Low temperature is one of the major abiotic stresses limiting the productivity and the geographical distribution of many important crops. To gain a better understanding of chilling stress responses in rice (Oryza sativa L. cv. Nipponbare), we carried out a comparative proteomic analysis. Three-week-old rice seedlings were treated at 6°C for 6 or 24 h and then recovered for 24 h. Chilling treatment resulted in stress phenotypes of rolling leaves, increased relative electrolyte leakage, and decreased net photosynthetic rate. The temporal changes of total proteins in rice leaves were examined using two-dimensional electrophoresis. Among ϳ1,000 protein spots reproducibly detected on each gel, 31 protein spots were downregulated, and 65 were up-regulated at least at one time point. Mass spectrometry analysis allowed the identification of 85 differentially expressed proteins, including well known and novel cold-responsive proteins. Several proteins showed enhanced degradation during chilling stress, especially the photosynthetic proteins such as Rubisco large subunit of which 19 fragments were detected. The identified proteins are involved in several processes, i.e. Among various abiotic stresses, low temperature (chilling and freezing temperature) is a major stress that limits the productivity and the geographical distribution of many important crops such as rice and maize. Chilling temperatures that range from 0 to 12°C are common during the growing season in temperate regions and can substantially decrease plant productivity (1). To defend against the stress, plants use several strategies, one of which is regulation of gene expression.

Salt stress is one of the major abiotic stresses in agriculture worldwide. We report here a systematic proteomic approach to investigate the salt stress-responsive proteins in rice (Oryza sativa L. cv. Nipponbare). Three-week-old seedlings were treated with 150 mM NaCl for 24, 48 and 72 h. Total proteins of roots were extracted and separated by two-dimensional gel electrophoresis. More than 1100 protein spots were reproducibly detected, including 34 that were up-regulated and 20 down-regulated. Mass spectrometry analysis and database searching helped us to identify 12 spots representing 10 different proteins. Three spots were identified as the same protein, enolase. While four of them were previously confirmed as salt stress-responsive proteins, six are novel ones, i.e. UDP-glucose pyrophosphorylase, cytochrome c oxidase subunit 6b-1, glutamine synthetase root isozyme, putative nascent polypeptide associated complex alpha chain, putative splicing factor-like protein and putative actin-binding protein. These proteins are involved in regulation of carbohydrate, nitrogen and energy metabolism, reactive oxygen species scavenging, mRNA and protein processing, and cytoskeleton stability. This study gives new insights into salt stress response in rice roots and demonstrates the power of the proteomic approach in plant biology studies.