Intact Potato Tubers Research Articles

Rapid Estimation of Moisture Content in Unpeeled Potato Tubers Using Hyperspectral Imaging

Potato (Solanum tuberosum L.) is one of the most significant vegetable crops grown globally, especially in developing countries. Over the last few years, global potato production has been increasing. This growth has created many opportunities for developing a wide range of value-added products from these crops. However, this requires monitoring the quality components of the tubers, such as moisture content, starch content, and soluble solid content. In particular, moisture content is one of the key quality parameters important for ensuring quality control throughout the supply chain and processing for consumer consumption. Ideally, moisture content would be estimated at the field level; however, current methods used by the industry to assess moisture content are time-consuming, labor-intensive, and destructive. Hence, the purpose of this study is to investigate the feasibility of hyperspectral imaging to quantify the moisture content of unpeeled potatoes before they were subsequently stored and processed. Hyperspectral images are collected from 47 intact potato tubers, with partial least squares regression (PLSR) models developed to predict moisture content from these spectra. The models showed predictive abilities for moisture content with acceptable ratios of prediction to deviation (RPDs) when considering the complete wavelength range (R2 = 0.53, RPD = 1.46, root mean square error (RMSE) = 5.04%) or the β-coefficient wavelength selection technique (R2 = 0.53, RPD = 1.47, RMSE = 5.02%). Furthermore, the prediction ability increased by more than 10% when the model wavelength was narrowed down to 733–970 nm. This study demonstrates the potential of using hyperspectral imaging for the quality assessment of intact, unpeeled potatoes, although further work is required to improve the model quality and implement this approach using remote sensing imagery.

The effect of pesticides on the NADH-supported mitochondrial respiration of permeabilized potato mitochondria

Pesticides can seriously affect the respiratory chain of the mitochondria of many crops, reducing the intensity of plant growth and its yield. Studying the effect of pesticides on the bioenergetic parameters of intact plant mitochondria is a promising approach for assessing their toxicity. In this study, we investigated the effect of some pesticides on isolated potato mitochondria, which used exogenous NADH as a substrate for respiration. We showed that succinate is the most preferred substrate for phosphorylating respiration of intact potato tubers mitochondria. Potato mitochondria poorly oxidize exogenous NADH, despite of the presence of external NADH dehydrogenases. Permeabilization of the mitochondrial membrane with alamethicin increased the availability of exogenous NADH to complex I. However, the pathway of electrons through complex I to complex IV makes intact potato mitochondria susceptible to a number of pesticides such as difenoconazole, fenazaquin, pyridaben and tolfenpyrad, which strongly inhibit the rate of mitochondrial respiration. However, these pesticides only slightly inhibited the rate of oxygen consumption during succinate-supported respiration. Dithianon, the inhibitor of Complex II, is the only pesticide which significantly increased the respiratory rate of NADH-supported respiration of permeabilized mitochondria of potato. Thus, it can be assumed that the alternative NADH dehydrogenases for electron flow represent a factor responsible for plant resistance to xenobiotics, such as mitochondria-targeted pesticides.

Nano-emulsified savory and thyme formulation show limited efficacy to suppress Pectobacterium carotovorum subsp. carotovorum compared with pure oil

Herbal volatile oils suggested as preserver coatings for potato (Solanum tuberosum L.) tubers against soft rot, a postharvest bacterial disease. The antibacterial potential of savory (Satureja khuzistanica Jamzad) and thyme (Zataria multiflora Boiss) stable nano-emulsified oil prepared with tween 80 and lecithin was evaluated towards Pectobacterium carotovorum subsp. carotovorum (Pcc). For this purpose, the antimicrobial activity of the nanoemulsion was compared with that of the pure oil by growth inhibition zone using well diffusion assay, minimum inhibitory and bactericidal concentrations (MIC and MBC) using microbroth dilution procedure, time-kill assay and potato tuber decay trial. The preventative efficacy of both optimized nanoemulsions was similar or reduced compared with the bulk oil on Pcc in plate assay. Savory and thyme nano-formulations displayed antibacterial capability against Pcc with a MIC of 0.59 and 0.29 g L−1, and MBC of 1.19 and 0.59 g L−1, respectively. The colony counts for Pcc were reduced to 0 in the range of 3–6 h based on time kill curves of MIC value. S. khuzistanica and Z. multiflora oils were as or more effective than nano-emulsions in the growth kinetic studies, although the viable cells number of Pcc was prevented at the MIC for both bulk and nano-formulations. The nano-encapsulated savory and thyme oil decreased disease development on intact potato tubers by 29.12 and 20.44 % in comparison with the control in the maceration assay. The data reported here, indicated that the usage of S. khuzistanica and Z. multiflora oil decreased soft rot incidence 1.82 and 2.18 times more than the nano-formulations, respectively. It seems that application of emulsified oil does not always more functional than bulk oil in the field of plant pathogens management.

Enzymatic Peeling of Potato: A Novel Processing Technology

Development of an innovative biotechnological method for potato peeling, closer to the ‘ideal’ peeling conditions of the product, was the main objective of the present research. Studies on enzymatic hydrolysis of potato peel were conducted. The efficacy of enzymatic peel hydrolysis was expressed in terms of reducing sugar content of the enzyme solution in which potato peel was incubated. Enzyme screening revealed that an enzyme solution containing a cellulase-xylanase mixture and amylase in a ratio of 1:1 showed good peel hydrolyzing efficiency of peeled peels. To further maximise the peel hydrolysis, condition parameters were optimised using response surface methodology (RSM). At the optimised conditions of 60 °C, pH 6 and 4 h, the reducing sugar yield in the solution was maximum. Characterization of the potato peel using microscopic techniques (scanning electron microscopy (SEM), atomic force microscopy (AFM)) further illustrated degradation of cell wall and reduction in the surface roughness of the peel after enzymatic treatment, which could enhance peel loosening from the intact potato. To further ascertain the efficiency of the process, studies were conducted with the selected enzyme on intact potato tubers under optimised conditions. Easy removal of peel was observed in enzyme-treated potato tubers, which showed 0.52% peel loss by abrasive peeling. The present process employing enzymes could be applied for peeling of intact potato as an alternative to conventional peeling process.

Detection of Internal Defects in Potato Based on Ultrasound Attenuation

A non-destructive method for distinguishing intact potato tubers from those already exposed to mechanical damage (pressure and impact stresses) has been evaluated on three potato varieties (Agria, Marfona, and Diamant) using four pairs of ceramic ultrasonic transducers (25, 32.8, 40, and 50-kHz). Attenuation coefficient of the ultrasonic wave was used as the parameter to determine the tuber damage condition. The results obtained from 25-kHz transducers were more accurate than those from other frequencies. Results of the 25-kHz tests showed accuracies of 83%, 94.5%, and 89% in differentiating damaged tubers from intact ones for Agria, Marfona, and Diamant, respectively. In order to determine deformation energy and tangential elastic modulus of potato varieties, triaxial and uniaxial tests were used. Due to the higher average values of tangential elastic modulus in the Agria variety, it was concluded that the potato tubers of this variety are stiffer than those of Marfona and that; therefore, there is a higher ultrasonic attenuation in Agria tubers.

Nondestructive Determination of Sugar Content in Potato Tubers Using Visible and Near Infrared Spectroscopy

Near infrared (NIR) spectroscopy was investigated as a method for the nondestructive measurement of sugar content in intact potato tubers. The NIR spectra (400-1100 nm) of potato samples were acquired by fiber optics in the interactance mode. Calibration models for the prediction of the fructose and glucose contents were developed by a partial least squares statistical analysis method. The calibration model gave standard errors of prediction of 0.26 mg/g for fructose and 0.46 mg/g for glucose. The preliminary results showed that NIR spectroscopy gives a reasonable estimate that can be used for nondestructive sorting of potatoes according to their sugar content.

A Cell Wall-Bound Adenosine Nucleosidase is Involved in the Salvage of Extracellular ATP in Solanum tuberosum

Extracellular ATP (eATP) has recently been demonstrated to play a crucial role in plant development and growth. To investigate the fate of eATP within the apoplast, we used intact potato (Solanum tuberosum) tuber slices as an experimental system enabling access to the apoplast without interference of cytosolic contamination. (i) Incubation of intact tuber slices with ATP led to the formation of ADP, AMP, adenosine, adenine and ribose, indicating operation of apyrase, 5'-nucleotidase and nucleosidase. (ii) Measurement of apyrase, 5'-nucleotidase and nucleosidase activities in fractionated tuber tissue confirmed the apoplastic localization for apyrase and phosphatase in potato and led to the identification of a novel cell wall-bound adenosine nucleosidase activity. (iii) When intact tuber slices were incubated with saturating concentrations of adenosine, the conversion of adenosine into adenine was much higher than adenosine import into the cell, suggesting a potential bypass of adenosine import. Consistent with this, import of radiolabeled adenine into tuber slices was inhibited when ATP, ADP or AMP were added to the slices. (iv) In wild-type plants, apyrase and adenosine nucleosidase activities were found to be co-regulated, indicating functional linkage of these enzymes in a shared pathway. (v) Moreover, adenosine nucleosidase activity was reduced in transgenic lines with strongly reduced apoplastic apyrase activity. When taken together, these results suggest that a complete ATP salvage pathway is present in the apoplast of plant cells.

Differential Attractiveness of Potato Tuber Volatiles to Phthorimaea operculella (Gelechiidae) and the Predator Orius insidiosus (Anthocoridae)

The behavioral responses of the potato tuberworm moth Phthorimaea operculella and the polyphagous predator Orius insidiosus to volatiles emanating from exposed tubers were studied by four-arm olfactometer bioassays. Mated females of P. operculella distinguished volatiles released by intact potato tubers from volatiles damaged mechanically or by conspecific larvae. Volatiles from intact potato tubers were attractive to them. On the other hand, unmated females of P. operculella did not respond to tuber volatiles. Adults of O. insidiosus were attracted to volatiles from tubers damaged by P. operculella larvae, but did not respond to intact or mechanically damaged tubers. Methyl jasmonate (MeJA) was the only compound identified from the headspace of potato tubers (GC-MS of direct headspace sampling). The amount varied with the type of induction, being 0.001 +/- 0.0003 ng g(-1) in tissues of intact fresh tubers, 0.002 +/- 0.0007 ng g(-1) in mechanically damaged tubers, and showing a six- to tenfold increase in P. operculella damaged tubers (0.090 +/- 0.006 ng g(-1)). Behavioral bioassays with synthetic MeJA confirmed that the response of the insects is dependent on MeJA concentration. Mated females of P. operculella showed the highest response at 0.001 ng g(-1) (concentration released by intact tubers), whereas O. insidiosus showed the highest response, between 0.01 and 0.05 ng g(-1), which is close to the concentration released by P. operculella damaged tubers. Based on these results, we postulate that P. operculella and O. insidiosus have adapted their responses to plant volatiles differently, enabling them to locate suitable hosts or prey.

Phosphorylation of Formate Dehydrogenase in Potato Tuber Mitochondria

Two highly phosphorylated proteins were detected after two-dimensional (blue native/SDS-PAGE) gel electrophoretic separation of the matrix fraction isolated from potato tuber mitochondria. These two phosphoproteins were identified by mass spectrometry as formate dehydrogenase (FDH) and the E1alpha-subunit of pyruvate dehydrogenase (PDH). Isoelectric focusing/SDS-PAGE two-dimensional gels separated FDH and PDH and resolved several different phosphorylated forms of FDH. By using combinations of matrix-assisted laser desorption/ionization mass spectrometry and electrospray ionization tandem mass spectrometry, several phosphorylation sites were identified for the first time in FDH and PDH. FDH was phosphorylated on Thr76 and Thr333, whereas PDH was phosphorylated on Ser294. Both Thr76 and Thr333 in FDH were accessible to protein kinases, as demonstrated by protein structure homology modeling. The extent of phosphorylation of both FDH and PDH was strongly decreased by NAD+, formate, and pyruvate, indicating that reversible phosphorylation of FDH and PDHs was regulated in a similar fashion. At low oxygen concentrations inside the intact potato tubers, FDH activity was strongly increased relative to cytochrome c oxidase activity pointing to a possible involvement of FDH in hypoxic metabolism. Computational sequence analysis indicated that a conserved local sequence motif of pyruvate formate-lyase is found in the Arabidopsis thaliana genome, and this enzyme might be the source of formate for FDH in plants.

Stimulation of potato tuber respiration by cold stress is associated with an increased capacity of both plant uncoupling mitochondrial protein (PUMP) and alternative oxidase.

The CO2 evolution of intact potato tubers (Solanum tuberosum, L., var. "Bintje") was analyzed during a 10-day period of their warm (25 +/- 2 degrees C) or cold (5 +/- 1 degrees C) storage, to evaluate cold-stress effects on expression and activities of plant uncoupling mitochondrial protein (PUMP) and alternative oxidase (AOX). CO2 evolution rates were analyzed at 20 degrees C, to reflect their possible capacities. The 20 degrees C CO2 production declined from 13 to 8 mg kg(-1) h(-1) after 2 days of warm storage and then (after 3 to 7 days) decreased from 8 to 6.5 mg kg(-1) h(-1). In contrast, 20 degrees C CO2 evolution did not change after the first day of cold storage, increased up to 14.5 mg kg(-1) h(-1) after 2 days, and decreased to about 12 mg kg(-1) h(-1) after 3 to 7 days of cold storage. Cold storage increased PUMP expression as detected by Western blots and led to elevated capacities of both PUMP (44%) and CN-resistant AOX (10 times), but not the cytochrome pathway. Since we found that cold storage led to about the same mitochondrial respiration of 40 nmol O2 min(-1) mg(-1) attributable to each of the respective proteins, we conclude that both AOX and PUMP equally contribute to adaptation of potato tubers to cold.

Alteration of Plant Mitochondrial Proton Conductance by Free Fatty Acids: UNCOUPLING PROTEIN INVOLVEMENT

We characterized the uncoupling activity of the plant uncoupling protein from Solanum tuberosum (StUCP) using mitochondria from intact potato tubers or from yeast (Saccharomyces cerevisiae) expressing the StUCP gene. Compared with mitochondria from transfected yeast, StUCP is present at very low levels in intact potato mitochondrial membranes (at least thirty times lower) as shown by immunodetection with anti-UCP1 antibodies. Under conditions that ruled out undesirable effects of nucleotides and free fatty acids on uncoupling activity measurement in plant mitochondria, the linoleic acid-induced depolarization in potato mitochondria was insensitive to the nucleotides ATP, GTP, or GDP. In addition, sensitivity to linoleic acid was similar in potato and in control yeast mitochondria, suggesting that uncoupling occurring in potato mitochondria was because of a UCP-independent proton diffusion process. By contrast, yeast mitochondria expressing StUCP exhibited a higher sensitivity to free fatty acids than those from the control yeast and especially a marked proton conductance in the presence of low amounts of linoleic acid. However, this fatty acid-induced uncoupling was also insensitive to nucleotides. Altogether, these results suggest that uncoupling of oxidative phosphorylation and heat production cannot be the dominant feature of StUCP expressed in native potato tissues. However, it could play a role in preventing reactive oxygen species production as proposed for mammalian UCP2 and UCP3.

Kunitz-type proteinase inhibitors from intact and Phytophthora-infected potato tubers

Three protein proteolytic enzyme inhibitors with molecular masses 21, 22, and 23 kDa have been isolated from intact potato tubers ( Solanum tuberosum L. cv. Istrinskii). The 21 and 22 kDa proteins denoted as PSPI-21 and PSPI-22, respectively, are serine proteinase inhibitors with different specificity. The 23 kDa protein denoted as PCPI-23 is an inhibitor of plant cysteine proteinases. The PSPI-21 molecule consists of two disulfide-linked polypeptide chains with molecular masses of 16.5 kDa and 4.5 kDa. The PSPI-22 and PCPI-23 have one polypeptide chain. Their amino-termini numbered 21–25 amino acid residues have significant homology to other plant inhibitors which are members of the soybean Kunitz inhibitor family. It is found that at least PSPI-21 and PSPI-22 can predominantly accumulate in potato tubers infected with Phytophthora infestans zoospores.

Resistance to the potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), in potato (Solanum tuberosum ssp. tuberosum L.) tubers

Tests were undertaken with tubers of four potato cultivars to determine whether differences were apparent in susceptibility to the insect pest the potato tuber moth (Phthorimaea operculella). Under choice test conditions, in which neonates were allowed to invade intact potato tubers, there was no significant difference in the numbers of larval mines established within the tubers of four potato cultivars. However, significantly more mines were initiated in the vicinity of tuber eyes than elsewhere for all cultivars. Under non‐choice test conditions, in which neonates were placed on the surface of intact tubers, resistance was indicated by significantly fewer larvae surviving to eclose as adults on tubers of cultivar Sequoia than on cultivars Kennebec and Tarago. Cultivar Netted Gem yielded an intermediate number of adults. In a third experiment using cultivar Kennebec alone, survival of neonates to adults was significantly increased by pricking the tuber surface immediately prior to inoculation, indicating that the tuber periderm may constitute a significant barrier to invasion. Results are discussed in relation to possible resistance mechanisms and further work required for developing host plant resistance against this pest.

Ubiquinone-1 Induces External Deamino-NADH Oxidation in Potato Tuber Mitochondria.

The addition of ubiquinone-1 (UQ-1) induced Ca2+-independent oxidation of deamino-NADH and NADH by intact potato (Solanum tuberosum L. cv Bintje) tuber mitochondria. The induced oxidation was coupled to the generation of a membrane potential. Measurements of NAD+-malate dehydrogenase activity indicated that the permeability of the inner mitochondrial membrane to NADH and deamino-NADH was not altered by the addition of UQ-1. We conclude that UQ-1-induced external deamino-NADH oxidation is due to a change in specificity of the external rotenone-insensitive NADH dehydrogenase. The addition of UQ-1 also induced rotenone-insensitive oxidation of deamino-NADH by inside-out submitochondrial particles, but whether this was due to a change in the specificity of the internal rotenone-insensitive NAD(P)H dehydrogenase or to a bypass in complex I could not be determined.

The presence of a short redox chain in the membrane of intact potato tuber peroxisomes and the association of malate dehydrogenase with the peroxisomal membrane

The presence of a short redox chain in the membrane of intact potato tuber peroxisomes and the association of malate dehydrogenase with the peroxisomal membrane

The presence of a short redox chain in the membrane of intact potato tuber peroxisomes and the association of malate dehydrogenase with the peroxisomal membrane

Peroxisomes and mitochondria were purified from potato tubers (Solanum tuberosum L. cv. Bintje) by differential centrifugation followed by separation on a continuous Percoll gradient containing 0.3 M sucrose in the lower half and 0.3 M mannitol in the upper half. The peroxisomes band at the bottom and the mitochondria in the middle of this type of gradient. Mitochondrial contamination of the peroxisomes was only 2% [as judged by cytochrome c oxidase (EC 1.3.9.1) activity]. Contamination by amyloplasts, plasma membrane and endoplasmic reticulum was also minimal. The peroxisomes were 80% intact as judged by malate dehydrogenase (MDH, NAD−‐dependent; EC 1.1.1.37) latency.The specific activity of NADH‐ferricyanide reductase and NADH‐Cyt c reductase was 0.22 and 0.051 μmol (mg protein)−1 min−1 in freshly isolated peroxisomes, respectively. The active site of the reductase appeared to be on the inner surface of the membrane. The peroxisomes also contained a b‐type cytochrome. Frozen peroxisomes were subfractionated by osmotic rupture followed by centrifugation to separate the soluble proteins from the peroxisomal membrane. About half the MDH and 30% of the NADH‐ferricyanide reductase activity was associated with the membrane but only 6% of the catalase (EC 1.11.1.6) activity. A further wash removed 75% of the residual catalase with only a small loss of MDH or NADH‐ferricyanide reductase activity. MDH appears to be closely associated with the peroxisomal membrane.When the purified peroxisomal membrane was analyzed by SDS‐PAGE followed by silver staining, prominent bands at 22, 40, 41, 48, 53 and 74 kDa were observed. After immunoblotting the purified peroxisomal membrane, a band at 53 kDa showed strong cross‐reactivity with antibodies raised against NADH‐ferricyanide reductase. Since the NADH‐ferricyanide reductase activity in the peroxisomal membrane could be shown to be specific for the β‐hydrogen of NADH, the activity could not be due to contamination by endoplasmic reticulum where the reductase is α‐specific. We conclude that the peroxisomal membrane contains a short redox chain, consisting of a NADH‐ferricyanide reductase and a b‐type cytochrome, similar to that of e.g. the plasma membrane. The role of this redox chain has yet to be elucidated.

Use of near infrared analysis for the nondestructive measurement of dry matter in potatoes

Near infrared spectrophotometry in the direct transmittance mode and in the wavelength range of 800 to 1000 nm was used to measure the % dry matter (DM) in sliced and intact potato tubers (cv Russet Burbank). With thin tissue slices, the correlation (r) between spectral and DM data was-0.975 with a standard error of calibration (SEC) of 0.91. With thick slices and intact potatoes the r, SEC, and standard error of prediction (SEP) values were -0.952, 1.28, 1.69 and -0.918, 1.04 and 1.52, respectively.

Multiplication and Virulence in Plant Tissues of Escherichia coli Clones Producing Pectate Lyase Isozymes PLb and PLe at High Levels and of an Erwinia chrysanthemi Mutant Deficient in PLe

The phytopathogenic enterobacterium Erwinia chrysanthemi strain EC16 produces four isozymes of pectate lyase (PL), an extracellular enzyme that macerates parenchymatous plant tissues and kills plant cells. A 1.8-kilobase EcoRI DNA fragment containing the entire pelE gene was deleted from the E. chrysanthemi chromosome by marker exchange of a cloned fragment that had been modified in vitro. The resulting mutant, UM1001, produced the isozymes PLa, PLb, and PLc, but not PLe. Mutant UM1001 was compared with wild-type E. chrysanthemi, with Escherichia coli JA221, and with JA221 containing expression vectors with cloned pel genes producing high levels of PLe (pPEL748) or PLb (pPEL343) for the ability to multiply and cause symptoms in intact potato tubers. Tubers were injected with less than 100 bacteria per inoculation site and incubated aerobically or anaerobically. While maceration occurred only in anaerobically incubated tubers, all of the bacteria, including nonpectolytic E. coli controls, multiplied substantially under all conditions. E. coli JA221(pPEL748) caused significantly more maceration than E. coli JA221(pPEL343) or wild-type E. chrysanthemi. Mutant UM1001 caused significantly less maceration than the wild-type E. chrysanthemi. The results establish the importance of PLe in the pectolytic arsenal of E. chrysanthemi by demonstrating that production of PLe can enable E. coli to aggressively macerate tuber tissue and that deletion of pelE significantly diminishes the virulence of E. chrysanthemi.

LABORATORY STUDIES ON DAMAGE TO POTATO TUBERS BY SLUGS

The ability of eight species of slugs to damage intact potato tubers c .v. Maris Piper was investigated. Four species, previously implicated as pests of field crops, caused primary damage to tubers. Interactions between three of the species Milax budapestensis (Hazay), Arion hortensis (Fèrussac) and Deroceras reticulatum (Müller) were studied using potato tubers of five cultivars. Single species groups caused most damage to tubers and interaction between species reduced damage irrespective of cultivar. The results are discussed in relation to past work.

Differenzierungsverhalten und Stoffwechselaktivitäten in Kalluskulturen aus Stolonen und Knollen von Solanum tuberosum

Summary Induction of callus formation, growth rate and differentiation pattern of calli derived from potato tuber tissue or from stolons were investigated depending on the hormone content and composition of nutrient media. Media are described giving callus induction, various types of organ differentiations (roots, shoots with or without tubers) and regenerates. Metabolic activity of various tissues was examined by following [ 14 CO 2 ]-fixation via the phosphoenol-pyruvate-carboxylase pathway and by studying uptake and metabolisation of U-[ 14 C]-glucose. On a fresh weight basis, both tissues of intact potato tubers and derived calli showed a rather similar rate and labelling pattern of [ 14 CO 2 ]-fixation. Native potato tuber tissue, however, metabolized added U-[ 14 C]-glucose with a much higher rate than callus tissue. Also, in the former a major part of label from U-[ 14 C]-glucose was found in sucrose, whereas callus tissue from the same plant material showed little sucrose formation. Starch formation from U-[ 14 C]-glucose was equally low in both kinds of tissue.