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.     

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).     

Beta-1,3-glucooligosaccharide induced activation of four enzymes responsible for N-p-coumaroyloctopamine biosynthesis in potato (Solanum tuberosum cv.) tuber tissue

Potato tuber disks, when treated with laminarin, a beta-1,3-glucooligosaccharide from Laminaria digitata, accumulate a hydroxycinnamoyl amide compound, N-p-coumaroyloctopamine (p-CO). The biosynthesis of p-CO was investigated by feeding experiments, in order to show that the precursors of N-p-coumaroyl and octopamine moieties of p-CO are L-phenylalanine and L-tyrosine, respectively. The treatment of potato tuber tissue with laminarin resulted in elevated activities of four enzymes which are putatively involved in p-CO biosynthesis: phenylalanine ammonia lyase (PAL; EC 4.3.1.5), 4-hydroxycinnamic acid:CoA ligase (4CL; EC 6.2.1.12), hydroxycinnamoyl-CoA:tyramine N-(hydroxycinnamoyl)transferase (THT; EC 2.3.1.110) and tyrosine decarboxylase (TyrDC; EC 4.1.1.25). Among these, the response of TyrDC was specific to laminarin treatment, thus indicating that the regulation of TyrDC activity is critical for the accumulation of p-CO in potato tuber tissue.     

Activities of enzymes catalyzing benzylisoquinoline alkaloid biosynthesis in Annona diversifolia saff. during early development

In species of the Annonaceae family, particularly Annona diversifolia Safford, benzylisoquinoline alkaloids (BIA) are secondary metabolites that appear to contribute to the phytopathogen defense mechanisms of plants. Polyphenol oxidase (PPO, EC 1.14.18.1), amine oxidase (AO, EC 1.4.3.4), tyrosine decarboxylase (TYDC, EC 4.1.1.25), and norcoclaurine synthase (NCS, EC 4.2.1.78) catalyze the initial steps in BIA biosynthesis. This study reports the activity of these enzymes in different plant organs at four stages of the early development of A. diversifolia seedlings: seeds imbibed for 5 days, seeds after 3 days of germination, seedlings with leaf primordia, and seedlings with two true leaves. Evaluations were performed according to specific protocols for each of the enzymes. All four enzymes were active in the developing embryos during imbibition and germination, but no activity was detected in the endosperm. In seedlings with leaf primordia and seedlings with two true leaves (25 and 30 days after the start of imbibition, respectively), the activities of three enzymes (TYDC, PPO, and AO) were observed in all of the tissues, while NCS activity was only observed in the stems and roots. The activities of these enzymes in embryos provides evidence that alkaloid biosynthesis at early developmental stages is related to embryo growth and development. This study is the first report that has described some aspects of alkaloid biosynthesis in Annonaceae.     

Influence of cold exposure and thyroid hormones on regulation of adrenal catecholamines.

Since thyroid hormones influence urinary excretion of catecholamines after exposure to cold, the effects of hyper- and hypo-thyroidism on adrenal tyrosine hydroxylase (TH) (EC 1.14.16.2), phenylethanolamine-N-methyl transferase (PNMT) (EC 2.1.1.28), and serum dopamine-beta-hydroxylase (DbetaH) (EC 1.14.17.1) of rats of 23 and 4 degrees C were studied. TH changes resembled the urinary excretion pattern at 4 degrees C in being higher after 8 days than after 1 day of exposure, and in declining as acclimation occurred. At 23 degrees C, TH activity of hypothyroid rats was significantly higher than in euthyroid or hyperthyroid animals, and after 1 day at 4 degrees C the value increased even more. While in the hypothyroid animals at 4 degrees C the concentration of adrenal catecholamines was less, the epinephrine to norepinephrine ratio was higher than at 23 degrees C. Very high TH activity with a decline in catecholamine concentration suggests that the capacity of TH had been exceeded. PNMT activity was significantly elevated in this group. TH activity was not decreased in the hyperthyroid group at 23 degrees C, and was increased after 8 days at 4 degrees C, suggesting that circulating thyroid hormones have no direct inhibitory effect on TH. Serum DbetaH was elevated after exposure to 4 degrees C, regardless of thyroid hormonal status. The activation of adrenal TH in hypothyroid rats at 23 degrees C and of TH, PNMT, and serum DbetaH at 4 degrees C is probably the result of increased activity of the sympathetic nervous system.     

Optimization of growth conditions for the induction of tyrosine decarboxylase inStreptococcus faecalis

Summary Growth conditions were investigated for optimal tyrosine decarboxylase (EC 4.1.1.25) activity in acetone dried cells ofStreptococcus faecalis. A growth pH of 6.0 was found optimal for enzyme induction. The enzyme was also shown to be growth-associated which indicates that continuous fermentation is preferable for optimal process productivity.     

Salinity-induced tissue-specific diurnal changes in nitrogen assimilatory enzymes in tomato seedlings grown under high or low nitrate medium.

We studied the salt stress (100 mM NaCl) effects on the diurnal changes in N metabolism enzymes in tomato seedlings (Lycopersicon esculentum Mill. cv. Chibli F1) that were grown under high nitrogen (HN, 5 mM NO(3)(-)) or low nitrogen (LN, 0.1 mM NO(3)(-)). NaCl stress led to a decrease in plant DW production and leaf surface to higher extent in HN than in LN plants. Total leaf chlorophyll (Chl) content was decreased by salinity in HN plants, but unchanged in LN plants. Soluble protein content was decreased by salt in the leaves from HN and LN plants, but increased in the stems-petioles from LN plants. Nitrate reductase (NR, EC 1.6.1.6) showed an activity peak during first part of the light period, but no diurnal changes were observed for the nitrite reductase (NiR, EC 1.7.7.1) activity. Glutamine synthetase (GS, EC 6.3.1.2) and glutamate synthase (Fd-GOGAT, EC 1.4.7.1) activities increased in HN plant leaves during the second part of the light period, probably when enough ammonium is produced by nitrate reduction. NR and NiR activities in the leaves were more decreased by NaCl in LN than in HN plants, whereas the opposite response was obtained for the GS activity. Fd-GOGAT activity was inhibited by NaCl in HN plant leaves, while salinity did not shift the peak of the NR and Fd-GOGAT activities during a diurnal cycle. The induction by NaCl stress occurred for the NR and GS activities in the roots of both HN and LN plants. Glutamate dehydrogenase (GDH, EC 1.4.1.2) activity shifted from the deaminating activity to the aminating activity in all tissues of HN plants. In LN plants, both aminating and deaminating activities were increased by salinity in the leaves and roots. The differences in the sensitivity to NaCl between HN and LN plants are discussed in relation to the N metabolism status brought on by salt stress.     

The effect of salt stress on polyamine biosynthesis and content in mung bean plants and in halophytes

The activity of L-arginine decarboxylase (EC 4.1.1.19) and L-ornithine decarboxylase (EC 4.1.1.17), polyamine content, and incorporation of arginine and ornithine into polyamines, were determined in mung bean [Vigna radiata (L.) Wilczek] plants subjected to salt (hypertonic) stress (NaCl at 0.51–2.27 MPa). Changes in enzyme activity in response to hypotonic stress were determined as well in several halophytes [Pulicaria undulata (L.), Kostei, Salsola rosmarinus (Ehr.) Solms-Laub, Mesembryanthemum forskahlei Hochst, and Atriplex halimus L.]. NaCl stress, possibly combined with other types of stress that accompanied the experimental conditions, resulted in organ-specific changes in polyamine biosynthesis and content in mung bean plants. The activity of both enzymes was inhibited in salt-stressed leaves. In roots, however, NaCl induced a 2 to 8-fold increase in ornithine decarboxylase activity. Promotion of ornithine decarboxylase in roots could be detected already 2 h after exposure of excised roots to NaCl, and iso-osmotic concentrations of NaCl and KCl resulted in similar changes in the activity of both enzymes. Putrescine level in shoots of salt-stressed mung bean plants increased considerably, but its level in roots decreased. The effect of NaCl stress on spermidine content was similar, but generally more moderate, resulting in an increased putrescine/spermidine ratio in salt-stressed plants. Exposure of plants to NaCl resulted also in organ-specific changes in the incorporation of both arginine and ornithine into putrescine: incorporation was inhibited in leaf discs but promoted in excised roots of salt-stressed mung bean plants. In contrast to mung bean (and several other glycophytes), ornithine and arginine decarboxylase activity in roots of halophytes increased when plants were exposed to tap water or grown in a pre-washed soil—i.e. a hypotonic stress with respect to their natural habitat. NaCl, when present in the enzymatic assay mixture, inhibited arginine and ornithine decarboxylase in curde extracts of mung bean roots, but did not affect the activity of enzymes extracted from roots of the halophyte Pulicaria. Although no distinct separation between NaCl stress and osmotic stress could be made in the present study, the data suggest that changes in polyamines in response to NaCl stress in mung bean plants are coordinated at the organ level: activation of biosynthetic enzymes concomitant with increased putrescine biosynthesis from its precursors in the root system, and accumulation of putrescine in leaves of salt-stressed plants. In addition, hypertonic stress applied to glycophytes and hypotonic stress applied to halophytes both resulted in an increase in the activity of polyamine biosynthetic enzymes in roots.     

Glucocorticoids Increase Catecholamine Synthesis and Storage in PC 12 Pheochromocytoma Cell Cultures

Abstract: Glucocorticoids, cholera toxin and high plating density all increase the activity of tyrosine 3-monooxygenase (TH) in cultured PC12 pheochromocytoma cells. Glucocorticoids increase enzyme activity in cells treated with cholera toxin and in cells grown at high plating density. Glucocorticoids also increase the content of stored catecholamines in the cells. In cells cultured under routine conditions, glucocorticoids primarily increase the stores of dopamine. The addition of ascorbate to the culture medium increases the storage of norepinephrine in both steroid-treated and untreated cells. Incubation of the cells in media containing 56 n M K⁺ causes the release of the same percentage of stored dopamine from steroid-treated as from untreated cells. Steroid-treated cells contain more dopamine than do untreated cells and therefore, in response to high K⁺, the steroid-treated cells secrete more dopamine than do untreated cells. We conclude that the activity of tyrosine 3-monooxygenase in PC12 cells can be regulated by several distinct mechanisms; that glucocorticoids cause a coordinate increase in TH activity and in catecholamine storage; that steroids increase the storage of catecholamines in a releasable pool; and that the steroid-induced increase in catecholamine storage may result in increased secretion of catecholamines from steroid-treated cells.     

Elevated tyrosine decarboxylase and tyramine hydroxycinnamoyltransferase levels increase wound-induced tyramine-derived hydroxycinnamic acid amide accumulation in transgenic tobacco leaves

Feruloyltyramine (FT) and 4-coumaroyltyramine (4CT) participate in the defense of plants against pathogens through their extracellular peroxidative polymerization, which is thought to reduce cell wall digestibility. Hydroxycinnamoyl-CoA:tyramine N-(hydroxycinnamoyl)transferase (THT; EC 2.3.1.110) and tyrosine decarboxylase (TYDC; EC 4.1.1.25) are purported to play key roles in the stress-induced regulation of tyramine-derived hydroxycinnamic acid amide (HCAAT) metabolism. Transgenic tobacco (Nicotiana tabacum cv. Xanthi) was engineered to constitutively express tobacco THT. A T₁ plant over-expressing THT was crossbred with T₁ tobacco expressing opium poppy TYDC2, to produce a T₂ line with elevated THT and TYDC activities compared with wild type plants. The effects of an independent increase in TYDC or THT activity, or a dual increase in both TYDC and THT on the cellular pools of HCAAT pathway intermediates and the accumulation of soluble and cell wall-bound FT and 4CT were examined. Increased TYDC activity resulted in a larger cellular pool of tyramine and lower levels of L-phenylalanine in transgenic leaves. In contrast, elevated THT activity reduced tyramine levels. HCAAT levels were low in healthy leaves, but were induced in response to wounding and accumulated around wound sites. Similarly, endogenous THT and TYDC activities were wound-induced. The rate of wound-induced HCAAT accumulation was highest in transgenic plants with elevated THT and TYDC activities showing that both enzymes exert control over the flux of intermediates involved in HCAAT biosynthesis under some conditions.