Abstract

Recent studies have revealed an important role of hormones in plant immunity. Cytokinins are phytohormones that are involved in various regulatory processes including plant defense. Zeatin a cytokinin antagonizes the effect of Alternaria brassicae pathotoxin in cell culture of Brassica juncea. Phytohormones are also the inducers of MAP Kinase signaling pathways which are the important signaling modules in eukaryotic cells. In this paper, an attempt was made to study the exogenous application of zeatin on the disease score, infection behavior of A. brassicae, expression pattern of MAPK-4 in the non host Sinapsis alba, host B. junceasusceptible c.v Varuna, B. juncea moderately tolerant c.v. Divya and transgenicBrassica to confer its role in plant immunity. We observed that high concentration of zeatin led to increased defense responses by delaying the infection process as well as significantly reducing the disease score. Semi-quantitative RT-PCR reveals that zeatin also increases the expression of MAPK-4 at early hours of infection. Our result supports that zeatin up regulates plant immunity via an elevation of MAPK-4 andclearly reflects that it antagonizes the effect of A. brassicae. The crosstalk between zeatin and MAPK signaling pathway may help plants fine-tune defense responses against A. brassicae in the disease Alternaria blight.

Key words: Alternaria blight, Brassica, disease score, MAPK, pathogenesis, infection process.