Abstract
In the present study, the possibility of enhancing cold stress tolerance of young soybean plants (Glycine max [L.] Merr) by exogenous application of 5-aminolevulinic acid (ALA) was investigated. ALA was applied at various concentrations (0, 0.3, 0.6 and 0.9 mM) by seed priming and foliar application method. After ALA treatment, the plants were subjected to cold stress at 10 ± 0.5 °C for 72 h. Cold stress significantly decreased plant growth, relative water content, chlorophyll, photosynthesis and stomatal conductivity, while it increased electrolyte leakage and proline accumulation. ALA at low concentrations (0.3 mM) protected plants against cold stress, enhancing plant height, shoot fresh and dry weight, chlorophyll content, photosynthesis, stomatal conductivity as well as relative water content. Increase of electrolyte leakage was also prevented by 0.6 mM ALA. ALA also enhanced superoxide dismutase and catalase activities at 0.6 mM concentration especially under cold stress conditions. Proline increased with increasing in ALA concentration under both temperature conditions. In most cases, application of ALA by spraying method was better than seed priming method. Results showed that ALA, which is considered as an endogenous plant growth regulator, can be used effectively to protect soybean plants from the damaging effects of cold stress, by enhancing the activity of antioxidative enzymes, protecting cell membrane against reactive oxygen species and finally by promoting chlorophyll synthesis, leading to more intense photosynthesis and more carbon fixation, without any adverse effect on the plant growth.
Highlights
About two thirds of the world’s landmass is annually subjected to temperatures below the freezing point and about half of it suffers from temperatures below -20 °C (Larcher, 2001)
The probable reason behind the decreased electrolyte leakage is the application of aminolevulinic acid (ALA), as it is an essential precursor in the biosynthesis of haeme, so its exogenous application boasts up the activity of haeme-based biomolecules (APX, POD and CAT) and helped to scavenge the ROS to protect against the potentially harmful effects caused by reactive oxygen under cold stress condition (Liu et al, 2011)
The present study provides evidence for the protective role of ALA against cold stress in young soybean plants
Summary
About two thirds of the world’s landmass is annually subjected to temperatures below the freezing point and about half of it suffers from temperatures below -20 °C (Larcher, 2001). There are few reports about assessing the effects of exogenous application of ALA on soybean under cold stress conditions. In the current study, the effects of exogenous ALA at different concentration and two methods of application, seed priming and foliar application, regarding the cold stress induced growth, physiological and biochemical responses in soybean were investigated. Superoxide dismutase (SOD) Superoxide dismutase activity was determined by measuring the ability of the enzyme extract to inhibit the photochemical reduction of nitroblue tetrazolium according to the method of Giannopolitis and Ries (1977). Analysis of variance showed that there was a significant effect of the cold stress and ALA treatments as well as the interaction of them on plant height. Plant height significantly decreased by cold stress treatment and increased by ALA application (Table 2).
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