Photosynthetic apparatus of potato plants (Solanum tuberosum L.) grown in vitro as influenced by different spectral composition of LED radiation

In vitro reproduction is an important stage in seed potato propagation. Various radiation spectra can be used to regulate in vitro the growth and morphogenesis of potato seedlings ( Solanum tuberosum L.). We studied the effect of light emitting diodes (LEDs) light sources, which differ in the spectral composition of the radiation, on the growth processes and functional parameters of the photosynthetic apparatus in potato plants (variety Agria) grown in vitro. The red LEDs with λm = 635 nm and the half-width of the emission band (HW) of 45 nm, blue LEDs with λm = 463 nm (HW = 23 nm), green LEDs with λm = 521 nm (HW = 38 nm), and white LEDs (400-730 nm) with an intensity of light equal to 60-65 micromol photons∕m-2∕s-1 at plant level, and white fluorescent lamps (OSRAM AG, Germany) of the same light intensity were used. On day 28 the growth parameters, CO2 gas exchange rate and parameters of variable chlorophyll fluorescence were measured. The highest biomass accumulation was observed during irradiation of plants with fluorescent lamps. A smaller plant biomass accumulation was observed when plants were irradiated with white LEDs. Blue LEDs was shown to reduce the accumulation of plant biomass by 49.5 % compared to the white LEDs. Irradiation with green and red LFDs led to decrease biomass accumulation by 75.6 and 67.5 %, respectively. The observed changes in the accumulation of dry plant biomass for different spectral ranges are associated with a higher activity of the photosynthetic apparatus of the plants grown under irradiation with blue and white LEDs. The rate of photosynthesis (per unit of the leaf surface) in these plants was higher than in those grown under green or red LEDs. The effective quantum yield of PS 2 in all studied plants had small changes in the range of 0.47 to 0.53, but higher values were observed in the plants grown under fluorescent lamps and white and green LEDs. Electron transport rate (ETR) and non-photochemical quenching (NPQ) were changed in similar manner under different growth conditions. Curve analysis showed that in the conditions when the input of CO2 was not limited the rate of photosynthesis decreased depending on lighters as follows: fluorescent lamps > white LEDs > red LEDs > blue LEDs > green LEDs. Maximal rate of carboxylation and greater efficiency of the reaction were observed when plants were exposed to fluorescent light and white LEDs. The irradiation of plants with blue, red and, especially, the green LEDs led to a decrease in carboxylation rate to 77.9, 67.9 and 11.1 % of the maximum values. Efficiency of carboxylation in plants grown under red and green LEDs sharply decreased to 37.5 % and 6.7 % of the maximum values. Electron transport rate when using fluorescent lamps, white, red, blue and green LEDs was equal to 100, 97.3, 75.1, 68.0 and 20.8 %, respectively. At the same time there has been a decrease in the utilization rate of triosophosphates to a value of 88.9, 48.7, 28.2 and 9.4 %, respectively, compared to 100 % under fluorescent lamps. Thus, at low levels of light intensity we did not observe significant changes in the activity of both light and dark photosynthetic reactions and the accumulation of plant dry matter. These results allow us to understand the role of separate regions of visible light on the functioning of the photosynthetic apparatus, and more effectively to use LEDs for plant cultivation.