Phytohormones in Plant Biotechnology and Agriculture

Phytohormone research is a crucially important area of plant sciences. Phytohormones are one of the key systems integrating metabolic and developmental events in the whole plant and the response of plants to external factors. Thus, they influence the yield and quality of crops. During the last decade we have slowly begun to understand the molecular mechanisms underlying phytohormone action, largely as a result of the rapid developments that have been made internationally in the field of plant molecular genetics. Putative receptor proteins for ethylene (1993- 95), brassinosteroids (1997) and cytokinins (2001) have been identified and the genes that encode them cloned. Primary response genes and elements of hormonal signal transduction have also been identified for most known phytohormones. There is now little doubt that phytohormones, like their animal counterparts, function as signal molecules and create a signalling network in the whole plant organism. The in vivo activity of hormones depends, among other things, on their rate of biosynthesis and metabolism, and on their transport into and out of target cells. Consequently, genes and enzymes involved in these processes are of particular interest. In recent years a number of genes encoding enzymes for the synthesis, modification and degradation of different phytohormones have been cloned and identified, as have genes encoding proteins involved in phytohormone transport and its regulation. Some classes of phytohormone have been shown to participate in stress reactions and can increase the resistance of plants to unfavorable environmental factors.