Role of Polyamines in the Physiological Responses of Plants

Abstract

Polyamines (PAs) are aliphatic nitrogenous bases containing two or more amino groups. These organic compounds have a low molecular weight and play essential role in the growth and development of plants. They contribute to the tolerance of plants against all abiotic and biotic stresses. They occur in the free form as cations, but are often found in the conjugated form to different macromolecules such as proteins and nucleic acids and to small molecules like phenolic acids. They are produced by plants during metabolism and are ubiquitous in plant cells. They are considered to be a new kind of plant biostimulant because they are intimately associated with a wide range of metabolic process in plants, ranging from cell division and organogenesis to protection against abiotic and biotic stress. Their chemistry, biosynthetic pathway and metabolism are now well characterized. Their titer varies and depends on the environmental conditions, especially stress. With the development of molecular biotechnology, genes for several key biosynthetic enzymes of the PA pathway have been cloned from different plants species, and antibodies to some of the genes are now available. The antisense transgenic approaches and over-expressed PA biosynthetic genes have given further evidence that PAs are required for plant growth, productivity and development of stress tolerance. This paper aims to review the various physiological responses of plants to PA with special emphasis to abiotic stress response and to provide a basis for future research on the role of polyamines in plant physiology.