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. LG 11 was studied under ambient and sub-ambient oxygen partial pressures (p 0 2) using a gas flow-through system linked to a photoacoustic laser detector. Despite precautions to minimize physical perturbation to seedlings while setting-up, ethylene produc­ tion 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 O2) to 3 or 5kPa 0 2 after 6h, ethylene production increased within 2 -3 h. When, the roots were returned to air 16 h later, ethylene production decreased within 2-3 h. The presence of lOkPa C 0 2 did not interfere with the effect of 3kPa 0 2. Transferring roots from air to 12 5kPa did not change ethylene production, while a reduction to 1 kPa 0 2 induced a small increase. The extra ethylene formed in 3 and 5kPa 0 2 was associated with plagiotropism, swelling, root hair production, and after 72 h, increased amounts of intercellu­ lar 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 16 h. Key-words: Zea mays L.; roots; flooding; environmental stress; ethylene; oxygen; carbon dioxide; aerenchyma; photoacoustic laser detector.