Physiological and biochemical characteristics of a nickel-tolerant cell line of tobacco (Nicotiana tabacum L. cv BY-2) suspension culture

摘要

We selected a Ni-tolerant tobacco cell line, termed NIT cells, from BY-2 suspension culture to clarify the cellular/ molecular mechanisms of Ni tolerance in higher plants. Examination of response to various abiotic stresses showed that the NIT cells acquired remarkable tolerance to excess Ni, Cu, and Al. That the NIT cells accumulated approximately 2 mM Ni and 160 μM Cu under 700 μM Ni and 30 μM Cu conditions, respectively, is an indication that the NIT cells are Ni or Cu accumulators and possess internal detoxification mechanisms for these metals. Citrate content was approximately 2-fold higher in the NIT cells with or without Ni than in the WT cells, and the contents of other organic acids were also higher in the NIT cells. In addition, histidine content was increased by 3-fold in the NIT cells under the 700 μM Ni condition. We also investigated the localization and transport of Ni in the NIT cells with isolated vacuoplasts (vacuole-enriched protoplasts). Newport green DCF diacetate (NPG), a Ni fluorescence indicator, was used for observing the subcellular localization of Ni in both WT and NIT cells. After the addition of the NPG probe into the cells, the fluorescence of the NPG was localized only in the vacuoles regardless of the WT or NIT cells under the 200 μM or 700 μM Ni condition. It is surmised that the transport of Ni-citrate and/or Ni-histidine complex into the vacuoles might be an important mechanism underlying the high tolerance to Ni of and hyperaccumulation of Ni in the NIT cells.