The Effect of Selenium–Arabinogalactan Nanocomposite on Fatty Acid Composition in Soybean Seedlings Grown from Pectobacterium carotovorum–Infected Seeds

The phytopathogenic bacterium Pectobacterium carotovorum (Pcc) infects a wide range of crop plants and causes substantial economic losses. The authors of this study previously demonstrated that the selenium–arabinogalactan nanocomposite (Se/AG NC) is capable of mitigating the negative effects of infection of soybean seeds with Pcc during germination and can influence physiological and biochemical factors in the seedlings. This study investigated changes in the membrane fatty acid (FA) profile of soybean seedlings grown under different treatments and in control using chromatography–mass spectrometry (CMS). The soybean seed treatments included the following: (1) infection by Pcc alone; (2) nanopriming with Se/AG NC alone; and (3) infection by Pcc followed by nanopriming with Se/AG NC. The infection was performed by soaking seeds in a bacterial suspension. Nanopriming was performed by placing the seeds in an aqueous solution of Se/AG NC (6.25 µg/mL) with a Se concentration of 0.000625%. Then, the seeds were germinated over 5 days in the darkness at 25 °C. The FA profile of soybean seeds was characterized by 13 FAs dominated by linoleic (LA), linolenic (LNA), oleic (OA), palmitic (PA) and stearic (SA) acids. Se/AG NC nanopriming had no influence on the FA profile of soybean seeds. A unique FA profile of soybean seedlings was demonstrated. It consisted of 18 FAs containing 12 to 20 carbon atoms. The following FAs were dominant in the control samples: PA (28%), LA (32.8%), LNA (18.6%), and SA (7.5%). Pcc infection of the seeds amplified the content of unsaturated FAs. Nanopriming of the seeds with Se/AG NC had an obvious influence on the seedling FA profile. Treatment of soybean seeds infected with Pcc using Se/AG NC caused weakening of the detrimental effects of the pathogen, while giving the possibility to maintain soybean seedlings’ FA profile at the control level. Transcript levels of the GmFAD8-2 gene encoding the membrane-bound omega-3 FA desaturase (FAD) were elevated for soybean seedlings after both Pcc and Se/AG NC seed treatment processes. The FA double-bond index (DBI) grew under the influence of seed infection and dropped under other treatments. Nanopriming of the seeds with Se/AG NC effectively reduced stress in Pcc-infected plants, as evidenced by analysis of the abscisic acid (ABA) content. Variations in the membrane FA composition under nanopriming with Se/AG NC may be one of the forms of its phytoprotective effect.