Phospholipase A2 induced effects on the structural organization and physical properties of pea chloroplast membranes.

Phospholipase A2 (PLA2)-induced effects on the membrane organization, fluidity properties and surface charge density of pea chloroplasts were investigated. It was observed that lipolytic treatment with PLA2 altered the chloroplast structure having as a result a swelling of thylakoids and a total destruction of normal granal structure. In spite of this, the thylakoid membranes remained in close contact. At the same time, a slight decrease of surface charge density was registered, thus explaining the adhesion of swelled membranes. Fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) was measured during PLA2 treatment. A pronounced decrease of DPH fluorescence polarization was found, indicating that phospholipase treatment resulted in considerable disordering and/or fluidization of the thylakoid membranes. The increased fluidity could be attributed to the destabilizing effect of the products of enzymatic hydrolysis of the phospholipids (free fatty acids, lysophospholipids) on the bilayer structure of thylakoids membranes.