. 1992. F,lectrical impedance analysis in plant tissues: The effect of freeze-thaw injury on the electrical properties of potato tuber and carrot root tissue.Can. J. Plant Sci.72: [545][546][547][548][549][550][551][552][553]. Electrical impedances in the range 100 Hz to 800 KHz were measured in potato tubers and carrot root cortex both before and after freeze-thaw cycles. These impedance data were analyzed using equivalent circuit modelling based on complex nonlinear least squares (CNLS) (Zhang and Willison l99la). After freezing to and thawing from -3, -6, -9 and -12oC, carrot root tissues were best characterized by a double shell model composed of extracellular resistance, cytoplasmic resistance, plasma membrance capacitance, vacuole interior resistance, and tonoplast capacitance. Although freeze-thaw cycles to -3 or -6'C did not kill the carrot tissues, extracellul,ar resistance and vacuole interior resistance were halved relative to control tissues, and cytoplasmic resistance decreased to a third ofthe control value. Plasma membrane capacitance and tonoplast capacitance were not affected by the -3 and -6"C noninjurious stresses. After carrot root or potato tuber tissues had been killed by freezing (-3'C for potato tuber and -18'C for carrot), the tissues were best represented by a single-shell model composed of extravesicular resistance, intravesicular resistance, and vesicle membrane. Compared with unfrozen controls, freeze-killed potato tubers were characterized by a 30-fold decrease in extracellular resistance, a7-fold decrease in intracellular resistance, and a l0-fold decrease in plasma membrane capacitance. Freeze-killed carrot roots were characterized by a 30-fold decrease in extracellular resistance, 3-fold decrease in intracellular resistance, and 3.5-fold decrease in plasma membrane capacitance. These results are compatible with massive rupturing of protoplasts during lethal freeze-thaw injury. (CNLS). Aprds des gels de -3, -6, -9 et -12'C,les tissus d6gel6s de carotte pouvaient se caract6riser par un moddle ir deux enveloppes compos6 de r6sistance extracellulaire, r6sistance cytoplasmique, capacitance de la membrane plasmatique, r6sistance intra-vacuolaire et capacitance des tonoplastes.Bien que des gels de -3 ou de -6'C n'aient pas tu6 les tissus, la r6sistance extracellulaire et la r6sistance intra-vacuolaire 6taient r6duites de moiti6 par rapport 2r celles des tissus t6moins et Ia r6sistance cytoplasmique 6tait r6duite des deux tiers. La capacitance de la membrane plasmatique et celle des tonoplastes n'dtaient pas affect6es par ces stress non destructeurs. Aprbs gel destructeur (-3"C pour la pomme de terre et -l8'C pour la carotte), les tissus pouvaient s'adapter )r un moddle ir enveloppe simple com-
Turnip (Brassica rapa L.) root tissue was exposed to freeze-thaw stresses of −7, −9, -−11 and −19 °C. The post-thawed tissues were either subjected to leaching in deionized water for 2 h or left at 100% humidity. Tissue survival was then assayed by vital staining using modified 2,3,5-triphenyltetrazolium chloride (TTC) staining in 0.2 M phosphate buffer. Tissue survival was significantly lower for leached samples than for non-leached samples. It is concluded that freeze-thaw injury in plant tissues is enhanced by post-thaw leaching in water. The 0.05 M phosphate buffer commonly used for TTC staining also damaged freeze-thaw injured tissue. Key words:Brassica rapa L., 2,3,5-triphenyltetrazolium chloride (TTC), freeze-thaw injury, leaching
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