Anaerobic respiration and ethanol production in root tips from wild type and Adh1-null seedlings acclimated or not acclimated to low oxygen

--D.J. Hole, P.S. Hole, M.C. Drew and B.G. Cobb

Wild type root tips from the inbred line Tx5855 and from Adh1-null seedlings (seeds were originally provided by R. Ferl, Univ. of Florida and had been backcrossed 3 times into Tx5855) were hypoxically pretreated (HPT, 4.0% O2 for 16 hrs.) and non-hypoxically pretreated (NHPT, 40.0% O2 at 25 C) then placed under anoxic (100% N2) conditions. Evolution of CO2 and ethanol were monitored for 5 hours (Table). In both wild type and Adh1-null root tips, HPT tissue consistently metabolized more glucose and produced more ethanol and CO2 than NHPT root tips indicating that the low oxygen treatment is necessary to permit acclimatization of the tissue to anoxic conditions. Interestingly, there were no noticeable differences in the production of ethanol or CO2 between WT and Adh1-null root tips in any treatment. ADH activity was assayed using the method of Rumpho and Kennedy (Plant Phys. 68:165-168), and although ADH activity was detected in wild type root tips, no activity was detected in the Adh1-null root tips. The rate of production of ethanol was the same for both tissues indicating that the in vitro assay does not equally detect both ADH1 and ADH2. It is important to note that HPT Adh1-null root tips carried out anaerobic respiration at the same rate as HPT wild type tips suggesting that Adh2 may play a more important role in anaerobic metabolism in cells acclimated to low oxygen levels than we have previously thought.
 
 
CO2 Production (µl CO2 g FW-1 h-1)
  NHPT HPT
Tx5855 298  397
Adh1-Tx5855 314  384
     
  Ethanol production (nmol EtOH g FW-1 h-1)  
  NHPT HPT
Tx5855 5.65  9.18
Adh1-Tx5855 4.16  8.31


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