Activity In Tubers Research Articles

Potato infection with viruses in the Republic of Bashkortostan and ribonuclease activity in tubers

The paper presents the results of enzyme immunoassay (ELISA) of the presence of potato viruses S (PVS), M (PVM), Y (PVY), X (PVX), and Potato Leaf Roll Virus (PLRV) in tubers of various potato varieties grown in 2019 in the Republic of Bashkortostan. PVS, PVM, PVY, PVX were detected, the VSLK virus was not detected. The greatest infection with PVS, PVM, and PVX was observed in samples of tubers of early-maturing varieties. Tubers of mid-early and late-maturing varieties were more often affected by PVY than early-maturing ones, and PVX was not detected in plants of those varieties. Ribonuclease (RNase) activity in potato tubers of 14 varieties depended on the earliness of the variety, regardless of the soil and climatic conditions. A statistically significant positive correlation (P<0.05) was found between the abundance of PVS and PVM viruses and RNase activity in tubers of medium-early and late-maturing varieties, whereas, on the contrary, a negative correlation between PVM and RNase activity was revealed when analyzing tubers of early-maturing varieties. It is concluded that the prevalence of potato viruses in the territory of the Republic of Bashkortostan and the activity of RNase in tuber seedlings depend on the potato variety and the type of viruses.

Storage Property Is Positively Correlated With Antioxidant Capacity in Different Sweet Potato Cultivars.

Sweet potato decays easily due to its high respiration rate and reactive oxygen species (ROS) accumulation during postharvest storage. In this study, we explored the relationship between antioxidant capacity in leaves and storage properties in different sweet potato cultivars, the tuberous roots of 10 sweet potato cultivars were used as the experimental materials to analyze the storage property during storage at 11–15°C. According to the decay percentage after 290 days of storage, Xu 32 was defined as a storage-tolerant cultivar (rot percentage less than 25%); Xu 55-2, Z 15-1, Shangshu 19, Yushu, and Zhezi 3 as above-moderate storage-tolerant cultivars (rot percentage ranging from 25 to 50%); Sushu 16, Yanshu 5, and Hanzi as medium-storable cultivars (rot percentage 50–75%); and Yan 25 as a storage-sensitive cultivar (rot percentage greater than 75%). Meanwhile, analysis of the α-amylase activity in root tubers of the 10 sweet potato cultivars during storage indicated that α-amylase activity was lowest in the storage-tolerant cultivar Xu 32 and highest in the storage-sensitive cultivar Yan 25. Evaluation of antioxidant enzyme activities and ROS content in the leaves of these 10 cultivars demonstrated that cultivar Xu 32, which showed the best storage property, had higher antioxidant enzyme activity [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and peroxidase (POD)] but lower lipoxygenase (LOX) activity, hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, and superoxide anion radical (O2⋅–) production rates compared with those of the storage-sensitive cultivar Yan 25 and the medium-storability cultivars Hanzi, Yanshu 5, and Sushu 16. Additionally, principal component analysis (PCA) suggested that sweet potato cultivars with different storage properties were clustered separately. Correlation and heat map analysis further indicated that CAT, APX, POD, and SOD activities were negatively correlated with α-amylase activity, while LOX activity and MDA and H2O2 contents were negatively correlated with the storage property of sweet potato. Combined, our findings revealed that storage property is highly correlated with antioxidant capacity in sweet potato leaves and negatively correlated with α-amylase activity in tuberous roots, which provides a convenient means for the screening of storage-tolerant sweet potato cultivars.

Effect of Drip Fertigation with Nitrogen Application on Bioactive Compounds and the Nutritional Value of Potato Tubers before and after Their Long-Term Storage

The nutritional value and the content of bioactive compounds in potato tubers are influenced by many soil, climate and agrotechnical factors. This study investigated the effect of drip irrigation and nitrogen fertilization by broadcasting and fertigation on the content of dry matter, starch, monosaccharides, total sugars, vitamin C, polyphenolic compounds, chlorogenic acid and antioxidant activity in tubers of “Augusta” potatoes. Additionally, the magnitude of the changes in the tested components during their long-term storage (6 months) was also assessed. Drip irrigation had a significant positive effect on the content of dry matter, starch, vitamin C, monosaccharides, sucrose, total sugars, total polyphenols, chlorogenic acid and antioxidant capacity. Compared to broadcasting fertilization, fertigation significantly increased the content of vitamin C, total polyphenols and chlorogenic acid, as well as the antioxidant activity of potato tubers. Long-term storage contributed to a decrease in the tested components. The exception was the content of monosaccharides, where a more than twofold increase was noted, especially in the case of irrigated tubers. The results of the research showed a beneficial effect of drip irrigation and fertigation on the content of bioactive compounds and the nutritional value of “Augusta” potato tubers.

Antioxidant activity of tuber apical and basal ends of potato during cold storage

ABSTRACT Little is known about relation between cold-induced sweetening (CIS) resistance and antioxidant activity of Irish potato (Solanum tuberosum L) tubers during cold storage. Tuber ends produce more CIS than the rest of the tuber, and ends vary for dry matter and carbohydrate metabolism during storage but have not been sufficiently studied for antioxidants. Antioxidant activity of basal and apical tuber ends of potato genotypes, which varied in processing quality, was studied in 4°C storage up to 150 d after harvest. During 0–20 d period, there was a decrease of some antioxidants, but levels at 20 d remained higher in processing genotypes while H2O2 and malondialdehyde levels were higher in non-processing genotypes. During 20–120 d, non-enzymatic antioxidants increased, but decreased from 120 to 150 d. Among enzymatic antioxidants, catalase increased while other enzymatic antioxidants decreased to 120 d and then remained stable to 150 d. The H2O2/nitric oxide, malondialdehyde, and protein carbonyls increased during storage. Antioxidant levels were higher in apical than basal ends during storage. Antioxidant activity relates to H2O2/nitric oxide signals and tuber quality during storage and relates to processing quality of the genotype. The antioxidant activity of tubers during storage may be regulated by H2O2/nitric oxide signals and is important for CIS-resistance and tuber quality. Tuber apical end may have higher antioxidant activity than basal end during storage. Antioxidant activity of the tuber during cold storage can be used as a marker to screen potato genotypes for CIS-resistance and quality storage.

Ralstonia solanacearum as a potato pathogen in Serbia: Characterization of strains and influence on peroxidase activity in tubers

AbstractSince 2011, the outbreaks of brown rot caused by Ralstonia solanacearum race 3, biovar 2, phylotype IIB‐1 (R3/B2/PIIB‐1) have significantly compromised potato production in Serbia. During 6 years of monitoring (2013–2018) among 3,524 potato tuber samples, 344 were found positive for brown rot disease. R. solanacearum R3/B2/PIIB‐1 was isolated from seven cultivars among 12 monitored, and in five localities among 17 monitored. Cultivar Lady Claire was found to have the highest disease frequency (31.98%). A total of 78 isolates were identified by R. solanacearum‐specific primer pairs (PS‐1/PS‐2 and OLI‐1/Y‐2), as well as the following tests: restriction fragment length polymorphism analysis, biovar determination, immunofluorescence, biochemical analysis, and pathogenicity. The genetic composition of 36 selected isolates assessed using multilocus sequence analysis with seven genes (adk, gapA, gdhA, gyrB, ppsA, hrpB, and fliC) showed that all isolates originating from Serbian potato were homogeneous. By using the TCS algorithm of concatenated sequences to get insight into the phylogeography of isolates and other R. solanacearum strains deposited in the NCBI database, we showed that their origin is undetermined. Peroxidase (POD) activity was measured in brown rotted potato tubers. A positive correlation was found between POD activity and disease severity rated on the analysed tubers. In general, POD activity increased by 2–22 times in vascular necrotic tissues compared to non‐necrotic ones, and depended on disease severity but not on cultivar. Native polyacrylamide gel electrophoresis analysis of POD profiles resulted in a total of 10 distinct POD isoforms, of which PODs 3–5 were highly intensified in response to R. solanacearum.

Physiological and Physicochemical Responses of Potato to Selenium Biofortification in Tropical Soil

The technique of biofortification with selenium (Se) in several agricultural crops has been well researched by the scientific community. However, for vegetable crops cultivated in tropical conditions, there is still little information. The objective of this study was to evaluate the effect of the application of Se in the soil on physiological, agronomic, biofortification and antioxidant enzyme activity in tubers of Solanum tuberosum L. grown in tropical soil. Potato plants (cv. Agata) were cultivated in pots (7 kg) with soil that received two sources of Se (selenate and selenite) and five doses of Se (0; 0.75; 1.5; 3.0 and 5.0 mg kg−1). The results showed that the application of Se by both sources increased its content in the tubers. When applied in small doses, it provided beneficial effects on the production of tubers, increased Ca content in shoots and activated enzymes of the antioxidant system. High doses, in addition to decreasing production, reduced S content, pH and peroxidase activity in the tubers. Thus, selenate is the most efficient source for biofortification of potato under tropical conditions when supplied in low doses.

Spatiotemporal activities of Douglas-fir BiP Pro1 promoter in transgenic potato.

The PmBiPPro1 promoter of the luminal binding protein (BiP) from Douglas-fir is fully functional in transgenic potato, responsive to wounding, and has high transcriptional activity in tubers. A predefined pattern and level of transgene expression targeted to specific tissues or organs and at a particular developmental stage is a pre-requisite for the successful development of plants with desired traits. Here, we evaluated the transcriptional activity of the PmBiPPro1 promoter of the luminal binding protein (BiP) from Douglas-fir, by expressing reporter β-D-glucuronidase (GUS) gene constructs containing three different PmBiPPro1 promoter versions (2258bp, 1259bp, and 278bp) in transgenic potato. In conifers, this promoter regulates the endoplasmic reticulum (ER) molecular chaperon of the HSP70 stress-related protein family and is essential for proper functioning of the ER. Stable expression analysis demonstrated that two of three PmBiPPro1 promoter versions (PmBiPPro1-1 and PmBiPPro1-3) were fully functional in the heterologous host, exhibited high transcriptional activities in the leaves of unstressed potatoes, and were responsive to wounding. Deletion analysis showed that the positive cis-active regulatory elements necessary for higher level expression resided within the - 1243 to - 261 region, whereas negative cis-active elements encompassed nucleotides - 2242 to - 1243. Histochemical staining revealed high level of GUS activities in tissues associated with a high rate of cell division and secretory activities. Most importantly, the PmBiPPro1 promoters, especially the full-length version, had activity in microtubers at a level that was much higher than in any other potato organ or tissue. The - 2242 to - 1243bp region likely contains important cis element(s) that interact with tuber-specific transcription factors required for promoter activation in the storage organs. The organ-specific activity of the PmBiPPro1 promoters may be useful for targeted expression of heterologous molecules in potato tubers.

Effect of biodynamic preparations on the phenolic antioxidants in potatoes with coloured-flesh

The aim of this research, which was undertaken in two years (2013–2014), was to evaluate the effect of cultivars and biodynamic (BD) preparations 500 and 501 on concentrations of phenolic compounds, quantitative and qualitative anthocyanins and phenolic acids compositions, and antioxidant activity in the tubers of coloured potatoes. It was shown that when sprayed with BD preparation 501, the concentrations of total phenolic compounds in the tubers of cultivars Blue Congo and Red Emmalie was significantly higher, 20.1 and 5.4%, respectively; anthocyanins were 59.8 and 10.4% higher, respectively and antioxidant activity was approximately 1.3 times higher in the two varieties. The use of both preparations (500 and 501) had significant effects on anthocyanins accumulation in the tubers of Blue Congo and Vitelotte. However, preparation 500 had the tendency to reduce the concentrations of antioxidant compounds and antioxidant activity in tubers of all potato cultivars. The cultivar was a dominant factor affecting the phenolic antioxidants and the highest concentrations of phenolic compounds, anthocyanins and phenolic acids and the highest antioxidant activity found in the tubers of Vitelotte. Malvidin and petunidin compounds were identified as the main anthocyanins in the tubers of Blue Congo and Vitelotte, and pelargonidin compounds in Red Emmalie. The predominant phenolic acid was chlorogenic acid. A strong positive correlation was determined between antioxidant activity and the concentration of total phenolic compounds (r = 0.953, p < 0.01) as well as total phenolic acids (r = 0.951, p < 0.01).

Structure of Two Solanum tuberosum Steroidal Glycoalkaloid Glycosyltransferase Genes and Expression of their Promoters in Transgenic Potatoes

The Sgt2 gene in potato encodes a solanidine glucosyltransferase and is present as two distinct alleles expressed in cultivated potatoes. Promoter regions of both steroidal glycoalkaloid biosynthetic gene alleles, Sgt2.1 and Sgt2.2, were isolated from Solanum tuberosum cv. Russet Burbank genomic DNA. The genomic sequences of Sgt2.1 and Sgt2.2 were isolated by PCR amplification using a conserved region of Sgt2 and artificial upstream primers. The longest sequences for each allele were used to create β-glucuronidase (GUS) reporter gene fusions. Fusion constructs were mobilized into stable transgenic lines for analysis of promoter expression in leaves and tubers under control and wounded conditions. S. tuberosum promoters from Sgt2.1 and from Sgt2.1 produced GUS activity in transgenic potato leaves and tubers comparable to GUS activity produced by the CaMV35S promoter. The CaMV35S promoter is a strong promoter frequently used in plant biotechnology. Both Sgt2 promoters exhibited activities similar to the CaMV35S promoter in tubers and lower relative activities in leaves. On average the Sgt2.2 promoter exhibited higher activity in both leaves and tubers relative to the Sgt2.1. There was no consistent effect of wounding on GUS activity from the Sgt2.2 promoter in leaves or tubers. The Sgt2.1 promoter supported higher transgene activity in tubers versus leaves and exhibited small but consistent increases in response to wounding in tubers only. This may be due to the presence of a MITE sequence in the Sgt2.1 promoter.

Bromoethane-induced changes in respiration rate, ethylene synthesis, and enzyme activities in potato tubers in relation to dormancy breakage

SummaryThis paper describes the effect of bromoethane, which promotes the breakage of dormancy of potato tuber buds, on the metabolic activity of tubers, up to the stage of visible sprouting. The respiratory activity of treated tubers increased to a maximum 2 d after treatment, which, despite a subsequent decline, remained at a higher level than that of untreated controls for a further 8 d. Similarly, bromoethane induced a higher level of ethylene release from tubers over 10 d from its application compared to the controls. With the exception of invertases (acid and alkaline), all the other enzymes studied (i.e., hexokinase, fructokinase, glucose-6-phosphate dehydrogenase, uridine-5-diphosphoglucose pyrophosphorylase, adenosine-5-diphosphoglucose pyrophosphorylase and -glucosidase) exhibited higher rates of activity in bromoethane-treated tubers than in the controls. From the results of this study, it appears that the application of bromoethane increased the metabolic activity of potato tubers prior to the first visible sign of bud sprouting, which occurred approx. 10 d after treatment.

Normal starch content and composition in tubers of antisense potato plants lacking D-enzyme (4-α-glucanotransferase)

Transgenic potato (Solanum tuberosum L.) plants were created with sense and antisense copies of the potato D-enzyme (disproportionating enzyme; EC␣2.4.1.25) cDNA linked to patatin and cauliflower mosaic virus 35 S promoters, and screened for D-enzyme activity in tubers. Transformants with sense constructs mostly had wild type D-enzyme activity but two plants had only about 1% wild-type activity. Transformants with antisense constructs had activity ranging from 90% to about 1% of wild type. Three 35 S antisense plants with very low activity were analysed in detail. Western blot analysis showed that D-enzyme was present in greatly reduced amounts in tubers and in leaves, whereas plastidic starch phosphorylase (EC 2.4.1.1) was unaffected. The lack of D-enzyme resulted in slow plant growth but development was otherwise apparently normal. Furthermore, the starch content of tubers was not appreciably altered in amount, proportion of amylose, molecular weight of debranched amylopectin, or branch chain length, despite the lack of D-enzyme. These results do not indicate a direct requirement for D-enzyme in the synthesis and accumulation of storage starch in tubers. The results are discussed in terms of the known reactions catalysed by D-enzyme and possible involvement of D-enzyme in starch metabolism.

Antisense expression of a sucrose non‐fermenting‐1‐related protein kinase sequence in potato results in decreased expression of sucrose synthase in tubers and loss of sucrose‐inducibility of sucrose synthase transcripts in leaves

SummaryThis report describes the analysis of transgenic potato plants stably transformed with chimeric genes comprising either a patatin (tuber‐specific) or a ST‐LS1 (leaf‐ and stem‐specific) gene promoter and a potato sucrose non‐fermenting‐1 (SNF1)‐related protein kinase gene (PKIN1) sequence in the antisense orientation. Presence of the transgene was confirmed by Southern analysis. The transformants were screened using a peptide kinase activity assay for SNF1‐related activity and/or Northern blot analysis, and two independent transgenic lines from each transformation, PAT 1.3, PAT 1.10, LS 1.4 and LS 1.11, were selected. Antisense PKIN1 transcripts were detectable in all four of the selected lines, and measurements made using the specific peptide phosphorylation assay showed that SNF1‐related protein kinase activity had decreased in both PAT 1.3 and PAT 1.10 compared with controls. SNF1 regulates the expression of many genes encoding enzymes of carbohydrate metabolism in yeast. In order to investigate an analogous role for PKIN1, the activities of fructokinase, glucokinase, neutral and acid invertase and sucrose synthase in the tubers of PAT 1.3 and PAT 1.10 were compared with those in wild‐type controls. Sucrose synthase activity was decreased to 36% of wild‐type activity in tubers of PAT 1.10, and sucrose synthase transcript levels were decreased in tubers of both PAT 1.3 and PAT 1.10. Activities of the other enzymes were unaffected. Leaves of lines LS 1.4, LS 1.11 and controls were then excised and cultured on a medium containing 250 mM sucrose. This treatment induced sucrose synthase gene expression in the control leaves but not those of the transgenic lines. This finding is the first demonstration of a role for SNF1‐related protein kinases in the regulation of carbohydrate metabolism of higher plants.

Effect of chlorocholine chloride sprays on the carbohydrate composition and activities of sucrose metabolising enzymes in potato (Solanum tuberosum L.)

Chlorocholine chloride (CCC) was sprayed on a potato crop 25 days after sowing (DAS) at 5 day intervals for a total of 7 sprays. Activity of sucrose synthase (SS) in the sucrose cleavage direction was many fold higher than that of acid invertase in all the tissues. The activity of alkaline invertase was negligible. A sharp decline in the starch content of stolons of the CCC-sprayed crop was observed between 60 DAS and 70 DAS. This could divert the carbon towards tubers and thus enhancing its availability for starch synthesis. The CCC-treated crop, in general, had higher SS (cleavage) activity in stem, stolons and tubers. A higher sucrose content in the stem of the CCC-treated crop could be due to the high sucrose phosphate synthase (SPS) activity observed in this plant part. In tubers of CCC-treated crops a higher SS (cleavage) activity along with a high sucrose content in tubers during the active tuber filling stage could lead to better availability of UDP-glucose for its conversion to glucose-1-phosphate, which could enter into the amyloplast leading to higher starch content. High SPS activity in tubers of CCC-treated plants ensures that reducing sugars formed are reconverted efficiently to sucrose. The efficiency of developing tubers from CCC-sprayed plants to convert 14C sucrose fed through stolons into starch was about 2.5 times more than in the control.

Catabolism of linamarin in cassava (Manihot esculenta crantz)

The catabolism of cyanoglucoside linamarin in cassava was examined by studying the activity and kinetic characteristics of various enzymes involved in these reactions in different tissues. Hydroxy-nitrile-lyase (HNLyase) which catalysed hydrolysis of acetone cyanohydrin to cyanide at pH 5.5 was present in leaf, rind and tuber and showed maximum activity in leaves. It followed a complex saturation kinetics and has a high Km value (30–50 mM). While rhodanese and thiocyanate levels are very low, significant activity of different enzymes of β-cyanoalanine pathway for utilisation of cyanide was found in leaf, rind and tuber tissues. β-cyanoalanine hydrolase which converts β-cyanoalanine to asparagine showed maximum activity in tuber when compared to leaf and rind, similar to that reported for β-cyanoalanine synthase. Significantly lower activity of asparaginase in tuber and its high Km value (500–625 mM) suggest that asparagine may accumulate in tuber while in leaf and rind it gets hydrolysed to ammonia. While the degradation of linamarin to cyanide occurs at acidic pH 5–6, the β-cyanoalanine pathway operates at alkaline pH 8–9 suggesting a compartmentalisation of these two processes.

A [beta]-Amylase in Potato Tubers Is Induced by Storage at Low Temperature.

A new starch-degrading enzyme activity is induced by storage of potato (Solanum tuberosum L.) tubers at low temperatures (L. Hill, R. Reimholz, R. Schroder, T.H. Nielsen, M. Stitt [1996] Plant Cell Environ 14: 1223-1237). The cold-induced activity was separated from other amylolytic activities in zymograms based on iodine staining of polyacrylamide gels containing amylopectin. A similar band of activity was detected at normal growth temperatures in leaves, stems, and growing tubers but was present only at low activity in warm-stored tubers. The cold-induced enzyme was separated by ion-exchange chromatography from other amylolytic activities. It has a broad neutral pH optimum. Characterization of its hydrolytic activity with different substrates showed that the cold-induced activity is a [beta]-amylase present at low activity in tubers stored at 20[deg]C and induced progressively when temperatures are decreased to 5 and 3[deg]C. The first clear induction of [beta]-amylase activity was observed within 3 d of storage at 3[deg]C, and the activity increased 4- to 5-fold within 10 d. The possible involvement of the cold-induced [beta]-amylase in sugar accumulation during cold storage is discussed.

Effect of Defoliation on Growth and Physiological Developments in Tubers of Purple Nutsedge (Cyperus rotundus L.)

AbstractThe starch metabolism and hydrolytic enzyme activities in growing tubers of purple nutsedge (Cyperus rotundus L.) in response to defoliation were examined to elucidate the regrowth physiology of the plant. Effects of complete or partial defoliation imposed at 2 or 4 weeks (single defoliation), or 2 and 4 weeks (repeated defoliation) after emergence (WAE) on plant growth were studied.Leaf area and leaf dry weight per plant in the control plots increased with time. In the mother tuber, dry weight and starch content were reduced by 16 % and 18 %, respectively, during the first 2 WAE, and then increased with time. Endoamylase (EC 3.2.1.1) activity of tubers (3.8 units g−1 dry tuber) increased by 42 % during the first 4 WAE, but decreased rapidly up to 8 WAE.Repeated defoliation significantly reduced the regrowth ability of nutsedge tubers when compared to single defoliation and the control. Repeated complete defoliation reduced the leaf area and leaf dry weight by 56 % and 69 %, respectively. The dry weights of mother tuber and total tubers 100 cm −2 were reduced by 41 % and 63 %, respectively, when compared to the control at 8 WAE. Endoamylase activity and starch content in the mother tuber in this treatment were reduced by 72 % and 56 %, respectively. Defoliation did not have any significant effect on the exoamylase activity.Endoamylase is the major starch hydrolysing enzyme in tubers and the activity of this enzyme could be a limiting factor in regrowth of nutsedge tubers. Repeated complete defoliation effectively suppressed the regrowth of purple nutsedge.

Cloning and characterization of a cathepsin D inhibitor gene from Solanum tuberosum L.

A DNA clone encoding a cathepsin D inhibitor CathInh was isolated from a potato genomic library using a CathInh cDNA as hybridization probe. The amino acid sequence of the coding region is nearly identical with a CathInh cDNA and CathInh proteins previously isolated from a tuber-specific cDNA library and from tubers, respectively. Analysis of GUS activity resulting from expression of chimeric CathInh promoter-GUS genes in transgenic potato plants revealed expression exclusively confined to potato tubers. No GUS activity could be detected in any other organ of the transgenic plants either constitutively or after wounding or treatment with abscisic and jasmonic acid (JA). Interestingly, part of the promoter region of the CathInh gene, essential for GUS activity in tubers, shows striking similarity to promoter regions of tuber-specific class I patatin genes.

Isolation of a ubiquitin-ribosomal protein gene (ubi3) from potato and expression of its promoter in transgenic plants

A genomic clone encoding the potato homolog of the yeast ubiquitin-ribosomal protein fusion gene ubi3 was isolated and characterized. Chimeric genes containing the ubi3 promoter (920 bp of 5' to the ubiquitin start codon) were constructed in which the reporter gene beta-glucuronidase (GUS) was either fused directly to the promoter, or introduced as a translational fusion to the ubiquitin-coding region. After introduction into the potato by Agrobacterium-mediated transformation, GUS activities were measured in leaves and in tubers of transgenic clones. GUS activity was 5- to 10-fold higher in clones expressing the ubiquitin-GUS translational fusion than in clones containing GUS fused directly to the ubi3 promoter. For both types of constructs, GUS activity was highest in meristematic leaves and declined during leaf expansion, then rose again to near the meristematic levels during senescence. GUS activity in tubers was similar to that in young leaves. In contrast to the native ubi3 genes, the chimeric ubi3-GUS transgenes were not activated in the tuber by wounding.

Partial purification from potato tubers of three fructokinases and three hexokinases which show differing organ and developmental specificity

A combination of chromatography on DE-52 cellulose, Cibacron Blue agarose, Mono Q anion exchanger and gel filtration was used to resolve different hexose-phosphorylating enzymes from growing “sink” potato tubers (Solanum tuberosum L.). Three enzymes (fructokinases: FK1, FK2 and FK3) are active with fructose and inactive with glucose, and three (hexokinases: HK1, HK2 and HK3) are active with glucose but not with fructose. Elution from DE-52 columns showed that the relative abundance of the six activities changes, depending on the organ and on the developmental stage. FK1 and FK2 were present at high activities in tubers but at very low activity in leaves; conversely FK3 was present at very low activity in tubers but at high activity in leaves. During storage of potato tuber, and also during sprouting, there was a decrease of FK1 and FK2. In contrast, glucose-phosphorylating activity was very low in growing tubers. During storage and sprouting the activity of the glucose-phosphorylating enzymes rose, until they exceeded FK1 and FK2. This was due particularly to an increase of HK1, whereas HK2 declined relative to HK1, and HK3 was always negligible. These changes in the pattern of hexose-phosphorylating enzyme forms are compared with the changing metabolic fluxes and pools of hexose sugars in potato tubers. It is concluded that organ- and development-specific changes in the abundance of the various enzyme forms contribute to the regulation of hexose metabolism in the potato.

Analysis of the region in between two closely linked patatin genes: class II promoter activity in tuber, root and leaf

From a potato genomic library a phage lambda clone was isolated that carried nucleotide sequences of two patatin genes, thus demonstrating a close physical linkage between these two members of the patatin gene family. Sequence and restriction analysis showed the genes to be oriented in tandem. The more upstream gene was a pseudogene truncated at the 3' end, whereas the downstream gene was a class II patatin gene. In addition to a 208 bp fragment also present in patatin class I promoters, the region in between both genes contained various direct repeats also found in other patatin genes. To study the promoter activity of this intergenic region, a 2.78 kb fragment was transcriptionally fused to the beta-glucuronidase gene and reintroduced into potato cultivar Bintje. Histochemical analysis revealed expression in the outermost layer of cells of the cortex, in the tuber phellogen, in or around the root vascular system, and also in the abaxial phloem layer of the vascular bundle in leaves.