Detection of calmodulin and calmodulin-binding proteins in pure phloem sap of rice plants

Abstract

Calcium-ligand blots using ⁴⁵Ca²⁺ revealed that there were at least four calcium-binding proteins (17, 18.5, 48 and 52 kDa) in the phloem sap of rice plants. Furthermore, an anti-spinach calmodulin antibody cross-reacted strongly with an 18.5 kDa protein from the phloem sap. When electrophoresed on native gels, the anti-calmodulin cross-reacting protein migrated more slowly in the presence of calcium than in its absence. Based on these results, we concluded that the cross-reacting protein was a calmodulin. An ¹²⁵I-CaM overlay assay revealed that two calmodulin-binding proteins (20 kDa and 40 kDa) were present in the rice phloem sap. Based on these data, it is possible that a calmodulin signal cascade is present in the sieve tubes of rice plants.

Key words:

• calcium
• calmodulin
• calmodulin-binding protein
• phloem
• rice (Oryza sativa L.)

ACKNOWLEDGMENT

We thank Dr Shoshi Muto (Nagoya University) for providing us with the antibody against spinach calmodulin.

Notes

Present address: 694 Futago, Aki, Higashikunisaki, Oita 873-0356, Japan.