Association of Latex Pressure with Tipburn Injury of Lettuce

Abstract

Latex pressures in laticifers of lettuce, Lactuca sativa L., were obtained by inserting capillary tubes into vascular traces within leaves and stems. The pressure was determined by monitoring the counter pressure of compressed gas required to prevent latex entrance into the capillary. The latex pressure in seedling plants was 1.5 bars. This pressure increased during vegetative development to 9.3 bars and increased additionally during flowering stages to 12.5 bars. A maximum of 15.2 bars was measured in a flowering plant. Latex pressures were reduced in plants grown at reduced irradiance levels. Latex pressures also decreased with soil water stress, but, with rewatering of the soil, pressures increased to a level greater than present before initiation of the water stress. Osmotic potential of latex in plants in the vegetative stages was –13.5 bars. The pressure potentials and osmotic potential of the laticifers was compared to potentials in the xylem and mesophyll. It was concluded that turgor pressure fluctuations in laticifers can be a contributing factor for laticifer rupture and tipburn injury in lettuce.