Iron resupply-mediated deactivation of Fe-deficiency stress responses in roots of sugar beet

Different root zones with or without increased Fe-reducing activities have been studied in Fe-deficient sugar beet (Beta vulgaris L.) plants after Fe resupply to the nutrient solution. The subapical regions of roots from Fe-deficient plants decreased by 19 and 88% their capacity to reduce ferric chelates after 24 and 96 h of Fe resupply, respectively. Iron resupply caused 52 and 96% decreases in phosphoenolpyruvate carboxylase activity in root extracts after 24 and 96 h, respectively, and also caused general decreases in other enzyme activities involved in carboxylic acid metabolism. The large pools of carboxylic acids in Fe-deficient roots decreased by 9 and 48% after 24 and 96 h of Fe resupply, respectively. The activities of pyruvate decarboxylase and lactate dehydrogenase, enzymes related to anaerobic metabolism, decreased by 88% after 24 h of Fe resupply. The mitochondrial quinone and pyridine nucleotide pools became more oxidised in the Fe-deficient root tips after Fe resupply. Iron resupply caused a 70% decrease in root oxygen consumption rates 96 h after Fe resupply. Results indicate that deactivation of the Fe deficiency stress responses of sugar beet roots upon Fe resupply occurs in a progressive manner in a time scale of several days.