effects of copper on the photosynthetic response of Phaeocystis cordata

• Published in: Photosynthesis research 2011-05, Vol.108 (1), p.77-87
• Main Authors: Lombardi, Ana T, Maldonado, Maria T
• Format: Article
• Language: English
• Subjects: Analysis; Analysis of Variance; Biochemistry; Biomedical and Life Sciences; Chlorophyll; Chlorophyll - metabolism; Copper; Copper - pharmacology; Fluorescence; fluorometry; Fluorometry - methods; Haptophyta - drug effects; Haptophyta - growth & development; Haptophyta - physiology; Life Sciences; Phaeocystis; photochemistry; Photosynthesis; Photosynthesis - drug effects; photosystem II; Physiological aspects; Phytochemistry; Plankton; Plant biology; Plant Genetics and Genomics; Plant Physiology; Plant Sciences; Regular Paper; Time Factors; toxicity
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-011-9655-z

We investigated the effects of limiting (1.96 × 10⁻⁹ mol l⁻¹ total Cu, corresponding to pCu 14.8; where pCu = −log [Cu²⁺]) and toxic Cu concentrations up to 8.0 × 10⁻⁵ mol l⁻¹ total Cu (equivalent to pCu 9.5) on growth rates and photosynthetic activity of exponentially grown Phaeocystis cordata, using batch and semi-continuous cultures. With pulse amplitude modulated (PAM) fluorometry, we determined the photochemical response of P. cordata to the various Cu levels, and showed contrasting results for the batch and semi-continuous cultures. Although maximum photosystem II (PSII) quantum yield (ΦM) was optimal and constant in the semi-continuous P. cordata, the batch cultures showed a significant decrease in ΦM with culture age (0-72 h). The EC50 for the batch cultures was higher (2.0 × 10⁻¹⁰ mol l⁻¹, pCu9.7), than that for the semi-continuous cultures (6.3 × 10⁻¹¹ mol l⁻¹, pCu10.2). The semi-continuous cultures exhibited a systematic and linear decrease in ΦM as Cu levels increased (for [Cu²⁺] < 1.0 × 10⁻¹² mol l⁻¹, pCu12.0), however, no effect of high Cu was observed on their operational PSII quantum yield (Φ′M). Similarly, semi-continuous cultures exhibited a significant decrease in ΦM, but not in Φ′M, because of low-Cu levels. Thus, Cu toxicity and Cu limitation damage the PSII reaction centers, but not the processes downstream of PSII. Quenching mechanisms (NPQ and Q n) were lower under high Cu relative to the controls, suggesting that toxic Cu impairs photo-protective mechanisms. PAM fluorometry is a sensitive tool for detecting minor physiological variations. However, culturing techniques (batch vs. semi-continuous) and sampling time might account for literature discrepancies on the effects of Cu on PSII. Semi-continuous culturing might be the most adequate technique to investigate Cu effects on PSII photochemistry.