A proteomic approach to analyze salt-responsive proteins in rice leaf sheath Fida Mohammad Abbasi and Setsuko Komatsu National Institute of Agrobiological Sciences, Tsukuba, Japan To examine the response of rice to salt stress, changes in protein expression were analyzed using a proteomic approach. To investigate dose- and time-dependent responses, rice seed- lings were exposed to 50, 100 and 150 mM NaCl for 6 to 48 h. Proteins were extracted from leaf sheath and separated by two-dimensional polyacrylamide gel electrophoresis. Eight proteins showed 1- to 3-fold up-regulation in leaf sheath, in response to 50 mM NaCl for 24 h. Among these, three proteins were unidentified (LSY081, LSY262 and LSY363) while five proteins were identified as fructose bisphosphate aldolases, photosystem II (PSII) oxygen evolving complex protein, oxygen evolving enhancer protein 2 (OEE2) and superoxide dismutase (SOD). The maximum expression levels of seven proteins were at 24 h. Their expression declined after 48 h of 50 mM NaCl treatment. In contrast, SOD maintained its elevated expression throughout these conditions. The increased expression of proteins seen in the 50 mM NaCl treatment group was less pronounced in the groups receiving 100 or 150 mM NaCl for 24 h. The expres- sion of SOD was a common response to cold, drought, salt and abscisic acid (ABA) stresses while the expression of LSY081, LSY363 and OEE2 was enhanced by salt and ABA stresses. LSY262 was expressed in leaf sheath and root, while fructose bisphosphate aldolases, PSII oxygen evolving complex protein and OEE2 were expressed in leaf sheath and leaf blade. LSY363 was expressed in leaf sheath but was below the level of detection in leaf blade and root. These results indicate that specific proteins expressed in specific regions of rice show a coordinated response to salt stress. Keywords: Leaf sheath / Rice / Salt Received 1/10/03 Revised 22/12/03 Accepted 10/1/04 2072 Proteomics 2004, 4, 2072–2081 1 Introduction The genus Oryza, to which cultivated rice (Oryza sativa L.) belongs, consists mostly of perennial species native to fresh swamps and marshes [1]. Rice is grown under dif- ferent agro-ecological conditions and is subjected to a vari- ety of environmental stresses throughout its life cycle. Rice recovers from the initial effects of low salt. Long term effect resulting from accumulation of salt within expanded leaves [2] include reduced photosynthetic activities, metabolic damage [3–4], and loss of chloroplast activities [5]. The influx of salt into the transpiration stream and its dis- tribution between apoplast and protoplast accounts for its long term toxicity even at low external concentrations. Maintenance of growth in the presence of salinity is vital to survival [6]. Response to salinity is a very complex quantitative trait. Physiological studies of rice suggest that a range of characteristics such as low shoot sodium concentration, compartmentation of salt in older rather than younger leaves, tolerance of leaves to salt and plant vigor increase the ability of the plant to cope with salinity. Phenotypic resistance to salinity is defined as the ability of the plant to survive and grow in salinized medium [2]. Responses of plants to stress conditions include altera- tion in gene expression that lead to alterations in protein synthesis. Responses of plants to salt, drought and, to some extent, cold stresses, are regulated by growth reg- ulators like abscisic acid (ABA) [7]. When plants are sub- jected to dehydration and cold and salt stress, the amount of ABA is endogenously increased [8]. This is a Correspondence: Setsuko Komatsu, National Institute of Agro- biological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki 305- 8602, Japan E-mail: skomatsu@affrc.go.jp Fax: 181-29-838-7408 Abbreviations: ABA, Abscisic acid; OEE2, Oxygen evolving enhancer protein 2; PSII, Photosystem II; SOD, Superoxide dis- mutase  2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.proteomics-journal.de DOI 10.1002/pmic.200300741