Gibberellic acid and the inhibition of aerial tuberisation in Solanum tuberosum L.

The sensitivity of aerial and subterranean tuberisation to photoperiod was studied in potato (Solanum tuberosum cv. Aracy). Although photoperiodic sensitivity varied with the position along the stem, all buds could be induced to develop tubers under SD. Gibberellic acid (GA₃) applied to induced (30 short days) cuttings inhibited the photoperiodic effect. No tubers were formed and orthotropic shoots developed instead. The GA₃ caused a reduction in starch content in induced buds, lowering it to the same level as found in long-day treated plants. However, -amylase activity of buds of induced plants was not affected by GA₃, suggesting that GA₃ does not inhibit tuberisation by promotion of starch hydrolysis.     

Comparative genome analysis of Solanum lycopersicum and Solanum tuberosum

Solanum lycopersicum and Solanum tuberosum are agriculturally important crop species as they are rich sources of starch, protein, antioxidants, lycopene, beta-carotene, vitamin C, and fiber. The genomes of S. lycopersicum and S. tuberosum are currently available. However the linear strings of nucleotides that together comprise a genome sequence are of limited significance by themselves. Computational and bioinformatics approaches can be used to exploit the genomes for fundamental research for improving their varieties. The comparative genome analysis, Pfam analysis of predicted reviewed paralogous proteins was performed. It was found that S. lycopersicum proteins belong to more families, domains and clans in comparison with S. tuberosum. It was also found that mostly intergenic regions are conserved in two genomes followed by exons, intron and UTR. This can be exploited to predict regions between genomes that are similar to each other and to study the evolutionary relationship between two genomes, leading towards the development of disease resistance, stress tolerance and improved varieties of tomato.     

Induced ADH gene expression and enzyme activity in pollinated pistils of Solanum tuberosum

 The regulation of alcohol dehydrogenase (ADH) in relation to in vivo pollen tube growth of Solanum tuberosum was investigated. Adh gene expression as well as ADH enzyme activity were induced in pollinated pistils. The induced ADH isozyme in pollinated pistils is not present in pollen or anthers. The same ADH isozyme is induced in leaves submerged in water. The significance of the induction of ADH activity for pollen tube growth is discussed. Received: 13 November 1996 / Revision accepted: 8 January 1997     

Genomic instability in Solanum tuberosum x Solanum kurtzianum interspecific hybrids.

The use of interspecific crosses in breeding is an important strategy in improving the genetic base of the modern cultivated potato, Solanum tuberosum L. Until now, it has normally been interspecific Solanum hybrids that have been morphologically and cytologically characterized. However, little is known about the genomic changes that may occur in the hybrid nucleus owing to the combination of genomes of different origin. We have observed novel AFLP bands in Solanum tuberosum x Solanum kurtzianum diploid hybrids; 40 novel fragments were detected out of 138 AFLP fragments analyzed. No cytological abnormalities were observed in the hybrids; however, we found DNA methylation changes that could be the cause of the observed genomic instabilities. Of 277 MSAP fragments analyzed, 14% showed methylation patterns that differed between the parental species and the hybrids. We also observed frequent methylation changes in the BC1 progeny. Variation patterns among F1 and BC1 plants suggest that some methylation changes occurred at random. The changes observed may have implications for potato breeding as an additional source of variability.     

Membrane disruption and enzyme inhibition by naturally-occurring and modified chacotriose-containing Solanum steroidal glycoalkaloids

Naturally-occurring 3beta-O-chacotriosides of solasodine (solamargine), of its 22S, 25S isomer tomatidenol (beta-solamarine), and of solanidine (chaconine), as well as ring E- and F-modified derivatives of solamargine were prepared and assayed in order to assess the relevance of aglycone structural features to membrane-disruption and enzyme-inhibitory activities of the related glycoalkaloids. A ring E-opened dihydro-derivative of solasodine (the chacotrioside of dihydrosolasodine A) did not bind to cholesterol, stigmasterol or ergosterol in vitro, disrupt PC/cholesterol liposomes or mammalian erythrocytes. or inhibit acetylcholinesterase in vitro. It did not synergise with the solatrioside of dihydrosolasodine A or solasonine (nor did solamargine with dihydrosolasodine A solatrioside) in haemolysis tests. The ring F modified derivative, N-nitrososolamargine, did not inhibit acetylcholinesterase in vitro, but lysed liposomes at > or = 150 microM and pH 7. Increasing the pH to 8 (but not 9) further enhanced disruption. The combination of N-nitrososolamargine and solasonine did not cause any disruption of liposomes. Beta-solamarine showed no anti-acetylcholinesterase activity in vitro at up to 100 microM, but disrupted liposomes at 75 and 150 microM, although not to the extent caused by solamargine or chaconine. In combination with both the (inactive) solatriosides, solasonine and solanine, 75 microM beta-solamarine produced synergistic effects, with liposome disruption greater than 150 microM beta-solamarine alone. Beta-solamarine, solamargine and chaconine showed similar haemolytic activity. Beta-solamarine synergised with the solatriosides solasonine and solanine in disrupting erythrocytes. Preliminary structure-activity relationships were evaluated for the active chacotriosides in an attempt to define the scope and limitations of this model study.     

Changes in enzyme activity during elongation and tuberization of stolons of Solanum tuberosum L. cultured in vitro

Isolated stolons of Solanum tuberosam L. were cultured in vitroin the presence of kinetin, which induced tuber initiation orgibberellic acid which inhibited initiation. Progressive changes in enzyme activity, at the locus of tuberinitiation, were monitored at specified intervals. In the presenceof kinetin soluble invertase activity was decreased with timewhereas gibberellic acid (GA) evoked substantial increases inactivity. Acid phosphatase activity was enhanced by GA but changedonly slightly under tuber inducing conditions. Enzymic hydrolysisof glucose-6-phosphate and fructose-6-phosphate decreased duringthe course of tuber induction but increased in the presenceof GA. In contrast hydrolysis of 3'AMP was stimulated undertuber inducing conditions. GA evoked substantial increases in peroxidase activity duringthe initial stages of incubation while under tuber inducingconditions increased activity was only observed after 5 days.Substantially higher levels of IAA oxidase activity were associatedwith tuber initiation. RNase activity decreased with time undertuber inducing conditions but showed an initial stimulationin the presence of GA. These results are discussed with referenceto the role of these enzymes in carbohydrate metabolism andthe regulation of hormone levels. (Received February 29, 1972; )     

Structure of barogenin from Solanum tuberosum

The budding tuber of Solanum tuberosum accumulated barogenin. Its structure was determined by chemical and spectroscopic studies as (25S)-3β, 26-dihydroxy-cholest-5-ene-16,22-dione, the (25S)-epimer of kryptogenin. The biogenetic relationship between barogenin and spirostanols is discussed.     

Steady-state approximation of enzyme activation and inhibition

This article deals with the effects of the initial concentration of effector (inhibitor or activator) on the steady-state approximation of enzyme kinetics. The results could be summarized as follows: (1) In competitive inhibition, the increase in the initial concentration of inhibitor led to the reduction of steady state time. (2) In noncompetitive and uncompetitive inhibitions, the steady state time was not changed with the increase in the initial concentration of inhibitor. (3) In nonessential activation, the increase in the initial concentration of activator led to the reduction of steadystate time. (4) It was specially noted that in nonessential activation, even if the reaction is in the steady-state, activation constant (K(A)) can not be determined exactly unless the initial concentration of activator is very small.     

Growth-inhibitory volatile aromatic compounds produced by Solanum tuberosum tubers

Some of the aromatic compounds evolved by stored potato tubers have been identified by combined GLC-MS. Of the identified compounds, benzothiazole, 1,4-dimethylnaphthalene and 1,6-dimethylnaphthalene are comparatively potent inhibitors of sprout growth in the potato tuber. The growth suppressing activity of the two dimethylnaphthalenes is comparable with that of isopropyl-(N-3-chlorophenyl)-carbamate, which is used commercially in potato storage.     

Formation of stable platelet aggregates by lectin from Solanum tuberosum

The GlcNAc-specific lectin from Solanum tuberosum is shown to induce haptenic-sugar-resistant contacts in platelet aggregation but not to induce stable neutrophil and lymphocyte aggregation. The formation of such contacts in platelets was significantly hindered by the inhibitors of cAMP phosphodiesterase (papaverine) or arachidonic acid metabolism (indomethacin, aristolochic acid, or MK-886) and by a sulfhydryl reagent (N-ethylmaleimide). This lectin can be useful in studying the mechanisms of stable platelet aggregation, drug screening for antithrombotic activity, and developing the cell engineering techniques.     

Mitochondrial DNA rearrangements in somatic hybrids of Solanum tuberosum and Solanum brevidens

Summary Thirty somatic hybrids between Solanum tuberosum and Solanum brevidens were analysed for mitochondrial and chloroplast genome rearrangements. In all cases, the chloroplast genomes were inherited from one of the parental protoplast populations. No chloroplast DNA alterations were evident but a range of mitochondrial DNA alterations, from zero to extensive intra- and inter-molecular recombinations, were found. Such recombinations involved specific recombination hot spots in the mitochondrial genome. Not all hybrids regenerated from a common callus possessed identical mitochondrial genomes, suggesting that sorting out of mitochondrial populations in the callus may have been incomplete at the plant regeneration stage. Sorting out of organelles in planta was not observed.     

Wound-induced phenylalanine ammonia-lyase in potato (Solanum tuberosum) tuber discs. Significance of glycosylation and immunolocalization of enzyme subunits.

1. Excised discs of potato (Solanum tuberosum) tuber were incubated with [3H]fucose and extracts were prepared and incubated with an antibody to phenylalanine ammonia-lyase. Analysis of the resulting immunoprecipitated proteins by SDS/PAGE showed [3H]mannose- and [3H]fucose-labelled bands with Mr values corresponding to those of phenylalanine ammonia-lyase subunits. 2. When potato discs were incubated with [3H]sugars in the presence of tunicamycin, an inhibitor of N-linked protein glycosylation, incorporation of radioactivity from [3H]mannose into the immunoprecipitated enzyme subunits was virtually eliminated, whereas that from [3H]fucose was only marginally inhibited. 3. Tunicamycin reduced the level of extractable phenylalanine ammonia-lyase activity induced in excised potato tuber discs. Kinetic analysis revealed that the Vmax value of the enzyme in crude extracts from tunicamycin-treated tissue was reduced, whereas the apparent Km values were unaffected. 4. Immunoprecipitation of the enzyme labelled in vivo with [35S]methionine showed that tunicamycin did not inhibit the synthesis of the enzyme protein per se, nor did it increase the degradation of the enzyme protein. 5. Immunoprecipitation of the enzyme labelled in vitro with [14C]nitromethane showed that tunicamycin did not affect the introduction of the dehydroalanine residue into the active site. 6. These results are consistent with the following hypothesis: tunicamycin inhibits the N-linked glycosylation of phenylalanine ammonia-lyase which, in turn, results in imperfect folding of the enzyme protein. The orientation of the active site is changed in such a way that the affinity of the enzyme for its substrate is unaffected, whereas the catalytic activity of the enzyme is reduced. 7. Both optical- and electron-microscopic immunolocalization studies with antibody to phenylalanine ammonia-lyase showed increased deposition of silver granules in cells in sections of potato discs in which induction of the enzyme was allowed to occur compared with cells from newly wounded tissue. The enzyme was located in the cytoplasm, and was possibly membrane-associated.     

Local and systemic responses induced by aphids in Solanum tuberosum plants

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Homoptera: Aphididae) are serious pests of potato (Solanum tuberosum L.) (Solanaceae), notably in transmitting several plant viruses. Heterospecific interactions may occur between these two species as they are often seen at the same time on the same potato plant in the field. As aphid infestation is known to induce both local and systemic changes, we conducted experiments to determine the effect of previous infestation on probing behaviour and feeding‐related parameters. We used the DC electrical penetration graph technique to characterize the influence of previous infestation by conspecific M. persicae or by heterospecific Ma. euphorbiae on M. persicae feeding behaviour at both local and systemic levels, i.e., on previously infested leaves and on non‐previously infested leaves of infested plants, respectively. Conspecific and heterospecific infestation led to similar modification of M. persicae feeding activities. However, the effects of previous infestation occurring at the local level were opposite to those observed at the systemic level. Myzus persicae food acceptance was slightly enhanced on previously infested leaves, whereas it was inhibited on non‐infested leaves of infested plants, which indicated an induced resistance mechanism. Our results advance the understanding of the mechanisms involved in aphid–host plant acceptance and colonization processes on potato plants in conspecific and heterospecific situations.     

Endogenous Cytokinins in Solanum tuberosum as Influenced by Photoperiod and Temperature

Using the cucumber cotyledon bioassay, in combination with paper and column chromatographic techniques, 4 compounds exhibiting cytokinin activity were detected in extracts of Katahdin potato plant tissues. Two of these compounds were significantly higher in plants grown under inducing conditions (26°C day and 12°C night with an 8-h photoperiod) than those grown under non-inducing conditions (28°C day and 25°C night with a 16-h photoperiod). One compound increased 10-fold in above-ground tissue after only 2 Inductive cycles. Both compounds reached their maximum values in below-ground tissue after 6 days under inducing conditions, with tuber initiation observed after 8 to 10 days.     

Protein conformation of potato (Solanum tuberosum) lectin determined by circular dichroism.

The structure of potato (Solanum tuberosum) lectin, which is a hydroxyproline-rich glycoprotein, has been investigated by circular dichroism. The spectra of the native lectin, and of the oxidized, reduced and carboxymethylated and deglycosylated derivatives were examined, as was a hydroxyproline-rich glycopeptide and its deglycosylated derivative. It is concluded that the lectin contains about 35% polyproline II conformation, 34% type II beta-turn and 31% irregular conformation. No indications were found for the presence of alpha-helix or beta-sheet conformations. The polyproline II conformation is heat-stable, but is markedly destabilized by deglycosylation. The type II beta-turn is destabilized by cleavage of disulphide bonds.     

Somatic hybrid potato plants after electrofusion of diploid Solanum tuberosum and Solanum phureja

Protoplasts from diploid S. tuberosum and diploid S. phureja were electrofused followed by selection of the heterokaryons with a micromanipulator. Visual identification of the heterokaryons was facilitated by fluorescein diacetate staining of the protoplasts from one of the parents, which was grown on herbicide containing medium to induce bleaching of the chlorophyll. In total, 840 heterokaryons showing red (chlorophyll) and yellow-green (fluorescein) fluorescence were selected and cultured at relatively low densities using various feeder systems. Finally, 18 putative hybrid plantlets were obtained and grown to maturity. DNA histograms indicated that the plants were hexaploid, octoploid or mixoploid. With Giemsa C-band pattern analysis of the chromosomes the hybrid character and the combinations of the chromosome sets of all plants investigated could be established.