Role of Phosphatidic Acid in High Temperature Tolerance in Maize

Maize (Zea mays L.) germplasm exhibits large genetic variations in tolerance to high temperature (HT) stress under fi eld conditions, but the mechanisms underling this variation are largely unknown. Based on many years of fi eld observation, maize inbred line B76 consistently displays better tolerance to HT than B106. Heat waves during growing season cause leaf fi ring in developing leaves and tassel blasting in B106 but not in B76. The difference in HT tolerance between the two inbred lines was confi rmed in growth chambers under controlled conditions. The two inbred lines showed similar level in the induction of heat shock proteins and a maize chloroplast protein synthesis elongation factor (EF-Tu), two mechanisms known to involve in HT tolerance in maize. A drastic decrease in photosynthetic system II (PSII) quantum effi ciency occurred at 34 to 35°C in B106; in B76, it occurred at a much higher temperature (>38°C). Cell membranes of B76 appeared to be more stable under HT than those of B106 based on electrolyte leakage analysis. Lipid profi les of young developing leaves by lipidomics showed that, among all lipids detected, only phosphatidic acid (PA) exhibited signifi cant higher level in B76 than in B106 under both normal and HT stressed conditions (p < 0.02). Moreover, PA was the only lipid that was signifi cantly increased by HT treatment (p < 0.05). Our results suggest that membrane thermostability is essential to HT tolerance and that PA may play an important role in imparting membrane thermostability, and, hence, HT tolerance in maize. J. Chen, J.J. Burke, and Z. Xin, USDA-ARS, Plant Stress and Germplasm Development Unit, 3810 4th St., Lubbock, TX 79415; W. Xu, AgriLife Research, Texas A&M System, 1102 East F.M. 1294, Lubbock, TX 79403. This paper is a joint contribution of USDA-ARS and the Texas A&M AgriLife Research. Mention of a trademark, warranty, proprietary product or vendor does not constitute a guarantee by the U. S. Department of Agriculture and does not imply approval or recommendation of the product to the exclusion of others that may be suitable. Received 13 Dec. 2009. *Corresponding author ( junping.chen@ ars.usda.gov). Abbreviations: CI, class 1; CII, class 2; EF-Tu, maize chloroplast protein synthesis elongation factor; Fvs/Fms, steady state photosynthetic system II quantum yield; HSP, heat shock protein; HT, high temperature; KLRC, Kansas Lipidomics Research Center; PA, phosphatidic acid; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; PSII, photosynthetic system II; RI, relative injury; sHSP, small heat shock protein. Published in Crop Sci. 50:2506–2515 (2010). doi: 10.2135/cropsci2009.12.0716 Published online 27 Sept. 2010. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.