Chlorophyll fluorescence responses to short-term drought in Mesembryanthemum nodiflorum

The halophyte Mesembryanthemum nodiflorum (Aizoaceae) was reported to shift its photosynthetic pathway from C3 to CAM under drought conditions. The aim of the present work was to test whether its photosynthetic apparatus is drought-sensitive. Plants were grown for 7 days on a nutrient medium added (drought) or not (control) with 10% polyethylene glycol (PEG) 6000. Growth and root water content of stressed plants were not affected, whereas their shoot water status and pigment concentrations were markedly affected. This was probably due to D1 damage as proved by the increased minimal fluorescence (F-0) and the unchanged maximal one (F-m). Photosystem II (PSII) energy distribution revealed a decrease in photochemical process and an increase in the non-regulated non-photochemical quenching, the regulated non-photochemical quenching being unchanged. This sensitivity of the photosynthetic machinery of M. nodiflorum to drought may explain why this species shifts its photosynthetic pathway from C3 to CAM under such conditions.