Morphogenesis of Norway spruce and Scots pine seedlings assimilating organs under the influence of red and blue LED light

In the article, the effect of red and blue LEDs light on the growth and development of 6-week-old seedlings of Scots pine and Norway spruce was studied. We carried out morphometric and anatomical studies of the cotyledons and needles, which showed that the red LED light has a similar stimulating effect on plants of Scots pine and Norway spruce, and the blue light reveals differences in the reaction of photosynthesizing organs. Species-specific feature of red LED light action was different in the reaction of shoot tips and activation or inhibition formation of new needles of pine and spruce. The analysis of the main photosynthetic pigments exposed to red or blue light showed the lack in the qualitative composition of photosynthetic pigments of needles seedlings. At the same time, there was reduction in pigment content in the needles of pine seedlings in growing under a red light. It is assumed that the observed difference between the reactions of seedlings of pine and spruce on red and blue light is associated with features of their habitats, which may significantly affect the photoregulation processes and adaptive capacity of the test plants. The studied seedlings species grown under red light differed from control plants by bigger needles, cotyledons and low content of photosynthetic pigments. As the red light is predominant in spectrum of photosynthesis and effectively absorbed by chlorophyll, the cultivation of plants under the red light should increase their productivity and stimulate photosynthesis and energy storage organ growth, as was observed in our experiments. It should be noted that the thickness of the mesophyll of the needles on the red light apparently occur in various ways in the studied plants: in pine needles increase in diameter by increasing cell size and in spruce activation of bilateral thickening is due to an increase in the number of the cells of mesophyll. The reduction in photosynthetic pigments on the red light in the two plants species in the range of 40-50% can be determined by a less need for the reaction centers of photosystems under the conditions of excess of light energy. Probably, the difference of signal properties of the red-light signal for the studied plants due to the peculiarities of habitat of seedlings of pine and spruce. Pine seedlings prefer open spaces, providing a full range of light, while the young spruce are formed mainly under the forest canopy, where the light is rich in red and far-red regions of the spectrum. The effect of blue LED light reveals a significant difference between the studied species. Photosynthesizing organs of pine seedlings grown in blue light did not have any strong differences from plants which were grown on "white" polychromatic light of fluorescent lamps. Spruce development was significantly inhibited by blue light: the plants had the smallest mass and thin needles, with a high content of chlorophyll. Despite the fact that the blue light has maximum energy, it is an important signaling factor for the plants involved in a variety of physiological and developmental processes. Growing conditions in which the plants of spruce got only blue light are so much different from the conditions of the natural environment where the region of the spectrum is significantly suppressed that seedlings were unable to adapt to this condition and were substantially behind the development of the control plants. It should not be ruled out that at later stages of growing of the studied plants they will react differently to the effects of red and blue light; as for the realization of certain stages of the life cycle (for example, during the formation of reproductive organs, embryogenesis, etc.), different spectral composition of light, including high blue light, may be favorable.

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