Study of salt-stress tolerance and defensive mechanisms in Brassica rapa CAX1a TILLING mutants

Abstract

Crop production is facing the increasing salinity in soils and irrigation waters. This is a widespread problem that affects crops with high economic importance and severely reduces yields. Oxidative stress caused by salinity induces in plants complex defensive mechanisms involving the antioxidant system and osmoprotector compounds. In this strategy, Ca2+ plays a pivotal role in counteracting salt stress, and the modification of the Ca2+ vacuolar transporter CAX1 could represent a potential method to improve tolerance to salinity. Three new CAX1 variants in Brassica rapa (BraA.cax1a) were generated using TILLING strategy. BraA.cax1a and parental line R-o-18 were grown under saline conditions and biomass, ions accumulation, antioxidant system, heat shock protein 70 (HSP70) occurrence, and proline (Pro) levels were measured. According to the results, BraA.cax1a-4 mutation provided a higher tolerance to salinity stress. Thus, BraA.cax1a-4 plants showed higher biomass; higher Ca2+ and K+ in the shoot, an enhanced ROS scavenging (increased superoxide dismutase and catalase activities) and enhanced redox state, measured as ascorbate levels. In addition, an increased occurrence of cytosolic and chloroplastic HSP70 isoforms and Pro levels could contribute to protect these B. rapa mutants from saline stress. Therefore, this study identifies a potential useful genotype that could be applied to enhance salt tolerance in crops.