INTERNAL CO2 CONCENTRATIONS IN ONION BULBS AT DIFFERENT STORAGE TEMPERATURES AND IN RESPONSE TO SEALING OF THE NECK AND BASE

Internal CO2 concentrations were measured in onion (Allium cepa L. cv. TG 1015Y) bulbs stored at 1, 7, 13, 20, 27, or 34 degrees C for 12 we eks and their relationships with shoot growth and respiration rates we re investigated. Maximum shoot growth was observed at 13 and 20 degree s C. Respiration rates were greatest at 13 and 20 degrees C for 8 week s, then linearly increased with storage temperatures after 12 weeks. I nternal CO2 concentrations ranging from 2 to 5% increased with increas ing storage temperatures, while internal gas volume decreased. Bicarbo nate concentrations in outer scales ranged from 130 to 190 mu M and in creased with increasing storage temperatures. The centre scale tissues contained 11-17% CO2, which paralleled respiration rates. Searing the neck area of onion bulbs stored at 1 or 27 degrees C significantly in creased internal CO2 concentrations, but had no effect on inhibiting s hoot growth. Internal CO2 concentrations appeared to be regulated by g as exchange rates through the neck area and/or elevated HCO3- concentr ations in outer scales. Elevated internal CO2 concentrations or high l evels in centre scale tissues did not appear to be a primary reason fo r inhibited shoot growth at high storage temperatures. There seems to be thermo-dormancy controlling shoot growth and respiration in onion b ulbs. (C) 1997 Elsevier Science B.V.