Abstract
The exact relationship between polyamine, abscisic acid and proline metabolisms is still poorly understood. In the present study, the effects of putrescine and abscisic acid treatments alone or in combination with polyethylene glycol-induced osmotic stress were investigated in young wheat plants. It was observed that abscisic acid plays a role in the coordinated regulation of the proline and polyamine biosynthetic pathways, which compounds are related to each other through a common precursor. Abscisic acid pre-treatment induced similar alteration of polyamine contents as the osmotic stress, namely increased the putrescine, but decreased the spermidine contents in the leaves. These changes were mainly related to the polyamine cycle, as both the synthesis and peroxisomal oxidation of polyamines have been induced at gene expression level. Although abscisic acid and osmotic stress influenced the proline metabolism differently, the highest proline accumulation was observed in the case of abscisic acid treatments. The proline metabolism was partly regulated independently and not in an antagonistic manner from polyamine synthesis. Results suggest that the connection, which exists between polyamine metabolism and abscisic acid signalling leads to the controlled regulation and maintenance of polyamine and proline levels under osmotic stress conditions in wheat seedlings.
Highlights
There is increasing evidence that plant responses to unfavourable environment can be modulated by various plant hormones and plant growth regulators
Before the present work demonstrated in this paper a pilot experiment was carried out using 2 wheat genotypes including TC33 and a winter wheat variety Mv Hombár from Agricultural Institute, Centre for Agricultural Research, Hungarian Academy of Sciences, Martonvásár. These preliminary results revealed that 0.15 mM abscisic acid (ABA) for 1 day provided protection against osmotic stress induced by 15% polyethylene glycol (PEG) manifested in the gas exchange parameters
It has been demonstrated that rapid increase in PUT levels is required for ABA accumulation in response to low temperature in Arabidopsis, and the gene expression level of NCED was increased by PUT addition[23]
Summary
There is increasing evidence that plant responses to unfavourable environment can be modulated by various plant hormones and plant growth regulators. PAs are double face molecules, act as direct ROS scavenging and influence antioxidant activity at molecular and gene expression level. They are ROS sources due to their apoplastic catabolism and the PA-cycle[1] The plant hormone abscisic acid (ABA) regulates several physiological processes and may induce tolerance to various abiotic stresses[4]. ABA plays a central role for improvement of plant drought resistance by its effect on stomatal closure and by inducing activities or gene expression of antioxidant enzymes[6]. Overexpression of the genes of PA synthesis enzymes, such as ADC, SAMDC or SPMS, resulted in increased ABA biosynthesis due to the higher expression level of 9-cis-epoxycarotenoid dioxygenase (NCED). These results suggest that there is a positive feedback loop between ABA and PAs
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