Abstract: | Tobacco (Nicotiana tabacum) plants expressing a
partial ferredoxin-dependent glutamine-2-oxoglutarate aminotransferase (Fd-GOGAT) cDNA in the antisense orientation under
the control of the 35S promoter, were used to study the metabolism of amino acids, 2-oxoglutarate and ammonium following the
transition from CO2 enrichment (where photorespiration is inhibited) to air (where photorespiration is a major process of ammonium production
in leaves). The leaves of the lowest Fd-GOGAT expressors accumulated more foliar glutamine (Gln) and α-ketoglutarate (α-KG)
than the untransformed controls in both growth conditions. Photorespiration-dependent increases in foliar ammonium, glutamine,
α-KG and total amino acids were proportional to the decreases in foliar Fd-GOGAT activity. No change in endoprotease activity
was observed following transfer to air in the Fd-GOGAT transformants or the untransformed controls which has similar activities
over a broad range of pH values. We conclude that several pathways of amino acid biosynthesis are modified when NH3
+ and Gln accumulate in leaves.
This revised version was published online in June 2006 with corrections to the Cover Date. |