Effect of Pre-sowing Treatment with Exogenous TCA Cycle Intermediates on Germination and Physiological Characteristics of Lactuca sativa L. Seedlings

Introduction. In modern crop production, there is a need for environmentally friendly biostimulants that are alternatives to synthetic growth regulators. Intermediates of the tricarboxylic acid cycle (Krebs cycle) are considered as promising endogenous compounds capable of activating energy metabolism at the initial stages of ontogenesis, but their effect on the germination of lettuce seeds has not been sufficiently studied.

Purpose. The aim of the study was to evaluate the effect of pre-sowing treatment of Lactuca sativa L. seeds with exogenous intermediates of the Krebs cycle (succinic, malic, citric and fumaric acids) in various concentrations on germination energy, morphometric parameters of seedlings and biochemical parameters characterizing respiration and oxidative status.

Materials and Methods. Lettuce seeds of the cv. 'Moskovskiy Parnikovyy'  were treated with acid solutions at concentrations of 0.001%, 0.005%, 0.01% and 0.1% for 4 hours. To separate the effects of acid stress and the specific effects of TCA cycle intermediates , a control variant HCl was used. The assessment of germination energy (4th day) and germination (7th day) was carried out according to GOST 12038-84. The length of the root and hypocotyl, the activity of succinate dehydrogenase (SDH), the content of malondialdehyde (MDA) and photosynthetic pigments were determined.

Results. A nonlinear concentration-dependent response was observed. The highest germination energy was recorded after treatment with 0.005% succinic acid and reached 88.0 ± 2.3% compared with 72.0 ± 2.3% in the water control, corresponding to a 22.2% relative increase. Final germination percentage was 95.0 ± 1.0% compared with 87.0 ± 1.9% in the control. Treatment with 0.005% succinic acid was accompanied by a 45% increase in SDH activity, a 43.6% increase in chlorophyll a content, and a 30.6% decrease in MDA content. At a concentration of 0.1%, the tested organic acids reduced germination and seedling growth and increased MDA content; the maximum MDA level was observed after treatment with 0.1% fumaric acid and was 1.89-fold higher than in the control.

Conclusion. The obtained results indicate that low concentrations of exogenous TCA cycle intermediates can regulate the early stages of seed germination, whereas high concentrations induce inhibitory effects. Succinic acid at a concentration of 0.005% is a promising environmentally friendly biostimulator for the pre-sowing treatment of lettuce seeds, which improves seed quality and the physiological state of seedlings by activating energy metabolism and reducing oxidative processes. The results obtained confirm the prospects for further study of exogenous TCA cycle intermediates  as components of biostimulating compositions for vegetable crops.

Keywords: pre-sowing treatment; TCA cycle intermediates; organic acids; germination energy; succinate dehydrogenase; malondialdehyde; plant biostimulants; Lactuca sativa.

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