Root protein profile changes induced by Al exposure in two rice cultivars differing in Al tolerance.

Aluminum (Al) toxicity is a primary limitation to crop growth in acidic soils. Rice (Oryza sativa L.) seedlings exposed to Al show significantly inhibited root growth. To understand the precise mechanisms underlying Al toxicity, a comparative protein profile analysis of roots from two rice cultivars was conducted using 2-DE and MALDI-TOF/TOF-MS. A total of 79 Al-regulated proteins were identified, from which 54 and 45 proteins were differentially regulated in Kasalath (Al-sensitive) and Koshihikari (Al-resistant) cultivars, respectively. Gene Ontology and clustering analysis revealed an increase in relative abundance in vacuolar H(+)-ATPase, whereas structural proteins were decreased in both cultivars. Under Al toxicity, proteins involved in the antioxidative system, carbohydrate and nucleotide anabolism were increased in Koshihikari, whereas proteins participating in pathogenesis and carbohydrate catabolism were increased in Kasalath. Furthermore, the abundance of proteins involved in signal transduction, translation and transcription were different between the two cultivars. Our results suggest that destruction of the molecular structure is a major cause of cellular damage, and vacuolar sequestration of Al ions is an important Al resistant mechanism in rice. Both active oxygen scavenging systems and carbohydrate metabolism could play important roles in determining the Al tolerance among rice cultivars.