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PubMed2001

The Interaction of Gibberellins and Photoperiod in the Control of Potato Tuberization.

Solanum tuberosum ssp. andigena plants require a short-day (SD) photoperiod for tuber formation, a process that is also affected by gibberellins (GAs). Grafting experiments have confirmed that the photoperiod is perceived in the leaves. Tuber formation, however, usually takes place in the underground stolons. In this review, photoperiod-dependent tuberization has been divided into five chronological events: SD photoperiod perception, short-term adaptive responses to SD conditions, generation and transport of tuber-inducing signal(s), tuber formation, and long-term adaptive responses to tuber growth. Within this frame of study, the interaction of GAs and photoperiod is revised. Similar to the flowering process in Arabidopsis, we suggest the existence of two independent pathways that control tuber formation: a photoperiod-dependent pathway and a GA-dependent pathway. Nevertheless, photoperiod-dependent tuber formation requires the action of GAs at specific stages to orchestrate this complex process of development.

Journal Article↗
PubMed2001

Tissue-specific signal(s) activate the promoter of a metallocarboxypeptidase inhibitor gene family in potato tuber and berry.

The molecular basis of the differential expression of the GM7-type metallocarboxypeptidase inhibitor (MCPI) genes in tuberizing (StMCPI) and non-tuberizing Solanum species (SbMCPI) was investigated. It was shown that the StMCPI is encoded by a gene family in Solanum tuberosum (potato), but SbMCPI might be a single-copy gene in the non-tuberizing species Solanum brevidens. The StMCPI promoter shows evolutionary relatedness to the S. brevidens-derived SbMCPI and to the fruit-specific tomato promoter 2A11. Both StMCPI and SbMCPI promoter regions were able to confer tuber- and berry-specific expression for the beta-glucuronidase reporter gene in potato suggesting that the difference in MCPI gene expression is in trans regulatory factors between the tuberizing and the non-tuberizing Solanum species. The MCPI promoters did not respond to metabolic, environmental or hormonal signals in leaves. Thus, the MCPI genes are regulated in a different way than the other known tuber-specific genes and potentially are suitable for biotechnological application in potato to provide specific transgene expression in tuber and berry.

Amino Acid Sequence↗
PubMed2002

Characterization of gene expression during potato tuber development in individuals and populations using the luciferase reporter system.

Analysis of gene expression and enzyme activity in pooled tuber samples has previously indicated different developmental events occurring in a fixed sequential order during tuber development, starting with the up-regulation of starch synthesis then induction of protein storage followed by cell division and cell enlargement. In this report we analysed in vivo promoter activity of genes related to cell division and storage of reserves during tuber development in individual in vitro tubers, using the non invasive firefly luciferase reporter system. The average activity of the storage related promoters (AGPaseS and lambdaPat21) was up-regulated prior to visible swelling, while the average activity of both cell cycle genes (cycB1;1 and CDC2a) showed an up-regulation after the onset of swelling. However, this novel system allowed expression analysis in individual tubers, which showed a variable up-regulation of both storage genes in relation to the moment of swelling, from 4 days before to 10 days after the onset of swelling. We conclude that during the first stages of tuber development, the moment of storage gene induction is independent from swelling. These results indicate that the developmental program of potato tubers does not consist of a fixed sequential order of events, but consists of independent developmental programs (storage and swelling), together resulting in the formation of a potato tuber. It is concluded that analysis of developmental programs by studying individuals may result in new insights, possibly obscured when using pooled samples.

Arabidopsis Proteins↗
PubMed2003

Evidence that SNF1-related kinase and hexokinase are involved in separate sugar-signalling pathways modulating post-translational redox activation of ADP-glucose pyrophosphorylase in potato tubers.

We recently discovered that post-translational redox modulation of ADP-glucose pyrophosphorylase (AGPase) is a powerful new mechanism to adjust the rate of starch synthesis to the availability of sucrose in growing potato tubers. A strong correlation was observed between the endogenous levels of sucrose and the redox-activation state of AGPase. To identify candidate components linking AGPase redox modulation to sugar supply, we used potato tuber discs as a model system. When the discs were cut from growing wild-type potato tubers and incubated for 2 h in the absence of sugars, redox activation of AGPase decreased because of a decrease in internal sugar levels. The decrease in AGPase redox activation could be prevented when glucose or sucrose was supplied to the discs. Both sucrose uptake and redox activation of AGPase were increased when EDTA was used to prepare the tuber discs. However, EDTA treatment of discs had no effect on glucose uptake. Feeding of different glucose analogues revealed that the phosphorylation of hexoses by hexokinase is an essential component in the glucose-dependent redox activation of AGPase. In contrast to this, feeding of the non-metabolisable sucrose analogue, palatinose, leads to a similar activation as with sucrose, indicating that metabolism of sucrose is not necessary in the sucrose-dependent AGPase activation. The influence of sucrose and glucose on redox activation of AGPase was also investigated in discs cut from tubers of antisense plants with reduced SNF1-related protein kinase activity (SnRK1). Feeding of sucrose to tuber discs prevented AGPase redox inactivation in the wild type but not in SnRK1 antisense lines. However, feeding of glucose leads to a similar activation of AGPase in the wild type and in SnRK1 transformants. AGPase redox activation was also increased in transgenic tubers with ectopic overexpression of invertase, containing high levels of glucose and low sucrose levels. Expression of a bacterial glucokinase in the invertase-expressing background led to a decrease in AGPase activation state and tuber starch content. These results show that both sucrose and glucose lead to post-translational redox activation of AGPase, and that they do this by two different pathways involving SnRK1 and an endogenous hexokinase, respectively.

Enzyme Activation↗
PubMed2025

An allelic resolution gene atlas for tetraploid potato provides insights into tuberization and stress resilience.

Tubers are modified underground stems that enable asexual, clonal reproduction and serve as a mechanism for overwintering and avoidance of herbivory. Tubers are wide-spread across angiosperms with some species such as Solanum tuberosum L. (potato) serving as a vital crop for human consumption. Genes responsible for tuber initiation and disease resistance have been characterized in potato including StSP6A, a homolog of Flowering Time, that functions as tuberigen, the equivalent of florigen. To elucidate additional molecular and genetic mechanisms underlying potato biology including tuber initiation, tuber development, and stress responses, we generated a developmental and abiotic/biotic-stress gene expression atlas from 34 tissues and treatments of Atlantic, a tetraploid cultivar. Using the haplotype-phased tetraploid Atlantic genome assembly and expression abundances of 129,218 genes, we constructed gene coexpression modules that represent networks associated with distinct developmental stages as well as stress responses. Functional annotations were given to modules and used to identify genes involved in tuberization and stress resilience. Structural variation from a pan-genomic analysis across four cultivated potato genome assemblies as well as domestication and wild introgression data allowed for deeper insights into the modules to identify key genes involved in tuberization and stress responses. This study underscores the importance of transcriptional regulation in tuberization and provides a comprehensive framework for future research on potato development and improvement.

Journal Article↗
PubMed1994

Expression of lipoxygenase in wounded tubers of Solanum tuberosum L.

A lipoxygenase cDNA clone from Solanum tuberosum L. was analyzed to study the role of lipoxygenases in potato development and wound response. Sequence analysis and comparison of the deduced amino acid sequence revealed high homology to other plant lipoxygenases. Expression of the cDNA sequences in Escherichia coli and subsequent analysis of bacterial protein extracts showed lipoxygenase activity using linoleic, linolenic, or arachidonic acid as substrates. Transcripts encoding the potato lipoxygenase were most abundant in tuber tissue, lower in roots, and hardly detectable in leaves, petioles, and stems. The induction of lipoxygenase expression in tubers by wounding was dependent on various parameters. Whereas lipoxygenase transcript levels increased in discs from stored tubers incubated under aerobic conditions, tubers taken from a growing plant did not accumulate lipoxygenase transcripts in response to wounding. Incubation of tuber discs in buffer did not lead to an increase in lipoxygenase RNA levels; however, methyl jasmonate stimulated lipoxygenase expression after 24 h in stored tubers. Proteinase inhibitor II mRNAs decreased in stored tubers as well as in discs from growing tubers.

Amino Acid Sequence↗
PubMed1996

Oxidative Stress Results in Increased Sinks for Metabolic Energy during Aging and Sprouting of Potato Seed-Tubers.

Glutathione-mediated free-radical-scavenging and plasma membrane ATPase activities increase as sinks for metabolic energy with advancing tuber age. Plasma membrane ATPase activity from 19-month-old tubers was 77% higher than that from 7-month-old tubers throughout sprouting. The higher activity was not attended by an increase in the amount of ATPase per unit plasma membrane protein. Concentrations of oxidized (GSSG) and reduced glutathione more than doubled as tuber age advanced from 6 to 30 months, but the proportion of GSSG to total glutathione remained constant with age. The activity of glutathione transferase, an enzyme that catabolizes lipid-hydroperoxides, increased by 44 and 205% on a fresh weight and protein basis, respectively, as tubers aged from 6 to 30 months. Glutathione reductase activity also increased with advancing age, by 90% on a fresh weight basis and 305% on a protein basis. Older tubers had more glutathione reductase per unit of soluble and mitochondrial protein. The age-induced increase in cytosolic glutathione transferase activity was likely due to increased availability of lipid-hydroperoxides and/or a positive effector. Synthesis of glutathione requires ATP, and the increased reduction of GSSG resulting from catalysis of lipid-hydroperoxides is NADPH-dependent. Thus, increased plasma membrane ATPase and glutathione-mediated free-radical-scavenging activities likely constitute substantial sinks for ATP in older tubers prior to and during sprouting. Increased oxidative stress and loss in membrane integrity and central features of aging that undoubtedly contribute to the enhanced respiration of sprouting older tubers.

Journal Article↗
PubMed1973

Effects of Oxygen and Respiratory Inhibitors on Induction and Release of Dormancy in Aerial Tubers of Begonia evansiana.

Effects of O(2) and some respiratory inhibitors on the induction and release of bud dormancy were examined with the aerial tubers of different ages of Begonia evansiana Andr. Oxygen was needed not only for tuber sprouting but also during the chilling process at 2 to 5 C to break tuber dormancy. If the mature tubers were exposed to blue light during the chilling period, their dormancy was strikingly released even by the chilling given under an O(2) concentration as low as 3%. Blue light pretreatment promoted photo-sprouting of immature tubers only when given under lower O(2) concentrations. On the other hand, red light became effective in inducing dormancy in the immature tubers and in prolonging dormancy in the mature tubers as O(2) tension was increased. This was also the case with the induction of dormancy in the immature tubers by exposing them to a lower temperature (17 C) in the dark. The development of dormancy was suppressed by 2,4-dinitrophenol, p-nitrophenol, and sodium azide.

Journal Article↗
PubMed1978

Pentose phosphate metabolism of potato tuber discs as influenced by prior storage temperature.

Tubers of Solanum tuberosum L. var. Russet Burbank, Kennebec, and Targhee were stored at 95% relative humidity and at 1.7, 4.4, 5.8, 7.2 or 10 C. Rates of O(2) consumption were measured periodically by removing individual tubers from storage, excising discs of pith parenchyma tissue, and incubating the discs in a Gilson respirometer at 30 C. With all three varieties, data suggest a greater involvement of pentose phosphate metabolism with tissues from tubers stored at 1.7 C as compared to those from higher temperatures. Discs from tubers stored at 1.7 C had higher respiratory quotient values (CO(2)/O(2)), were substantially less sensitive to the inhibitory effects of iodoacetic acid, and were somewhat more sensitive to the inhibitory effects of salicylhydroxamic acid than the discs from tubers stored at higher temperatures. Using [(14)C]glucose labeled in the 1 or the 6 carbon, mean C(1) to C(6) ratios in the Gilson after 3.5 hours of aging were 4.8:1 with discs from tubers stored at 1.7 C and 2.5:1 with discs from tubers stored at 7.2 C. Prior storage history is important in metabolic studies using potato tubers.

Journal Article↗
PubMed1983

Induction and accumulation of major tuber proteins of potato in stems and petioles.

A family of immunologically identical glycoproteins with apparent molecular weights of approximately 40,000 are among the major tuber proteins of potato (Solanum tuberosum L.). These proteins, as purified by ion-exchange and affinity chromatography, have been given the trivial name ;patatin.' To determine if patatin can be used as a biochemical marker to study the process of tuberization, its amount was measured in a variety of tissues by rocket immunoelectrophoresis and by enzyme-linked immunosorbent assay (ELISA).Patatin comprises 40 to 45% of the soluble protein in tubers regardless of whether they are formed on underground stolons or from axillary buds of stem cuttings. Under normal conditions, patatin is present in only trace amounts, if at all, in leaves, stems, or roots of plants which are either actively forming tubers or which have been grown under long days to prevent tuberization. However, if tubers and axillary buds are removed, patatin can accumulate in stems and petioles. This accumulation occurred without any obvious tuber-like swelling and would occur even under long days. In all tissues containing large amounts of patatin, the other tuber proteins were also found as well as large amounts of starch.

Journal Article↗
PubMed2002

Starch synthesis in potato tubers is regulated by post-translational redox modification of ADP-glucose pyrophosphorylase: a novel regulatory mechanism linking starch synthesis to the sucrose supply.

Transcriptional and allosteric regulation of ADP-Glc pyrophosphorylase (AGPase) plays a major role in the regulation of starch synthesis. Analysis of the response after detachment of growing potato tubers from the mother plant revealed that this concept requires extension. Starch synthesis was inhibited within 24 h of tuber detachment, even though the catalytic subunit of AGPase (AGPB) and overall AGPase activity remained high, the substrates ATP and Glc-1-P increased, and the glycerate-3-phosphate/inorganic orthophosphate (the allosteric activator and inhibitor, respectively) ratio increased. This inhibition was abolished in transformants in which a bacterial AGPase replaced the potato AGPase. Measurements of the subcellular levels of each metabolite between Suc and starch established AGPase as the only step whose substrates increase and mass action ratio decreases after detachment of wild-type tubers. Separation of extracts on nonreducing SDS gels revealed that AGPB is present as a mixture of monomers and dimers in growing tubers and becomes dimerized completely in detached tubers. Dimerization led to inactivation of the enzyme as a result of a marked decrease of the substrate affinity and sensitivity to allosteric effectors. Dimerization could be reversed and AGPase reactivated in vitro by incubating extracts with DTT. Incubation of tuber slices with DTT or high Suc levels reduced dimerization, increased AGPase activation, and stimulated starch synthesis in vivo. In intact tubers, the Suc content correlated strongly with AGPase activation across a range of treatments, including tuber detachment, aging of the mother plant, heterologous overexpression of Suc phosphorylase, and antisense inhibition of endogenous AGPase activity. Furthermore, activation of AGPase resulted in a stimulation of starch synthesis and decreased levels of glycolytic intermediates.

Chloroplasts↗
PubMed2001

Tuberization in potato involves a switch from apoplastic to symplastic phloem unloading.

Phloem unloading was studied in potato plants in real time during the early stages of tuberization using carboxyfluorescein (CF) as a phloem-mobile tracer, and the unloading pattern was compared with autoradiography of tubers that had transported (14)C assimilates. In stolons undergoing extension growth, apoplastic phloem unloading predominated. However, during the first visible signs of tuberization, a transition occurred from apoplastic to symplastic transport, and both CF and (14)C assimilates subsequently followed identical patterns of phloem unloading. It is suggested that the switch to symplastic sucrose unloading may be responsible for the upregulation of several genes involved in sucrose metabolism. A detailed analysis of sugar levels and (14)C sugar partitioning in tuberizing stolons revealed a distinct difference between the apical region of the tuber and the subapical region. Analysis of invertase activity in nontuberizing and tuberizing stolons revealed a marked decline in soluble invertase in the subapical region of swelling stolons, consistent with the switch from apoplastic to symplastic unloading. However, cell wall-bound invertase activity remained high in the apical 1 to 2 mm of tuberizing stolons. Histochemical analysis of potato lines transformed with the promoter of an apoplastic invertase gene (invGE) linked to a reporter gene also revealed discrete gene expression in the apical bud region. Evidence is presented that the apical and lateral tuber buds function as isolated domains with respect to sucrose unloading and metabolism.

Carbohydrate Metabolism↗
PubMed2004

Modulation of Corydalis tuber on glycine-induced ion current in acutely dissociated rat periaqueductal gray neurons.

Traditionally, Corydalis tuber has been used for the control of pain including headache, stomach ache, and neuralgia. In the present study, modulation of the Corydalis tuber on glycine-activated ion current in the acutely dissociated periaqueductal gray (PAG) neurons was studied by a nystatin-perforated patch-clamp technique. High concentrations of Corydalis tuber elicited ion current, which was suppressed by strychnine application, while low concentrations of Corydalis tuber reduced glycine-induced ion current in the PAG neurons. Inhibitory action of Corydalis tuber on glycine-activated ion current was partially abolished by treatment with naltrexone, a non-selective opioid antagonist. Application of N-methylmalemide (NEM), a sulfhydryl alkylating agent, also partially abolished the inhibitory action of Corydalis tuber on glycine-activated ion current in the PAG neurons. These results suggest that the inhibitory effect of Corydalis tuber on glycine-activated ion current in the PAG neurons is one of the analgesic mechanisms of the Corydalis tuber.

Animals↗
PubMed1996

Embryonic neuronal markers in tuberous sclerosis: single-cell molecular pathology.

One hallmark of tuberous sclerosis (TSC) is the presence of highly epileptogenic dysplastic cerebral cortex (tubers) composed of abnormally shaped neurons and giant cells. Mutation of the TSC gene (TSC2) may disrupt differentiation and maturation of neuronal precursors, since the TSC2 gene product tuberin is believed to regulate cellular proliferation. To test the hypothesis that cells in tubers may retain the molecular phenotype of embryonic or immature neurons, tubers from five TSC patients were probed with antibodies to proteins expressed in neuronal precursors (nestin, Ki-67, and proliferating cell nuclear antigen). Many dysmorphic neurons and giant cells in tubers were stained by these antibodies, while neurons in adjacent normal and control cortex were not labeled. To further characterize the molecular phenotype of cells in tubers, we developed a methodology in which poly(A)+ mRNA was amplified from immunohistochemically labeled single cells in paraffin-embedded brain specimens. This approach enabled us to detect mRNAs encoding nestin, and other cytoskeletal elements, cell cycle markers, and synthetic enzymes present in individual nestin-stained cells by means of reverse Northern blotting. We conclude that the presence of immature phenotypic markers (mRNAs and proteins) within tubers suggests disruption of cell cycle regulation and neuronal maturation in TSC during cortical development. Characterization of multiple mRNAs within fixed, immunohistochemically labeled cells provides a powerful tool for studying gene expression and the molecular pathophysiology of many neurologic diseases.

Biomarkers↗
PubMed2001

Selective alterations in glutamate and GABA receptor subunit mRNA expression in dysplastic neurons and giant cells of cortical tubers.

The molecular pharmacologic basis of epileptogenesis in cortical tubers in the tuberous sclerosis complex is unknown. Altered transcription of genes encoding glutamatergic and gamma-aminobutyric acid (GABA)-ergic receptors and uptake sites may contribute to seizure initiation and may occur selectively in dysplastic neurons and giant cells. Arrays containing GABA A (GABAAR), GluR, NMDA receptor (NR) subunits, GAD65, the vesicular GABA transporter (VGAT), and the neuronal glutamate transporter (EAAC1) cDNAs were probed with amplified poly (A) mRNA from tubers or normal neocortex to identify changes in gene expression. Increased levels of EAAC1, and NR2B and 2D subunit mRNAs and diminished levels of GAD65, VGAT, GluR1, and GABAAR alpha1 and alpha2 were observed in tubers. Ligand-binding experiments in frozen tuber homogenates demonstrated an increase in functional NR2B-containing receptors. Arrays were then probed with poly (A) mRNA from single, microdissected dysplastic neurons, giant cells, or normal neurons (n = 30 each). Enhanced expression of GluR 3, 4, and 6 and NR2B and 2C subunit mRNAs was noted in the dysplastic neurons, whereas only the NR2D mRNA was upregulated in giant cells. GABAAR alpha1 and alpha2 mRNA levels were reduced in both dysplastic neurons and giant cells compared to control neurons. Differential expression of GluR, NR, and GABAAR mRNAs in tubers reflects cell-specific changes in gene transcription that argue for a distinct molecular phenotype of dysplastic neurons and giant cells and suggests that dysplastic neurons and giant cells make differential contributions to epileptogenesis in the tuberous sclerosis complex.

Adolescent↗
PubMed2004

Cerebral diffusion tensor images in children with tuberous sclerosis: a preliminary report.

BACKGROUND: In tuberous sclerosis (TS), tubers usually involve the white matter. Diffusion tensor (DT) images are used to demonstrate white-matter tracts. OBJECTIVE: To determine the changes in DT indices in supratentorial tubers and associated changes in the white-matter tracts adjacent to tubers in patients with TS. MATERIALS AND METHODS: The DT imaging indices, including first, second and third eigenvalues (EVs), apparent diffusion coefficients (ADCs), and fractional anisotropy (FA) in the white-matter lesions of tubers, were assessed in seven patients with TS exhibiting developmental delay and compared with controls. RESULTS: EV1, EV2, EV3, ADC and FA of the white-matter lesions of tubers were significantly different from contralateral unremarkable regions of the brain and from controls (P<0.05). The number of frontal and parietal tubers was significantly negatively correlated with EV1 of the superior longitudinal fasciculi of TS patients (r=-0.60, P =0.04). In addition, TS patients had significantly larger ADCs in the corona radiata and sagittal stratum than the control subjects. EV3s of the inferior longitudinal fasciculus and sagittal stratum were significantly more increased in the TS patients than in the control subjects. CONCLUSIONS: EV1, EV2, EV3, ADC and FA maps are potential tools for demonstrating cerebral white-matter changes owing to TS.

Adolescent↗
PubMed2005

Volumetric localization of epileptic activities in tuberous sclerosis using synthetic aperture magnetometry.

BACKGROUND: Magnetoencephalography (MEG) is a novel noninvasive technique for localizing epileptic zones. Tuberous sclerosis complex (TSC) is often associated with medically refractory epilepsy with multiple epileptic zones. Surgical treatment of TSC requires accurate localization of epileptogenic tubers. OBJECTIVE: The objective of this study was to introduce a new MEG technique, synthetic aperture magnetometry (SAM), to volumetrically localize irritable zones and clarify the correlations between SAM, dipole modeling and anatomical tubers. MATERIALS AND METHODS: Eight pediatric patients with TSC confirmed by clinical and neuroimaging findings were retrospectively studied. MEG data were recorded using a whole-cortex CTF OMEGA system. Sleep deprivation was employed to provoke epileptiform activity. Irritable zones were localized using both dipole modeling and SAM. RESULTS: MRI detected 42 tubers in the eight patients. Dipole modeling localized 28 irritable zones, and 19 out of the 28 zones were near tubers (19/42, 45%). SAM found 51 irritable zones, and 31 out of the 51 zones were near tubers (31/42, 74%). Among the 51 irritable zones determined by SAM, thirty-five zones were in 1-35 Hz, nine zones were in 35-60 Hz, and seven zones were in 60-120 Hz. CONCLUSIONS: The new method, SAM, yielded very plausible equivalent sources for patients who showed anatomical tubers on MRI. Compared to conventional dipole modeling, SAM appeared to offer increased detection of irritable zones and beneficial volumetric and frequency descriptions.

Brain Mapping↗
PubMed1989

Absence of linkage of ABO blood group locus to familial tuberous sclerosis.

A mutation leading to tuberous sclerosis was linked to the ABO blood group locus (9q34) on the long arm of chromosome 9. In an effort to confirm this assignment, nine multigenerational families with tuberous sclerosis, comprising 126 sampled individuals, were assessed for linkage of the ABO locus to tuberous sclerosis. Two-point linkage analysis and multilocus linkage analysis were used to evaluate linkage between tuberous sclerosis and the markers ABO, MCT136, and AblK2. Linkage of ABO to tuberous sclerosis was excluded for a distance of 20 centimorgans (cM) encompassing the region of the ABO locus. There was no evidence for genetic heterogeneity within this data set. Using 23 polymorphic markers, exclusion mapping demonstrated only a 1% probability that the tuberous sclerosis locus was on the distal short arm of chromosome 9 and provided no evidence in support of a tuberous sclerosis locus on the remainder of chromosome 9 including the area of the ABO locus.

ABO Blood-Group System↗