Photosynthetic adaptation to salt stress in three-color leaves of a C-4 plant Amaranthus tricolor

We examined the photosynthetic adaptation mechanisms for salt stress in Ama ranthus tricolor, which has leaves with green, yellow and red regions, in r elation to the accumulation of glycinebetaine as osmoprotectants. The conte nt of Chi, especially of Chl b in the red and yellow regions was 3 similar to 4% of that in the green region. The levels of Chi proteins such as LHCII , PSI and PSII were significantly lower than those in the green region, How ever, the contents of other photosynthetic proteins in these regions seem t o be relatively high. We observed the net photosynthetic CO2 fixation activ ity in the red and yellow regions which was about 40% of that in the green region. Upon salt stress (0.3 M NaCl) for 5 d the levels of Chi, PSI, PSII, ribulose 1,5-bis phosphate carboxygenase and oxygenase, and the CO2 fixati on rate in the green region decreased by about 20 similar to 35% whereas th ose in the non-green regions remained almost at the same levels, A. tricolo r was found to accumulates glycinebetaine, betainealdehyde dehydrogenase an d choline monooxygenase at similar levels in all three color regions and th eir contents increased upon salt stress. These results suggest that the low capacity of light harvesting in non-green regions would be favor of salt s tress since the photosynthetic components in these regions were retained at relatively high levels under high salinity.