Role of Mineral Nutrients in Tolerance of Crop Plants to Environmental Stress Factors

Around 60% of cultivated soils worldwide have plant-growth-limiting problems caused by mineral nutrient deficiencies and toxicities. Therefore, improving the mineral nutritional status of plants under marginal environmental conditions is of great importance for maintenance of crop productivity. In most cases plants growing under marginal environmental conditions (e.g. salinity, low and high temperatures, and drought) receive much more sunlight than they can utilize in photosynthetic electron transport and CO2 fixation. This causes excessive accumulation of absorbed light energy and of photoreductants in the chloroplasts, which leads to activation of molecular O2 to reactive oxygen species (ROS). When ROS are not adequately scavenged, photooxidative damage occurs in the chloroplasts, and leads to chlorophyll damage, lipid peroxidation and, consequently, cell death. By limiting the utilization of absorbed light energy in photosynthesis, environmental stress factors increase the potential for photooxidative damage in chloroplasts. Because an adequate supply of mineral nutrients is indispensable for maintenance of photosynthetic electron transport and carbon metabolism, impairment of the mineral nutritional status of plants under marginal environmental conditions can exacerbate photooxidative damage and limit plant performance. In the present study, several examples are given, which show that plants exposed to environmental stresses require additional supplies of mineral nutrients, particularly nitrogen (N), potassium (K), magnesium (Mg), calcium (Ca) and zinc (Zn) to minimize the adverse affects of stresses. Enhanced production of ROS in plants under marginal conditions is not caused only by impairment of photosynthetic electron transport. It appears likely that an NADPH-dependent oxidase is another important source of ROS, which is stimulated by drought, chilling, and/or salinity. Of the mineral nutrients, K and Zn seem to interfere with the NADPHoxidizing enzyme and thus to provide additional protection against damaging attack of ROS under salinity, drought and chilling stress. It is concluded that improving the mineral nutritional status of crop plants is of great importance for