Short Stories

A comparison of microtubers and field-grown tubers of potato (Solanum tuberosum L.) for hexoses, sucrose and their ratios following postharvest cold storage

Description
Cold-induced sweetening (CIS) is a significant postharvest problem in processing potato (Solanum tuberosum L.) tubers. A rise in hexose sugar levels during cold storage results in a brown, bitter tasting and unmarketable product. We tested if potato
Categories
Published
of 5
All materials on our website are shared by users. If you have any questions about copyright issues, please report us to resolve them. We are always happy to assist you.
Related Documents
Share
Transcript
   Available online at www.sciencedirect.com Postharvest Biology and Technology 49 (2008) 180–184 Research Note A comparison of microtubers and field-grown tubers of potato( Solanum tuberosum  L.) for hexoses, sucrose and theirratios following postharvest cold storage Ranjith Pathirana ∗ , John C. Harris, Marian J. McKenzie  New Zealand Institute for Crop & Food Research Ltd., Food Industry Science Centre, Batchelar Road, Palmerston North 4442, New Zealand  Received 9 July 2007; accepted 16 November 2007 Abstract Cold-induced sweetening (CIS) is a significant postharvest problem in processing potato ( Solanum tuberosum  L.) tubers. A rise in hexose sugarlevelsduringcoldstorageresultsinabrown,bittertastingandunmarketableproduct.Wetestedifpotatomicrotubers(MicroT)canundergoCISandif this corresponds to the CIS response in field-grown tubers (FieldT) with the hope of fast-tracking breeding programmes using a MicroT system.Using MicroT from potato genotypes representing a range of CIS response levels we have demonstrated that MicroT undergo CIS more rapidlythan FieldT. Correlations of glucose:sucrose and hexose:sucrose ratios were highly significant between the two tuber types after cold treatmentand these ratios are known to be good predictors of invertase activity, a key regulator of CIS. Correlations of individual sugars were non-significantbefore and after postharvest cold treatment.© 2007 Elsevier B.V. All rights reserved. Keywords:  Cold-induced sweetening; Fructose; Glucose; Maillard browning; Processing 1. Introduction Potato tubers are stored year-round at 4–8 ◦ C to meet thedemands of the potato processing industry, which requires aconstant supply of high quality tubers. Cold temperature stor-age reduces sprouting, reducing reliance on chemical sproutsuppressants. Moreover, at these temperatures the progress of postharvest diseases can be controlled effectively. However,storage at cold temperatures increases the risk of cold-inducedsweetening (CIS), a rise in the hexoses glucose (glu) and fruc-tose (fru). During high temperature processing, such as duringtheproductionofchipsorFrenchfries,materialwithhighreduc-ing sugar content undergoes Maillard browning, resulting in abrown,bittertastingandunmarketableproduct.Therefore,accu-mulation of reducing sugars is a costly postharvest problem forboth producers and processors.CIS resistance has been a potato breeding objective for over25 years in countries where processing potatoes are grown ∗ Corresponding author at: Crop & Food Research, Private Bag 11 600,Palmerston North, New Zealand. Tel.: +64 6 3556169; fax: +64 6 3517050.  E-mail address:  pathiranar@crop.cri.nz (R. Pathirana). (Brown et al., 1990). Increased potato production and the rapid development of associated processing industries in non-traditional potato growing countries such as China and India(Ezekiel and Shekhawat, 2002) are also increasing the demand forCIS-resistantcultivars.Unfortunately,selectionforthischar-acteristic is not direct and requires laboratory testing after coldstorage. Tuber dormancy and seasonal factors limit the progressoftraditionalmethodsofbreeding.Further,CISresistanceoftenhastobetransferredfromwilddiploidspecies(HayesandThill,2002;OltmansandNovy,2002)sobreedingforCISresistanceisnot straightforward, requiring sexual polyploidisation and earlygeneration selection, often with low genetic gain (Hayes andThill, 2003).Despite the common use of microtubers (MicroT) as propag-ules for commercial production (Donnelly et al., 2003; Pruski etal.,2003)orconvenientstoragesystemsforgermplasm(Fletcher et al., 1998; Donnelly et al., 2003), they remain in limited use asresearch tools for understanding the biochemical and molecularbasisofpotatotuberphysiologyorinconventionalbreedingpro-grammes, even though traits such as dormancy (Leclerc et al.,1995; Suttle, 1998) and salinity tolerance (Zhang et al., 2005) appear to be amenable to examination using microtubers. Ourobjective was to investigate the use of a MicroT system for fast- 0925-5214/$ – see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.postharvbio.2007.11.005   R. Pathirana et al. / Postharvest Biology and Technology 49 (2008) 180–184  181 tracking breeding programmes by providing a rapid postharvestcold storage screen. As a first step we investigated whetherMicroT undergo CIS in a similar way to field-grown tubers(FieldT), since the few previously reported studies are limitedto comparisons of MicroT and FieldT in single cultivars, withsome reporting similar patterns of CIS (Claassen et al., 1992;Veramendi et al., 1999) and others reporting no CIS response inMicroT (Xiong et al., 2002). 2. Materials and methods Potato ( Solanum tuberosum  L.) tubers of 17 genotypes(breedinglines:2852.5,2885.1,3011.6,3144.1,3175.2,578/37,719/44, 810/7, 913/7, 937/3, 964/8, 989/10; cultivars Fraser,Kaimai, L115.1, Red Rascal and White Delight) representinga broad range of resistances to CIS, from 1 to 8 in a scale of 1–9 (John Anderson, personal communication), were obtainedfrom Crop & Food Research, Lincoln, New Zealand. Tuberssprouted in the greenhouse provided shoots to initiate cultures.Shoots (10–15cm long) were surface-sterilised in 1% sodiumhypochloritewith0.5%Tween20for20minwithgentleshakingand washed with sterile water three times. Single node explantswere aseptically transferred to solid media in tissue culturetubs and maintained under a 16h light, 8h dark photoperiod at30  molm − 2 s − 1 light intensity at 24 ◦ C. Modified Murashigeand Skoog (1962) medium with half strength macro salts, fullstrengthmicrosalts,B5vitamins(Gamborgetal.,1968)and3% sucrose (suc) solidified with 0.75% agar was used. Media wereadjusted to pH 5.8 before autoclaving.The tuberisation medium was as above, but with increasedsuc content (9%) and pH 6. Single node cuttings from asepticcultures were transferred to tuberisation media and maintainedunder short-day conditions (8h light, 16h dark) with low lightintensity (12  molm − 2 s − 1 ). The temperature in the cultureroom was 24 ◦ C during the light period and 18 ◦ C during thedark period. MicroT were harvested over 3 months, starting 10weeks after initiation of cultures, and stored in paper bags in thedarkat14 ◦ Cuntiltreatment.MatureFieldTwereobtainedfromCrop & Food Research, Lincoln, New Zealand.MicroT and FieldT from each genotype were split into twogroups and stored at 10 and 4 ◦ C. Samples were taken prior tostorage (time zero control), and after 2 and 4 weeks of storageat each temperature. Tuber samples consisted of the combinedmaterial from three tubers of each line at each time point, forboth FieldT and MicroT.Glu, suc and fructose (fru) content was determined usingthe Sucrose/D-Glucose/D-Fructose kit (Roche, Darmstadt, Ger-many) scaled down to a microplate format, essentially asdescribed by Hurst et al. (1995), except that 60mg of freeze- dried tissue was extracted over 1h at 55 ◦ C with vortexing every20min. Extracts were diluted 1:10 in water before assaying.Log-transformed data for glu, fructose, total reducing sugars(hexose), suc and glu:suc ratio in MicroT and FieldT were sub- jected to one-way, randomized block, analysis of variance usingthe five storage treatments (time zero control, 2 and 4 weeksafter storage at 10 and 4 ◦ C) as treatments, and the 17 genotypesas blocks. Paired Student’s  t  -tests were used to compare initial  T   a    b    l   e    1    M   e   a   n   s   u   g   a   r   c   o   n    t   e   n    t    (         m   o    l    /   g    D    W    )   o    f   m    i   c   r   o    t   u    b   e   r   s    (    M    T    )   a   n    d    fi   e    l    d  -   g   r   o   w   n    t   u    b   e   r   s    (    F    T    )   o    f    1    7   p   o    t   a    t   o   g   e   n   o    t   y   p   e   s    b   e    f   o   r   e   c   o    l    d    t   r   e   a    t   m   e   n    t    (   c   o   n    t   r   o    l    )   a   n    d   a    f    t   e   r    2   a   n    d    4   w   e   e    k   s   o    f   s    t   o   r   a   g   e   a    t    1    0   a   n    d    4     ◦     C    T   r   e   a    t   m   e   n    t    F   r   u   c    t   o   s   e    G    l   u   c   o   s   e    H   e   x   o   s   e    S   u   c   r   o   s   e    G   :    S   r   a    t    i   o    M    T    F    T    M    T    F    T    M    T    F    T    M    T    F    T    M    T    F    T    C   o   n    t   r   o    l    6 .    1    (    0 .    7    9   a    )    3    1 .    0    (    1 .    4    9    b    )    7 .    9    (    0 .    9   a    )    2    5 .    6    (    1 .    4    1    b    )    1    4 .    5    (    1 .    1    6   a    )    5    7 .    3    (    1 .    7    6    b    )    3    4 .    4    (    1 .    5    4    b    )    1    0 .    7    (    1 .    0    3   a    b    )    0 .    2    2    9    (    −     0 .    6    4    1   a    )    2 .    3    9    5    (    0 .    3    7    9    b    )    1    0     ◦     C    2   w   e   e    k   s    8 .    1    (    0 .    9    1   a    )    2    6 .    0    (    1 .    4    2   a    b    )    9 .    1    (    0 .    9    6   a    )    2    1 .    5    (    1 .    3    3    b    )    1    7 .    5    (    1 .    2    4   a    )    4    8 .    1    (    1 .    6    8    b    )    2    9 .    2    (    1 .    4    7   a    b    )    8 .    7    (    0 .    9    4   a    )    0 .    3    1    3    (    −     0 .    5    0    5   a    )    2 .    2    4    3    (    0 .    3    5    1    b    )    1    0     ◦     C    4   w   e   e    k   s    6 .    8    (    0 .    8    3   a    )    1    9 .    5    (    1 .    2    9   a    )    6 .    8    (    0 .    8    4   a    )    1    4 .    6    (    1 .    1    7   a    )    1    3 .    8    (    1 .    1    4   a    )    3    4 .    8    (    1 .    5    4   a    )    2    2 .    5    (    1 .    3    5   a    )    1    2 .    6    (    1 .    1    0    b    )    0 .    3    0    4    (    −     0 .    5    1    8   a    )    1 .    0    3    2    (    0 .    0    1    4   a    )    4     ◦     C    2   w   e   e    k   s    3    5 .    5    (    1 .    5    5    b    )    5    7 .    3    (    1 .    7    6   c    )    3    7 .    1    (    1 .    5    7    b    )    5    5 .    0    (    1 .    7    4   c    )    7    2 .    7    (    1 .    8    6    b    )    1    1    2 .    5    (    2 .    0    5   c    )    5    5 .    7    (    1 .    7    5   c    )    2    8 .    5    (    1 .    4    5   c    )    0 .    6    6    6    (    −     0 .    1    7    8    b    )    1 .    9    3    4    (    0 .    2    8    6    b    )    4     ◦     C    4   w   e   e    k   s    5    2 .    1    (    1 .    7    2    b    )    9    5 .    4    (    1 .    9    8    d    )    5    0 .    8    (    1 .    7    1    b    )    7    5 .    5    (    1 .    8    8   c    )    1    0    3 .    0    (    2 .    0    1    b    )    1    7    8 .    6    (    2 .    2    5    d    )    5    0 .    4    (    1 .    7    0   c    )    3    4 .    3    (    1 .    5    4   c    )    1 .    0    0    7    (    0 .    0    0    3    b    )    2 .    2    0    4    (    0 .    3    4    3    b    )    L    S    D    5    %    0 .    1    9    2    0 .    1    3    2    0 .    1    9    8    0 .    1    6    3    0 .    1    8    7    0 .    1    3    8    0 .    1    2    2    0 .    1    2    4    0 .    2    1    6    0 .    2    0    2    F   o   r    t    h   e   a   n   a    l   y   s    i   s   o    f   v   a   r    i   a   n   c   e ,    t    h   e    d   a    t   a   w   e   r   e    l   o   g  -    t   r   a   n   s    f   o   r   m   e    d .    B   a   c    k  -    t   r   a   n   s    f   o   r   m   e    d   m   e   a   n   v   a    l   u   e   s   a   r   e    f   o    l    l   o   w   e    d    b   y    l   o   g  -    t   r   a   n   s    f   o   r   m   e    d   v   a    l   u   e   s    i   n   p   a   r   e   n    t    h   e   s   e   s .    V   a    l   u   e   s   w    i    t    h    t    h   e   s   a   m   e    l   e    t    t   e   r   s    i   n   a   c   o    l   u   m   n   a   r   e   n   o    t   s    i   g   n    i    fi   c   a   n    t    l   y    d    i    f    f   e   r   e   n    t   a    t      p    =    0 .    0    5   a   c   c   o   r    d    i   n   g    t   o    L    S    D    t   e   s    t .  182  R. Pathirana et al. / Postharvest Biology and Technology 49 (2008) 180–184 sugar levels between MicroT and FieldT. Pearson correlationcoefficients were calculated between MicroT and FieldT for allthe sugars measured and their ratios in 17 genotypes. 3. Results and discussion 3.1. Microtuber production and initial sugar content  After3monthsofcultureundershort-daysandhighsuc,ade-quatenumbersofMicroTwereproducedforthepostharvestcoldstorageexperiment.Thereweregenotypicdifferencesintherateof  invitro MicroTproduction:from10weeks(e.g.719/44,913/7and 937/3) to almost 16 weeks (e.g. Red Rascal, 989/10, 810/7,578/37and3011.6).TheaverageweightofaMicroTwas0.55g,ranging from 0.22g (Red Rascal) to 1.20g (White Delight).TheMicroThadsignificantlymoresucandlesshexosesugarsthan FieldT (Table 1). When individual genotypes were com- pared, MicroT had higher suc levels in all the genotypes tested,and lower hexoses except for lines 2885.1 and 989/10 (Fig. 1),indicating immaturity at harvest. Xiong et al. (2002) also found that MicroT from three hybrid families had higher levels of sucthan FieldT but, in contrast to our study, found higher glu con-tent in MicroT than in FieldT. Their material arose from a crossof parents with high processing qualities, whereas our materialcovered a wide range of resistances to CIS. These differences instarting material may have resulted in altered sugar metabolismresponse during maturation of MicroT and FieldT in these twostudies. 3.2. Effect of postharvest storage of MicroT and FieldT onsugar content  In response to postharvest cold storage at 4 ◦ C the glu, fruand hexose content of both the MicroT and the FieldT increasedsignificantly compared to those stored at 10 ◦ C, confirming thatboth tuber types were capable of cold sweetening (Table 1 and Fig. 2). As expected, FieldT of several lines bred for CIS resis-tance, such as 2852.5, 2885.1, 3011.6 and 810/7, showed muchsmaller increases in hexoses than CIS sensitive lines such asWhite Delight, 3144.1, 719/44 and 913/7 (Fig. 2B). Interestingly, MicroT recorded a much more rapid increasein reducing sugars after cold storage than FieldT. This increasewas achieved in 2 weeks with no significant difference in eitherthe sugars or glu:suc ratio after a further 2 weeks of cold storage(Table 1). In contrast, the increase in sugar content in FieldT was more gradual, with significant differences in fru and hexosecontent between 2 and 4 weeks of storage at 4 ◦ C (Table 1). Furthermore, a significant increase in glu:suc ratio was onlyrecorded for MicroT (Table 1).Taken together these data demonstrate that MicroT fromacross a range of cultivars with different CIS responses undergoCIS. Previous research with Kennebec MicroT also showed aclassic CIS response after 2 months of storage at 2 ◦ C (Claassenet al., 1992). However, Xiong et al. (2002) did not observe any increaseinMicroTglucontentafter2monthsofstorageat4 ◦ C.It is not clear why a CIS response in this material was not seen,especially considering that FieldT and minitubers of the samelines underwent CIS after the same treatment.As a further control we maintained the MicroT and FieldT at10 ◦ C for the same period as the 4 ◦ C cold storage. The levels of differentsugarsdidnotchangesignificantlyinMicroTfollowing10 ◦ C storage except for a decrease in suc after 4 weeks, and inFieldTtherewasasignificantdecreaseingluandhexosecontent(Table 1). The glu:suc ratio was not significantly affected by cold treatment of FieldT, but at 10 ◦ C it showed a significantdecrease after 4 weeks. We also observed an increase in succontent during postharvest cold treatment both in MicroT andFieldT (Table 1). The increase was smaller in MicroT; a 1.5- fold increase on average compared with a 3.2-fold increase forFieldT(Table1).Theonlyothergrouptoinvestigatesuccontent Fig. 1. Sucrose and hexose sugar contents in microtubers (MT) and field-grown tubers (FT) of individual potato genotypes at harvest.   R. Pathirana et al. / Postharvest Biology and Technology 49 (2008) 180–184  183Fig. 2. Fructose and glucose content in microtubers (A) and field-grown tubers (B) in 17 potato genotypes after 4 weeks of storage at 10 or 4 ◦ C. inMicroTaftercoldtreatmentdidnotobserveasimilarincreasein suc even though they did report it for FieldT and minitubersin the same experiment (Xiong et al., 2002).Thus, compared with both the control treatments (beforecoldstorageandparallel10 ◦ Cstorage)microtubershaveshownpostharvest CIS in our experiment over a range of cultivars. 3.3. Relationship between microtubers and field-growntubers for sugar content  To our knowledge this is the first time that a CIS responsehas been observed in the MicroT of several independent potatocultivars and lines within the same experiment. Therefore, wewere interested in determining if the cold treatment response of MicroT from a range of genotypes correlated with that of theFieldT. Correlation analysis revealed no significant relationshipbetween MicroT and FieldT for any of the sugars or their ratiosbefore cold treatment. Although non-significant, a correlationcoefficient of   r  =0.4 was recorded for glu:suc and hexose:sucratios before postharvest cold treatment (Table 2). Although moderate positive correlations were detected for the reducingsugars after cold treatment they were not significant. However,there was a positive and highly significant correlation betweenMicroT and FieldT for the glu:suc ratio and the hexose:suc ratio  184  R. Pathirana et al. / Postharvest Biology and Technology 49 (2008) 180–184 Table 2Pearson correlation coefficients between sugar content in microtubers and field-grown tubers before and after cold treatment for 4 weeks ( n =17)Before cold treatment 4 ◦ C for 4 weeksSucrose 0.14 ns 0.03 nsGlucose 0.08 ns 0.33 nsFructose  − 0.08 ns 0.38 nsHexose 0.01 ns 0.36 nsGlucose:sucrose ratio 0.39 ns 0.63**Hexose:sucrose ratio 0.41 ns 0.64****Significant at  p =0.01; ns: non-significant. after cold storage (Table 2). This is interesting as it indicates that while the change in individual sugar contents of MicroTand FieldT in response to a period of postharvest cold treatmentis somewhat different, the change is proportional when the ratioof reducing sugars to suc is considered. The fact that the glu:sucand hexose:suc ratios are significantly correlated in MicroT andFieldT after cold treatment is important, as we have previouslyfoundtheglu:sucratiotobeagoodpredictorofinvertaseactivity(McKenzieetal.,2005),whichisakeyregulatorofCIS(Pressey and Shaw, 1966; Greiner et al., 1999; McKenzie et al., 2005).Furthermore, the hexose:suc ratio has previously been found byZrenner et al. (1996) to be a good predictor of invertase activity.In this postharvest study of 17 independent potato geno-types with a range of resistances to CIS, we have confirmedthat MicroT do undergo CIS and that there is a strong corre-lation between the CIS response of MicroT and FieldT whenglu:suc or hexose:suc ratios are determined. These results indi-cate that MicroT may well be a suitable substitute for FieldT inthe study of CIS, allowing a more rapid postharvest screen thanconventional methods. Acknowledgements We thank Russell Genet for supplying tubers for the exper-iments, John Anderson for information on the CIS response of the cultivars, Andrew Mullan for media preparation, AndrewMcLachlan for statistical analysis and John Seelye for criticalremarks on the manuscript. This research was partly funded bythe New Zealand Foundation for Research, Science and Tech-nology. References Brown, J., Mackay, G.R., Bain, H., Griffith, D.W., Allison, M.J., 1990. Theprocessing potential of tubers of the cultivated potato,  Solanum tuberosum L. after storage at low-temperatures. 2. Sugar concentration. Potato Res. 33,219–227.Claassen, P.A.M., Vancalker, M.H., Marinus, J., 1992. Accumulation of sugarsin microtubers of potato node cuttings (cv Kennebec) during cold-storage.Potato Res. 35, 191–194.Donnelly, D.J., Coleman, W.K., Coleman, S.E., 2003. Potato microtuber pro-duction and performance: a review. Am. J. Potato Res. 80, 103–115.Ezekiel, R., Shekhawat, G.S., 2002. Potato processing in developing countrieswith special reference to India. Potato, global research & development. In:Proceedings of the Global Conference on Potato, vol. 2, New Delhi, India,December 6–11, 1999, pp. 1010–1020.Fletcher,P.J.,Fletcher,J.D.,Cross,R.J.,1998.Potatogermplasm:invitrostorageand virus reduction. NZ J. Crop Hort. Sci. 26, 249–252.Gamborg,O.,Miller,R.A.,Ojima,K.,1968.Nutrientrequirementsofsuspensioncultures of soybean root cells. Exp. Cell. Res. 50, 151–158.Greiner, S., Rausch, T., Sonnewald, U., Herbers, K., 1999. Ectopic expressionof a tobacco invertase inhibitor homolog prevents cold-induced sweeteningof potato tubers. Nat. Biotechnol. 17, 708–711.Hayes, R.J., Thill, C.A., 2002. Introgression of cold (4C) chipping from 2x (2endosperm balance number) potato species into 4x(4EBN) cultivated potatousing sexual polyploidization. Am. J. Potato Res. 79, 421–431.Hayes, R.J., Thill, C.A., 2003. Genetic gain from early generation selection forcold chipping genotypes in potato. Plant Breed. 122, 158–163.Hurst, P.L., Corrigan, V.K., Hannan, P.J., Lill, R.E., 1995. Storage rots, compo-sitional analysis, and sensory quality of three cultivars of buttercup squash.NZ J. Crop Hort. Sci. 23, 89–95.Leclerc, Y., Donnelly, D.J., Coleman, W.K., King, R.R., 1995. Microtuber dor-mancy in three potato cultivars. Am. Potato J. 72, 215–223.McKenzie, M.J., Sowokinos, J.R., Shea, I.M., Gupta, S.K., Lindlauf, R.R.,Anderson, J.A.D., 2005. Investigations on the role of acid invertase andUDP-glucose pyrophosphorylase in potato clones with varying resistance tocold-induced sweetening. Am. J. Potato Res. 82, 231–239.Murashige,T.,Skoog,F.,1962.Arevisedmediumforrapidgrowthandbioassayswith tobacco tissue cultures. Physiol. Plant. 15, 473–497.Oltmans, S.M., Novy, R.G., 2002. Identification of potato ( Solanum tuberosum L.) haploid × wild species hybrids with the capacity to cold-chip. Am. J.Potato Res. 79, 263–268.Pressey, R., Shaw, R., 1966. Effect of temperature on invertase, invertaseinhibitor, and sugars in potato tubers. Plant Physiol. 41, 1657–1661.Pruski, K., Astatkie, T., Duplessis, P., Stewart, L., Nowak, J., Struik, P.C., 2003.Manipulation of microtubers for direct field utilization in seed production.Am. J. Potato Res. 80, 173–181.Suttle,J.C.,1998.Involvementofethyleneinpotatomicrotuberdormancy.PlantPhysiol. 118, 843–848.Veramendi, J., Willmitzer, L., Trethewey, R.N., 1999. In vitro grown potatomicrotubers are a suitable system for the study of primary carbohydratemetabolism. Plant Physiol. Biochem. 37, 693–697.Xiong, X., Tai, G.C.C., Seabrook, J.E.A., 2002. Effectiveness of selection forquality traits during the early stage in the potato breeding population. PlantBreed. 121, 441–444.Zhang, Z.J., Mao, B.Z., Li, H.Z., Zhou, W.J., Takeuchi, Y., Yoneyama, K.,2005. Effect of salinity on physiological characteristics, yield and qualityof microtubers in vitro in potato. Acta Physiol. Planta. 27, 481–489.Zrenner,R.,Schuler,K.,Sonnewald,U.,1996.Solubleacidinvertasedeterminesthehexose-to-sucroseratioincold-storedpotatotubers.Planta198,246–252.
Search
Similar documents
View more...
Related Search
We Need Your Support
Thank you for visiting our website and your interest in our free products and services. We are nonprofit website to share and download documents. To the running of this website, we need your help to support us.

Thanks to everyone for your continued support.

No, Thanks