Relationship of Phenolic Metabolism to Growth in Plant and Cell Cultures Under Stress

Higher plants synthesize large array of phenolic metabolites. Phenolics are defined as "specialized metabolites" due to the observation that each plant lineage synthesizes a distinct set of specialized metabolites appropriate for its environment. These metabolites provide the plant with specific adaptations to changing environmental conditions, and, therefore, they are essential for plant defense mechanisms. These defense mechanisms are costly for plants due to the energy drain from growth and development toward defensive metabolite production. Therefore, being limited with environmental resources, plants have to decide how to allocate these resources to various competing functions. This decision brings about trade-off between growth and adaptive response. This chapter suggests that perception of abiotic stress and consequent increased level of defensive phenolic metabolites are linked by a sequence of biochemical processes that also involves the intracellular free proline and the oxidative pentose phosphate pathway. The chapter also shows that, once plant tissues respond to stress, in acclimated tissues, the establishment of a negative correlation between primary metabolism (growth) and secondary metabolism (defense compounds) is observed.