Low temperature-induced alkalization of vacuoles in suspension-cultured cells of mung bean (Vigna radiata (L.) wilczek)
1995
Yoshida, S. (Hokkaido Univ., Sapporo (Japan). Inst. of Low Temperature Science)
In mung bean (Vigna radiata (L.) Wilczek) suspension-cultured cells,which are extremely chilling-sensitive at the early stage of exponential growth, cold-induced acidification of the cytoplasm has been shown to be closely correlated with the cold-induced in activation of the vacuolar H(+)-ATPase. To gain more insight into the mechanism of the cold-induced acidification of the cytoplasm in these suspension-cultured cells, we focused in the present study on changes in the vacuolar pH during cold incubation. The vacuolar pH was measured by fluorescence-ratio imaging cryomicroscopy, with CDCF-DA [5-(and 6-)carboxy-2'-7'-dichlorofluorescein diacetate] as a pH-sensitive probe. During cold incubation of the CDCF-loaded protoplasts from cells at the early stage of exponential growth, the vacuolar pH shifted toward alkaline values with time, increasing from 5.1 to 5.7 over the course of 8 hours. The increase in vacuolar pH was closely correlated with the acidification of cytoplasm. The cold-induced acidification of the cytoplasm appeared to be less dependent on the pH of the external medium. From the results, it appears that the cold-induced acidification of the cytoplasm probably reflects, to a considerable extent, the passive release of protons or proton equivalents from vacuoles as a consequence of the cold-induced inhibition of the ATP-driven transport of protons across vacuolar membranes
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