Changes in the pools of carotenoids and protochlorophyll(ide) in etiolatedcucumber (Cucumis sativus) cotyledons treated with norflurazon and KC 6361

Changes in the pools of carotenoids and protochlorophyll(ide) were investig ated in etiolated cucumber cotyledons treated with norflurazon (NF) and an experimental herbicide KC 6361 (KC). Both the NF- and the KC-treated tissue s considerably accumulated the colourless carotenes phytoene and phytofluen e with a concomitant depletion of the coloured carotenoids lutein and beta- carotene in darkness. However, the profiles of changes in chlorophylls (Chl s) and carotenoids were different for the two herbicides. The plants were a lso influenced by the photosynthetic photon flux densities (PPFD's), with a more pronounced decline of Chi under high PPFD than under low PPFD. The ra tios of protochlorophyll (PChl)/protochlorophyllide (PChlide) were greatly altered due to a decrease and an increase of PChl in the NF- and the KC-tre ated etiolated tissues, respectively, whereas the PChlide content was not s ignificantly influenced by the inhibitors. Large increase of PChls in the K C-treated tissues seems to derive from the binding of accumulated geranylge raniol (GG) equivalents, through carotenogenic inhibition, to PChlide. Ther efore, the alterations of PChl and PChlide occurring under disturbed carote nogenesis may suggest an interaction between the biosynthetic pathways of C hls and carotenoids. In addition, the great proportion of PChl GG and PChl dihydro-GG in the KC-treated tissues implies that PChl formation is regulat ed at the level of hydrogenation.