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JXB Advance Access originally published online on September 10, 2004
Journal of Experimental Botany 2004 55(406):2201-2211; doi:10.1093/jxb/erh241
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Journal of Experimental Botany, Vol. 55, No. 406, © Society for Experimental Biology 2004; all rights reserved

RESEARCH PAPER

Respiratory properties and malate metabolism in Percoll-purified mitochondria isolated from pineapple, Ananas comosus (L.) Merr. cv. smooth cayenne

Hoang Thi Kim Hong1,2, Akihiro Nose1,* and Sakae Agarie1

1Faculty of Agriculture, Saga University, 1 Honjo-machi, Saga, 840-8502, Japan
2Department of Biology, Faculty of Sciences, Hue University, 77 Nguyen Hue, Hue, Vietnam

* To whom correspondence should be addressed. Fax: +81 952 288737. E-mail: nosea{at}cc.saga-u.ac.jp

An investigation was made of the respiratory properties and the role of the mitochondria isolated from one phosphoenolpyruvate carboxykinase (PCK)-CAM plant Ananas comosus (pineapple) in malate metabolism during CAM phase III. Pineapple mitochondria showed very high malate dehydrogenase (MDH), and low malic enzyme (ME) and glutamate–oxaloacetate transaminase (GOT) activities. The mitochondria readily oxidized succinate and NADH with high rates and coupling, while they only oxidized NADPH in the presence of Ca2+. Pineapple mitochondria oxidized malate with low rates under most assay conditions, despite increasing malate concentrations, optimizing pH, providing cofactors such as coenzyme A, thiamine pyrophosphate, and NAD+, and supplying individually external glutamate or GOT. However, providing glutamate and GOT simultaneously strongly increased the rates of malate oxidation. The OAA easily permeated the mitochondrial membranes to import into or export out of pineapple mitochondria during malate oxidation, but the mitochondria did not consume external Asp or {alpha}-KG. These results suggest that OAA played a significant role in the mitochondrial malate metabolism of pineapple, in which malate was mainly oxidized by active mMDH to produce OAA which could be exported outside the mitochondria via a malate-OAA shuttle. Cytosolic GOT then consumed OAA by transamination in the presence of glutamate, leading to a large increase in respiration rates. The malate–OAA shuttle might operate as a supporting system for decarboxylation in phase III of PCK-CAM pineapple. This shuttle system may be important in pineapple to provide a source of energy and substrate OAA for cytosolic PCK activity during the day when cytosolic OAA and ATP was limited for the overall decarboxylation process.

Key words: Ca2+, malate–OAA shuttle, malate oxidation, NADPH oxidation, PCK-CAM, pineapple mitochondria


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