Original article
Enhancement of photosynthetic O2 evolution in Chlorella vulgaris under high light and increased CO2 concentration as a sign of acclimation to phosphate deficiency

https://doi.org/10.1016/j.plaphy.2004.02.010Get rights and content

Abstract

The photosynthetic oxygen evolution of Chlorella vulgaris (Beijer.) cells taken from phosphate-deficient (–P) and control cultures was measured during 8 days of culture growth. Under inorganic carbon concentration (50 μM) in the measuring cell suspension and irradiance (150 μmol m–2 s–1), the same as during culture growth, there were no marked differences in the photosynthetic O2 evolution rate between the –P cells and the controls. The much slower growth of –P cultures indicated that the utilization of absorbed photosynthetically active radiation (PAR) in the CO2 assimilation and biomass production were in –P cells less efficient than in the controls. Alga cells under the phosphorus stress utilized more of the absorbed PAR in the nitrate reduction than the control cells. However, under conditions of more efficient CO2 supply (inorganic carbon concentration 150 μM, introducing of exogenous carbonic anhydrase to the measuring cell suspension) and under increased irradiance (500 μmol m–2 s–1), the photosynthetic O2 evolution in –P cells reached a higher rate than in the controls. The results suggest that in –P cells the restricted CO2 availability limits the total photosynthetic process. But under conditions more favorable for the CO2 uptake and under high irradiance, the –P cells may reveal a higher photosynthetic oxygen evolution rate than the controls. It is concluded that an increased potential activity of the photosynthetic light energy absorption and conversion in the C. vulgaris cells from –P cultures is a sign of acclimation to phosphorus stress by a sun-type like adaptation response of the photosynthetic apparatus.

Introduction

Phosphorus is the component of several intermediate and final biological compounds, it participates in energy conversion and in the transfer of genetic information. Cellular inorganic orthophosphate (Pi) regulates enzyme activity and metabolic pathways as well as the transport processes. It affects various aspects of photosynthesis [1], [7], [28], [34]. Phosphate insufficient feeding limits plant growth [4], [21], [22]. However, under conditions of phosphorus deficiency, the rates of net photosynthesis were found decreased [10], [14], [16], [32], unchanged [9], [20], or even increased [6], [22]. These divergent data strongly suggest that the ultimate effect may depend on the depth of phosphate stress as well as on the influence of other factors, both endogenous and environmental.

In our previous work, we have stated that Chlorella vulgaris (Beijer.) cells, from cultures grown at medium phosphate-deficient (–P), showed an increased potential capacity (higher Pmax and 1/K0.5 [dissolved inorganic carbon, DIC]) for photosynthetic oxygen evolution than cells from cultures well supplied with phosphate [22]. In the present study, we focused on the explanation of these acclimation modifications of the algal photosynthetic apparatus.

Section snippets

Culture growth, phosphates and photosynthetic pigments contents

Data obtained in the preliminary characteristics of C. vulgaris cultures used were concordant with the results presented in our previous publication [22]. During the first 8 days of culture, the phosphorus deficiency caused a decrease in the cell density in the medium by about 40% on the average (results are not presented).

The total phosphate content in the medium of the control cultures (initial content was close to 60 mg Pi cultures–1) did not reveal a significant decrease. This substrate was

Discussion and conclusion

Insufficient phosphate feeding limits net photosynthetic carbon assimilation and plant growth [1], [4], [7], [21], [22], [28], [29], [34]. The photosynthetically active radiation (PAR) absorption, energy transfer and conversion as well as the reactions of electron transport are only slightly dependent on the level of phosphate feeding. It suggests that the phosphate deficiency, at least at its initial phase, directly affects mainly the reactions of photosynthetic carbon assimilation and

Culture growth

Cells of C. vulgaris Beijerinck were grown axenically in batch culture [42], in 500 ml conical flasks, containing 250 ml of continuously stirred medium. Complete or P-deficient Knop medium (pH 6.8) was used. The flasks were closed with bacteriological cotton plugs. Growth of cultures was initiated by introduction of inoculum containing about 107 alga cells. Cultures were grown under air. The photosynthetic photon flux density at the cultures level was about 150 μmol m–2 s–1, the photoperiod was

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      The P levels in the present work were always relatively high (≥20 mg L−1, or ≥10.9 mg PO43− L−1) and did not affect the chlorophyll content of the cells. In other studies, P-deficient media have reduced growth of C. vulgaris without having much effect on the chlorophylls content of the cells (Kozlowska-Szerenos et al., 2000; Kozlowska-Szerenos et al., 2004). Phenolics, or polyphenolics, are compounds with multiple aromatic rings containing hydroxyl functional groups (Del Rio et al., 2013; Wang et al., 2014).

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