A transgenic approach was taken to manipulate the levels of pyruvate
decarboxylase (PDC) and alcohol dehydrogenase (ADH) in rice, in order to
investigate whether alteration of ethanol fermentation can affect anaerobic
tolerance. A line transformed with an antisense Adh1
construct had only 4–8% of the ADH activity of untransformed
plants. This line showed reduced ethanol production and coleoptile growth
under anoxia. Mature plants had reduced survival when submerged in water and
exposed to anoxia, suggesting that ADH plays an essential role in seed
germination and plant survival in the absence of O2. A transgenic line
transformed with a cotton Adh2 cDNA in the sense
orientation relative to a constitutive promoter, showed 3–4-fold more
ADH activity than either untransformed controls, or a flooding-tolerant rice
variety (FR13A), both in air and under hypoxia. However, ethanol production by
this line was only slightly higher than that of untransformed controls, and
there was no increase in survival following anoxia treatments.
Three independent transgenic lines containing the
ricePdc1 cDNA driven by an anaerobically-inducible
promoter (6XARE) showed an increase in PDC1 polypeptide
in shoots, but not in roots or endosperm. A moderate increase in PDC activity
and ethanol production was observed in shoots of these lines under anaerobic
conditions, as well as decreased survival of shoots when submerged and exposed
to anoxia. F1 plants containing both the PDC and ADH constructs showed levels
of anoxia-tolerance similar to those of untransformed plants. These results
suggest that over-production of PDC may be toxic to rice plants because of
increased acetaldehyde. Consistent with this view, acetaldehyde levels were
appreciably higher in plants over-producing PDC, compared with untransformed
plants, or hybrid lines containing both the PDC and ADH constructs.
Triticale-wheat hybrid lines with the vaviloid type of spike branching
