Photosynthetic Adaptation to Salt Stress in Three-Color Leaves of a C4 Plant Amaranthus tricolor

Abstract

We examined the photosynthetic adaptation mechanisms for salt stress in Amaranthus tricolor, which has leaves with green, yellow and red regions, in relation to the accumulation of glycinebetain e as osmoprotectants. The content of Chi, especially of Chi b in the red and yellow regions was 3~4% 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. However, the contents of other photosynthetic proteins in these regions seem to be relatively high. We observed the net photosynthetic CO2 fixation activity 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 fixation rate in the green region decreased by about 20~35% whereas those in the non-green regions remained almost at the same levels. A. tricolor was found to accumulates glycinebetaine, betainealdehyde dehydrogenase and choline monooxygenase at similar levels in all three color regions and their contents increased upon salt stress. These results suggest that the low capacity of light harvesting in non-green regions would be favor of salt stress since the photosynthetic components in these regions were retained at relatively high levels under high salinity.