The ascorbate peroxidase regulated by H(2)O(2) and ethylene is involved in cotton fiber cell elongation by modulating ROS homeostasis.

Ascorbate peroxidase (APX) is a reactive oxygen species (ROSs) scavenging enzyme involved in regulation of intracellular ROS levels by reduction of H(2)O(2) to water using ascorbate as an electron donor. In New Phytologist 2007; 175:462-71, we identified a cotton cytosolic APX1 (GhAPX1) that was significantly accumulated during the fast fiber-cell elongation period, through a proteomics approach. Both the transcript levels of GhAPX1 and the total APX activity were highly induced in response to in vitro applied H(2)O(2) or ethylene. Further analysis showed that ethylene promoted H(2)O(2) production 1 day after it was included in the culture medium, suggesting that H(2)O(2) induced cell elongation processes may be placed downstream of the ethylene signal transduction pathway. In this addendum, quantitative real-time RT-PCR showed that only cytosolic APX1, not other cotton APX genes including a second cytosolic APX2, a glyoxysomal and a stromal APXs, was up-regulated during fiber cell elongating. Exogenous H(2)O(2) was found to induce ethylene production if wild-type cotton ovules were cultured for a longer period of time, implying that there was a feedback regulatory mechanism from H(2)O(2) to ethylene biosynthesis in modulating cotton fiber development.