J. Plant Physiol. 161. 557 – 562 (2004) http://www.elsevier.de/jplhp Marked changes in volume of mesophyll protoplasts of pea (Pisum sativum ) on exposure to growth hormones Venkat Apparao Kolla, Dontamala Suhita,Agepati S. Raghavendra* Department of Plant Sciences, School of Life Sciences, University of Hyderabad, Hyderabad 500046, India Received February 10, 2003 · Accepted April 15, 2003 Summary 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 chan- nels appear to play an important role in swelling/shrinkage of the protoplasts as indicated by the sup- pression of volume changes by HgCl 2 and reversal by mercaptoethanol. The possible role of second- ary messengers in volume changes induced by GA 3 was investigated by using selected pharmaco- logical 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-bu- tanol (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. Key words: abscisic acid – gibberellic acid – indole 3-acetic acid – methyl jasmonate – plant hormo- nes – shrinkage – swelling Abbreviations: GDP-β-S = Guanosine 5′-O-(2-thiodiphosphate). – GTP-γ-S = Guanosine 5′-O-(3- thiotriphosphate). – PLC = phospholipase C. – PLD = phospholipase D. – TFP = Trifluoperazine. – U73122 = 1-(6-[([17β]-3-methoxyestra-1,3,5[10]-trien-17-yl)amino]hexyl)-1H-pyrrole-2,5-dione Introduction Plant protoplasts can be prepared from a wide range of tis- sues (e.g., cells, suspension cultures, epidermis, coleoptiles, or root tips) by simple enzymatic methods involving the com- * E-mail corresponding author: asrsl@uohyd.ernet.in, as_raghavendra@yahoo.com bined use of cellulase and macerozyme (Evans 1976, Schlangstedt et al. 1992, Devi et al. 1992). Protoplasts have been extensively used for plant regeneration and genetic engineering, e.g. including tissue culture (Takeuchi et al. 1998, Maurel et al. 1995) and generation of somatic hybrids (Cai 1988). Besides their use in plant biotechnology, proto- plasts have been model systems to study various aspects of plant metabolism, such as photosynthesis, respiration and 0176-1617/04/161/05-557 $ 30.00/0