Gas-liquid chromatography analysis of the mitochondrial pool of free fatty acids of Zea mays (L.) plants under the influence of kinetin phytohormone in different aeration conditions

Abstract

Plant mitochondria play an important role in how plants respond to stress. Hypoxia, a form of stress caused by low content of oxygen in the environment, results in both morphological and metabolic adjustments in plants. Under stress, membrane lipids serve as substrates for the formation of various signalling molecules, which include lysophospholipids, phosphatidic acids, and free fatty acids. However, it is still unclear how phytohormones, in particular kinetin, affect the composition of free fatty acids of mitochondria, the primary energy organelle of plant cells, under various aeration conditions. During the experiment, a kinetin solution was injected into maize seedlings. Then the seedlings were transferred to various gaseous media. Free fatty acids were isolated by extraction of the lipid fraction with a mixture of hexane:isopropanol (3:2). The isolated free fatty acids were converted to methyl esters with diazomethane and separated by gas-liquid chromatography. It was shown that under the influence of kinetin, the content of palmitic, stearic, and unsaturated linoleic acids increased in the mitochondrial pool of free fatty acids of maize seedlings, however this did not change the degree of unsaturation (U/S). Under short-term oxygen deficiency, the content of saturated fatty acids (C14 and C20) decreased, while the content of unsaturated palmitoleic (C16:1) and linoleic (C18:2) acids increased. As a result, the degree of unsaturation grew from 0.57 to 0.72 under the conditions of hypoxia and to 0.62 in a CO2 medium. These changes may be due to increased breakdown of the phospholipid components of mitochondrial membranes under the conditions of oxygen deficiency, as was shown in our previous experiments. Pre-treatment of maize plants with the kinetin phytohormone, which has recently been used to increase the resistance of agricultural plants to various stresses, prevented a decrease in the content of saturated free fatty acids (C16 and C18) in the mitochondrial pool and the accumulation of palmitoleic (C16:1) and linoleic (C18:2) acids. This made it possible to maintain the level of unsaturation of free fatty acids (U/S) of mitochondria under the conditions of oxygen deficiency at the level of aerated plants.

The conducted study showed that the protective effect of kinetin also includes the ability of this phytohormone to reduce in the mitochondrial pool of free fatty acids the content of unsaturated palmitoleic and linoleic acids, which serve as a substrate for lipoxygenases. This blocks the processes of free radical oxidation, protecting mitochondria membranes from oxidative destruction and disruption of ETC respiration under hypoxic stress and in a CO₂ medium.