EFFECTS OF PACLOBUTRAZOL AND CHILLING TEMPERATURES ON LIPIDS, ANTIOXIDANTS AND ATPASE ACTIVITY OF PLASMA-MEMBRANE ISOLATED FROM GREEN BELL PEPPER FRUITS

The effects of paclobutrazol treatment on plasma membrane lipid compos ition and ATPase activity of bell pepper fruit (Capsicum annuum) subje cted to chilling temperatures were assessed. Application of the growth regulator paclobutrazol affected plant growth and fruit morphology. T he plants were more compact and the fruits were e less elongated than control fruits. There was about 60% more plasma membrane on a fresh we ight basis from treated fruit. At harvest there was no difference in s terol to phospholipid ratio, or in phospholipid fatty acid composition of control compared with paclobutrazol treated fruit. However, plasma membrane ATPase activity of treated fruit was two times higher than t hat of control fruit. After storage at chilling temperature (2 degrees C), the control fruit developed more chilling injury, and had greater weight loss and a higher rate of K+ leakage than paclobutrazol treate d fruit. Plasma membrane phospholipid content decreased and saturation of phospholipid fatty acids was higher than in control fruit. These t wo changes were largely absent in plasma membrane from treated fruit. At harvest antioxidant levels in the plasma membrane of paclobutrazol treated peppers were higher than in those of controls and changed litt le during storage, whereas levels in control fruit plasma membrane dec reased 66%. ATPase activity increased and then decreased in control fr uit held at low temperature, whereas in treated fruit activity was con stant. The protective effect of paclobutrazol against chilling injury of pepper fruit may result from a combination of its effect on fruit m orphology, and protection of the lipids against oxidative stress.