ZHANG, M. I. N., and WILLISON, J. H. M. 1987. An improved conductivity method for the measurement of frost hardiness.Can. J. Bot. 65: 710-715. A suspension culture of Bromus inermis Leyss was grown under a variety of conditions to provide a range of frost hardiness. The growth conditions involved both low-temperature treatment and the addition of abscisic acid to the culture medium. Frost hardiness (LT,,, i.e., subzero temperature causing 50% mortality) was estimated by both fluorescein diacetate vital staining and by a conventional method involving estimation of ion leakage from frost-damaged cells by measurement of the conductivity of a bathing solution. It was found that the latter method always underestimated the frost hardiness by comparison with the former. Evidence that the vital staining estimates were reliable is presented. A subsequent time-course study of ion leakage from frost-stressed cultures showed that leakage increased with time of immersion in deionized water, and that the extent of the difference was dependent upon the growth conditions and the minimum temperature experienced. Analysis of the experimental data showed that this ion leakage differential can be used to estimate LT,, reliably by comparison with the vital staining estimates, and it is proposed that the protocol might be useful as an improved standard method in testing the frost hardiness of plant tissues. The physiological basis for this test is discussed. ZHANG, M. I. N., et WILLISON, J. H. M. 1987. An improved conductivity method for the measurement of frost hardiness.Can. J. Bot. 65 : 710-715. Une suspension de cellules de Bromus inermis Leyss a Ct C cultivCe sous diverses conditions d'endurcissement au gel. Les conditions de croissance comportaient un traitement 2 basse tempCrature et l'addition d'acide abscisique au milieu de culture. La rksistance au gel (TL,,, i.e., la temperature sous zCro causant 50% de mortalit&) fut CvaluCe par deux mCthodes differentes : la coloration vitale avec le diacCtate de fluorescCine et la conductivitC Clectrique de la solution, mesurant la sortie des ions des cellules, suite aux dommages causCs par le gel. L'on trouvC que cette demibre mCthode, comparativement B la premzre, sousestimait l'endurcissement au gel. Une preuve de la fiabilitC de la coloration vitale est prCsentCe. Une Ctude subsCquente des temps de sortie des ions, chez les cellules ayant subi le gel, a montrC que la perte d'ions augmentait avec le temps d'immersion dans l'eau dCsionisCe, et que l'importance de la diffkrence dCpendait des conditions de croissance et de la tempkrature minimale subie. L'analyse des risultats a rev616 que cette difference de sortie d'ions peut Ctre utiliske de faqon fiable pour la TL,, en comparaison avec les valeurs estimCes de la coloration vitale. L'on propose que le protocole pourrait Ctre utile en tant que mCthode uniformisCe et amCliorCe dans les essais d'endurcissement au gel des tissus vCgCtaux. La base physiologique de la mCthode est discutCe.

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