Immunological Evidence Of The IP₃R-Like Protein In Oryza Sativa And Arabidopsis Thaliana

Inositol 1, 4, 5-triphophate (IP3)-Ca2+ signal transduction pathway plays a very important role in animal cells. IP3- IP3 receptor (IP3R) interaction mediates the release of Ca2+ from the endoplasmic reticulum in response to many different extracellular stimulus.For higher plants, however, though it is now generally accepted that IP3 participates in signal transduction in many important cellular processes, only limited evidence is available for the presence and properties of the IP3R-like protein so far. Here, using the immunological methods with an antibody raised against a mammalian inositol 1, 4, 5-triphophate receptor (type 1), we found that, 1) the antibody across-reacted the proteins with about 200kD in microsomes from Oryza sativa and about 200kD from Arabidopsis thaliana respectively. Additionally, protein bands were found in the range of 62 kD in microsomes from Oryza sativa and 45 kD from Arabidopsis thaliana-, 2) The IPaR-Like protein was mainly localized in the vacuolar membrane (tonoplast) and plasma membrane in the leaf and root tip of Arabidopsis thalianaFor confirming the biological role of the IP3R-like protein, we investigated the effects of methyl viologen (stimulating IP3 produce) and heparin (a competitive inhibitor of Inositol 1, 4, 5-triphophate in animal) on stomatal movement by epidermal strip bioassay. When the epidermal strips of Arabidopsis thaliana were treated with methyl viologen, it stimulates the stomatal closure. But the effects are inhibited partially by heparin. It showed that the IP3R-like protein in plant may mediate IP3 signal to regulate the stomatal guard cell movement.All above results suggest that the plant IP3R-like protein may occur in plant cells and participate in the phosohoinositide signal transduction pathway.