Abstract. The work is devoted to the study of the dependence chlorophyll a and P700 ratio (Chl a / P700) on light intensity. Literature data on the structure of pigment-protein supercomplexes, mechanisms of redistribution of excess light energy are reviewed. The literature analysis showed that Chl a / P700 ratio in the culture of lower photoautotrophic organisms determines the specific growth rate or photosynthesis rate. Chl a / P700 value of can be used as indicator of the microalgae culture physiological state. The basic principles of the photobiosynthesis modeling were used for described the light influence on Chl a / P700 value. The division of the whole chlorophyll pool into two conventional groups is proposed. Structural chlorophyll is associated with the nuclear part of the photosystems. Antenna chlorophyll is linked with peripheral proteins of the light-harvesting complex. The ratio of all biomass structural components is considered to be unchanged. The antenna chlorophyll content is determined by the rate of its synthesis from reserve biomass pool and light-dependent degradation. The system of equations is solved for the stationary state of turbidostat. It is shown that the ratio of antenna chlorophyll and structural biomass concentrations determines Chl a / P700 value. The relationship between this parameter and light intensity was established. The verification of the model was carried out for the turbidostat Arthrospira platensis culture. Three ranges of light intensity were identified, which are characterized by different photoadaptation mechanisms: the area of antenna chlorophyll loss at low intensities; the area of antenna chlorophyll accumulation; the area of metabolic limitation of antenna protein biosynthesis with the participation of hydrogen peroxide. The theoretical basis for this division is provided by experimental results that describe the different mechanisms of light energy excess distribution at low and high light intensities. For each area an analytical expression which describing the Chl a / P700 light kinetics was obtained. Comparison of theoretical curves and experimental data for A. platensis culture allowed us to determine species-specific model coefficients, which remained unchanged at all three curve sections. The obtained results allow us to develop mathematical algorithms for regulating the pigments content in the microalgae biomass.

 

Key words: photosynthesis, pigments, light-harvesting complex, modeling, linear splines, reserve and structural biomass, photosynthetic unit size