About 75% of the tea fields in Japan grow cv. ‘Yabukita,’ which is susceptible to many diseases such as anthracnose and gray blight. Therefore, broad range effective and long-lasting disease control methods are required. Plant activators (PAs) are compounds that induce disease resistance in plants. In the present study, we used AGREVO EX (a yeast extract preparation), probenazole, prohydrojasmon, and tiadinil as PAs and estimated their disease resistance-inducing activity on tea plants by wound-inoculation assays and field trials. An aqueous solution of each PA was sprayed on field-grown ‘Yabukita’. PA-treated leaves were harvested and assayed for disease resistance-inducing activity. Lesion development of gray blight and anthracnose in PA-treated leaves was suppressed by each PA, and the induced resistance continued for at least 30 days after PA treatment. All the tested PAs induced disease resistance in tea plants systemically. In field trials, PAs were effective to the diseases of anthracnose and gray blight with control efficacies from 50.1 to 50.8 and 63.7 to 69.8 respectively. The growth and chemical composition of tea shoots were not changed by PA treatment. Based on these experiments, induced resistance by PAs is useful for the development of new disease control methods for tea production.

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Induction of disease resistance in tea (Camellia sinensis L.) by plant activators.

Historically, peptidases have been considered as housekeeping proteins involved in protein degradation and amino acid turnover. However, recent work has highlighted the fact that peptidases, including aminopeptidases, have critical regulatory roles in the cell including modulation of growth, development and stress responses. Recently, plant leucine aminopeptidases (LAPs) have been recognized for their roles in modulation of late wound-responses and insect defense. While no known mechanism of action has been identified, LAPs were presumed to act through their aminopeptidase function to affect the stability, activity, or localization of a peptide and protein involved in defense. In my dissertation studies, I have identified two new molecular functions for plant LAPs as molecular chaperones and Cys-Gly dipeptidases. In addition, microarray analyses has demonstrated the tomato LAP-A regulates early and late wound responses both positively and negatively. In particular, microarray analyses identified two new sets of genes modulated by LAP-A: late wound dehydrins and Pathogenesis-Related 1. This study also provides evidence LAP-A may act though the negative regulator salicylic acid or the positive regulator hydrogen peroxide to modulate wound signaling. The role of LAP-A in glutathione metabolism is also discussed. Together this study has provided evidence that LAP-A's role in wound signaling and insect defense is more complex than initially anticipated and may be the result of LAP-A utilizing multiple functions (aminopeptidase, chaperone and/or Cys-Gly dipeptidase activities) in different environments and in response to different stresses.

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M. Miyazaki

Papers

Systemic wound responses in tea plants.