Expression of human dopamine receptor in potato (Solanum tuberosum) results in altered tuber carbon metabolism.

BACKGROUND: 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 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). RESULTS: Tuber 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. CONCLUSIONS: Our data support the possible involvement of catecholamines in regulating plant carbon metabolism via cAMP signalling pathway.

The catecholamine biosynthesis route in potato is affected by stress.

The catecholamine compounds in potato (Solanum tuberosum L.) leaves and tubers have been identified by gas chromatography coupled to mass spectrometry (GC-MS) measurements. The finding that the catecholamine level is dramatically increased upon tyrosine decarboxylase (TD) overexpression potentiates the investigation on their physiological significance in plants. It was then evidenced that catecholamines play an important role in regulation of starch-sucrose conversion in plants. In this paper we investigated catecholamine biosynthetic pathway in potato plants exposed to the different stress conditions. The activation of TD (EC 4.1.1.25), tyrosine hydroxylase (TH, EC 1.14.18.1) and l-Dopa decarboxylase (DD, EC 4.1.1.25) was a characteristic feature of the potato leaves treated with abscisic acid (ABA). In high salt condition only TD activity was increased and in drought both TH and DD were activated. UV light activated predominantly DD activity. Leaves of plants grown in the dark and in red light circumstances were characterized by significantly decreased activities of all the three enzymes whereas those grown in cold were characterized by the decreased activity of DD only. In all, stress conditions the normetanephrine level and thus catecholamine catabolism was significantly decreased. Increased catecholamine level in TD-overexpressing potato resulted in enhanced pathogen resistance. Our data suggest that plant catecholamines are involved in plant responses towards biotic and abiotic stresses. It has to be pointed out that this is the first report proposing catecholamine as new stress agent compounds in plants.

The catecholamine potentiates starch mobilization in transgenic potato tubers.

In human and animal cells, the catecholamines are involved in glycogen mobilization. Since the compounds are found in a potato, their function in starch mobilization was hypothesized. In order to verify this hypothesis, the transgenic potato plants Solanum tuberosum L. cv. Desiree overexpressing tyrosine decarboxylase (TD EC 4.1.1.25) cDNA from parsley has been generated. The cDNA expression was judged by the northern blot analysis and the enzyme activity measurements. Four independent transgenic lines with the highest TD mRNA expression were selected and analyzed. The expected substantial decrease in tyrosine content was followed by significant increase in tyramine and dramatic enhancement of norepinephrine synthesis was detected. The level of L-3,4-dihydroxyphenylalanin (L-Dopa) was only slightly increased and dopamine significantly decreased in most cases in these plants. The increase in norepinephrine was accompanied by changes in carbohydrate metabolism. The significant increase in glucose and sucrose and the decrease in starch content were characteristic features of TD overexpressed transgenic potato tubers. The features mentioned above indicate that catecholamines potentiate starch mobilization in potato plants in common with animal cells. The decrease in tyrosine content in transgenic plants is also compensated by significant increase in chlorogenic acid synthesis thus potentially increasing the antioxidant capacity of transgenic tubers. The glycoalkaloids content is changed in the transformants. This may originate from glucose accumulation and glycolysis activation. The obtained transgenic potato provides material for further detailed studies of the physiological function of catecholamines in plants.

A high frequency of apoptosis was found in cultures of lymphocytes isolated from the venous blood of children born with a low birth weight.

Children born with a low birth weight (below 2500 g) exhibit a slower rate of development, and a greater tendency towards morbidity and mortality, together with a deficit of weight and height. One reason could be an increase in the level of cell elimination by apoptosis. The aim of this study was to evaluate and compare the incidence of apoptotic and necrotic (dead) cells in cultures of peripheral blood lymphocytes obtained from children born with a low birth weight and from children with a normal birth weight. Peripheral blood lymphocytes were obtained by venipuncture (10 ml) and isolated using the density gradient centrifugation method. The lymphocytes were cultured for 48 h in a culture medium containing low concentrations of fetal calf serum. A comparison study was performed between low birth weight children and normal birth weight children and the susceptibility of their lymphocytes to apoptosis and to necrosis in serum-deficient feeding culture conditions. The amount of apoptotic cells and the percentage of dead cells were significantly higher in cultures of lymphocytes obtained from low birth weight children than in cultures from normal birth weight children. The two estimated parameters inversely correlated with the concentration of fetal calf serum in the culture medium. Pulsed field gel electrophoresis showed increased DNA degradation patterns in the cultures of lymphocytes obtained from low birth weight children. Our results should be perceived as an indication that, under worse feeding conditions, the elimination of cells by apoptosis and by necrosis is significantly higher for lymphocytes of low birth weight children than for those of normal birth weight children. The enhanced elimination of lymphocytes is related to a greater susceptibility to infections, especially of the respiratory tract, as established in the retrospective analysis of the anamneses of the examined group of low birth weight children.

Repression of the 14-3-3 gene affects the amino acid and mineral composition of potato tubers.

Recently, transgenic potato plants were created showing underexpression of the 20R isoform of the 14-3-3 protein. The transgenic plants grown in tissue culture showed a significant increase in nitrate reductase activity and a decrease in nitrate level. The transgenic line with the lowest 14-3-3 quantity was field-trialed (1997-2000) and analyzed. The reduction in the 14-3-3 protein level consistently resulted in a starch content increase and in an increase in the ratio of soluble sugars to starch in the tubers, although the latter was only barely visible. The determination of amino acid composition in the tubers showed a significant increase in methionine, proline, and arginine content and a slight but consistent increase in hydrophobic amino acid and lysine content in the cells of the transgenic potato plants. We also observed an increase in the crude protein content, from 19 to 22.1% of the control value in consecutive years. It is proposed that all of these changes might have resulted from the downregulation of nitrate reductase and sucrose phosphate synthase activities by 14-3-3, although other potential mechanisms cannot be excluded (e.g., an increase in enzyme protein level). 14-3-3-repressed transgenic plants showed a significant increase in calcium content in their tubers. It is thus proposed that a function of the isolated 14-3-3 isoform is in the control of amino acid synthesis and calcium metabolism. However, the mechanism of this control is as yet unknown.