Content of proline and flavonoids in the shoots of halophytes inhabiting the South Urals

Growth parameters, the content of proline and flavonoids. Na⁺and K⁺ion accumulation in the shoots of four species of halophytes from the family Chenopodiaceae inhabiting the territory of the South Urals at different levels of salinity were studied. Within a single taxonomic group, different strategies of salt tolerance related to the level of soil salinity and specific features of salt accumulation in the shoots were revealed. Differences were manifested in the contents of protective compounds (proline and flavonoids) in dependence on the Na⁺and K⁺ion accumulation in the plant shoots. To characterize the participation of these compounds in plant adaptation to salinity, the ratio proline/flavonoids (Pro/Fl) was introduced. The highest value of Pro/Fl (4.9) was observed in Artiplex tatarica L. growing at weak salinity; in this plant, salt accumulation in the shoots depended on the sodium content in soil. Species Bassia sedoides (Pall.) Aschers., Atriplex verrucifera M. Bieb, and Kochia prostrate (L.) Schrad., with salt accumulation in the shoots independent on the level of soil salinity, inhabited the regions with the higher salinity. In these species the ratio Pro/Fl was 0.2–1.4, i.e., flavonoids, which concentration was positively correlated with the K⁺content, played a great and equal to proline role in protective mechanisms. In species B. sedoides and A. verrucifera, the high content of both flavonoids and K+ are indices correlating with high productivity and adaptation to the environment. Proline can be used as a marker of stress only in A. verrucifera, the most salt-tolerant among the studied halophytes. It is concluded that the Pro/Fl ratio in halophytes from the family Chenopodiaceae characterizes the strategies of adaptation depending on salt accumulation in plants.