Hydroponic growth system and physiological responses to NaCl treatments. a) A raft of Arabidopsis plants at 21 dpi, preceding treatment. This raft has been removed from the hydroponic growth medium for the purpose of this photograph; although individual roots cling together in air, they are well separated when submerged in the growth medium. b) Anthocyanin accumulation in Arabidopsis leaves. Plants were mock treated or exposed to 150 mM NaCl for 6, 24 and 48 h. The means of six experiments ± standard deviation are shown. Anthocyanin concentration is reported as an absorbance ratio: (A530-1/4*A657)/g fresh weight. c) Proline accumulation in roots and leaves of Arabidopsis plants. Arabidopsis plants were mock treated or exposed to 150 mM NaCl for 6, 24 and 48 h, and proline concentration was determined in both leaves and roots. The means of six experiments ± standard deviation are shown.