The metabolites of autotrophic and heterotrophic leaves of Amaranthus tricolor L. Early splendor variety

An important area of systemic biology (metabolomics) is the study of the composition and properties of low-molecular metabolites of agricultural plants with different modes of nutrition. The use of metabolic technologies expands the possibilities of analyzing biochemical changes in the composition and structural modifications of metabolites occurring during the transition from autotrophic to heterotrophic nutrition. Most photosynthetic plants are capable of autotrophic nutrition, but in their lifetime, there are periods of appearance of the achlorophyllic organs which receive nutritients from the organic substances stored earlier. Thus, among Amaranthus tricolor L. plants there are varieties with leaves which differ from each other in the way of nutrition. For example, Early Splendor variety plants form brightly colored red heterotrophic leaves along with green photosynthesis leaf blades at the end of the vegetative phase. The comparative study of the low-molecular metabolites composition in these leaves is important for understanding the relationship between heterotrophic and autotrophic nutrition in the whole plant. In this paper, significant qualitative differences in metabolites composition between autotrophic and heterotrophic leaves were stated for the first time during the metabolome analysis of water and alcohol extracts of heterotrophic and autotrophic amaranth leaves of Early Splendor variety using the method of gas chromato-mass spectrometry. It was found that the low-molecular metabolites of autotrophic and heterotrophic leaves contained both non-specific metabolites common for both type of nutrition and specific metabolites characteristic for each of the ways separately. On the one hand, it indicates the close interaction between two ways of nutrition and, on the other hand, the ability to synthesize and modify the metabolites which demonstrates partial autonomy of heterotrophic leaves. The purpose of the work is to study the composition of low-molecular metabolites and to identify new biologically active metabolites antioxidants in heterotrophic and autotrophic amaranth leaves of Early Splendor variety. Experiments were carried out in 2017-2019 with amaranth plants of the Early Splendor variety at the end of flowering-the beginning of seed formation phase. The plants were grown in a film greenhouse (the Federal Research Center for Vegetable Growing). The fresh red-colored heterotrophic leaves formed at the top of the main stem and the underlying photosynthetic leaves with a fully formed leaf blade were collected for analysis. The leaves were homogenized (T18 homogenizer, IKA, Germany) and extracted for 30 min at 24 °C with either 96 % ethanol or distilled water (leaves weighing batch: extragent 1:10). The metabolites were profiled by gas chromato-mass spectrometry method (GH-MC) with a chromograph GH-MC JMS-Q1050GC (JEOL Ltd., Japan). According to the mass spectra library of the NIST-5 National Institute of Standards and Technology (USA), a total of 87 metabolites were totally identified. Heterotrophic leaves contained 19 substances in water extracts and 38 metabolites in alcohol extracts, while photosynthetic leaves contained 21 substances in the water extract and 57 metabolites in alcohol extracts. Twenty-nine identical metabolites were found in water and alcohol extracts. In heterotrophic and autotrophic amaranth leaves of Early Splendor variety squalene (C30H50), a biologically active compound with antioxidant properties was identified for the first time. Also, in heterotrophic leaves monopelargonine (monononanoin) (C15H11O7) was identified. Monopelargonine is an intermediate product of flavonoid o-glycosylation, is referred to phenolic compounds and possesses high antioxidant activity. Metabolites have been identified that are present in both autotrophic and heterotrophic amaranth leaves, which suggests a close interaction of the two types of nutrition during the appearance, growth and development of heterotrophic leaves. At the same time, photosynthesizing leaves serve as donors of key metabolites for heterotrophic leaves, while the latter are not only acceptors, but also can synthesize and modify metabolites necessary for cell formation. Due to revealed rich composition of carbohydrates, essential amino acids, lipids and organic acids, the photosynthesizing leaf biomass is a source of antioxidants and biologically active substances. It should be stressed that not all metabolites were identified. Nevertheless, the set of metabolites that we identified in the photosynthetic leaves allows us to suggest these substances to be key and sufficient compounds for the construction and functioning of cells and tissues in heterotrophic leaves.