Correlated influence of cation concentration and excitation intensity on PS II activity-II. Comparative study between green plant and brown-alga chloroplasts

✍ Scribed by C. Berkaloff; J. C. Duval

• Publisher: Springer
• Year: 1980
• Tongue: English
• Weight: 378 KB
• Volume: 1
• Category: Article
• ISSN: 0166-8595
• DOI: 10.1007/bf00018229

✦ Synopsis

A preparation of photochernically active chloroplasts of Fucus was added to a low-salt medium with high osmolarity (HEPES*-AMPD buffer, 1M sorbitol). The rate of DCIP reduction (DCIPr) and the variable fluorescence (Fv) of these phaeoplasts were measured and compared with the same activities in spinach chloroplasts. A study of the influence of mono-and divalent-cations showed that salt effects on PS II activity also exist in Fucus.

(i)

Mg ÷÷ action on Fv is similar, although noticeably weaker in Fucus than in spinach chloroplasts. (ii)

Na ÷ has no effect on Fv of Fucus chloroplasts, but its influence on DCIPr is more pronounced than in spinach. (iii) Mg ÷÷ influence on DCIPr is largely dependent upon excitation energy. In subsaturating light (100-1000Wm-2), Mg ÷÷ stimulation increases up to 100raM, almost doubling the level. In very low light conditions (3Wm-2), however, this stimulation saturates at about 10mM; higher concentrations are no longer effective but do not quench DCIPr noticeably, unlike the ease in spinach. Therefore, cations act through ~ pathways on Fucus as on spinach isolated chloroplasts but the effects on PS II centers are preponderant in Fucus whereas the modifications in non-radiative decay or pigment array size are weaker.