Ethanolic Fermentation in Hypoxic Cotton Seed

Cotton ( Gossypium hirsutum L.) roots die within a few hours in the total absence of O2, but can continue growing for several hours at a reduced rate very low at O 2 concentrations, even <10 mmol O 2 mol −1 . The physiology of this adaptive response has not been well characterized. The objective of this study was to determine if ethanolic fermentation occurs in cotton seeds under hypoxic conditions that inhibit but do not prevent radicle growth. Germinating seeds, after 23 h imbibition at 32 °C, were incubated for ≤4.5 h at 28 °C in sealed flasks. Hypoxic conditions (6‐9 mmol O 2 mol −1 ) were imposed by gassing flasks with either N 2 or CO 2 . Fermentation was measured as the production of ethanol and acetaldehyde, which were quantified by gas‐liquid chromatography. Both ethanol and acetaldehyde were readily produced during hypoxia at an average rate of 439 and 9.69 nmol h −1 seed −1 , respectively, at 28 °C. Acetaldehyde‐and ethanol‐forming capacity increased substantially during the first 16 h following onset of imbibition. Seeds imbibed under hypoxia for only 3 h produced little ethanol or acetaldehyde. Small amounts of acetaldehyde and ethanol were produced by hydrated seeds imbibed in air. Ethanol produced during fermentation was rapidly assimilated if O 2 stress was relieved. During a 2‐h hypoxic stress that promoted fermentation, radicle growth was halted, but resumed at a reduced rate. Inhibition was short‐lived and radicle growth recovered fully in air. Results indicate that ethanolic fermentation is a major metabolic response to hypoxia in germinating cotton seeds.