Functional Electron Microscopy in Studies of Plant response and adaptation to Anaerobic Stress

This article reviews the contribution made by functional electronmicroscopy towards identifying and understanding the reactionsof plant roots and shoots to anaerobic stress. Topics examinedinclude: (1) unexpected hypersensitivity, rather than hyper-resistance,to anoxia of root tips of flooding-tolerant plants; (2) protective,rather than damaging, effects of a stimulated energy metabolism(glycolysis and fermentation) under anaerobic conditions; (3)the concept of two main strategies of plant adaptation to anaerobicenvironments, namely avoidance of anaerobiosis on the wholeplant level, termed ‘apparent’ tolerance, and metabolicadaptation at the cellular and molecular levels, termed ‘true’tolerance; (4) the importance of protein synthesis during hypoxiaand anoxia for enhanced energy production and metabolic adaptation;(5) a general adaptive syndrome in plants to stress at the ultrastructurallevel and a possible molecular mechanism for its realizationunder anoxia; (6) the physiological role of anaerobically synthesizedlipids and nitrate as alternative electron acceptors in an oxygen-freemedium; and (7) the selection of cell lines derived from calluscultures that possess enhanced tolerance to anoxia and can regeneratewhole plants with improved tolerance of soil waterlogging.     

Reproductive behaviour indicates specificity in resource use: phylogenetic examples from temperate and tropical insects

Specificity (= the degree of ecological specialisation) is one of the fundamental concepts of the science of ecology. Ambiguities on how to define and measure specificity have however complicated respective research efforts. Here we propose that, in insects, a behavioural trait – adult oviposition latency in captivity without a favourable host plant – correlates with a species’ specificity in larval host use. In the absence of a suitable host, monophagous insects are expected to wait for a long time before commencing oviposition, with the long waiting time corresponding to careful host location behaviour in nature. Polyphagous insects, in contrast, should be selected for an increased oviposition rate at the expense of the quality of oviposition substrate encountered and will on average have a short latency time. Using experimentally derived data on oviposition latency, we performed a phylogenetically informed analysis based on Bayesian inference to show that this variable correlates with host specificity (larval diet breadth) in a sample of north European species of geometrid moths. A closely related index – the probability to lay any eggs on an unfavourable substrate – shows an analogous pattern. To provide an example of how these indices can be applied, we compare our sample of geometrid moths from northern Europe with a sample from equatorial Africa. A comparative analysis based on an original phylogenetic reconstruction found no differences between the two study sites in parameters of oviposition behaviour. We conclude that behavioural tests can provide information about ecological interactions when the latter can not be directly recorded. Our example study also hints at the possibility that host specificity of herbivores is not necessarily higher in a tropical region compared to a temperate one.     

Effects of temperature and sediment properties on benthic CO2 production in an oligotrophic boreal lake

1. Temperature and many other physical and chemical factors affecting CO₂ production in lake sediments vary significantly both seasonally and spatially. The effects of temperature and sediment properties on benthic CO₂ production were studied in in situ and in vitro experiments in the boreal oligotrophic Lake Pääjärvi, southern Finland. 2. In in situ experiments, temperature of the water overlying the shallow littoral sediment varied seasonally between 0.5 and 15.7 °C, but in deep water (≥20 m) the range was only 1.1–6.6 °C. The same exponential model (r² = 0.70) described the temperature dependence at 1.2, 10 and 20 m depths. At 2.5 and 5 m depths, however, the slopes of the two regression models (r² = 0.94) were identical but the intercept values were different. Sediment properties (wet, dry, mineral and organic mass) varied seasonally and with depth, but they did not explain a significantly larger proportion of variation in the CO₂ output rate than temperature. 3. In in vitro experiments, there was a clear and uniform exponential dependence of CO₂ production on temperature, with a 2.7‐fold increase per 10 °C temperature rise. The temperature response (slope of regression) was always the same, but the basic value of CO₂ production (intercept) varied, indicating that other factors also contributed to the benthic CO₂ output rate. 4. The annual CO₂ production of the sediment in Lake Pääjärvi averaged 62 g CO₂ m^?2, the shallow littoral at 0–3 m depth releasing 114 g CO₂ m^?2 and deep profundal (>15 m) 30 g CO₂ m^?2. On the whole lake basis, the shallow littoral at 0–3 m depth accounted for 53% and the sediment area in contact with the summer epilimnion (down to a depth c. 10 m) 75% of the estimated total annual CO₂ output of the lake sediment, respectively. Of the annual production, 83% was released during the spring and summer. 5. Using the temperature‐CO₂ production equations and climate change scenarios we estimated that climatic warming might increase littoral benthic CO₂ production in summer by nearly 30% from the period 1961–90 to the period 2071–2100.     

Natural variation in ozone sensitivity among Arabidopsis thaliana accessions and its relation to stomatal conductance

Genetic variation between naturally occurring populations provides a unique source to unravel the complex mechanisms of stress tolerance. Here, we have analysed O₃ sensitivity of 93 natural Arabidopsis thaliana accessions together with five O₃‐sensitive mutants to acute O₃ exposure. The variation in O₃ sensitivity among the natural accessions was much higher than among the O₃‐sensitive mutants and corresponding wild types. A subset of nine accessions with major variation in their O₃ responses was studied in more detail. Among the traits assayed, stomatal conductance (g_st) was an important factor determining O₃ sensitivity of the selected accessions. The most O₃‐sensitive accession, Cvi‐0, had constitutively high g_st, leading to high initial O₃ uptake rate and dose received during the first 30 min of exposure. Analyzing O₃‐induced changes in stress hormone concentrations indicated that jasmonate (JA) concentration was also positively correlated with leaf damage. Quantitative trait loci (QTL) mapping in a Col‐0 × Cvi‐0 recombinant inbred line (RIL) population identified three QTLs for O₃ sensitivity, and one for high water loss of Cvi‐0. The major O₃ QTL mapped to the same position as the water loss QTL further supporting the role of stomata in regulating O₃ entry and damage.     

Humidity-driven changes in growth rate, photosynthetic capacity, hydraulic properties and other functional traits in silver birch (Betula pendula)

A study was performed on saplings of silver birch (Betula pendula Roth) growing at the free air humidity manipulation site, which was established to investigate the effect of increased air humidity on tree performance and canopy functioning. The aim of the experiment was to simulate the impact of the increasing atmospheric humidity on forest ecosystems predicted for northern Europe. Artificially elevated relative humidity (RH), which causes transpirational flux to decrease, diminished nutrient supply to the foliage; leaf nitrogen content, phosphorus content and P:N ratio decreased. The changes in leaf nutritional status brought about a considerable decline in both photosynthetic capacity (A _max, V _cmax, J _max) and tree growth rate. The manipulation induced diverse changes in tree hydraulic architecture and other functional traits. Different segments of the soil-to-leaf water transport pathway responded differently: leaf hydraulic conductance (K _L) decreased, while hydraulic conductance of root systems (K _R) and leaf-specific conductivity of stem-wood increased in response to elevated RH. Humidification caused the Huber values of stems to increase, thus reflecting changes in allocation patterns; relatively more resources were allocated to vascular tissue and less to foliage. The elevated RH induced substantial changes in specific leaf area (increased), branch- (decreased) and stem-wood density (decreased). The observed responses suggest that the expected climate-change-induced increase in the growth rate of trees at northern latitudes (boreal areas) due to the earlier start of the growing season in spring or higher carbon assimilation rate could be smaller or null if temperature rise is accompanied by a rise in atmospheric absolute humidity.     

毛木耳子实体蛛网病的病害特征及致病菌Cladobotryum cubitense的生理特性和防控策略

从2010年起,在江苏省丰县毛木耳Auricularia cornea 产区观察到蛛网病症状,该病害的发生呈逐年上升趋势,对毛木耳产量和产业造成了严重的损失。经过2015-2016年两年的调查研究,分析毛木耳蛛网病的发病规律。致病菌分别与毛木耳菌丝体和子实体的互作研究表明,该病原真菌仅危害毛木耳子实体,使毛木耳子实体的子实层出现裂缝,进而引起子实体畸形甚至停止生长。该病原本被鉴定为Cladobotryum cubitense。经37℃高温处理7d可抑制其菌丝的生长,50%咪鲜胺锰盐也能够抑制C. cubitense菌丝的生长,为减轻或控制毛木耳蛛网病的发生和传播提供了可行性策略。     

Comparative Analysis of Hair Melanins by Chemical and Electron Spin Resonance Methods

Eighteen hair samples from Karakul newborn lambs with various colors were estimated for eumelanin and pheomelanin contents (C_e and C_p, respectively) by electron spin resonance (ESR) spectrometry and by high-performance liquid chromatography (HPLC). Correlation coefficients between the values estimated by the ESR and HPLC methods were 0.96, 0.93, and 0.99 for C_e, C_p, and C_e/C_p, respectively. The high correlation coefficients show that both methods fit well for estimation of relative values of these parameters. The absolute values of C_e and C_e/C_p coincide rather well when C_e is high, but considerable discrepancies appear when C_e is low. The reasons for these discrepancies are discussed. The HPLC method appears to be more sensitive for detection of low concentrations of pheomelanin, while the ESR method fits well for mass selection purposes.