Introduction

In the environment, any organism is confronted with stress, for instance, stress caused by fluctuating or changing environmental conditions and disturbances by man or by pollution. In a polymorphic population, natural selection may favor one particular way of dealing with stress over others and thus change the genetic make-up of the population. The study of stress responses therefore may reveal important knowledge about how cellular processes are regulated. In addition, there are many interactions between the stress response systems directed at different types of stress. There are two major sources of cellular stress in an organism. The first source is endogenous factors, mainly of a biological origin, such as pathogens. The second source is environmental factors, which may have a physical character, such as heat, cold, drought, and osmotic conditions, or may be of a chemical nature, such as oxidants, heavy metals, and organic chemicals. The chapter also presents an overview of the key concepts discussed in this book.