Growth of buckwheat (Fagopyrum esculentum Moench) seedlings and the accumulation of primary and secondary metabolites under various mineral nutrition conditions

Buckwheat ( Fagopyrum esculentum Moench) is an important agricultural crop; Russia, China and Ukraine are the world leaders of its production. In addition to the unique nutritional characteristics, it is characterized by the formation of various phenolic compounds including rutin widely used in medicine. The study of the various metabolites formation at the initial growth stages as well as those under the different conditions of mineral nutrition is important for estimation of plant potential productivity and adaptation to environmental conditions. In this paper, we showed the regulatory effect of macro- and microelements on the growth and accumulation of primary and secondary metabolites in buckwheat plants. For the first time, the formation of primary and secondary metabolites in the aerial parts of a new and promising Russian buckwheat variety Dasha (approved by the State Register of the Russian Federation in 2018) has been characterized. The aim of this work was to study the initial stages of F. esculentum ontogenesis, including the assessment of the morphophysiological characteristics of seedlings under various mineral nutrition conditions, as well as the accumulation of photosynthetic pigments, sugars, and phenolic compounds in cotyledon leaves. Studies were conducted using two varieties of this culture included in the State Register of the Russian Federation in 2004 and 2018 (Devyatka and Dasha, respectively). Plant cultivation was carried out by a roll method in water (control) and Hoagland-Arnon nutrient medium (sample) at 24 °C and 16-hour illumination in laboratory conditions. In the seedlings, the height of the hypocotyls, the length of the roots, and the mass of cotyledon leaves was determined. The water content of the plant material was analyzed after it was dried to constant weight at 70 °C. The spectrophotometric method was used to determine the amount of chlorophylls a and b (λ = 665 nm and λ = 649 nm), carotenoids (λ = 440 nm), sugars (λ = 490 nm), the total amount of soluble phenolic compounds (λ = 725 nm), flavono-ids (λ = 415 nm) and phenylpropanoids (λ = 330 nm) in ethanol extracts from cotyledon leaves of seedlings of different ages. The cultivation of buckwheat on Hoagland-Arnon nutrient medium contributed to faster growth of aboveground organs compared to control; in contrast, the growth of underground organs was the same in both cases. In most cases, in the experimental samples, the differences in the accumulation of photosynthetic pigments (chlorophyll a and b, carotenoids) and soluble sugars in the cotyledons of two buckwheat varieties were revealed to be higher than in control. As for the accumulation of phenolic compounds, it was not obviously dependent on the level of mineral nutrition. As an exception, in cotyledons of seedlings cultivated on a nutrient medium, the content of phenylpropanoids changed to a greater extent compared to control and reached high values at the end of the investigation period. It should also be noted that on a nutrient medium at the late ontogenesis stages cotyledons of Dasha seedlings significantly accumulate pigments, sugars and phenolic compounds in comparison with Devyatka. Thus, the obtained data indicate that the amount of mineral elements is important for the initial stages of F. esculentum ontogenesis. Faster growth of seedlings and the accumulation of primary and secondary metabolites in their leaves is characteristic of the experimental samples, compared to the control. Therefore, in plant cultivation, the different levels of mineral nutrition make it possible to regulate the plant growth and development, as well as the accumulation of various metabolites.