Adventures with cyanobacteria: a personal perspective

Abstract

Cyanobacteria, or the blue-green algae as they used to be called until 1974, are the oldest oxygenic photosynthesizers. We summarize here adventures with them since the early 1960s. This includes studies on light absorption by cyanobacteria, excitation energy transfer at room temperature down to liquid helium temperature, fluorescence (kinetics as well as spectra) and its relationship to photosynthesis, and afterglow (or thermoluminescence) from them. Further, we summarize experiments on their two-light reaction – two-pigment system, as well as the unique role of bicarbonate (hydrogen carbonate) on the electron-acceptor side of their photosystem II, PSII. This review, in addition, includes a discussion on the regulation of changes in phycobilins (mostly in PSII) and chlorophyll a (Chl a; mostly in photosystem I, PSI) under oscillating light, on the relationship of the slow fluorescence increase (the so-called S to M rise, especially in the presence of diuron) in minute time scale with the so-called state-changes, and on the possibility of limited oxygen evolution in mixotrophic PSI (minus) mutants, up to 30 min, in the presence of glucose. We end this review with a brief discussion on the position of cyanobacteria in the evolution of photosynthetic systems.

Response of growth, photosynthetic pigments, laser-induced pigment fluorescence, antioxidant enzymes and lipid peroxidation to ultraviolet-B radiation in two cyanobacteria

“…3). The fluorescence maxima near 660 nm was due to the allophycocyanin (Kana et al 2009;Govindjee and Shevela 2011), whereas fluorescence maxima near 684 and 715 nm were due to the Chl a fluorescence. Other than these three maxima, a tiny hump was present at 645 nm, which was the region of fluorescence emission of phycocyanin (Kana et al 2009).…”

“…At room temperature, PSII is mainly responsible for the Chl a fluorescence maxima (Govindjee 2004) and there is little contribution of PSI for the second Chl a maxima near 725 nm (Kana et al 2009). As in cyanobacterial PSI, Chl a is present in large quantity (Govindjee and Shevela 2011) and UV-B interrupts the electron transfer from PSII to PSI, there is possibility of increase in Chl a fluorescence from PSI. Most probably due to this reason UV-B treatment for 36 h or more increased the fluorescence maxima at 725 nm in comparison to fluorescence maxima near 685 nm in case of Anabaena cylindrica.…”

The Non-Photochemical Quenching of the Electronically Excited State of Chlorophyll a in Plants: Definitions, Timelines, Viewpoints, Open Questions

“…First of all, internal antenna were structurally more stable than external PBS whose structural integrity is known to be temperature-and ionic strength-dependent (Gantt et al 1979). Considering the structural integrity, therefore, the internalization of the Govindjee and Shevela (2011) and Shevela et al (2013). peripheral light harvesting antenna in the thylakoid membranes can definitely be viewed as an advantage.…”

Govindjee at 80: more than 50 years of free energy for photosynthesis

“…First was a discovery of a pigment that absorbs at 750 nm, called P750, in the cyanobacterium Anacystis nidulans (now Synechococcus elongatus strain PCC 7942) (Govindjee et al 1961): it was rediscovered by many and a full story is summarized in Govindjee and Shevela (2011); it is, unfortunately, not involved in photosynthesis. Second, was the independent discovery, in 1963, of a fluorescence band at 696 nm (F696) at 77 K, this was later proved to arise from the PS II core antenna protein CP47 (its history is also discussed by Govindjee and Shevela (2011)); and lastly, he discovered an emission band in the 693 nm-700 nm range when photosynthesis is saturated at high light, or inhibited by the addition of DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea); this is the counterpart of the 77 K F696 at room temperature, but was unraveled by taking difference emission spectra (see e.g., Krey and Govindjee 1964;Govindjee and Briantais 1972). Further, due to the closure of PS II under these conditions, Govindjee and Briantais were also able to see chlorophyll b fluorescence due to reduced energy transfer from it to chlorophyll a!…”

“…All of them deal mostly with PS II. They include: Shevela et al (2012) and Govindjee and Shevela (2011) as well as the two chapters on oxygenic photosynthesis which are in two different books (Shevela et al 2013a, b)…”