Starch Synthesis in Developing Potato Tubers

The activities of enzymes involved in starch metabolism were measured at intervals during tuberization and the early stages of tuber growth in Solanum tubersum grown in water culture under controlled environmental conditions. Starch synthase, ADPglucose pyrophosphorylase, UDPglucose pyrophosphorylase and phosphorylase activities all increased during tuber development, the most pronounced increases occurring in the activities of ADP-glucose pyrophosphorylase and phosphorylase. The activity ratio ADPglucose pyrophosphorylase/phosphorylase was lowest in slow growing tubers and hightest in fast growing tubers. In addition, high sugar concentrations in fast growing tubers and low sugar concentrations in slow growing tubers suggested that enzyme levels might be influenced by sugar concentration. The activities of starch synthase, phosphorylase and ADPglucose pyrophosphorylase were increased 2–2.5 fold by the presence of 100 mM K⁺. It is concluded that the major enzyme changes occur as a consequence of tuber initiation and that starch accumulation is controlled, at least in part, by the activities of ADPglucose pyrophosphorylase and phosphorylase.     

Transport Pathways in Sprouting Tubers of the Potato

The transport of potassium, calcium, water, and carbohydratesfrom a potato tuber to a developing sprout has been followedover an 8-week period. From the resulting balance-sheet calculationshave been made of the concentration of ions in the xylem andphloem saps entering the sprout. Similarly, the concentrationof carbohydrates in the phloem has been calculated. Predictedionic concentrations in the xylem have been confirmed from analysesof xylem exudate. The pattern of results thus obtained indicatesthe presence of a circulatory system necessitating bidirectionaltransport within the phloem. The results obtained are thereforeinconsistent with the hypothesis that a mass flow of solutesis the mechanism of translocation within the phloem     

Sugar Transport into Protoplasts Isolated from Developing Soybean Cotyledons : II. Sucrose Transport Kinetics, Selectivity, and Modeling Studies

The effects of metabolic inhibitors, pH, and temperature on the kinetics of sucrose uptake protoplasts isolated from developing soybean Glycine max L. cv Wye cotyledons were studied. Structural requirements for substrate recognition by the sucrose carrier were examined by observing the effects of potential alternate substrates for the saturable component on sucrose uptake.     

Isolation, Crystallization, and Partial Identification of Potato Factor II from Potato Tubers

The isolation, crystallization, and partial identification of potato factor II, a stimulator from the chemically neutral fraction of potato extract, is described. The compound was originally found to stimulate elongation of dwarf peas grown under red light, a gibberellin bioassay. It melts between 137° and 139°. In paper chromatography it migrates to R_F 0.62 in isopropyl alcohol: ammonium hydroxide: H₂O (10:1:1, v/v). Based on infrared and NMR data, it does not contain a lactone ring and possibly possesses an amide radical and an OH⁻ group, as well as many methylene radicals. Potato factor II may be similar to certain of the fatty acid derivatives previously reported to stimulate growth of excised sections, but it is unique in that it stimulates growth of intact plants. This effect points to the need for completely separating neutral from acid gibberellin-like substances when the latter are assayed on dwarf peas.     

Purification and Properties of Fructokinase from Developing Tubers of Potato (Solanum tuberosum L.)

Fructokinase has been purified from developing potato (Solanum tuberosum L.) tubers by a combination of hydrophobic interaction, affinity chromatography, and gel filtration. The protein has a native molecular mass of approximately 70 kD but is apparently a dimer. Ion-exchange chromatography and two-dimensional western blots resolved three major fructokinases, designated FK-I, FK-II, and FK-III in order of their elution from a Mono-Q column. Fructokinase activity proved labile when proteins were purified in the absence of fructose. Kinetically, FKs I, II, and III all have broad pH optima with peaks at about pH 8.5. The enzymes have a high specificity for fructose (K_m values ranging from 0.041 to 0.128 mm), and can utilize a range of nucleoside triphosphates. Unlike FKs I and II, FK-III is not inhibited by fructose concentrations in excess of 1 mm. MgADP inhibited activity of the three FKs (between 68 and 75% inhibition at 1.0 mm), whereas fructose 6-P caused inhibition at concentrations of 10 mm. There were no regulatory effects observed with a range of other metabolites. K⁺ (10 mm) activated FK-I by 4-fold and FKs II and III by only about 50%.     

The Effect of Gamma-Irradiation on the Sucrose Content in Sweet Potato Roots and Potato Tubers

The sucrose content in both potato tubers and sweet potato roots was considerably increased by gamma-irradiation. The maximum increase was achieved by an irradiation dose of 3 to 4 kGy for potatoes and 0.8 to 2 kGy for sweet potatoes. Cooling treatment (15°C, 2 weeks) for sweet potato roots also enhanced the sucrose content (almost 2 times) but was not additive to the irradiation treatment; the maximum sucrose content in irradiated sweet potato roots was in the range of 7 to 12% irrespective of the cooling treatment, depending on the variety of sweet potatoes. Irradiation made the sucrose content in the roots 2 to 4 times higher.     

Detection of Potato Tuber-Inducing Activity in Potato Leaves and Old Tubers

Potato tuberization is induced under short days but substancewhich triggers it is still unknown. Tuber-inducing activitywas detected in leaves and old tubers using single-node stemsegment culture in vitro as a bioassay method. The activityin leaves increased under short days, but remained almost constantunder long days. It was also found in physiologically old tubers.Anion exchange chromatography of the ethanol extract gave aneluate that exhibited strong tuber-inducing activity. Partialpurification revealed the presence of two kinds of active substances,one of which seemed to be a glycoside of the other. These substancesappear to be different from known plant hormones. (Received October 19, 1987; Accepted June 9, 1988)     

Superoxide Dismutase, Catalase, and alpha-Tocopherol Content of Stored Potato Tubers

Activated oxygen or oxygen free radical mediated damage to plants has been established or implicated in many plant stress situations. The extent of activated oxygen damage to potato (Solanum tuberosum L.) tubers during low temperature storage and long-term storage is not known. Quantitation of oxygen free radical mediated damage in plant tissues is difficult. However, it is comparatively easy to quantitate endogenous antioxidants, which detoxify potentially damaging forms of activated oxygen. Three tuber antioxidants, superoxide dismutase, catalase, and α-tocopherol were assayed from four potato cultivars stored at 3°C and 9°C for 40 weeks. Tubers stored at 3°C demonstrated increased superoxide dismutase activities (up to 72%) compared to tubers stored at 9°C. Time dependent increases in the levels of superoxide dismutase, catalase, and α-tocopherol occurred during the course of the 40 week storage. The possible relationship between these increases in antioxidants and the rate of activated oxygen production in the tubers is discussed.     

Sucrose Synthetase of Rice Grains and Potato Tubers

ABSTRACT

Human coagulation factor XII, the initiating factor in the intrinsic coagulation pathway, is critical for pathological thrombosis but not for hemostasis. Pharmacologic inhibition of factor XII is an attractive alternative in providing protection from pathologic thrombus formation while minimizing hemorrhagic risk. Large quantity of recombinant active factor XII is required for screening inhibitors and further research. In the present study, we designed and expressed the recombinant serine protease domain of factor XII in Pichia pastoris strain X-33, which is a eukaryotic expression model organism with low cost. The purification protocol was simplified and the protein yield was high (~20 mg/L medium). The purified serine protease domain of factor XII behaved homogeneously as a monomer, exhibited comparable activity with the human βFXIIa, and accelerated clot formation in human plasma. This study provides the groundwork for factor XII inhibitors screening and further research.     

Sugar Transport into Storage Tubers of Stachys sieboldii Miq.: Evidence for Symplastic Unloading and Stachyose Uptake into Storage Vacuoles by an H+-Antiport Mechanism*

Following assimilation of ¹⁴CO₂ by leaves of Stachys sieboldii, ¹⁴C-stachyose is translocated into the tubers. Stachyose is accumulated and stored in the vacuoles of the pith parenchyma. Protoplasts and vacuoles were isolated and the uptake of sugars was examined. Uptake of sucrose and sucrosyl oligosaccharides of the raffinose family by protoplasts was very low compared to glucose. Transport parameters for glucose indicated a carrier mediated transport in the lower concentration range which was superimposed by diffusion at higher concentrations (> 10 mM). The very low sugar uptake by protoplasts and the sparse enzyme activities of stachyose synthase in the storage parenchyma as well as acid invertase and α-galactosidase in the cell walls indicated symplastic unloading of stachyose in the tubers. Experiments on ¹⁴C-stachyose uptake by isolated vacuoles confirmed previous observations by Keller (1992). Isolated vacuoles exhibited ATP and PP hydrolysis and were capable of generating a proton gradient across the tonoplast by a V-type H⁺-ATPase and H⁺-PPase. This was demonstrated by fluorescence quenching of quinacrine. Fluorescence could be restored by the addition of gramicidin and partly recovered by the addition of stachyose; mannitol, sorbitol and glucose had no effect. Fluorescence recovery depended on the concentration of stachyose and revealed saturation kinetics (K_m = 28 mM). Comparable results have been obtained with tonoplast vesicles by Greutert and Keller (1993). Experimental data presented here provide circumstantial evidence for symplastic unloading of stachyose in the tubers of Stachys sieboldii and demonstrate that the stachyose concentration in the cytoplasm of storage parenchyma cells is kept low by active stachyose transport into the vacuoles. The results suggest a stachyose/H⁺-antiport system.     

Fluoride-Induced Inhibition of Starch Biosynthesis in Developing Potato, Solanum tuberosum L., Tubers Is Associated with Pyrophosphate Accumulation

Pretreatment of discs excised from developing tubers of potato (Solanum tuberosum L.) with 10 millimolar sodium fluoride induced a transient increase in 3-phosphoglycerate content. This was followed by increases in triose-phosphate, fructose 1,6-bisphosphate and hexose-phosphate (glucose 6-phosphate + fructose 6-phosphate + glucose 1-phosphate). The effect of fluoride is attributed to an inhibition of glycolysis and a stimulation of triose-phosphate recycling (the latter confirmed by the pattern of ¹³C-labeling [NMR] in sucrose when tissue was supplied with [2-¹³C]glucose). Fluoride inhibited the incorporation of [U-¹⁴C] glucose, [U-¹⁴C]sucrose, [U-¹⁴C]glucose 1-phosphate, and [U-¹⁴C] glycerol into starch. The incorporation of [U-¹⁴C]ADPglucose was unaffected. Inhibition of starch biosynthesis was accompanied by an almost proportional increase in the incorporation of ¹⁴C into sucrose. The inhibition of starch synthesis was accompanied by a 10-fold increase in tissue pyrophosphate (PPi) content. Although the subcellular localization of PPi was not determined, a hypothesis is presented that argues that the PPi accumulates in the amyloplast due to inhibition of alkaline inorganic pyrophosphatase by fluoride ions.     

Tissue-Specific Distribution of Glutamine Synthetase in Potato Tubers

Cytosolic isoforms of the enzyme glutamine synthetase (GS) locatedin the phloem have been implicated in the mobilization of nitrogenfor intracellular transport in higher plants. The potato tuberrepresents an important reservoir of nitrogen and an approachwas made to the characterization of GS in this organ, particularlyat the stages of sprouting and of new tuber formation. By immunoblottingafter SDS-PAGE, and by immunological tissue printing, it waspossible to conclude that a cytosolic GS is present in tubersand sprouts, and that it is mainly expressed in the internalphloem, in a very precise tissue-specific pattern of distribution.These data provide additional clues to the interpretation ofthe functional role of GS in the mobilization of nitrogen andits utilization in growing parts of the plant. The importanceof morphological data and localization studies in complementingmolecular and biochemical work is emphasized. The proposed functionalimportance of the internal phloem inSolanum tuberosum organsis also reinforced. Solanum tuberosum L. cv. Desirée; potato; tubers; plant glutamine synthetase; tissue-specific distribution; phloem; nitrogen mobilization; in situlocalization; tissue printing     

The Influences of Jasmonic Acid Methyl Ester on Microtubules in Potato Cells and Formation of Potato Tubers

Amides in a CH₂Cl₂ extract from the fruits of Piper retrofractum were detected by HPLC/APCI-MS. Seven new unsaturated amides, together with six known ones, were isolated, and their structures were determined to be N-isobutyl-2E,4E,12Z-octadecatrienamide (1), N-isobutyl-2E,4E,14Z-eicosatrienamide (2), 1-(octadeca-2E,4E,12Z-trienoyl)piperidine (3), 1-(eicosa-2E,4E,14Z-trienoyl)piperidine (4), 1-(octadeca-2E,4E-dienoyl)piperidine (5), 1-(eicosa-2E,4E-dienoyl)piperidine (6), and 1-(eicosa-2E,14Z-dienoyl)piperidine (7) on the basis of chemical and spectroscopic evidence.     

人乳铁蛋白在转基因马铃薯块茎中的表达

人乳铁蛋白(human lactoferrin,hLF)是人体非特异性免疫系统的重要成员之一,具有抗细菌、真菌和抗病毒活性及其他多种功能.报道将hLF基因的cDNA与马铃薯(Solarium tuberosum L.)块茎专一性表达patain基因启动子融合后通过农杆菌介导导入马铃薯,PCR检测证实获得了多个转基因株系,RT-PCR阳性结果说明hLF mRNA在马铃薯植株中得到了表达.同时,经过ELISA及Western blot检测证实,转基因马铃薯表达了hLF并具有人乳铁蛋白的活性.     

Tissue Browning of Potato Tubers Induced by Gamma Irradiation

A considerable browning was observed especially in cortex tissue and along xylem of potato tubers harvested at Sakai in Osaka Prefecture, after irradiation with 10, 20 and 50 krad doses of cobalt-60 gamma rays. This phenomenon was accompanied by the marked increase in polyphenol content and peroxidase activity, and the transient increase in o-diphenol oxidase activity. Total reducing compounds in the tissue were also increased by gamma irradiation.

The browning phenomenon depended on the storage period from the harvest to gamma irradiation treatment. The browning and the transient increase in o-diphenol oxidase activity were completely suppressed in the case of tubers irradiated 3 months after harvest.

There was no significant change in α-amylase activity in all tubers tested.