PLANT PHYSIOLOGY , Vol 105, Issue 2 535-543, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Growth at Low Temperature Mimics High-Light Acclimation in Chlorella vulgaris
D. P. Maxwell, S. Falk, C. G. Trick and NPA. Huner
Department of Plant Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7
Structural and functional alterations to the photosynthetic apparatus after
growth at low temperature (5[deg]C) were investigated in the green alga
Chlorella vulgaris Beijer. Cells grown at 5[deg]C had a 2-fold higher ratio
of chlorophyll a/b, 5-fold lower chlorophyll content, and an increased
xanthophyll content compared to cells grown at 27[deg]C even though growth
irradiance was kept constant at 150 [mu]mol m-2 s-1. Concomitant with the
increase in the chlorophyll a/b ratio was a lower abundance of
light-harvesting polypeptides in 5[deg]C-grown cells as observed by sodium
dodecyl sulfate-polyacrylamide gel electrophoresis and confirmed by western
blotting.The differences in pigment composition were found to be alleviated
within 12 h of transferring 5[deg]C-grown cells to 27[deg]C. Furthermore,
exposure of 5[deg]C-grown cells to a 30-fold lower growth irradiance (5
[mu]mol m-2 s-1) resulted in pigment content and composition similar to
that in cells grown at 27[deg]C and 150 [mu]mol m-2 s-1. Although both cell
types exhibited similar measuring-temperature effects on CO2-saturated O2
evolution, 5[deg]C-grown cells exhibited light-saturated rates of O2
evolution that were 2.8-and 3.9-fold higher than 27[deg]C-grown cells
measured at 27[deg]C and 5[deg]C, respectively. Steady-state chlorophyll a
fluorescence indicated that the yield of photosystem II electron transport
of 5[deg]C-grown cells was less temperature sensitive than that of
27[deg]C-grown cells. This appears to be due to an increased capacity to
keep the primary, stable quinone electron acceptor of photosystem II (QA)
oxidized at low temperature in 5[deg]C- compared with 27[deg]C-grown cells
regardless of irradiance. We conclude that Chlorella acclimated to low
temperature adjusts its photosynthetic apparatus in response to the
excitation pressure on photosystem II and not to the absolute external
irradiance. We suggest that the redox state of QA may act as a signal for
this photosynthetic acclimation to low temperature in Chlorella.
