Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2007
Publication Date: 9/2/2008
Citation: Klotz, K.L., Finger, F.L., Anderson, M.D. 2008. Respiration in Postharvest Sugarbeet Roots is not Limited by Respiratory Capacity or Adenylates. Journal of Plant Physiology. 165(14):1500-1510. doi:10.1016/j.jplph.2007.12.001.
Interpretive Summary: During storage, sugarbeet roots rely on respiration to provide the metabolic substrates and energy needed to heal wounds incurred in harvest, maintain healthy tissue and defend against pathogens. Although respiration is essential for the root, it occurs at the expense of sucrose. Reductions in root respiration rate, therefore, would be beneficial to the sugarbeet industry. In plants, respiration is regulated by respiratory substrate availability, respiratory capacity or energy status. The mechanism(s) that operate in stored sugarbeet roots, however, is unknown. Here, we demonstrate that respiratory capacity, ADP availability and cellular energy status do not limit respiration in stored sugarbeet roots and suggest that respiration is likely to be limited by the availability of a respiratory substrate, other than ADP.
Technical Abstract: Control of respiration has largely been studied with growing and/or photosynthetic tissues or organs, but has rarely been examined in harvested and stored plant products. As nongrowing, heterotrophic organs that are reliant on respiration to provide all of their metabolic needs, harvested plant products differ dramatically in their metabolism and respiratory needs from growing and photosynthetically active plant organs, and it cannot be assumed that the same mechanism controls respiration in both actively growing and harvested plant organs. To elucidate mechanisms of respiratory control for a harvested and stored plant product, sugarbeet (Beta vulgaris L.) root respiration was characterized with respect to respiratory capacity, adenylate levels, and cellular energy status in roots whose respiration was altered by wounding or cold treatment (1 degree C) and in response to potential effectors of respiration. Respiration rate was induced by wounding in roots stored at 10 degree C and by cold temperature in roots stored at 1 degree C for 11 to 13 d. Alterations in respiration rate due to wounding or storage temperature were unrelated to changes in total respiratory capacity, the capacities of the cytochrome c oxidase (COX) or alternative oxidase (AOX) pathways, adenylate concentrations or cellular energy status, measured by the ATP:ADP ratio. In root tissue, respiration was induced by exogenous NADH indicating that respiratory capacity was capable of oxidizing additional electrons fed into the electron transport chain via an external NADH dehydrogenase. Respiration was not induced by addition of ADP or a respiratory uncoupler. These results suggest that respiration rate in stored sugarbeet roots is not limited by respiratory capacity, ADP availability or cellular energy status. Since respiration in plants can be regulated by substrate availability, respiratory capacity or energy status, it is likely that a substrate, other than ADP, limits respiration in stored sugarbeet roots.