ENHANCED ETHYLENE PRODUCTION BY PRIMARY ROOTS OF ZEA-MAYS L IN RESPONSE TO SUB-AMBIENT PARTIAL PRESSURES OF OXYGEN

Ethylene production by primary roots of 72-h-old intact seedlings of Zea mays L. cv. LG11 was studied under ambient and sub-ambient oxygen partial pressures (pO(2)) using a gas how-through system linked to a photoacoustic laser detector. Despite precautions to minimize physical perturbation to seedlings while setting-up, ethylene production in air was faster during the first 6h than later, in association with a small temporary swelling of the roots. When roots were switched from air (20.8kPa O-2) to 3 or 5kPa O-2 after 6h, ethylene production increased within 2-3h. When, the roots were returned to air 16h later, ethylene production decreased within 2-3h. The presence of 1OkPa CO2 did not interfere with the effect of 3kPa O-2. Transferring roots from air to 12.5kPa did not change ethylene production, while a reduction to 1kPa O-2 induced a small increase. The extra ethylene formed in 3 and 5kPa O-2 was associated with plagiotropism, swelling, root hair production, and after 72h, increased amounts of intercellular space (aerenchyma) in the root cortex. Root extension was also slowed down, but the pattern of response to oxygen shortage did not always match that of ethylene production. On return to air, subsequent growth patterns became normal within a few hours. In the complete absence of oxygen, no ethylene production was detected, even when anaerobic roots were returned to air after 16h.