S08 - Session O3 - The role of Manganese in light stress induced tipburn of lettuce

Authors: Sissel Torre *, Gifty Kodua, YeonKyeong Lee

Tipburn is a physiological disorder visible as necrotic spots or lesions on the edge of outer older leaves or young inner leaves. It is a common injury of lettuce and leafy vegetables produced in protected environment and reduces the marketable yield and causes severe food loss. Light stress is known to increase the severity of tipburn. We found that increased irradiance triggered accumulation of reactive oxygen species (ROS) such as hydrogen peroxide (H 2 O 2 ) and superoxide (O2-) in tips of lettuce ( Lactuca sativa L 'Frillice'). To mitigate the effect of ROS, plants have antioxidant defense mechanisms which have the function of removing and transforming ROS into non-toxic substances. Manganese (Mn) is involved in redox reactions as a cofactor for enzymes known to mitigate ROS. Hence, we investigated the role of Mn in the development of tipburn and hypothesized that increased manganese alleviates tipburn incidence under high irradiance. Lettuce were grown with light emitting diodes (LEDs) at different light levels and with different Mn concentrations in the nutrient solution. Increased Mn content reduced the incidence of tipburn on young inner leaves but not on the old outer leaves. The uptake, pattern of distribution and translocation of Mn in different plant parts and leaves in response to Mn supply and irradiance will be discussed.