Wheat lectin as a factor in plant-microbial communication and a stress response protein

Wheat lectin (wheat germ agglutinin, WGA), a representative of a broad group of cereal lectins, is excreted by plant roots into the surrounding medium and interacts with both pathogenic microflora and growth-stimulating rhizobacteria. WGA was found to serve as a molecular signal for the rhizobacterium Azospirillum brasilense, which forms endophytic and associative symbioses with wheat plants. The bacterial response to the lectin was pleiotropic: WGA at concentrations from 10^?10 to 10^?6 M exerted a dose-dependent effect on a range of processes in the bacterium that are important for the establishment and functioning of symbiosis. Plants with different WGA content differed in their responses to severe nitrogen starvation and to seed treatment with Azospirillum.     

Mast fruiting of large ectomycorrhizal African rain forest trees: importance of dry season intensity, and the resource-limitation hypothesis

Mast fruiting is a distinctive reproductive trait in trees. This rain forest study, at a nutrient-poor site with a seasonal climate in tropical Africa, provides new insights into the causes of this mode of phenological patterning. At Korup, Cameroon, 150 trees of the large, ectomycorrhizal caesalp, Microberlinia bisulcata, were recorded almost monthly for leafing, flowering and fruiting during 1995-2000. The series was extended to 1988-2004 with less detailed data. Individual transitions in phenology were analysed. Masting occurred when the dry season before fruiting was drier, and the one before that was wetter, than average. Intervals between events were usually 2 or 3 yr. Masting was associated with early leaf exchange, followed by mass flowering, and was highly synchronous in the population. Trees at higher elevation showed more fruiting. Output declined between 1995 and 2000. Mast fruiting in M. bisulcata appears to be driven by climate variation and is regulated by internal tree processes. The resource-limitation hypothesis was supported. An 'alternative bearing' system seems to underlie masting. That ectomycorrhizal habit facilitates masting in trees is strongly implied.     

Root length density and water uptake distributions of winter wheat under sub-irrigation

As the critical information to study flow transport in soil–plant systems, root distributions and root-water-uptake (RWU) patterns have been studied extensively. However, most root distribution data in the past were collected under surface irrigation. Less research has been conducted to characterize root distributions under sub-irrigation. The objectives of this study were to (1) test if the generalized function of normalized root length density (NRLD) in the literature was applicable to root distributions of winter wheat under natural sub-irrigation, which provides water from subsurface by capillary rise from the water table, and (2) estimate RWU distributions of winter wheat under natural sub-irrigation. Column experiments were conducted to study the distributions of root length density (RLD) and RWU of winter wheat (Triticum aestivum L. cv. Nongda 189) during a growing period of 57 days from planting to tillering stages under surface irrigation and natural sub-irrigation. Data of root distributions and soil water content were collected in the experiments with different treatments of irrigation levels. Results showed that the RLD distributions of winter wheat under both surface irrigation and natural sub-irrigation were of similar patterns. The NRLD distributions under sub-irrigation were adequately characterized by the generalized function. An inverse method was employed to estimate the average RWU rate distributions of winter wheat. In addition, based on the potential RWU coefficient and the NRLD function, a simple approach was developed to predict RWU rates at different depths. The predicted RWU rates had a good agreement with the estimated RWU rate distributions using the inverse method.Section editor: R. E. Munns     

Performance of wheat crops with different chromosome ploidy: root-sourced signals, drought tolerance, and yield performance

Pot-culture experiments were carried out to estimate the role of non-hydraulic root signals (nHRS) and the relation of these signals to drought tolerance and grain yield formation under drought stress in six wheat varieties. These were two modern hexaploid wheat (Triticum aestivum L., AABBDD) Plateau602 and Longchun8139-2, two diploid wheat (Triticum monococcum L., AB) MO1 and MO4, and two tetraploid wheat (Triticum dicoccum Schuebl L., AABB) DM22 and DM31. In the two diploid relatives, the nHRS was switched on and off at a soil water content (SWC) of approximately 53–45% field water capacity (FWC). In contrast, in the modern hexaploid varieties, Longchun8139-2 and Plateau602 the nHRS occurred between a SWC of about 71 and 35% FWC, a much wider soil moisture range. The two tetraploid relatives, DM22 and DM31, were generally intermediate. The nHRS threshold range in SWC also narrowed as all six varieties went through successive developmental stages from shooting to grain filling. The two hexaploid wheat varieties had the longest duration of survival after the water supply ceased, and the best yield stability under drought stress, similar to with tetraploid wheat varieties; the diploid wheat varieties were least robust. These two parameters were both significantly correlated with the nHRS soil moisture threshold range (r=0.9456** and 0.8608*, respectively). Based on these patterns, we propose a ‘triple Z’ model to describe the features of non-hydraulic stomatal sensitivity versus soil drought in wheat growth.     

A novel ABA-hypersensitive mutant in Arabidopsis defines a genetic locus that confers tolerance to xerothermic stress

Hot and dry air (harmattan or xerothermic climate) greatly inhibits plant growth, particularly flowering and seed setting of crops. Little is known about the mechanism of plant response to this extreme environmental stress due to the lack of valuable genetic resource. Here, we report the isolation and characteristics of a unique Arabidopsis mutant, hat1 (h armattan t olerant 1), which shows high tolerance to hot and dry air. Under normal growth conditions, the mutant does not differ in morphology and soil drought tolerance compared to the wild type. When subjected to high temperature (42°C) and low humidity (10–15%), however, it could survive up to 6 days, while the wild type (Col-0) died after 24 h. The hat1 mutant also exhibits enhanced tolerance to soil drought, but only under xerothermic conditions. Mutant plants tightly close their stomata to retain water under xerothermic stress, and are more tolerant to high salinity at all developmental stages, accumulating less Na⁺ and more K⁺ than wild-type plants during NaCl treatment. Interestingly, hat1 plants are also ABA-hypersensitive. Genetic analysis revealed that the hat1 phenotype is caused by a dominant mutation at a single nuclear locus. Mapping studies indicate that Hat1 is located at an interval of 168 kb on chromosome 5 in which 21 genes are known to be regulated by diverse abiotic stresses. A mutant of this kind, to our knowledge, has not been previously reported. Thus, this report serves as a starting point in the genetic dissection of the plant response to xerothermic stress, and provides physiological and genetic evidence of the existence of a novel abiotic stress response pathway that is also ABA-dependent.     

Assessment of European streams with diatoms, macrophytes, macroinvertebrates and fish: a comparative metric-based analysis of organism response to stress

1. Periphytic diatoms, macrophytes, benthic macroinvertebrates and fish were sampled with standard methods in 185 streams in nine European countries to compare their response to degradation. Streams were classified into two main stream type groups (i.e. lowland, mountain streams); in addition, the lowland streams were grouped into four more specific stream types. 2. Principal components analysis with altogether 43 environmental parameters was used to construct complex stressor gradients for physical–chemical, hydromorphological and land use data. About 30 metrics were calculated for each sample and organism group. Metric responses to different stress types were analysed by Spearman Rank Correlation. 3. All four organism groups showed significant response to eutrophication/organic pollution gradients. Generally, diatom metrics were most strongly correlated to eutrophication gradients (85% and 89% of the diatom metrics tested correlated significantly in mountain and lowland streams, respectively), followed by invertebrate metrics (91% and 59%). 4. Responses of the four organism groups to other gradients were less strong; all organism groups responded to varying degrees to land use changes, hydromorphological degradation on the microhabitat scale and general degradation gradients, while the response to hydromorphological gradients on the reach scale was mainly limited to benthic macroinvertebrates (50% and 44% of the metrics tested correlated significantly in mountain and lowland streams, respectively) and fish (29% and 47%). 5. Fish and macrophyte metrics generally showed a poor response to degradation gradients in mountain streams and a strong response in lowland streams. 6. General recommendations on European bioassessment of streams were derived from the results.     

Computational Phlebology: The Simulation of a Vein Valve

We present a three-dimensional computer simulation of the dynamics of a vein valve. In particular, we couple the solid mechanics of the vein wall and valve leaflets with the fluid dynamics of the blood flow in the valve. Our model captures the unidirectional nature of blood flow in vein valves; blood is allowed to flow proximally back to the heart, while retrograde blood flow is prohibited through the occlusion of the vein by the valve cusps. Furthermore, we investigate the dynamics of the valve opening area and the blood flow rate through the valve, gaining new insights into the physics of vein valve operation. It is anticipated that through computer simulations we can help raise our understanding of venous hemodynamics and various forms of venous dysfunction.     

Occurrence and variability of mycotoxigenicFusarium species associated to wheat and maize in the South West of Spain

The contamination of cereals with mycotoxins produced by species ofFusarium is an important risk to human and animal health. The toxigenic profile is different depending on theFusarium species considered and, in some species, differences can also be observed at intraspecific level. Information about the distribution and variability of the mycotoxigenicFusarium species allow prediction of the toxins that may occur and to devise control strategies. In this work, the occurrence of mycotoxigenicFusarium species associated to cereals was analysed in a wide sample of durum wheat fields (Triticum durum Desf.) and maize from the South West of Spain (Andalucía).F. equiseti, F. graminearum andF. culmorum were the most frequentFusarium species detected in wheat fields followed byF. sambucinum andF. avenaceum, whereas in the case of maize,F. verticillioides andF. proliferatum were the onlyFusarium species present. The relationships of the Spanish isolates from theF. equiseti, F. avenaceum andF. sambucinum species were analysed by nucleotide sequence comparison of a partial region of the Elongation Factor 1 alpha (EF-1α) with other sequences available in data bases. The results indicated thatF. avenaceum andF. equiseti showed high variability and that the SpanishF. equiseti isolates seemed to belong toF. equiseti type II. Presented at the EU-USA Bilateral Workshop on Toxigenic Fungi & Mycotoxins, New Orleans, USA, July 5–7, 2005 Financial support: MCYT (AGL2004/07549/C05/5). M. Jurado was supported by pre-doctoral fellowship by the MCYT     

Seasonal variability in the palatability of freshwater macrophytes: a case study

The pond snail Lymnaea stagnalis (L.) was used for a laboratory assessment of seasonal variation in palatability of three freshwater macrophytes: Potamogeton lucens, Elodea canadensis and E. nuttallii. For each species, 2–5 populations were investigated in spring and in summer. Preliminary results showed that the feeding rate of similarly-aged snails bred under standard conditions was stable over time. In contrast, snail feeding rate on the three macrophyte species decreased from spring to summer, which was therefore interpreted as a decrease in plant palatability. This decrease was probably due to tissue maturation, as suggested by the concomitant increase in the dry matter content of leaves of the three species. The high palatability of the species studied during the spring may prove detrimental in cases of strong herbivore pressure, and could have consequences for macrophyte distribution among aquatic habitats.     

The Definition of British Water Beetle Species Pools (Coleoptera) and their Relationship to Altitude, Temperature, Precipitation and Land Cover Variables

Pooled water beetle species lists from 1826 British national grid 10-km squares were analysed using multivariate ordination and classification methods. The relationships of pool groups to the climate, altitude and land cover variables were assessed using constrained and partial ordinations. Ordination of the species pool data indicated a major trend between squares in the north-west of Scotland and those in southern England, illustrating differences in acid and basic water standing water. Secondary variation was from acid standing water to fast-flowing streams and rivers. Classification generated nine species pool groups. These showed a distinct north-west to south-east trend but there was no obvious coastal or brackish water effect on distribution. The climatic and land cover variables were all significantly related to each other, and to north-south variation in grid square location, but the constrained ordination results indicated that that the most important influence on water beetle species pool distribution was mean summer temperature. Although the amount of variation explained by the environmental variables was low, spatial variation in the environmental predictors was almost as important as the environmental variables themselves in determining species pool composition. Mean annual temperature was also strongly correlated with species pool distribution with two land cover variables slightly less important. Altitude and precipitation had the least influence. The water beetle national recording scheme database appears to be of sufficiently high quality for environmental investigations at the British scale. There is considerable potential for the synthesis of invertebrate species distribution, land cover and climate change predictions in the assessment of environmental change. The results, together with previous work on other invertebrate species, indicate that changing summer temperatures may have a considerable influence on the distribution British invertebrate species.