OXYGEN DIFFUSION IN LUPIN NODULES .2. MECHANISMS OF DIFFUSION BARRIEROPERATION

The oxygen diffusion resistance of Lupinus albus (L.) cv. Multolupa ro ot nodules was increased by subjection to short-term stresses; lowerin g rhizosphere temperature from 25 to 16-degrees-C (2 h), detopping pla nts (3 h), darkening plants (21 h) or exposing roots to 20 mol M-3 KNO 3 for 2, 4 or 6 d. Microscopic observations and measurements showed th at this resulted in the area of open intercellular spaces within the i nner cortex being reduced due to both cell expansion and increased pro duction of an occluding glycoprotein. Electrophoretic and Western Blot analysis using the monoclonal antibodies MAC236 and MAC265 showed two distinct glycoprotein antigens with molecular weights of 240 and 135 kDa, respectively. Both antigens are localized within intercellular sp aces of the inner cortex. The amount of glycoprotein was determined us ing either ELISA, with MAC265, or quantification of immunolabelling wi th MAC236. This immunolabelling also localized the glycoprotein within globules adhering to the inside of the inner cortical cell walls.