Pretreatment of etiolated cucumber cotyledons with potassium (K), benzyladenine (BA), or δ-aminolevulinic acid (ALA) for 20 h in the dark, followed by exposure to light for 24 h, increased chlorophyll and carotenoid content. A similar treatment with fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} decreased the levels of these photosynthetic pigments. However, when the etiolated cotyledons were pretreated with either BA or ALA for 20 h in the dark, followed by fluridone during a 24-h light period, the inhibitory effects of fluridone on chlorophyll content were reversed and the values were higher than the controls. In these treatments, ALA did not counteract the inhibitory effects of fluridone on carotenoids, but BA reduced the effects. In the cucumber cotyledon greening system, K was found to be most effective in stimulating both chlorophyll and carotenoid accumulation. When K was administered to the cotyledons either together with, prior to, or after the fluridone treatment, the inhibitory effect of fluridone on chlorophyll accumulation was totally eliminated and the stimulatory effects due to K were still maintained. Although K increased carotenoid content, it did not reverse the inhibitory effect of fluridone on carotenoids. From these findings it is concluded that the inhibition of chlorophyll and carotenoid accumulation by fluridone may be mediated via unrelated mechanisms at fluridone concentrations that do not totally eliminate or drastically reduce carotenoid content.
VlbZIP30 of grapevine functions in drought tolerance via the abscisic acid core signaling pathway