Besides their protective role, polyamines also serve as signalling molecules. However, further studies are needed to elucidate the polyamine signalling pathways, especially to identify polyamine-regulated mechanisms and their connections with other regulatory molecules. Reduced height (Rht) genes in wheat are often used in breeding programs to increase harvest index. Some of these genes are encoding DELLA proteins playing role in gibberellic acid signalling. The aim of the present paper was to reveal how the mutations in Rht gene modify the polyamine-regulated processes in wheat. Wild type and two Rht mutant genotypes (Rht 1: semi-dwarf; Rht 3: dwarf mutants) were treated with polyamines. Polyamine treatments differently influenced the polyamine metabolism, the plant growth parameters and certain hormone levels (salicylic acid and abscisic acid) in these genotypes. The observed distinct metabolism of Rht 3 may more likely reflect more intensive polyamine exodus from putrescine to spermidine and spermine, and the catabolism of the higher polyamines. The lower root to shoot translocation of putrescine can contribute to the regulation of polyamine pool, which in turn may be responsible for the observed lack of growth inhibition in Rht 3 after spermidine and spermine treatments. Lower accumulation of salicylic acid and abscisic acid, plant hormones usually linked with growth inhibition, in leaves may also be responsible for the diminished negative effect of higher polyamines on the shoot growth parameters observed in Rht 3. These results provide an insight into the role of polyamines in plant growth regulation based on the investigation of gibberellin-insensitive Rht mutants.

Botany Department Faculty of Science Benha University Benha 13518 Egypt

Department of Plant Ecophysiology Institute of Plant Physiology and Genetics Bulgarian Academy of Sciences 1113 Sofia Bulgaria

Department of Plant Physiology Agricultural Institute Centre for Agricultural Research Hungarian Academy of Sciences 2462 Martonvásár Hungary

Department of Plant Physiology Agricultural Institute Centre for Agricultural Research Hungarian Academy of Sciences 2462 Martonvásár Hungary; Plant Protection Institute Centre for Agricultural Research of the Hungarian Academy of Sciences Budapest Hungary

Laboratory of Hormonal Regulations in Plants Institute of Experimental Botany of the Academy of Sciences 16502 Prague Czech Republic

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Molecular background of cadmium tolerance in Rht dwarf wheat mutant is related to a metabolic shift from proline and polyamine to phytochelatin synthesis