The role of systemin in Pin2 gene expression was analyzed in wild-type plants of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.), as well as in abscisic acid (ABA)-deficient tomato (sitiens) and potato (droopy) plants. The results showed that systemin initiates Pin2 mRNA accumulation only in wildtype tomato and potato plants. As in the situation after mechanical wounding,Pin2 gene expression in ABA-deficient plants was not activated by systemin. Increased endogenous levels of jasmonic acid (JA) and accumulation of Pin2 mRNA were observed following treatment with α-linolenic acid, the precursor of JA biosynthesis, suggesting that these ABA mutants still have the capability to synthesize de novo JA. Measurement of endogenous levels of ABA and JA showed that systemin leads to an increase of both phytohormones (ABA and JA) only in wild-type but not in ABA-deficient plants.

A pathogen-elicitor-inducible acyltransferase [tyramine hydroxycinnamoyltransferase (THT); EC 2.3.1], which catalyzes the transfer of hydroxycinnamic acids from hydroxycinnamoyl-CoA esters to tyramine in the formation of N-hydroxycinnamoyltyramine, was purified to apparent homogeneity from cell-suspension cultures of potato (Solanum tuberosum L. cv. Datura), with a 1400-fold enrichment, a 5% recovery and a final specific activity of 208 mkat·(kg protein)−1. Affinity chromatography on Reactive Yellow-3-Agarose using the acyl donor (feruloyl-CoA) as eluent was the decisive step in the purification sequence. The purified protein showed a native molecular mass of ca. 49 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and in the absence of a reducing agent (2-mercaptoethanol) indicated that THT is a heterodimer in which the protein subunits (ca. 25 kDa) are non-covalently associated. The enzyme was stimulated fivefold by 10 mM Ca2+. The apparent K m value for tyramine was dependent on the nature of the hydroxycinnamoyl-CoA present. Thus, the K m value for tyramine was about tenfold greater (174 μM) in the presence of 4-coumaroyl-CoA than in the presence of feruloyl-CoA (20 μM).

Uridine 5′-diphosphoglucose-dependent glucosyl-transferases (UDP-glucose:betanidin 5-O- and 6-O-glucosyltransferases; 5-GT and 6-GT; EC 2.4.1) catalyze the regiospecific transfer of glucose to the 5- and 6-hydroxy group of betanidin in the formation of betanin and gomphrenin I, respectively. Both GT activities were partially purified from cell suspension cultures of Dorotheanthus bellidiformis (Burm. f.) N.E. Br. Isoelectric focusing of crude protein extracts indicated the presence of three 5-GT isoforms and a single 6-GT form. The 5-GT isoforms were partially separated from each other and completely from the 6-GT. Studies of the glucosyltransferase activities were focused on the major isoform of the 5-GTs and the 6-GT, which displayed the same pH optimum near 7.5 in K-phosphate buffer. A 3- and 2.5-fold enrichment and 11% and 10% recovery of the 5-GT and 6-GT, respectively, were routinely achieved; however, a 3300-fold enrichment of the major 5-GT isoform and a 6-fold enrichment of the 6-GT were also achieved. Both enzymes are monomers and displayed apparent native Mrs near 55 000. The maxima of the reaction temperature were at 50 °C for the 5-GT and at 37°C for the 6-GT with respective apparent energies of activation of 51 and 53 kJ · mol−1. Kinetic studies indicated that the apparent Michaelis constants (apparent K m) of the GTs for one substrate were dependent on the concentration of the second substrate. However, the relationship between the apparent K m values and the dissociation constants (K i) were different; m > K i applies for the 5-GT and K m < K i for the 6-GT activity. Consequently, this results in a predominant formation of betanin at low substrate concentrations, but a predominant formation of gomphrenin I at high substrate concentrations, assuming that both enzymes may compete freely for their substrates. This might explain why we could not observe a correlation between extractable 5-GT and 6-GT activities and the in-vivo accumulation of the respective products from cell-suspension cultures of D. bellidiformis.

Lipid bodies are degraded during germination. Whereas some proteins, e.g. oleosins, are synthesized during the formation of lipid bodies of maturating seeds, a new set of proteins, including a specific form of lipoxygenase (LOX; EC 1.13.11.12), is detectable in lipid bodies during the stage of fat degradation in seed germination. In cotyledons of cucumber (Cucumis sativus L.) seedlings at day 4 of germination, the most conspicuous staining with anti-LOX antibodies was observed in the cytosol. At very early stages of germination, however, the LOX form present in large amounts and synthesized preferentially was the lipid-body LOX. This was demonstrated by immunocytochemical staining of cotyledons from 1-h and 24-h-old seedlings: the immunodecoration of sections of 24-h-old seedlings with anti-LOX antiserum showed label exclusively correlated with lipid bodies of around 3 μm in diameter. In accordance, the profile of LOX protein isolated from lipid bodies during various stages of germination showed a maximum at day 1. By measuring biosynthesis of the protein in vivo we demonstrated that the highest rates of synthesis of lipid-body LOX occurred at day 1 of germination. The early and selective appearance of a LOX form associated with lipid bodies at this stage of development is discussed.

The role of systemin in Pin2 gene expression was analyzed in wild-type plants of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.), as well as in abscisic acid (ABA)-deficient tomato (sitiens) and potato (droopy) plants. The results showed that systemin initiates Pin2 mRNA accumulation only in wildtype tomato and potato plants. As in the situation after mechanical wounding,Pin2 gene expression in ABA-deficient plants was not activated by systemin. Increased endogenous levels of jasmonic acid (JA) and accumulation of Pin2 mRNA were observed following treatment with α-linolenic acid, the precursor of JA biosynthesis, suggesting that these ABA mutants still have the capability to synthesize de novo JA. Measurement of endogenous levels of ABA and JA showed that systemin leads to an increase of both phytohormones (ABA and JA) only in wild-type but not in ABA-deficient plants.

A pathogen-elicitor-inducible acyltransferase [tyramine hydroxycinnamoyltransferase (THT); EC 2.3.1], which catalyzes the transfer of hydroxycinnamic acids from hydroxycinnamoyl-CoA esters to tyramine in the formation of N-hydroxycinnamoyltyramine, was purified to apparent homogeneity from cell-suspension cultures of potato (Solanum tuberosum L. cv. Datura), with a 1400-fold enrichment, a 5% recovery and a final specific activity of 208 mkat·(kg protein)−1. Affinity chromatography on Reactive Yellow-3-Agarose using the acyl donor (feruloyl-CoA) as eluent was the decisive step in the purification sequence. The purified protein showed a native molecular mass of ca. 49 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and in the absence of a reducing agent (2-mercaptoethanol) indicated that THT is a heterodimer in which the protein subunits (ca. 25 kDa) are non-covalently associated. The enzyme was stimulated fivefold by 10 mM Ca2+. The apparent K m value for tyramine was dependent on the nature of the hydroxycinnamoyl-CoA present. Thus, the K m value for tyramine was about tenfold greater (174 μM) in the presence of 4-coumaroyl-CoA than in the presence of feruloyl-CoA (20 μM).

Uridine 5′-diphosphoglucose-dependent glucosyl-transferases (UDP-glucose:betanidin 5-O- and 6-O-glucosyltransferases; 5-GT and 6-GT; EC 2.4.1) catalyze the regiospecific transfer of glucose to the 5- and 6-hydroxy group of betanidin in the formation of betanin and gomphrenin I, respectively. Both GT activities were partially purified from cell suspension cultures of Dorotheanthus bellidiformis (Burm. f.) N.E. Br. Isoelectric focusing of crude protein extracts indicated the presence of three 5-GT isoforms and a single 6-GT form. The 5-GT isoforms were partially separated from each other and completely from the 6-GT. Studies of the glucosyltransferase activities were focused on the major isoform of the 5-GTs and the 6-GT, which displayed the same pH optimum near 7.5 in K-phosphate buffer. A 3- and 2.5-fold enrichment and 11% and 10% recovery of the 5-GT and 6-GT, respectively, were routinely achieved; however, a 3300-fold enrichment of the major 5-GT isoform and a 6-fold enrichment of the 6-GT were also achieved. Both enzymes are monomers and displayed apparent native Mrs near 55 000. The maxima of the reaction temperature were at 50 °C for the 5-GT and at 37°C for the 6-GT with respective apparent energies of activation of 51 and 53 kJ · mol−1. Kinetic studies indicated that the apparent Michaelis constants (apparent K m) of the GTs for one substrate were dependent on the concentration of the second substrate. However, the relationship between the apparent K m values and the dissociation constants (K i) were different; m > K i applies for the 5-GT and K m < K i for the 6-GT activity. Consequently, this results in a predominant formation of betanin at low substrate concentrations, but a predominant formation of gomphrenin I at high substrate concentrations, assuming that both enzymes may compete freely for their substrates. This might explain why we could not observe a correlation between extractable 5-GT and 6-GT activities and the in-vivo accumulation of the respective products from cell-suspension cultures of D. bellidiformis.

Lipid bodies are degraded during germination. Whereas some proteins, e.g. oleosins, are synthesized during the formation of lipid bodies of maturating seeds, a new set of proteins, including a specific form of lipoxygenase (LOX; EC 1.13.11.12), is detectable in lipid bodies during the stage of fat degradation in seed germination. In cotyledons of cucumber (Cucumis sativus L.) seedlings at day 4 of germination, the most conspicuous staining with anti-LOX antibodies was observed in the cytosol. At very early stages of germination, however, the LOX form present in large amounts and synthesized preferentially was the lipid-body LOX. This was demonstrated by immunocytochemical staining of cotyledons from 1-h and 24-h-old seedlings: the immunodecoration of sections of 24-h-old seedlings with anti-LOX antiserum showed label exclusively correlated with lipid bodies of around 3 μm in diameter. In accordance, the profile of LOX protein isolated from lipid bodies during various stages of germination showed a maximum at day 1. By measuring biosynthesis of the protein in vivo we demonstrated that the highest rates of synthesis of lipid-body LOX occurred at day 1 of germination. The early and selective appearance of a LOX form associated with lipid bodies at this stage of development is discussed.

The role of systemin in Pin2 gene expression was analyzed in wild-type plants of potato (Solanum tuberosum L.) and tomato (Lycopersicon esculentum Mill.), as well as in abscisic acid (ABA)-deficient tomato (sitiens) and potato (droopy) plants. The results showed that systemin initiates Pin2 mRNA accumulation only in wildtype tomato and potato plants. As in the situation after mechanical wounding,Pin2 gene expression in ABA-deficient plants was not activated by systemin. Increased endogenous levels of jasmonic acid (JA) and accumulation of Pin2 mRNA were observed following treatment with α-linolenic acid, the precursor of JA biosynthesis, suggesting that these ABA mutants still have the capability to synthesize de novo JA. Measurement of endogenous levels of ABA and JA showed that systemin leads to an increase of both phytohormones (ABA and JA) only in wild-type but not in ABA-deficient plants.

A pathogen-elicitor-inducible acyltransferase [tyramine hydroxycinnamoyltransferase (THT); EC 2.3.1], which catalyzes the transfer of hydroxycinnamic acids from hydroxycinnamoyl-CoA esters to tyramine in the formation of N-hydroxycinnamoyltyramine, was purified to apparent homogeneity from cell-suspension cultures of potato (Solanum tuberosum L. cv. Datura), with a 1400-fold enrichment, a 5% recovery and a final specific activity of 208 mkat·(kg protein)−1. Affinity chromatography on Reactive Yellow-3-Agarose using the acyl donor (feruloyl-CoA) as eluent was the decisive step in the purification sequence. The purified protein showed a native molecular mass of ca. 49 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence and in the absence of a reducing agent (2-mercaptoethanol) indicated that THT is a heterodimer in which the protein subunits (ca. 25 kDa) are non-covalently associated. The enzyme was stimulated fivefold by 10 mM Ca2+. The apparent K m value for tyramine was dependent on the nature of the hydroxycinnamoyl-CoA present. Thus, the K m value for tyramine was about tenfold greater (174 μM) in the presence of 4-coumaroyl-CoA than in the presence of feruloyl-CoA (20 μM).