develop a molecular map,for this population will facilitate the isolation of genes/QTL associated with PSR and provide a valuabletool for markerassistedselection(MAS). A candidate gene approach using genes with known function in Arabidopsisfruit development is being adoptedto investigate the genetic regulation of DZ development in B. napus.Previously, two QTL potentially linked to increased PSR in B.napus have been identified using a relatively small dataset.Furtheranalysisusing dataobtained during this study will be used to validate these and also to try to identify new QTL. doi:10.1016/j.cbpa.2007.01.633 P6.37 Towards understanding the physiological basis of root penetration QTLs in rice L. Clark, R. Whalley,(Rothamsted Research); A. Price, (University of Aberdeen) Strong soil due to soil compaction or drying can be a major constraint to root growth. Rice is an ideal model system for the study of root responses to mechanical impedance as there is evidence for cultivardifferences in root penetration. Several quantitative trait loci (QTL) controlling root penetration have been identified in a Azucena × Bala mapping population (Price etal.,2000).Here,we present evidence from pairs of near- isogenic lines that differences in root penetration of wax layers are due to differences in bending stiffness. Root bending stiffnessis strongly dependent on root diameter, with an approximately fourth power relationship. Studies of this kind have the potential to help elucidate the mechanism of action of root penetration QTLs. Reference: Price et al., 2000. Theor. Appl. Genet. 100, 49–56. doi:10.1016/j.cbpa.2007.01.634 P6.38 Brassinosteroids protect plants against heat stress A. Confraria, (University of Porto and University of the West of England); R. Desikan, (Imperial College London); I. Santos, (University ofPorto);S. Neill,(University ofthe Westof England) Brassinosteroids (BRs) are plant steroid hormones that control a wide range of processes such as cell division and expansion, xylem differentiation, seed germination, vegetative growth and apical dominance (Sasse, 2003). BRs have also been reported to increase plant resistance to biotic and abiotic stresses. However, the mechanisms underlying such protective properties of BRs remainlargely unexplored. We haveobservedthat 24- epibrassinolide (EBR) could protect in vitro grown potato plants from heat stress.It is also apparentthat EBR effectiveness in protection is affected by the concentratio ethanol – the solventfor EBR – in the growth medium. Protective effects of EBR against heatstress have also been detected in Arabidopsis thaliana, in keeping with a recent report by Kagale et al. (2007). In order to search for potential explanations for these effects of EBR, the effects of EBR on enzymatic antioxidants were determined; no significant e were observed. Subsequently, a proteomics approach wa After 14 days of growth in modified MS medium supplem with 20 nM EBR,potato plants were heat-stressed and lea samples were harvested for protein extraction. Proteins e were then separated by 2D gel electrophoresis and differ regulated proteins were selected for identification by mass spectrometry. Data on specific proteins will be presented and discussed. A. Confraria is supported by FCT grant. Kagale, S., et al., 2007. Planta. 225, 353–364. Sasse, J.M., 2003. J. Plant Growth Regul. 22, 276–288. doi:10.1016/j.cbpa.2007.01.635 P6.39 Metabolism of fructans during the maturation of wheat kernels A. Paradiso, E. Greco,L. De Gara,(Dep.PlantBiology and Pathology University of Bari, Italy); M. D'Egidio, C. Cecchi (CRA Rome, Italy); C. Corradini,(Dep. of Chemistry University of Parma, Italy) Fructans are polysaccharides occurring in 15% of flowering species; their structure is specie-specific, varying in glyco linkage,branching and degree of polymerization. In plants, fructans are known to be involved in the responses again hydric and termic stresses. Moreover, they recently received much attention in food science as prebiotics. Fructansmetabolism was investigated in wheat kernels.It has previously been shown that kernels are particularly rich in fructans during the first period ofmaturation (9–17 days form anthesis);whereas,theircontentdecreaseas the development proceeded (De Gara et al. 2003).In this study the changes in the levels and polymerization degree of the fructansstored in different kerneltissueshasbeen further investigated. The variations in the activity/expression of the enzymesresponsible for fructansynthesisand hydrolysis have also beenanalysedat differentphasesof kernel maturation. Our results suggest that wheat are able to synthesise fru the kernels and that the enzymes involved in the biosynt hydrolysis change their expression and/or activity during development, according to the variations of fructan contents observed in kernel tissues. S279 Abstracts / Comparative Biochemistry and Physiology, Part A 146 (2007) S267 – S280