Marked changes in volume of mesophyll protoplasts of pea ( Pisum sativum) on exposure to growth hormones

The present study reports quick and significant changes induced by plant hormones in the volume of mesophyll protoplasts of pea ( Pisum sativum). Four plant hormones: gibberellic acid (GA 3), indole 3-acetic acid (IAA), abscisic acid (ABA)(±) and methyl jasmonate (MJ), caused marked changes in the volume of mesophyll protoplasts. GA 3 and IAA increased the volume of the protoplasts (up to 90 %) whereas the ABA and MJ decreased (by about 40 %) the volume. Aquaporins or water channels appear to play an important role in swelling/shrinkage of the protoplasts as indicated by the suppression of volume changes by HgCl 2 and reversal by mercaptoethanol. The possible role of secondary messengers in volume changes induced by GA 3 was investigated by using selected pharmacological reagents. The GA 3 induced swelling was restricted by GDP-β-S (G-protein antagonist), U73122 (phospholipase C inhibitor), and TFP (calmodulin antagonist), but was not affected by 1-butanol (phospholipase D inhibitor), GTP-γ-S (G-protein agonist), or verapamil (calcium channel blocker). The results suggest that the mesophyll protoplasts can be a simple and useful system for further studies on volume changes in plant tissues.