Abstract
BackgroundEven though the catecholamines (dopamine, norepinephrine and epinephrine) have been detected in plants their role is poorly documented. Correlations between norepinephrine, soluble sugars and starch concentration have been recently reported for potato plants over-expressing tyrosine decarboxylase, the enzyme mediating the first step of catecholamine synthesis. More recently norepinephrine level was shown to significantly increase after osmotic stress, abscisic acid treatment and wounding. Therefore, it is possible that catecholamines might play a role in plant stress responses by modulating primary carbon metabolism, possibly by a mechanism similar to that in animal cells. Since to date no catecholamine receptor has been identified in plants we transformed potato plants with a cDNA encoding human dopamine receptor (HD1).ResultsTuber analysis of transgenic plants revealed changes in the activities of key enzymes mediating sucrose to starch conversion (ADP-glucose phosphorylase and sucrose synthase) and sucrose synthesis (sucrose phosphate synthase) leading to altered content of both soluble sugars and starch. Surprisingly the catecholamine level measured in transgenic plants was significantly increased; the reason for this is as yet unknown. However the presence of the receptor affected a broader range of enzyme activities than those affected by the massive accumulation of norepinephrine reported for plants over-expressing tyrosine decarboxylase. Therefore, it is suggested that the presence of the exogenous receptor activates catecholamine cAMP signalling in plants.ConclusionsOur data support the possible involvement of catecholamines in regulating plant carbon metabolism via cAMP signalling pathway.
Highlights
Even though the catecholamines have been detected in plants their role is poorly documented
Transgenic plant selection Solanum tuberosum plants transformed with pHD1-BinAR, a plasmid carrying a cDNA for the human dopamine receptor under the control of the CaMV 35S promoter (Figure 1A), were pre-selected by means of PCR with the primers for neomycin phosphotransferase gene and selected by northern blot analysis with a HD1 specific cDNA as a probe (Figure 1B)
As the translational machinery is very similar in plants and animals we suggest that the short form of receptor resulted from proteolytic action rather than de novo synthesis
Summary
Even though the catecholamines (dopamine, norepinephrine and epinephrine) have been detected in plants their role is poorly documented. Correlations between norepinephrine, soluble sugars and starch concentration have been recently reported for potato plants overexpressing tyrosine decarboxylase, the enzyme mediating the first step of catecholamine synthesis. Molecular techniques led to the identification of cAMP response element-binding proteins (CREBs) [13], cyclic nucleotidegated cation channels [14] and cAMP binding enzymes [15] These data strongly indicate the involvement of catecholamines in regulating plant carbohydrate metabolism, possibly by a mechanism similar to that in animal cells. This suggestion is limited by the fact that to date no catecholamine receptor has been identified in plants. Our analysis revealed a regulatory effect of HD1 on carbohydrate metabolism including changes in key enzyme activities
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