Investigations on the role of ethylene in phytochrome-mediated photomorphogenesis : II. Enzyme levels and chlorophyll synthesis.

The concept (Burg, 1973) that ethylene mediates the action of phytochrome in seedling photomorphogenesis was tested in the intact mustard (Sinapis alba L.) seedling. The effect of exogenous ethylene (100 μl l(-1)) on five distinct, phytochrome-mediated photoresponses of the cotyledons was investigated. It was found that anthocyanin contents (see Bühler et al., 1978) and phenylalanine ammonia-lyase levels (EC 4.3.1.5) are strongly reduced by ethylene while the capacity of chlorophyll synthesis is considerably enhanced. Levels of glutathione reductase (EC 1.6.4.2) and pools of photoconvertible protochlorophyll(ide) are unaffected by ethylene. It is concluded that these findings are incompatible with the idea that ethylene plays the role of a mediator in phytochrome-induced photomorphogenesis.