Glufosinate phytotoxicity to maize under salt stress conditions

In this report we describe the responses of two maize varieties (Koka and Limko) to combined action of glufosinate and salinity. Glufosinate (phosphinothricin) is a non-selective herbicide that binds to the active site of glutamine synthetase (GS) and irreversibly inhibits this enzyme. Maize seedlings were grown in hydroponic cultures in complete nutrient solution under the following conditions: 16h photoperiod (220 |j,mol-m-2-s -1) at 26/20°C day/night, 65-70% relative humidity. The growth experiment (determination of dry matter produc­tion) was 2 x 2 factorial arrangement with two levels of NaCl in nutrient solution, 0 and 60 mmol-dm-3 NaCl and four levels of glufosinate in nutrient 0, 0.010, 0.025, 0.050 mmol-dm-3. Salt stress significantly decreased dry weight of both maize varieties. Glufosinate also caused reduction in growth of maize seedlings and the amount of inhibition was dependent on herbicide concentration and part of plant. Combined action of glufos- inate and NaCl caused marked reduction in plant growth but in some cases (roots of Koka and shoots of Limko), this negative effect was mainly induced by NaCl. Biochemical analyses (determination of ammoni­um and nitrate concentration, content of water-soluble protein) were carried out at two levels of each treatment (0 and 0.050 mmol-dm-3 glufosinate, 0 and 60 mmol-dm-3 NaCl). Plants treated by glufosinate accumulated 3­4-fold more ammonium than control plants and also contained more nitrate than control. The combined action of glufosinate and NaCl resulted in a significant decrease in ammonium content in maize leaves compared to sole herbicide treatment, whereas in roots ammonium concentration remained at the same level. Under com­bined actions of herbicide and NaCl alterations in concentration of water-soluble protein and nitrate content were relatively small.