Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress

Salsomaggiore Terme, Italy - 26/29 September, 2001

ISBN 88-900622-1-5

Poster Abstract

CELLULAR AND MOLECULAR ANALYSIS OF THERMOTOLERANCE IN WHEAT

GULLÌ M.*, BOCCHIA G.P.*, CORRADI M.*, DE VITA P.**, DI FONZO N.**, PERROTTA C.*

* Dipartimento di Scienze Ambientali, Università di Parma

mgulli@unipr.it; cperrot@unipr.it

** Istituto Sperimentale per la Cerealicoltura Sez. Foggia

iscfg@isnet.it

thermotolerance, wheat, heat shock proteins

Organisms show a very different capacity to respond to environmental stimuli and inter and intra-specific variations are mostly due to genetic variability. Such differences in behaviour are fundamental for the determination of individual adaptability to sudden and sometimes abrupt environmental fluctuations. High temperature represents a major constraint affecting organisms adaptability and survival. Species can be classified into three groups: heat sensitive, relatively heat resistant and heat tolerant. Nevertheless the extent of the damage caused by exposure to high temperature may differ remarkably depending on the crop, stage of growth and type of plant tissue. Wild plants rarely die as a consequence of temperature fluctuation in natural environments and their heat tolerance is the result of a trade off between reproduction and productivity. On the contrary, temperature tolerance in many crop species was probably compromised by the centuries-long selection for yield potential and by the demand of single crop species to be ecologically ubiquitous. High temperature tolerance in plants has two components: I) inherent thermotolerance, a constitutive component resulting from the evolutionary thermal adaptation of species; II) acquired thermotolerance that relies on the induction of specific pathways during acclimation periods and corresponds to the ability of a plant to survive normally lethal temperatures after an initial exposure to mild heat stress. The basic aspect of heat shock response is represented by the synthesis of heat shock proteins (HSP). Quantitative and/or qualitative variation in HSPs expression was suggested to be correlated to the varying capacities of thermotolerant and thermosusceptible strains to acquire thermotolerance. The study of genetic variability in HSPs expression in wild and cultivated wheat species exhibiting different sensitivity to heat stress may allow the identification of new alleles, whose expression is correlated to thermotolerance. The final objective of this research will be the identification of genetic markers associated with an economically important trait such as thermotolerance, that could be used by plant breeders as selection tools. The plant material used consists of commercial genotypes, obsolete genotypes and wild wheat. Genetic variation in cellular thermotolerance was evaluated by cell membrane stability (CMS) and triphenyl tetrazolium chloride (TTC) cell viability assays. Both inherent and acquired thermotolerance have been evaluated on 20 wild, 14 commercial and 13 obsolete wheat genotypes using different stress conditions, and a good correlation was obtained between the assays. The results of thermotolerance analysis show that the CMS of the wild accessions was higher than that of the obsolete and currently used commercial varieties. These three groups of germplasms were also significantly different in terms of cell viability after heat stress, but in this analysis the differences were smaller and current cultivars were the least thermotolerant. Genetic variation in HSPs expression was evaluated in a group of 6 commercial wheat genotypes at the seedling stage. We analysed the amounts of several HSP mRNAs after two heat treatments (30 and 90 min at 40°C) and we calculated the HSP mRNA ratio between each time level. For all studied HSP mRNAs, ratios were different in a cultivar-dependent manner indicating that even in a limited set of modern cereal cultivars, significant differences could exist in heat stress response, and, hence, in thermotolerance potential. At the moment, field experiments are in progress to correlate the results obtained in a controlled environment to the conditions experienced by plants in natural environments.