Phytohormone profile and CiFL1 expression in young seedlings of Cichorium intybus L. var sativum exposed to high temperature in relation to vernalization and de-vernalization processes

Cichorium intybus is a biennial plant species forming a taproot and a leaf rosette during the first year and which requires low temperature during vernalization to flower during the second year of its cycle. Heat stress, however, is known to induce premature flowering during the first year. The present work aims to compare the effect of heat treatment (38 degrees C during 3 days) and vernalization (4 degrees C during 6 weeks) on the phytohormonal profile and the expression of two chicory genes (CiFL1 and CiFT) homologous to the Arabidopsis flowering genes FLOWERING LOCUS C (FLC) and FLOWERING LOCUS T (FT). In Arabidopsis, FLC and FT code, respectively, for a repressor and an activator of flowering. Although CiFL1 was inhibited by vernalization, its expression was increased by heat treatment in both vernalized and non-vernalized seedlings while high temperature unexpectedly inhibited FT expression in vernalized seedlings. Vernalization induced a modification in the hormonal profile of C. intybus (cv. Melci) in a sense of a decrease in ethylene production, abscisic acid and total jasmonates content, while the level of salicylic and benzoic acids as well as polyamine spermidine increased. A limited effect on the gibberellins' profile was observed. The subsequent impact of heat stress on phytohormone content was different in non-vernalized and vernalized seedlings, with a higher abscisic acid and jasmonates and a lower 1-aminocyclopropane-1-carboxylic acid concentration in the former than in the latter. These data are discussed in relation to the putative involvement of phytohormones in stress-induced flowering. It appears that heat stress implies different pathways than vernalization to hasten flowering process.