photosynthesis. This study provides insights into Cuscuta–host interactions under drought conditions in the tropics.     

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

Weed–pathogen interactions and elevated CO2: growth changes in favour of the biological control agent

In this study, we used Parthenium hysterophorus and one of its biological control agents, the winter rust (Puccinia abrupta var. partheniicola) as a model system to investigate how the weed may respond to infection under a climate change scenario involving an elevated atmospheric CO₂ (550 μmol mol^?1) concentration. Under such a scenario, P. hysterophorus plants grew significantly taller (52%) and produced more biomass (55%) than under the ambient atmospheric CO₂ concentration (380 μmol mol^?1). Following winter rust infection, biomass production was reduced by 17% under the ambient and by 30% under the elevated atmospheric CO₂ concentration. The production of branches and leaf area was significantly increased by 62% and 120%, under the elevated as compared with ambient CO₂ concentration, but unaffected by rust infection under either condition. The photosynthesis and water use efficiency (WUE) of P. hysterophorus plants were increased by 94% and 400%, under the elevated as compared with the ambient atmospheric CO₂ concentration. However, in the rust‐infected plants, the photosynthesis and WUE decreased by 18% and 28%, respectively, under the elevated CO₂ and were unaffected by the ambient atmospheric CO₂ concentration. The results suggest that although P. hysterophorus will benefit from a future climate involving an elevation of the atmospheric CO₂ concentration, it is also likely that the winter rust will perform more effectively as a biological control agent under these same conditions.     

Carbon dioxide assimilation by virus-free sugarcane plants and by plants which were infected by Sugarcane Yellow Leaf Virus

Infection of sugarcane by Sugarcane Yellow Leaf Virus (SCYLV) remains mostly asymptomatic. The assimilation rates and the water relations parameters were measured to test whether the plants are already inflicted by the infection. The assimilation rate and the stomatal conductance were 10–30% higher in virus-free plants than in infected plants. The observed differences were significant in young potted plants, not in older field plants. Virus-free leaves had a higher bundle sheath leakiness and a lower ¹³C discrimination rate than infected leaves. The water relations parameters of SCYLV-infected asymptomatic plants showed resemblance to those of salinity- and drought-stressed plants.     

百合无症病毒对百合光合生理、酶活性及叶绿体超微结构的影响

 以东方百合“西伯利亚”为试验材料,研究百合无症病毒(LSV)侵染百合对其叶片生理生化以及叶绿体超微结构的影响。检测结果表明:叶片中叶绿素a、b以及总叶绿素含量与健康对照相比分别下降了28.6%、33.3%和23.5%,净光合速率、气孔导度及胞间CO₂浓度分别下降33.3%、25%和13.8%;超氧化物歧化酶(SOD)、过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)与健康对照相比,分别增加了16.6%、29.4%、16.7%和22.2%。电镜观察发现:感病植株叶绿体膨胀变形,基质片层散乱,叶绿体内淀粉粒肿大且数目增多,从而证明LSV侵染破坏叶绿体结构,影响植株的光合作用。     

Accumulation of short interfering RNAs characteristic of RNA silencing precedes recovery of tomato plants from severe symptoms of <Emphasis Type="Italic">Potato spindle tuber viroid</Emphasis> infection

Tomato plants infected with Potato spindle tuber viroid (PSTVd) had severe leaf curling and vein necrosis. The disease symptoms began to diminish during the late stages of infection, however, and almost healthy-looking leaves began to appear on the upper portion of the plants. PSTVd concentrations reached their highest levels in leaves with severe symptoms and decreased in upper leaves recovering from severe symptoms. PSTVd-specific short interfering RNAs (siRNAs), characteristic of RNA silencing, accumulated in all leaves in which PSTVd reached a detectable level, suggesting that recovery from severe disease was induced by RNA silencing via sequence-specific degradation of PSTVd.