Hl. Macintyre et al., PHOTOSYNTHESIS AND REGULATION OF RUBISCO ACTIVITY IN NET PHYTOPLANKTON FROM DELAWARE BAY, Journal of phycology, 32(5), 1996, pp. 718-731
Net phytoplankton (> 20 mu m) comprised 51 +/- 9% of the total chlorop
hyll (Chl) in a Skeletonema costatum-dominated spring bloom in Delawar
e Bay. The net phytoplankton had low C:N and high protein: carbohydrat
e ratios, indicating that their growth was nutrient-replete. Their pho
tosynthetic responses were characterized by low specific absorption, l
ow light-limited and light-saturated rates of photosynthesis, and high
quantum yields, indicative of acclimation to low irradiance and inter
nal self-shading. High fucoxanthin: Chl ratios also indicated low ligh
t acclimation, but high photoprotective xanthophyll: Chl ratios sugges
ted a high capacity for photoprotective energy dissipation. Ribulose-1
,5-bisphosphate carboxylase/oxygenase (Rubisco) could be activated and
deactivated in response to changes in irradiance and was fully activa
ted at the surface of the water column and fully deactivated in aphoti
c deep water. Maximum Rubisco activity was correlated with Rubisco con
tent and bulk protein content of the phytoplankton and with light-satu
rated rates of photosynthesis measured in short (< 20-min) incubations
. Long (60-min) incubations caused a decrease in the light-saturated r
ate of photosynthesis, possibly because of feedback limitation. While
feedback limitation is unlikely to occur in the water column, it shoul
d be considered when estimating productivity in well-mixed waters from
fixed light-depth incubations.