ABSTRACT

The objective of this study was to examine the possible involvement of phospholipid signaling in the NaCl-induced up-regulation of antioxidant enzyme activity in cotton callus. This was accomplished by using callus tissue from a NaCl-tolerant cotton cell line in a series of time-course studies in which the tissue was subjected to one of the following treatments: no treatment (controls), 250 mM NaCl (NaCl stress), abscisic acid (ABA), myoinositol 1,4,5-triphosphate (IP3), diacylglycerol (DAG), phosphatidylinositol (PI), 1-butanol (an inhibitor of phospholipase D), U73122 (an inhibitor of phospholipase C), a pre-treatment with 1-butanol followed by treatment with ABA or 250 mM NaCl, and pre-treatment with U73122 followed by treatment with 250 mM NaCl. Both NaCl stress and ABA treatment resulted in rapid increases in antioxidant enzyme activity. Pretreatment of both control and NaCl stressed cotton callus with 1-butanol actually resulted in increases rather than decreases in most of the antioxidant enzyme activities; however, pretreatment with 1-butanol did inhibit the NaCl-induced increase in peroxidase activity. Thus, it would appear that phospholipase D has a very limited, and perhaps no role in the NaCl-induced up-regulation of antioxidant enzyme activity. Pretreatment with U73122 decreased and/or delayed the NaCl-induced up-regulation of glutathione reductase (GR), ascorbate peroxidase (APX), and peroxidase activities and completely inhibited the NaCl-induced increase in catalase activity in the NaCl-treated cotton callus tissue, while treatment of the control with either PI, IP3, or DAG (enzymatic products of phospholipase C) resulted in rapid increases in the activities in all four of the enzymes. These findings would suggest that phospholipase C may be involved in the NaCl-induced up-regulation of antioxidant enzyme activity in cotton callus tissue.