2019 ASHS Annual Conference

Calcium deficiency disorders in horticultural crops cause significant losses each year to the produce industry. Blossom-end rot (BER) in tomatoes is often used as a model system for studying calcium deficiency in fruit, as it is associated with reduced total tissue and apoplastic calcium concentrations. BER in tomatoes is characterized by discoloration, water-soaked tissue, and cell death in the distal portion of the fruit. Previous research suggests calcium deficiency disorders are also associated with reactive oxygen species (ROS) accumulation and abiotic stress. This research investigates the connections between calcium deficiency, abiotic stress, and ROS metabolism in tomato BER development. Tomato plants were grown under low calcium conditions with BER inducing stresses (drought stress and high salinity irrigation) and compared to unstressed plants as control. Catalase and peroxidase activity were assayed in blossom-end pericarp tissue of stressed and control fruit to test for conserved responses to calcium deficiency over different abiotic stresses. Stem-end pericarp tissue and tissue adjacent to BER affected tissue were also assayed in control fruit. Histochemical staining and gene-expression analysis were used to investigate cell response to ROS accumulation. Results showed a significant increase in soluble and ionically bound peroxidase activity and a significant decrease in catalase activity in BER affected tissue. These trends were conserved between drought stressed, high salinity irrigated, and control plants. Tissue adjacent to BER tissue exhibited reduced catalase activity compared to stem-end pericarp tissue in BER affected control fruit. Preliminary fluorescence microscopy results have indicated higher ROS accumulation in the water-soaked region of BER affected fruit compared to healthy tissue. These results suggest a peroxidase dependent mitigation of ROS accumulation. Of interest is the increase in ionically bound peroxidase activity, which is localized in the cell wall. Gene expression analysis showed increased expression of a lignification associated peroxidase gene in BER affected fruit. Toluidine blue O staining results suggested production of lignin in BER affected tissue. BER development is most prevalent during early cell expansion and treatment with gibberellic acid, a cell expansion promoting plant growth hormone, has been shown to induce BER development. Our results suggest that normal cell expansion may be disrupted through peroxidase mediated lignification in BER tissue and may play a significant role in BER development.