Effect of Helminthosporic Root Rot on the Lipid Content in Wheat Seedlings

The concentration of dry matter and the content of esterified fatty acids in total lipids of roots and etiolated shoots of 3- to 10-day-old seedlings of wheat (Triticum aestivum L.) infected with Bipolaris sorokiniana (Sacc.) Schoemaker, the agent of helminthosporic root rot, were determined in the course of germination. At the onset of germination, fungal infection caused a considerable increase in the dry matter concentration in both roots and shoots due to the enhanced mobilization of seed reserves. However, after the 7th day of germination, dry matter concentration fell below the level of noninfected control seedlings as a result of infection. The content of total lipids rose immediately after infection and always exceeded the control index up to the end of germination, in spite of a continuous decrease in this index in both control and infected seedling. It is concluded that an increase in the content of cellular lipids is a characteristic response of both shoots and roots to the root rot infection of wheat seedlings.     

The Effect of Helminthosporic Root Rot on the Composition of Acyl Lipids of Wheat Seedlings

The changes of the molecular species composition of esterified fatty acids (FAs) of total and nonextractable lipids were determined in roots and etiolated shoots of 3- to 10-day-old wheat (Triticum aestivumL.) seedlings infected with the fungus Bipolaris sorokiniana, the agent of helminthosporic root rot. A novel technique of assessing the extent of the infection-induced deviation of FA composition, mol %, from the control value was developed. It consists in the quantitative determination of both the deviations in this composition and the extent of contribution of separate FA species to the deviations observed. The application of this technique has shown that, for the total lipids, the maximum of such a deviation, in accordance with the membrane theory of stress, directly coincided in time with the onset of a decrease in the dry matter content in both roots and shoots. In each of these, the deviation was primarily caused by the change in the content of those FA species that usually dominate in a specific group of membrane lipids prevailing in a given organ, viz., plastid glycolipids in shoots and extraplastidal membrane phospholipids in roots. In both cases, C₂₀–C₂₂FAs significantly contributed to the deviations observed. This fact seems to reflect an enhanced formation of epicuticular waxes rich in these FAs on the shoot and root surfaces as an adaptive response of plants to fungal infection. Nonextractable (annular) membrane lipids, because of their vital importance for the survival of plant cells, differed from the total lipids with a far greater stability of their quantitative FA composition under conditions of infection-induced metabolic disturbances.     

The effect of Ca2+-stress on fluxes of Ca2+ and K+ in wheat and cucumber

Betula papyrifera Marsh, seedlings adapted very poorly to flooding for up to 60 days. Responses to flooding included increased ethylene production; stomatal closure; leaf senescence; drastic inhibition of shoot growth, cambial growth, and root growth; decay of roots, and death of many seedlings. Flooding inhibited growth of leaves that formed prior to flooding, inhibited formation of new leaves, and induced abscission of old leaves. As a result of extensive leaf abscission, fewer leaves were present after flooding than before flooding was initiated. The drastic reduction in leaf area was associated with greatly decreased growth of the lower stem and roots. No evidence was found of adaptive morphological changes to flooding. The data indicate that intolerance of B. papyrifera seedlings to flooding is an important barrier to regeneration of the species on sites subject to periodic inundation.     

The Effect of Local Cooling of Cucumber and Wheat Seedlings on Various Kinds of Stress Resistance of Their Leaves and Roots

Shoots and roots of wheat (Triticum aestivum L., cold-resistant species) and cucumber (Cucumis sativus L., cold-sensitive species) were chilled at 2°C or 10°C, respectively, for 7 h. The changes in cold, heat, and salt resistance in treated leaf and root cells were recorded. Local cooling of the leaf resulted in an increase of its cold and salt tolerance, but its heat tolerance remained unchanged. At the same time, cold tolerance of the root slightly increased as a result of local cooling, but its heat and salt tolerance decreased. Cooling of the shoot did not affect the cold and heat tolerance of root cells but caused a decrease in their salt tolerance. Finally, in the leaf maintained at a normal temperature, there was an increase in all kinds of stress resistance as a result of root cooling. We discuss the possibility of an unspecific change in stress resistance caused by metabolic shifts. These shifts are induced by a signal, which is transmitted inside the plant into plant organs located at a considerable distance from the chilled ones.     

小麦PAL基因的克隆及赤霉菌诱导下的表达分析

利用苯丙氨酸解氨酶(PAL,phenylalanine ammonia-lyase)基因保守区域从小麦抗赤霉病材料苏麦3号中克隆获得4个PAL基因,分别命名为Ta PAL1、Ta PAL2、Ta PAL3、Ta PAL4。4个基因的开放阅读框(ORF,open reading frame)长度分别为2142 bp、2016 bp、2118 bp和2139 bp,分别编码714个、672个、706个和713个氨基酸。基因序列比对发现其相似性达到88.35%,所编码的氨基酸相似性为91.92%,氨基酸序列分析表明4个基因都包含HAL-PAL结构域及PAL结构域。通过接种禾谷镰刀菌,利用荧光定量PCR对PAL基因进行表达分析发现,4个PAL基因全部为上调表达,其中Ta PAL2、Ta PAL3和Ta PAL4最为明显。PAL基因的上调表达,说明PAL基因在小麦抵抗赤霉病菌侵染的机制中可能起着重要作用。     

Effects of chlorosubstituted indoleacetic acids on root growth, ethylene and ATP formation

7-Chloroindoleacetic acid and dichloroindoleacetic acids with a Cl in the 7 position showed anti-auxinic activity and promoted root growth in wheat ( Triticum aestivum L. cv. Diamant II). In contrast, 4-, 5- and 6-chloroindoleatetic acids acted as strong auxins inhibiting the growth of wheat roots. Flax ( Linum usitatissimum L. cv. Concurrent) and cucumber ( Cucumis sativus L. cv. Favör) roots showed similar, but less clear-cut responses. 7-Chloroindoleacetic acid and 4,7-dichloroindoleacetic acid alleviated root growth inhibition in wheat caused by IAA, monochloroindoleacetic acids and benzyladenine. 2,4-D, 4- and 6-chloroindoleacetic acids strongly induced ethylene formation in cucumber seedlings; 4,7- and 6,7-dichloroindoleacetic acids did not, except at high concentrations. The more lipid-soluble dichloroindoleacetic acids were stronger inhibitors of ATP formation in cucumber mitochondria than monochloroindoleacetic acids, while IAA itself had only a very slight effect.     

Uptake of calcium in wheat and cucumber roots

Uptake of Ca²⁺(⁴⁵Ca) was investigated in plants of wheat ( Triticum aestivum L. var. Svenno) and cucumber ( Cucumis sativus L. var. Cilla) cultivated in a nutrient solution with various Ca²⁺ concentrations. The adsorption of Ca²⁺ was higher in cucumber roots than in wheat roots especially at lower Ca²⁺ levels in the external medium. The intracellular fraction of Ca²⁺ was less than 20% of the total Ca²⁺ in wheat roots and less than 10% of the total Ca²⁺ in cucumber roots. The uptake of Ca²⁺ in cucumber was about 40 times higher than in wheat. Transport of Ca²⁺ in the roots towards the endodermis is suggested to take place mainly in the apoplastic pathway regulated by the availability of negatively charged binding sites along the cell wall continuum. Further transport of Ca²⁺ towards the stele may involve diffusion of Ca²⁺ into the symplasm in the vicinity of the endodermis. An active extrusion of Ca²⁺ towards the stele or towards the external medium is suggested to play a role in the regulation of Ca²⁺ uptake.     

Paths to last in mixed crop–livestock farming: lessons from an assessment of farm trajectories of change

Mixed crop–livestock systems, combining livestock and cash crops at farm level, are considered to be suitable for sustainable intensification of agriculture. Ensuring the survival of mixed crop–livestock systems is a challenge for European agriculture: the number of European mixed crop–livestock farms has been decreasing since 1970. Analysis of farming system dynamics may elucidate past changes and the forces driving this decline. The objectives of this study were (i) to identify the diversity of paths that allowed the survival of mixed crop–livestock farming and (ii) to elucidate the driving forces behind such survival. We analysed the variety of farm trajectories from 1950 to 2005. We studied the entire farm population of a case study site, located in the ‘Coteaux de Gascogne’ region. In this less favoured area of south-western France, farmers have limited specialisation. Currently, half of the farms use mixed crop–livestock systems. The data set of 20 variables for 50 farms on the basis of six 10-year time steps was collected through retrospective surveys. We used a two-step analysis including (i) a visual assessment of the whole population of individual farm trajectories and (ii) a computer-based typology of farm trajectories on the basis of a series of multivariate analyses followed by automatic clustering. The European Common Agricultural Policy, market globalisation and decreasing workforce availability were identified as drivers of change that favoured the specialisation process. Nevertheless, farmers’ choices and values have opposed against these driving forces, ensuring the survival of some mixed crop–livestock farming systems. The trajectories were clustered into five types, four of which were compatible with mixed crop–livestock systems. The first type was the maximisation of autonomy by combining crops and livestock. The second type was diversification of production to exploit economies of scope and protect the farm against market fluctuations. The other two types involved enlargement and progressive adaptation of the farm to the familial workforce. The survival of mixed crop–livestock systems in these two types is largely dependent on workforce availability. Only one type of trajectory, on the basis of enlargement and economies of scale, did not lead to mixed crop–livestock systems. In view of the current evolution of the driving forces, maximising autonomy and diversification appear to be suitable paths to deal with current challenges and maintain mixed crop–livestock systems in Europe.     

Growth, light interception and yield responses of spring wheat (Triticum aestivum L.) grown under elevated CO2 and O3 in open-top chambers

Spring wheat cv. Minaret was grown to maturity under three carbon dioxide (CO₂) and two ozone (O₃) concentrations in open-top chambers (OTC). Green leaf area index (LAI) was increased by elevated CO₂ under ambient O₃ conditions as a direct result of increases in tillering, rather than individual leaf areas. Yellow LAI was also greater in the 550 and 680 μmol mol^–1 CO₂ treatments than in the chambered ambient control; individual leaves on the main shoot senesced more rapidly under 550 μmol mol^–1 CO₂, but senescence was delayed at 680 μmol mol^–1 CO₂. Fractional light interception (f) during the vegetative period was up to 26% greater under 680 μmol mol^–1 CO₂ than in the control treatment, but seasonal accumulated intercepted radiation was only increased by 8%. As a result of greater carbon assimilation during canopy development, plants grown under elevated CO₂ were taller at anthesis and stem and ear biomass were 27 and 16% greater than in control plants. At maturity, yield was 30% greater in the 680 μmol mol^–1 CO₂ treatment, due to a combination of increases in the number of ears per m^–2, grain number per ear and individual grain weight (IGW). Exposure to a seasonal mean (7 h d^–1) of 84 nmol mol^–1 O₃ under ambient CO₂ decreased green LAI and increased yellow LAI, thereby reducing both f and accumulated intercepted radiation by ≈ 16%. Individual leaves senesced completely 7–28 days earlier than in control plants. At anthesis, the plants were shorter than controls and exhibited reductions in stem and ear biomass of 15 and 23%. Grain yield at maturity was decreased by 30% due to a combination of reductions in ear number m^–2, the numbers of grains per spikelet and per ear and IGW. The presence of elevated CO₂ reduced the rate of O₃-induced leaf senescence and resulted in the maintenance of a higher green LAI during vegetative growth under ambient CO₂ conditions. Grain yields at maturity were nevertheless lower than those obtained in the corresponding elevated CO₂ treatments in the absence of elevated O₃. Thus, although the presence of elevated CO₂ reduced the damaging impact of ozone on radiation interception and vegetative growth, substantial yield losses were nevertheless induced. These data suggest that spring wheat may be susceptible to O₃-induced injury during anthesis irrespective of the atmospheric CO₂ concentration. Possible deleterious mechanisms operating through effects on pollen viability, seed set and the duration of grain filling are discussed.     

The Development of Leaf Heat-Tolerance during the Local Heating of Seedling Organs

Experiments using cucumber (Cucumis sativusL.), wheat (Triticum aestivumL.), and barley (Hordeum vulgareL.) seedlings showed that actinomycin D partially inhibited an increase in the heat-tolerance of leaves heated at 38°C for 7 h but did not affect this index when the roots were heated. Exogenous ABA increased heat-tolerance in both cases. These results, with regard to the data demonstrating an important contribution of protein synthesis to the specific increase in heat-tolerance during the heat acclimation of intact plants, make it possible to conclude that the development of leaf heat-tolerance resulting from the local heating of shoots depends on the induced synthesis of mRNAs and respective proteins. At the same time, there is little or no such dependence during root heating. ABA manifested itself as a factor of a general, nonspecific increase in heat-tolerance during the local heating of both shoots and roots.