Response of the Photosynthetic Apparatus in Dunaliella salina (Green Algae) to Irradiance Stress

Abstract

The response of the photosynthetic apparatus in the green alga Dunaliella salina, to irradiance stress was investigated. Cells were grown under physiological conditions at 500 millimoles per square meter per second (control) and under irradiance-stress conditions at 1700 millimoles per square meter per second incident intensity (high light, HL). In control cells, the light-harvesting antenna of photosystem I (PSI) contained 210 chlorophyll a/b molecules. It was reduced to 105 chlorophyll a/b in HL-grown cells. In control cells, the dominant form of photosystem 11 (PSII) was PSll,(about 63% of the total PSII) containing >250 chlorophyll a/b molecules. The smaller antenna size PSIIcenters (about 37% of PSII) contained 135 ± 10 chlorophyll a/b molecules. In sharp contrast, the dominant form of PSII in HL-grown cells accounted for about 95% of all PSII centers and had an antenna size of only about 60 chlorophyll a molecules. This newly identified PSII unit is termed PSII. The HL-grown cells showed a substantially elevated PSII/PSI stoichiometry ratio in their thylakoid membranes (PSII/PSI = 3.0/1.0) compared to that of control cells (PSII/PSI = 1.4/1.0). The steady state irradiance stress created a chronic photoinhibition condition in which D. salina thylakoids accumulate an excess of photochemically inactive PSII units. These PSII units contain both the reaction center proteins and the core chlorophyllprotein antenna complex but cannot perform a photochemical charge separation. The results are discussed in terms of regulatory mechanism(s) in the plant cell whose function is to alleviate the adverse effect of irradiance stress.

DCMU-resistance mutation confers resistance to high salt stress in the red microalgaPorphyridiumsp. (Rhodophyta)

“…Exposing the algal cells to the elevated salt concentration resulted in a decline in the D1 protein. This finding is in line with the well-documented role of the D1 protein in down-regulating the activity of PSII (Smith et al, 1990;Harrison et al, 1992;Shipton & Barber, 1994;Komenda & Masojidek, 1995;Zeng & Vonshak, 1998;Sudhir et al, 2005). The decrease in the level of the protein in response to high salt was much higher in wild-type cells.…”

Photosystem II Excitation Pressure and Development of Resistance to Photoinhibition (I. Light-Harvesting Complex II Abundance and Zeaxanthin Content in Chlorella vulgaris)

“…However, recently, through a study in which Cklorella vulgaris grown under continuous light at 5"C/150 pmol m-'s-' was compared to C. vulgaris grown at 27"C/150 pmol m-'s-', we concluded that this assumption is invalid (Maxwell et al, 1994). Based on published data concerning acclimation of algae to high irradiance (Sukenik et al, 1988;Senge and Senger, 1990;Smith et al, 1990;Harrison et al, 1992), we suggested that growth of C. vulgaris at low temperature mimics high-light acclimation even though C. vulgaris was grown at a low to moderate irradiance of 150 pmol m-'s-' (Maxwell et al, 1994). For example, compared to growth at 27"C/150 pmol m-' s-', Cklorella grown at 5"C/150 pmol m-'s-' exhibited a doubling in the light-saturated rate of C0,-saturated O, evolution, a 2-fold increase in the ratio of Chl a / b , a 5-fold lower total Chl per cell, decreased abundance of LHCII polypeptides, and increased total xanthophyll content (Maxwell et al, 1994).…”

Modulation of the light-harvesting chlorophyll antenna size in Chlamydomonas reinhardtii by TLA1 gene over-expression and RNA interference

“…The concentration of the photosystems in thylakoid membranes was estimated spectrophotometrically from the amplitude of the light-minus-dark absorbance difference signal at 700 nm (P700) for PSI, and 320 nm (Q A ) for PSII [45,46]. The functional light-harvesting Chl antenna size of PSI and PSII was measured from the kinetics of P700 photooxidation and Q A photo-reduction, respectively [47].…”

“…Following sonication, the crude cell extract was incubated in the presence of solubilization buffer [46]. Gel lanes were loaded with an equal amount of Chl, in the range of 1 -2 nmol Chl, as indicated.…”