Cr-induced changes in leaf protein profile, ultrastructure and photosynthetic traits in the two contrasting tobacco genotypes

Soil Cr contamination has emerged as an increasing problem worldwide. To investigate the genotypic difference on the effect of Cr in tobacco, Hydroponic experiments were performed, assessing changes in proteomes, transcriptional features as well as the ultrastructure and photosynthetic characteristics of two contrasting tobacco genotypes Guiyan 1 (Cr-tolerant) and Yunyan 2 (Cr-sensitive) under Cr exposure. Transmission electron microscopy observation depicted that Guiyan 1 was less influenced by Cr stress than Yunyan 2. Leaves of Guiyan 1 exhibited relatively well composed arrangement of photosynthetic apparatus as compared with that of Yunyan 2. A total of 86/74 and 107/77 proteins showed more-/less-abundance following Cr treatment in Guiyan 1 and Yunyan 2. Twelve Cr-tolerance-associated proteins were identified, using two-dimensional gel electrophoresis coupled with mass spectrometry, whose expressions were significantly induced in Guiyan 1 leaves but down-regulated/unchanged in Yunyan 2, or unchanged in Guiyan 1 but down-regulated in Yunyan 2 under 100 A mu M Cr stress. They are including mitochondrial processing peptidase, dehydrin, superoxide dismutase, adenine phosphoribosyl transferase, mitochondrial malate dehydrogenase proteins. Based upon their functions, they are categorized in four groups: stress response, energy, RNA-binding and metabolism related proteins. Furthermore, the expression patterns of four Cr-responsive proteins were validated by quantitative real-time PCR. The data extend our knowledge to understand the underlying Cr tolerance mechanisms and provide an insight into possible utilization of elite genetic resources for the development of Cr tolerant tobacco genotypes.