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 (GA3), indole 3-acetic acid (IAA), abscisic acid (ABA)(±) and methyl jasmonate (MJ), caused marked changes in the volume of mesophyll protoplasts. GA3 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 HgCl2 and reversal by mercaptoethanol. The possible role of secondary messengers in volume changes induced by GA3 was investigated by using selected pharmacological reagents. The GA3 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.