Conjugates of auxin and cytokinin

Active free forms of auxin and cytokinin are changed into multiple forms by acylation, esterification or glycosylation, for example. It seems that conjugated compounds could serve as pool of inactive phytohormones that can be converted to active forms by de-conjugation reactions. The concept of reversible conjugation of phytohormone suggests that under changeable environmental, developmental or physiological conditions these compounds can be a source of free hormones. All metabolic steps are in principle irreversible, except for some processes such as the formation of ester, glucoside and amide conjugates, where the free compound can be liberated by enzymatic hydrolysis. The nature of auxin and cytokinin conjugates is discussed.