Primary evidence for involvement of IP3 in heat-shock signal transduction in Arabidopsis

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Abstract
The role of inositol 1,4,5-trisphosphate (IP3) in transducing heat-shock (HS) signals was examined in Arabidopsis. The whole-plant IP3 level increased within 1 min of HS at 37 °C. After 3 min of HS, the IP3 level reached a maximum 2.5 fold increase. Using the transgenic Arabidopsis plants that have AtHsp18.2 promoter--glucuronidase (GUS) fusion gene, it was found that the level of GUS activity was up-regulated by the addition of caged IP3 at both non-HS and HS temperatures and was down-regulated by the phospholipase C (PLC) inhibitors {1-[6-((17-3-Methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-2,5-pyrrolidinedione}(U-73122). The intracellular-free calcium ion concentration ([Ca2+]i) increased during HS at 37 °C in suspension-cultured Arabidopsis cells expressing apoaequorin. Treatment with U-73122 prevented the increase of [Ca2+]i to some extent. Above results provided primary evidence for the possible involvement of IP3 in HS signal transduction in higher plants.