Maize (Zea mays L.) sprouts growth and activity dynamics of DMDH (decarboxylating malate-dehydrogenase, Malic enzyme EC:1.1.1.40) enzyme have undergone studies under combined stress conditions developed by gamma rays, salt solution, and nanoparticles. Three different factors comprising various doses of gamma radiation (250, 500, and 750 Gy), NaCl solution (100 mM), and iron oxide nanoparticles (maghemite, γ- Fe₂O₃) have been in use by the study to develop artificial stress conditions. These combined stress conditions have significantly affected and delayed the plant growth compared with the control variant. The higher doses of radiation (500 and 750 Gy) have slowed down the plant growth and caused destruction. The effect of gamma radiation (250 Gy) delayed the growth of plants. However, during the combined influence of nanoparticles (Fe₂O₃) with a dose of 250 Gy, plant development was better than with an individual dose of 250 Gy. This difference was not evident in the medium with high doses (500 and 750 Gy) of gamma radiation combined with nanoparticles (Fe₂O₃) and with salt stress (NaCl 100 mM). During the first 10 days of the experiment, DMDH enzyme activity, induced in the root and leaf cells in all variants, included the control, and inhibition occurred on the 15th day. This reaction product can be due to enzyme inhibition. However, the enzyme activity was higher during the combined stress conditions.

Keywords: Maize (Zea mays L.) seedlings, gamma radiation, salt stress, iron oxide nanoparticles, decarboxylating-malate dehydrogenase, combined stress conditions, growth traits

Key findings: Adding maghemite nanoparticles to the medium slightly reduced the stress effects, and thus, the stimulating effect of nanoparticles has manifested. In variants with NaCl solution (100 mM), no stimulating effect appeared; however, on the contrary, a retarding effect was noticeable. The DMDH enzyme (ME, EC:1.1.1.40) activity regarding corn plant growth was prominent at the beginning of the experiment (5^th and 10^th days) in the root and stem tissues under the combined stress conditions and both in control. Gamma irradiation has reduced the plant’s organic matter in applied variants compared with the control variant. However, this reduction was superior for the variants with NaCl solution.