20. G418-resistant Ba/F3 transfectants expressing the indicated proteins and control cells were grown in RPMI 1640 medium containing 10% fetal bovine serum and 2% WEHI conditioned medium as a source of IL-3. Cells were washed twice in the same IL-3free medium and then seeded in IL-3-free medium in 96-well plates at a concentration of 5 ϫ 10 4 cells/ml (10 4 cells per well). The number of wells showing proliferating cells in either the absence or presence of IL-3 was scored after 1 week in culture.

. Evaluation of field and laboratory predictors of drought and heat tolerance in winter cereals. Can. J. Plant Sci 77: 523-531. In Mediterranean regions, plant breeding programs are being conducted to select genotypes having high and stable yields. Screening techniques that are able to identify desirable genotypes based on the evaluation of physiological traits related to stress tolerance could be useful, particularly if they are rapid, simple and inexpensive. The objectives of this study were: i) to evaluate the validity of four laboratory screening tests to discriminate among bread wheat (Triticum aestivum L.), durum wheat (Triticum turgidum L.) and barley (Hordeum vulgare L.) cultivars differing in adaptation to the Mediterranean climate; ii) to evaluate the repeatability of determinations performed on cultivars grown in different locations and years, and iii) to evaluate relationships among the tests and yield performance under stress. The tests were: cellular membrane stability after heat (CMS-HS) and drought stress (CMS-DS), tolerance to leaf water loss (LWL), and translocation capacity after the chemical desiccation (CD) of the photosynthetic apparatus. The CMS-HS and CMS-DS tests revealed genetic variability in all the three species. The LWL test did not differentiate genotypes at some sites. Genetic differences for grain yield, kernel weight and harvest index after chemical desiccation were evident for wheat genotypes but the test did not differentiate barley genotypes. The test performed under laboratory controlled conditions (CMS-HS, CMS-DS and LWL) was less affected by environment compared with the test based on the evaluation of the translocation capacity after chemical desiccation carried out in the field. We concluded that, when good standardization of procedures are obtained, the tests investigated can be regarded as possible tools in breeding programs for tolerance to heat and drought stress. ) selon leur adaptation au climat de la Méditerranée, ii) d'évaluer la répétabilité des déterminations faites sur un certain nombre des cultivars cultivés à des emplacements et en des années différents et iii) d'évaluer les rapports existant entre les tests et le rendement en condition de stress. Les tests portaient i) sur la stabilité de la membrane cellulaire après un stress thermique (SMC-st) et hydrique (SMC-sh), ii) sur la tolérance aux déperditions d'eau par les feuilles (DEF) et iii) sur la capacité de transport après dessiccation chimique (DC) de l'appareil photosynthétique. Les tests SMC-st et SMC-sh ont permis de mettre à jour l'existence de variabilité génétique au sein des trois espèces. A certains endroits, il etait pas été possible de différencier les génotypes selon les DEF. Des différences génétiques quant au rendement grainier, au poids des grains et à l'indice de moisson, à la suite d'une dessiccation chimique ont pu être constatées chez le blé, mais pas chez l'orge. Les tests réalisés en milieu contrôlé (SMC-st, SMC-sh et DEF) étaient moins sensibles aux conditions environnementales que l...

High temperatures occurring during grain filling are known to affect wheat grain yield and quality considerably. In this paper we report the results of experiments carried out with two cultivars of bread wheat (Triticum aestivum L.) and two cultivars of durum wheat (Triticum durum Desf.). The plants, cultivated in pots, were subjected to 13 heat treatments (temperature up to 40°C) differing in duration and timing and starting 7 days after anthesis. Heat treatments were applied by temporary transfer of the pots to a glasshouse where the temperature rose to 40°C as a consequence of solar radiation for periods ranging from 5 to 30 days. The applied heat shocks substantially affected dry matter and protein accumulation in the different parts of the plant. Early heat shock (5 days with a total of 18 h of temperature in the range 35–40°C) caused a small reduction of kernel mass and no effect on protein per kernel; the damage was greater in the central and in the final stage of grain filling. Plants subjected to a progressive increase of temperature, or to an early heat shock, acquired thermotolerance to further heat shocks. Continuous exposure to very high temperatures from 27 days after pollination to maturity did not negatively affect grain yield and it facilitated the remobilisation of nitrogen from vegetative to reproductive organs. Rheological properties were severely affected by heat shocks at all stages of grain filling: 5 days of heat shock were sufficient to reduce mixing tolerance by 40–60%. These variations in rheological properties were accompanied by modification of the level of protein aggregation: soluble polymeric proteins and low molecular weight gliadins progressively increased according to the intensity of the stress, while insoluble polymeric proteins decreased. Our experiments, carried out in conditions close to the Mediterranean climate, indicate that the occurrence of very high temperature in the range 35–40°C during grain filling substantially affects dry matter and protein accumulation in the different parts of the plant. The formation of the complex protein aggregates responsible for positive dough mixing properties is significantly reduced by very high temperature. When heat shock came late in grain filling, grain yield and protein concentration were not negatively affected but a ‘dough weakening’ effect, which may reduce the commercial value of the production, is to be expected.