Effect of Putrescine Pretreatment to Roots on Growth and Lactate Metabolism in the Root of Tomato (Lycopersicon esculentum Mill.) under Root-zone Hypoxia

Root-zone-hypoxia-intolerant tomato plants (Lycopersicon esculentum Mill., cv. House-Momotaro) were grown in nutrient solution with a dissolved O2 concentration of either 1 mg·liter-1 (hypoxia) or 6 mg·liter-1 (normoxia) for 7 days starting at the fifth leaf stage. The dissolved O2 levels in nutrient solution did not affect polyamine biosynthetic enzyme activities and free polyamine contents in the roots. Plants in hypoxic nutrient solution grew poorly and exhibited a significant increase in lactate dehydrogenase activity and lactate content in the roots compared with those grown in normoxic nutrient solution. However, preincubation of plants in 0.5 mM putrescine-containing normoxic nutrient solution for 6 hr promoted root growth and inhibited the rise of lactate fermentation in the roots after day 5 under hypoxia. These results indicate that putrescine interferes with hypoxically induced lactate fermentation in the roots; it alleviates hypoxia injury of roots and increases the root-zone hypoxia tolerance of tomato plants.