Rice Genetics IV - IRRI books - International Rice Research Institute

lesions appeared over the entire leaf around 50 d after sowing and often containedyellowish lesions overlapped with brownish lesions. Cdr3 was a dominant mutationand, when homozygous, plants exhibited numerous lesions approximately 20 d aftersowing.Constitutive activation of defense reactions in the cdr mutantsSeveral histological markers for the defense response have been observed in plantschallenged with avirulent pathogens (reviewed in Hammond-Kosack and Jones 1996).We first examined autofluorescence and callose deposition, both of which are wellestablishedcellular markers observed in plants exhibiting disease resistance.Autofluorescence is strongly correlated with resistance to the blast fungus (Koga 1994).Autofluorescence was detected in leaf sheath cells of the three cdr mutants of rice,which were undergoing cell death in the absence of pathogens, whereas no signal wasdetected in the wild type. Callose deposition was detected in leaf blade cells, whichwere dying or dead, by aniline blue staining in the three mutants but not in the wildtype. These results indicate that these two histological markers for the defense responsewere constitutively activated in the leaves of the three cdr mutants of rice.We next analyzed the expression of two defense-related genes, PBZ1 and PR1(Fig. 5). The PBZ1 gene encodes an intracellular PR protein and is activated by treatmentof rice plants with probenazole (3-allyloxy-1,2-benzisothiazole-1,1-dioxide),LesionWT cdr1 cdr2 Cdr3PBZ1PR1rRNAFig. 5. Expression of PBZ1 and PR1 genes in the cdr mutants of rice. The (–)indicates leaves without lesions and (+) indicates leaves with lesions.330 Shimamoto et al