The role of fungi in abiotic stress tolerance of plants

Abstract Abiotic stresses, which include heavy metal, drought, salinity, cold and heat stress are a severe threat to agricultural ecosystems which greatly hampers the crop productivity and also deteriorates the environment. It was estimated that worldwide, these stresses are responsible for reduction of average yield of various major crops by more than 50%. These stresses cause many morphological, physiological, biochemical and molecular alterations that finally leads to loss of productivity and degradation of ecosystem. Climatic changes and excessive use of fertilizers and pesticides in modern agricultural practices to increase production worsen the effects of these abiotic stresses. Only 0.1% of the applied pesticides reach the target organism, while the residual contaminates the soil and decreases growth, productivity of crop and also alters the biological and chemical properties of the soil. Furthermore, increase and expansion of human population with time has caused degradation of habitats, increased pollution and increased salinization of agricultural fields. All the stresses mentioned above are often interconnected and these are known to initiate similar cellular damage, e.g. both, drought and salinity stress which are principally shown as osmotic stress, brings about the change in cell homeostasis and ion dispersal in the cell. High temperature causes denaturation and accumulation of deoxyribonucleic acid (DNA), cellular proteins, causes induction of thermo tolerance and accumulation of heat shock proteins (hsps) whereas low temperature impairs many metabolic processes, modifies membrane properties, changes structure of proteins and inhibits enzymatic activity. Heavy metals (HMs) like arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg) and nickel (Ni) interferes with photosynthesis, water and mineral uptake and also causes modification of amino acids, proteins, deoxyribonucleic acid (DNA) and cell membrane damage. All plants are considered capable of recognizing and responding to these stresses. Common plant responses against these stresses include altering water transport, production of different osmolytes and scavenging of harmful reactive oxygen species (ROS) by action of different enzymatic and non-enzymatic antioxidants.