Differentiation between osmotic injury and chloride toxicity of rice seedlings grown under saline conditions1

Abstract

Rice (Oryza sativa, L.) is most sensitive to salinity injury as a seedling. Information describing the effects of salinity on the seedling rice plant is limited. Therefore, the current study was conducted to determine if salinity injury to rice seedlings is the result of toxic levels of chloride, or if a change in osmotic potential interferes with the plant's ability to absorb water and nutrients. Rice was grown in controlled environmental conditions through the seedling growth stage. In hydroponic culture with a 50% Hoagland's solution, the rice was exposed to osmotic tensions of 0, 50, 100, 200, 400, 800, or 1,600 kPa imposed by either CaCl2 or polyethylene glycol (PEG). The rice was grown for 1 wk following imposition of the osmotic treatments. Visual ratings were then obtained and plants were harvested for dry matter determination and Cl‐ concentration. Shoot weights were lowered for PEG treatments compared to CaCl2. Root weights differed little between CaCl2 and PEG treatments. Root weights decreased with increasing osmotic tension whether decreased by CaCl2 or PEG. Salinity related damage to leaves and roots was worse for PEG than for CaCl2 treatments. Not surprisingly, uptake of Cl‐ tended to increase with increasing rates of CaCl2, but not with PEG. These data suggest that rice sensitivity to salinity is the result of changes in the osmotic potential gradient rather than to chloride toxicity.