The modification of phenylpropanoid profile affects sensitivity to heat stress in cell cultures of Daucus carota

Precursors and inhibitors of the phenylpropanoid pathway were used for modifying the level of specific secondary metabolites in R3M carrot cell culture, a red pigmented line characterised by the production of cyanidin and hydroxycinnamic acid (HCA) derivatives, in order to evaluate the effects of profile modification on heat stress response. The heat treatment (1h at 44 °C) caused the appearance of cytoplasmic patches surrounded by endoplasmic reticulum, the arrest of endocellular movements, and a strong reduction of the viable cell number, since the patched cells were committed to slow cell death. Cytochalasin D, an anti-microfilament agent, caused the formation of structures similar to the heat-induced patches at specific concentrations. These results suggest that the heat stress-determined microfilament damages caused the formation of cytoplasmic patches, structures which anticipate programmed cell death. Feeding R3M cells with dihydroquercetin (a precursor of cyanidin) and HCAs before the heat treatment caused an increase in acylated anthocyanins and HCA derivatives and a reduction in the number of patched and dead cells. The supply of piperonilic acid, an inhibitor of the biosynthesis of p-coumaric acid (an intermediate of anthocyanin biosynthesis and substrate of their acylation) caused a decrease in the level of specific phenylpropanoids and an increase in the number of cells with stressed phenotype. These data suggest that specific phenylpropanoids can play a protective role against heat stress even though the detailed analysis of the correlation between the level of single metabolites and stress response is in progress.