Abstract
Chilling stress greatly inhibited the seed germination, plant growth, development and productivity in this study. The current research aimed to study the effects of different polyamine (PA) inhibitor combinations (Co), e.g., D-arginine (D-Arg), difluoromethylormithine (DFMO), aminoguanidine (Ag) and methylglyoxyl–bis-(guanyhydrazone) (MGBG) at different doses, i.e., 10 µM Co, 100 µM Co, 500 µM Co, 1000 µM Co and 1000 µM Co + 1 mM Spd (Spermidine) in two inbred lines of maize (Zea mays L.), i.e., Mo17 and Huang C, a sensitive and tolerant chilling stress, respectively. The combination treatments of PA inhibitors reduced the biosynthesis of putrescine (Put) in the tissues of both studied inbred lines. Application with 500 µM Co and 1000 µM Co did not result in a significant difference in Put concentrations, except in the coleoptile of Mo17. However, combining Spd to 1000 μM of PA inhibitors enhanced the Put, Spd, spermine (Spm) and total PAs in the roots, coleoptile and mesocotyls. Put and total PAs were increased by 39.7% and 30.54%, respectively, when Spd + 1000 µM Co were applied relative to their controls. Chilling stress and PA inhibitors treatments affected both inbred lines and resulted in differences in the PA contents. Results showed that enzymes involved in the biosynthesis of PAs (ornithine decarboxylase as ODC and S-adenosylmethionine decarboxylase as SAMDC) were significantly downregulated by 1000 µM Co in the tissues of both inbred lines. In contrast, the activity of PAO, a Pas degradation enzyme, was significantly improved by 1000 µM Co under chilling stress. However, Spd + 1000 µM Co significantly improved the activities of ODC and SAMDC and their transcript levels (ODC and SAMDC2). While it significantly downregulated the PAO activity and their relative genes (PAO1, PAO2 and PAO3) under chilling stress. Overall, this study elucidates the specific roles of Spd on the pathway of PA inhibitors and PA biosynthesis metabolism in maize seed development in response to chilling stress. Moreover, the Huang C inbred line was more tolerant than Mo17, which was reflected by higher activities of PA biosynthesis-related enzymes and lower activities of PAs’ degradative-related enzymes in Huang C.
Highlights
IntroductionLowtemperature stress could reduce the growth and development of maize seedlings under field conditions
The application of all studied PA inhibitor combinations resulted in the reduction of PA biosynthesis and increase of polyamines’ degradation
The PA inhibitors in combination with Spd treatments enhanced the levels of PA contents, enzymes related to PA biosynthesis and their relative gene expressions in roots, coleoptiles and mesocotyls under chilling stress
Summary
Lowtemperature stress could reduce the growth and development of maize seedlings under field conditions. Maize has been reported to be sensitive to low temperature [7,8], especially at early growth stages, which results in the inhibition of seed germination and vegetative growth [9,10,11]. Low-temperature stress can reduce the crop productivity through various actions such as reduction in plant growth rates [14], water uptake disturbance [15], photosynthesis efficiency [16], changes in membrane properties [17], extra production of reactive oxygen species (ROS) [18] and enzymatic and non-enzymatic antioxidants [19]
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