Alteration of Abiotic Stress Responsive Genes in Polygonum minus Roots by Jasmonic Acid Elicitation

Abstract

Plants are continuously exposed to both biotic and abiotic stress in their natural environment. Unlike animals, plants are immobilized organisms which tend to be vulnerable to various environmental stresses. In order to survive, plants have evolved a wide range of defense mechanism to cope with these stresses. Both biotic and abiotic stresses might share some common signaling pathway in triggering the defense system in plants. Recent researches have revealed that phytohormones such as abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA) and ethylene (ET) are intermediate molecules which play key roles in the crosstalk between biotic and abiotic signaling network (Fujita et al. 2006). In this chapter, we highlight the effects of exogenous applied jasmonic acid in triggering the synthesis of some molecules and activating their respective biosynthetic genes in plants as a response towards abiotic stresses. Abiotic stress is defined as non-living external factors, usually environment conditions, which could reduce plant growth and cause huge devastation on agricultural productivity. Some of these major adverse environmental factors are drought, salinity, heavy metals, extreme temperatures, nutrient poor soils and other source of natural disasters. To our knowledge, these abiotic stresses have account for major crops lost worldwide where more than 50% of their average yields were decreased yearly (Rodriguez et al. 2005). However, not all effects are detrimental. Plants are able to exhibit various molecular mechanisms as a defense system and these responses could be generally divided into three main groups. Firstly, signalling of stress-activated molecules leading to changes of osmotic and ionic homeostasis as well as detoxification mechanism. Secondly, up-regulation of different gene expression leading to synthesis of specific proteins (e.g. heat-shock proteins and LEA proteins) and some protective molecules (e.g. sugars, polyalcohols and amino acids). Thirdly, generation of reactive oxygen species (ROS) and activation of antioxidant systems by synthesizing secondary metabolites such as flavonoids and phenolic compounds (Boscaiu et al. 2008). Among these changes, synthesis of secondary metabolites is at the highest interest because it has a wide range of functions, ranging from plant defense against abiotic stresses to human benefits. Plants have the ability to produce vast variety of secondary metabolites naturally. Secondary metabolites have been defined as compounds that did not play a vital role in