Abstract
Some agrochemicals have unique activities on plant, which modes of actions differ from those of herbicides and plant growth regulators. Because these induce useful and important phenotypic characteristics by activating physiological mechanisms in plant cell, understanding the underlying mechanism of their activities should be crucial for plant physiology and agriculture. As examples of such agrochemicals, studies on agrochemicals that activate the plant immune systems or root elongation, are described. Plant activators, inducers of systemic acquired resistance, were divided into two types, acting on upstream and downstream of salicylic acid (SA) biosynthesis, respectively. They have been useful research tools to clarify the regulation mechanism of SA-mediated disease resistance and to investigate another type of disease resistance mechanism mediated by brassinosteroids. By analyzing the roles of phytohormones in the isoprothiolane-induced root elongation indicated a positive effect of jasmonic acid and ethylene on primary root elongation. These types of research, categorized to one of chemical biology, would provide novel insight into plant physiology, which also contribute to control of crops.