Résumé
Key message Hypocotyl semi-dwarfism in BP was only due to less cell number. Daylight was required to inhibit cell division in the mutant. ABA, IAA and cytokinins would be involved.Abstract Coffea arabica ‘Laurina’ is a natural mutant of Coffea arabica ‘Bourbon’ (B) and is known under the trade name ‘Bourbon Pointu’ (BP). Under daylight, the laurina mutation leads to pleiotropic effects, including semi-dwarf hypocotyls. At the opposite, semi-dwarfism of BP seedlings disappeared under darkness conditions. The first step was to describe the morphological impact of the mutation in seedlings growing under daylight by comparison with seedlings growing under darkness. As the hypocotyl length was mainly affected, the second step was to investigate histological modifications in the organ comparing B and BP seedlings growing under daylight. Result of this investigation indicated that the mutation does not impact on cell length. Moreover, cytometry analyses showed absence of endoreduplication. Actually, the mutation influenced the cell number and this effect appeared before the 40th day after sowing. The length difference of hypocotyls between B and BP was due to lower cell number in BP, indicating possible involvement of phytohormones. Investigations showed the decrease of cytokinin and auxin levels in BP compared to B, while the cytokinin/auxin ratio remained constant in both varieties. By contrast, abscisic acid content increased in BP. Concurrently these results indicate the lowering of cell division, due to the mutation.