Antioxidant properties of the pollen exine polymer matrix

The antioxidant properties of the polymer matrix of exine, the outer layer of pollen grain wall, were studied. The main component of this matrix is sporopollenin, a unique biopolymer resistant to mechanical and chemical damage. Samples of isolated exine purified from soluble compounds were studied with EPR using a stable nitroxyl radical TEMPO and a spin trap DMPO. At the same time, we analyzed changes in fluorescence of DCFH which detected ROS in the solution. It has been established that exine effectively reduced TEMPO and eliminated the hydroxyl radical. Also, fluorimetric analysis demonstrated that exine decomposed H2O2, and this ability significantly decreased after treatment of exine with feruloyl esterase or mild alkaline hydrolysis (1 M NaOH), i.e. after hydrolysis of hydroxycinnamic acid esters. After harsh hydrolysis (4 M NaOH, 170°C) of ether bonds, a large amount of hydroxycinnamic acids was released, and the exine almost completely lost its antioxidant capacity. The obtained results point to the ability of the extracellular polymer matrix of the exine to eliminate free radicals and H2O2 during crucial periods of male gametophyte development. The participation of ferulic acid and, possibly, of other hydroxycinnamic acids of sporopollenin in these processes has been demonstrated.