Physiological and proteomic analysis of the response to drought stress in an inbred Korean maize line

Understanding the response of a crop to water deficiency is the first step towards breeding drought-tolerant varieties. In this study, inbred maize (Zea mays L.) line KS140 was subjected to drought stress by withholding water for 10 days at the V5 or V6 leaf stage. Water-deficient plants experienced a decrease in relative leaf water content, stomatal conductance, net CO2 assimilation rate, and water use efficiency compared to well-watered plants. This was accompanied by a decrease in the relative water content that resulted in severe growth retardation (75% decrease in leaf area, and 64% and 56% decrease in aerial tissue and root dry matter, respectively). Leaf chlorophyll content was unchanged. Two-dimensional electrophoresis protein expression profiles were compared between wellwatered and water-deficient plants. Differential expression was observed for 29 protein spots, and these were identified using MALDI-TOF mass spectrometry. Of these proteins, 34% were involved in metabolism, 24% in response to stress, 14% in photosynthesis, 7% in protein modification, and 14% were proteins of unknown function. Of the 29 differentially expressed proteins, 24 and 5 protein spots were up- and down-regulated in water-deficient plants, respectively. Two pathogenesis-related proteins, an abscisic stress-ripening protein and heat shock protein 1, were expressed only under drought conditions. This study provides a protein profile of a Korean maize inbred line during drought stress, which will be valuable for future studies of the molecular mechanisms underlying drought resistance and for development of selective breeding markers for drought tolerance in maize.