Wounding, anoxia and cold induce sugarbeet sucrose synthase transcriptional changes that are unrelated to protein expression and activity

Abstract

Wounding, anoxia, and cold are often encountered during crop production and postharvest storage of plant products. Although the effect of these stresses on the expression of sucrose synthase, a key enzyme in the carbon metabolism of many storage organs, has been investigated in several starch-accumulating plant organs, little information on their effect on sucrose synthase expression in sucrose-storing organs is available. To determine the effect of wounding, anoxia and cold on a sucrose-storing organ, sugarbeet ( Beta vulgaris) roots were wounded, subjected to anoxic conditions, or exposed to cold temperatures, and transcript and protein levels for the organ's two sucrose synthase genes (SBSS1 and SBSS2) and sucrose synthase enzyme activity were determined during 24 h and 7 d time course experiments. Wounding, anoxia and cold were associated with several-fold changes in sucrose synthase transcript levels. SBSS1 transcript levels were elevated in wounded, anoxic and cold-treated roots; SBSS2 transcript levels were elevated in response to wounding, cold, and short exposures (3–12 h) to anoxic conditions and reduced in roots exposed to anoxic conditions for more than 24 h. SBSS1 and SBSS2 protein levels, however, exhibited little change in stressed roots, even after 7 d. Enzyme activity was also relatively unchanged in stressed roots, except for small activity differences of 1–2 d duration that were unrelated to transcriptional changes. The disparity between transcript levels, protein abundance and enzyme activity indicate that SBSS1 and SBSS2 expression in response to wounding, anoxia and cold may be regulated by post-transcriptional mechanisms. The unresponsiveness of sucrose synthase protein levels or enzyme activity to wounding, anoxia and cold questions the importance of this enzyme to stress responses in sugarbeet root.