THE KINETICS OF THE PHOTOACCLIMATION RESPONSE OF NANNOCHLOROPSIS SP. (EUSTIGMATOPHYCEAE): A STUDY OF CHANGES IN ULTRASTRUCTURE AND PSU DENSITY

Abstract

In this study we report the kinetics of photoacclimation of the unicellular alga Nannochloropsis sp. grown under high light (HL), and subsequently transferred to low light (LL). We examined the changes in ultrastructural features, pigmentation, and photosynthetic parameters over short intervals until the LL steady state was reached. The ultrastructural changes were followed by quantitative morphometric measurements of transmission electron micrographs. We found that the increase in the relative volume of the chloroplast during acclimation to LL (twofold) was accompanied by an increase in number of stacks (twofold) and in the surface area of thylakoids per cell (2.5‐fold). The increase in photosynthetic unit (PSU) density was about 2.15‐fold. Maximal density was about 84 PSU·μm−2 in LL cells, and minimal density was 39 PSU·μm−2 in HL cells. The HL/LL ratio of the in vivo optical absorption cross‐section of PSU (σPSU) was 2.8, whereas in the in vivo optical absorption cross‐section of the cell (σcell), the trend of change was in the opposite direction: 1.7‐fold higher in LL‐acclimated cells than in HL‐acclimated cells. We propose a partial sequence of the photoacclimation processes based on our data and the derived rate constants.

Contrasting Responses of Marine and Freshwater Photosynthetic Organisms to UVB Radiation: A Meta-Analysis

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Seasonal Variation of Lipids and Fatty Acids of the Microalgae Nannochloropsis oculata Grown in Outdoor Large-Scale Photobioreactors

“…This relative fast decrease in effective day length (photoperiod x intensity) could result in lower photosynthetic rate followed by a rearrangement of the photosynthetic apparatus to achieve a more efficient light harvesting and utilization capacity. The algal cell adapts with a significant enlargement of thylakoid membranes, the enhancement of stacked thylakoid membranes and an increased synthesis of light harvesting complexes [25,36]. When facing a drastic change in light intensity, algal cells achieve the support of this new membrane structure by increasing lipid synthesis over a short time (2-3 days) [25], hence increasing thylakoid membranes fluidity.…”

Photoacclimation processes in phytoplankton: mechanisms, consequences, and applications

“…Under low light, there is always an increase in the number of thylakoids per granum (Berner et al 1989, Fisher et al 1998, resulting from an increase in the total area of these membranes required to accommodate the added pigment molecules (Fig. 5).…”