Dynamic Changes Of Reactive Oxygen Species In Wheat Roots Caused By Powdery Mildew Fungus And Its Function In Systemic Programmed Cell Death

Previous studies had shown that after infection of powdery mildew fungus (Blumeria graminis f.sp.tritici) with leaves, systemic programmed cell death (systemic PCD) occurred in the root cells of wheat (Triticum aestivum L.) and ROS was involved. To further study the role ROS played duiring systemic PCD, this study was carried out on powdery-mildew-fungus-infected wheat (Triticum aestivum L. cv. Huamai 8) seedlings and powdery-mildew-fungus-resistant wheat (Triticum aestivum L. cv. Shenmai 8) seedlings. After infection of powdery midew (PM) with leaves, exterior morphology and micrographic structure were observed to analyze the influence of powdery mildew on root development and structure. Fluorescence microscopy and transmission electron microscopy were used to detect the accumulation of ROS. Real-time PCR was used to investigate the changes of gene expression of two antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT) and agarose gel electrophoresis was used to detect the systemic PCD in adventitious roots. The main results were as follows:1. Root amount of both varieties decreased after infection of PM with leaves and Hua 8 decreased severer than Shen 8; most of the cortical cells of Hua 8, especially the external cortical cells, shrinked and arranged irregularly after infection of PM, while only a few cortical cells of Shen 8 shrinked.2. After infection of PM, degradation of marrow cells occurred in both varieties, while the phloem cells maintained intactly.6 d after infection of PM of Hua 8, distinct marrow cells were observed in stele; 10 d after infection, marrow cells decreased gradually and epigenetic vessels in stele started to fuse with each other; 12 d after infection, few marrow cells remained; 15 d and 18 d after infection, no marrow cells remained and a big cavum formed in the center of stele.10 d after infection of PM of Shen 8, distinct marrow cells were observed in stele; 12 d after infection, marrow cells decreased gradually and epigenetic vessels in stele started to fuse with each other; 15 d after infection, no marrow cells remained and a big cavum formed in the center of stele.3. After infection of PM with leaves, ROS accumulation in roots of Hua 8 maintained a high level, while it maintained a low one in roots of Shen 8.6 d and 10 d after infection of PM of Hua 8, a small quantity of ROS accumulated in root cells; 12 d after infection, plentiful ROS accumulated in cell walls of cortex and stele and ROS burst occurred; 15 d and 18 d after infection, ROS decreased gradually in cell walls of cortex and stele.6 d and 10 d after infection of PM of Shen 8, little ROS accumulated in root cells; 12 d and 15 d after infection, a small quantity of ROS accumulated cell walls of cortex and stele; 18 d after infection, no ROS accumulation was detected.4. After infection of PM with leaves, SOD and CAT gene expression of both varieties in root cells changed, which leaded to the increase of ROS accumulation. SOD gene expression of Hua 8 maintained a low level except that of 12 d after infection, while CAT gene expression maintained a high level except that of 12 d after infection. During the whole infecing-period, SOD gene expression of Shen 8 maintained a low level, while CAT gene expression maintained a relative high level. Compared with changes of SOD gene expression after infection of PM, CAT gene expression of both varieties maintained a relative high level.5.15 d and 18 d after infection of PM with leaves, DNA laddering was detected in roots of Hua 8, which indicated that systemic PCD occurred. But DNA laddering was not detected 12 d after infection, when plentiful ROS accumulated. That the ROS need to interact with other signals together to mediate systemic PCD might explain this phenomenon. No DNA laddering was detected in roots of Shen 8 during the whole infecting-period and the low level of ROS accumulation might be the reason.