Proteomic analysis of Mammillaria gracilis Pfeiff. in vitro-grown cultures exposed to iso-osmotic NaCl and mannitol

Salt and drought stress are important abiotic factors that negatively affect plant growth and productivity. Defense mechanisms, which plants have developed to cope with stress, are followed by alterations in a genome expression profile that in turn result in qualitative and quantitative change of the proteome. Although proteomic-based approach for studies of plant responses to salinity and drought has already been successfully employed in several plants, for cactus species such analyses have not been done so far. Therefore, in this study we have performed proteomic analysis of Mammillaria gracilis Pfeiff. in vitro-grown cultures, callus and tumor, exposed to iso-osmotic NaCl and mannitol. Obtained results differed among analyzed tissues. The higher number of differentially expressed proteins after either salt or mannitol treatment was revealed in tumor compared to callus. According to classification to different functional categories, majority of the identified callus responsive proteins belongs to protein synthesis and processing category, while the highest number of identified tumor proteins belongs to category of metabolism, which suggest that the mechanisms that mediate responses to salt- and mannitol-induced stress in cactus callus and tumor are dependent on tissue type. Down-regulation of proteins involved in cell protection suggests the inability of tumor to activate protective processes against salinity and osmotic stress.