THE SIGNIFICANCE OF THE ANTHER TAPETUM IN THE BIOCHEMISTRY OF POLLEN PIGMENTATION - AN OVERVIEW

Flavonoids such as chalcones, flavonol di- and triglycosides as well as anthocyanins are essentially involved in pollen pigmentation. Phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) represent two key enzymes in the biosynthetic pathway of flavonoids. In enzymatical studies the distribution of the two enzymes in anthers of Tulipa cv. 'Apeldoorn' was analysed. After separation of the loculus material in a pollen and a tapetum fraction the highest enzyme activities of both PAL and CHS were found in the tapetum fraction whereas the pollen fraction showed only low enzyme activities. This was confirmed by immunohistochemical studies using antibodies against CHS. The CHS was present in the tapetum and epidermal cells of anthers at an early and middle postmeiotic developmental stage. The results imply that the tapetum cells play a crucial role in the flavonoid biosynthesis in the loculus of the anthers and consequently in the pollen pigmentation.