Effects of KT and Ca2+ on the Change in Volume of Protoplasts and CaM Content in Hypocotyl of Etiolated Mung Bean Seedlings

Abstract:

The role of calcium ion in kinetin (KT) signal transduction was studied with etiolated mung bean (Phaseolus radiatus L) hypocotyl protoplasts. The volume of protoplasts maintained at a constant osmotic potential at 20±2℃ began to swell 10 minutes later when treated with 1 μmol/L KT in the present of CaCl₂, and reached their maximum at 30 minutes, then declined to the same level as the control one (CaCl₂ only) at 60 minutes. The swelling of protoplasts induced by KT could be significantly inhibited by Verapamil (Ca²⁺ channel blocker) or LaCl₃ (Ca²⁺ channel competitive inhibitor) respectively. Calmodulin antagonists TFP, CPZ and W₇ could obviously inhibit protoplasts swelling induced by KT. CaM levels in protoplasts reached their peaks at 30 minutes whether treated with or without KT, the CaM content of the treated one being about five times more than that in treatment without KT. However, when KT and CaCl₂ solutions were added with 5μmol/L CPZ, TFP or 0.5μmol/L W7, CaM level in protoplasts declined greatly. It is suggested that calcium acts as the second messenger in KT-induced swelling of protoplasts in this system and Ca²⁺-CaM may play an important role. The present study did not exclude the possibility of involvement of other cellular signaling system.