Sudden collapse of vacuoles in Saintpaulia sp. palisade cells induced by a rapid temperature decrease

PLoS One. 2013;8(2):e57259. doi: 10.1371/journal.pone.0057259. Epub 2013 Feb 25.

Abstract

It is well known that saintpaulia leaf is damaged by the rapid temperature decrease when cold water is irrigated onto the leaf surface. We investigated this temperature sensitivity and the mechanisms of leaf damage in saintpaulia (Saintpaulia sp. cv. 'Iceberg') and other Gesneriaceae plants. Saintpaulia leaves were damaged and discolored when subjected to a rapid decrease in temperature, but not when the temperature was decreased gradually. Sensitivity to rapid temperature decrease increased within 10 to 20 min during pre-incubation at higher temperature. Injury was restricted to the palisade mesophyll cells, where there was an obvious change in the color of the chloroplasts. During a rapid temperature decrease, chlorophyll fluorescence monitored by a pulse amplitude modulated fluorometer diminished and did not recover even after rewarming to the initial temperature. Isolated chloroplasts were not directly affected by the rapid temperature decrease. Intracellular pH was monitored with a pH-dependent fluorescent dye. In palisade mesophyll cells damaged by rapid temperature decrease, the cytosolic pH decreased and the vacuolar membrane collapsed soon after a temperature decrease. In isolated chloroplasts, chlorophyll fluorescence declined when the pH of the medium was lowered. These results suggest that a rapid temperature decrease directly or indirectly affects the vacuolar membrane, resulting in a pH change in the cytosol that subsequently affects the chloroplasts in palisade mesophyll cells. We further confirmed that the same physiological damage occurs in other Gesneriaceae plants. These results strongly suggested that the vacuoles of palisade mesophyll cells collapsed during the initial phase of leaf injury.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Fluorescent Dyes
  • Hydrogen-Ion Concentration
  • Magnoliopsida / cytology*
  • Plant Leaves / metabolism
  • Temperature*
  • Vacuoles*

Substances

  • Fluorescent Dyes

Grants and funding

This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas (22120006) by the Japanese Ministry of Education, Culture, Sports, Science and Technology (http://www.mext.go.jp/a_menu/shinkou/hojyo/main5_a5.htm) and CREST of JST (Japan Science and Technology Agency) (http://www.jst.go.jp/kisoken/crest/en/index.html) to TM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.