Systemic PCD occurs in TMV-tomato interaction

In hypersensitive response (HR), programmed cell death (PCD) is reported as a powerful defense mechanism in plant immune responses to pathogen. However, little is known about the PCD in systemic acquired resistance (SAR). Using tobacco mosaic virus (TMV) to infect the tomato (Lycopersicon esculentum cv. Jiafen 16) we found that localized TMV-infection could induce cell death in the uninoculated parts of the tomatoes, where the enzyme-linked immunosorbent assay (ELISA) showed no spreading virus. The biological and molecular characterization of this cell death was shown as following: chromatin condensed and formed peripheral conglomeration in nuclei; cell nucleus were TUNEL positive labeled; genomic DNA was fragmented and showed DNA laddering; mitochondria and chloroplast were disrupted; tonoplast and plasma membrane were shrunk and degradated. These results suggested that with an absence of TMV spread, the local TMV-infection on certain tomato leaves could induce systemic PCD in the root-tips, stem-apices and uninoculated leaves. The systemic PCD has various initiation and synchronization in such tissues and is distinct in inducement and exhibition from HR-PCD and SAR.