Tuber Sprouts Research Articles

In vitro production of PLRV and PSTVd-free plants of potato using electrotherapy

Potato leafroll virus (PLRV) and Potato spindle tuber viroid (PSTVd) were responsible for major economic losses in potato production. Effect of electrotherapy on the regeneration response and production of PLRV and PSTVd-free plants from potato explants is reported. DAS-ELISA and RT-PCR were used for indexing of infected and in vitro-regenerated potato plants. Shoot tips, nodal segments, and tuber sprouts of infected potato plants were exposing to electric current intensities of 5- 25 mA in separate lots for a time period of 5-25 min and cultured on medium. Regeneration response was not significantly changed by exposing explants to 5-10 mA for 5-10 min. Electrotherapy at 15, 20, and 25 mA for 15-25 min had slightly decreased regeneration response of explants and current treatment at 20 and 25 mA for 20 min gave an appreciable number of PLRV and PSTVd-free plants. In a comparative study, electrotherapy of shoot tips and sprouts at 20 mA/20 min proved effective for knocking out virus and viroid without any adverse effecta on regeneration response and production of plantlets. Shoot tips gave 46.72% PLRV and 45.90% PSTVd-free plants with regeneration response of 84.71% and sprouts gave 42.85% PLRV and 43.60% PSTVd-free plants with regeneration response of 92.35% by using 20 mA/20 min treatment. Nodal segments showed less regeneration response (78.47%) and produced a low frequency of PLRV (34.51%) and PSTVd (33.62%)-free plants after this treatment. The protocol is simple and effective for eradicating PLRV and PSTVd from infected potato germplasm.

Solanum tuberosum StCDPK1 is regulated by miR390 at the posttranscriptional level and phosphorylates the auxin efflux carrier StPIN4 in vitro, a potential downstream target in potato development.

Among many factors that regulate potato tuberization, calcium and calcium-dependent protein kinases (CDPKs) play an important role. CDPK activity increases at the onset of tuber formation with StCDPK1 expression being strongly induced in swollen stolons. However, not much is known about the transcriptional and posttranscriptional regulation of StCDPK1 or its downstream targets in potato development. To elucidate further, we analyzed its expression in different tissues and stages of the life cycle. Histochemical analysis of StCDPK1::GUS (β-glucuronidase) plants demonstrated that StCDPK1 is strongly associated with the vascular system in stems, roots, during stolon to tuber transition, and in tuber sprouts. In agreement with the observed GUS profile, we found specific cis-acting elements in StCDPK1 promoter. In silico analysis predicted miR390 to be a putative posttranscriptional regulator of StCDPK1. Quantitative real time-polymerase chain reaction (qRT-PCR) analysis showed ubiquitous expression of StCDPK1 in different tissues which correlated well with Western blot data except in leaves. On the contrary, miR390 expression exhibited an inverse pattern in leaves and tuber eyes suggesting a possible regulation of StCDPK1 by miR390. This was further confirmed by Agrobacterium co-infiltration assays. In addition, in vitro assays showed that recombinant StCDPK1-6xHis was able to phosphorylate the hydrophilic loop of the auxin efflux carrier StPIN4. Altogether, these results indicate that StCDPK1 expression is varied in a tissue-specific manner having significant expression in vasculature and in tuber eyes; is regulated by miR390 at posttranscriptional level and suggest that StPIN4 could be one of its downstream targets revealing the overall role of this kinase in potato development.

Impacts of water depth and substrate type on Vallisneria natans at wave-exposed and sheltered sites in a eutrophic large lake

Water depth, substrate type and wave exposure are major environmental factors influencing the growth and distribution of submerged macrophytes. However, we lack knowledge on the ecological reactions of submerged macrophytes to those factors during an entire growth period in a eutrophic lake with a Secchi depth of less than 50cm. We investigated the interactive effects of water depth (60, 120 and 200cm), waves (exposed vs. sheltered) and substrate nutrient level (fertile sludge vs. brown clay) on the survival, growth and morphology of Vallisneria natans using a new type of rhizotron in a 252-day field experiment. Plant length, leaf number, ramet number, root length, root number and biomass generally decreased with increased water depth at both wave conditions and in both substrates. When exposed to wave, the biomass of V. natans in water at 200cm depth rapidly declined in both substrates. When sheltered to wave, aboveground biomass at 60cm water depth first declined to zero with many buried rhizomes remained. The tuber germination rate decreased with increasing water depth during the second year of germination. No plants sprouted at 200cm water depth except at the case of exposed wave and sludge substrate. Ramet number was influenced most by water depth, followed by aboveground biomass, leaf number, plant length, and survival rate. Wave shelter and brown clay enhanced the impacting strength of the water depth. Wave exposure exhibited no negative influence on survival percentage, whereas sludge had a positive influence on plant survival in deep water after overwintering. Waves negatively affected the rate of increase of plant growth in sludge but positively in clay. The positive joint effects of wave exposure and low-nutrient substrate were mainly on plant length and biomass. Water depth had a negative influence that predominated over substrate and waves regarding plant survival and growth. Moreover, this negative influence may be aggravated by an increasing risk of submersed macrophyte loss caused by decreased belowground growth under high water levels, high wave exposure and high-nutrient conditions. Decreasing the water depth could be an useful measure for submerged macrophyte restoration in freshwater habitats, even in turbid eutrophic water.

Detection and genome characterization of <i>Potato virus</i> Y isolates infecting potato (<i>Solanum tuberosum</i> L.) in La Union (Antioquia, Colombia)

Potato virus Y (PVY) is one of the most severe viruses affecting the production of potato (Solanum tuberosum) in the world. This study presents a detailed molecular analysis using nextgeneration sequencing (NGS), IC-RT-qPCR and RT-PCR on the PVY isolates infecting seed-tubers and foliage of potato plants cv. Diacol-Capiro in La Union (Antioquia, Colombia). Analysis of incidence by IC-RT-qPCR in 15 random leaf samples of three cultivation plots and fifteen sprouting tuber eye-buds reveal infection levels between 13.4 and 80%; a higher incidence of 86.7% was observed in seed-tuber samples with threshold cycle (Ct) values as low as 24.3. Genome assembly from a bulk of foliage samples resulted in a consensus PVY genome (PVY_LaUnionF) of 9,702 nt and 399 polymorphic sites within the polyprotein ORF; while the assembled genome from sprouts of tubers has 9,704 nt (PVY_LaUnionT) and contained only six polymorphic nucleotide sites. Phylogenetic analysis demonstrates that the PVY isolates from leaf samples are in the recombinant PVYNTN group (sequence identity >99%); while those from tuber sprouts are in the PVYN/NTN group with identities above 95%. Sanger sequencing of viral capsid suggests the presence of a third variant related to PVYO, a prevalent strain reported in potato fields worldwide.

Asada-Halliwell pathway maintains redox status in Dioscorea alata tuber which helps in germination

Reactive Oxygen Species (ROS) are important regulatory molecules governing physiological processes. In the present study a biochemical and proteome level comparison of two contrasting growth stages of Dioscorea alata tuber namely germinating and mature tuber was performed in order to understand the tuber physiology and biochemistry. Existence of all the component enzymes [APx (ascorbate peroxidase), GR (glutathione reductase), DHAR (dehydroascorbate reductase), MDHAR (mono-dehydroascorbate reductase)] and major products [ascorbate (ASC) and glutathione (GSH)] of the cycle showed an operational Asada-Halliwell cycle in the tuber. A 2.65 fold increase in ASC content & a 3.8 fold increase in GR activity fortified the redox milieu during germination. In contrast a 5 fold higher H2O2 content (due to 3.08 fold lower APx activity) and accumulation of reactive nitrogen species (RNS) such as nitric oxide (NO, 2.4-fold) and S-nitrosothiol (SNO, 2.08 fold) contributed to overall oxidative conditions in the mature tuber. The carbonic anhydrase (CA, 7.5 fold), DHAR (5.31 fold) and MDHAR (7 fold) activities were higher in the germinating tuber in comparison with the mature tuber. GSNO negatively regulated the CA (3.6 & 3.95 fold), MDHAR (7.5 & 1.5 fold) and APx (2.3 & 1.81 fold) while another NO donor, CysNO negatively regulated the DHAR (2.24 & 1.32 fold) activity in the mature and germinating stages respectively indicating again that the lesser inhibition by NO (via nitrosylation) may be because of overall reducing environment in the germinating tuber. Increased SNO leading to S-nitrosylation of dioscorin was confirmed by Biotin switch assay. This is the first report showing dioscorin nitrosylation. The present analysis showed differential redox regulation and also suggests the physiological relevance of CA, DHAR, MDHAR, APx & GR in tuber germination for the first time. These enzymes may be used as potential markers of tuber germination in future.

Regulation, overexpression, and target gene identification ofPotato Homeobox 15(POTH15) – a class-IKNOXgene in potato

Potato Homeobox 15 (POTH15) is a KNOX-I (Knotted1-like homeobox) family gene in potato that is orthologous to Shoot Meristemless (STM) in Arabidopsis. Despite numerous reports on KNOX genes from different species, studies in potato are limited. Here, we describe photoperiodic regulation of POTH15, its overexpression phenotype, and identification of its potential targets in potato (Solanum tuberosum ssp. andigena). qRT-PCR analysis showed a higher abundance of POTH15 mRNA in shoot tips and stolons under tuber-inducing short-day conditions. POTH15 promoter activity was detected in apical and axillary meristems, stolon tips, tuber eyes, and meristems of tuber sprouts, indicating its role in meristem maintenance and leaf development. POTH15 overexpression altered multiple morphological traits including leaf and stem development, leaflet number, and number of nodes and branches. In particular, the rachis of the leaf was completely reduced and leaves appeared as a bouquet of leaflets. Comparative transcriptomic analysis of 35S::GUS and two POTH15 overexpression lines identified more than 6000 differentially expressed genes, including 2014 common genes between the two overexpression lines. Functional analysis of these genes revealed their involvement in responses to hormones, biotic/abiotic stresses, transcription regulation, and signal transduction. qRT-PCR of selected candidate target genes validated their differential expression in both overexpression lines. Out of 200 randomly chosen POTH15 targets, 173 were found to have at least one tandem TGAC core motif, characteristic of KNOX interaction, within 3.0kb in the upstream sequence of the transcription start site. Overall, this study provides insights to the role of POTH15 in controlling diverse developmental processes in potato.

Transcript profiling reveals that cysteine protease inhibitors are up-regulated in tuber sprouts after extended darkness.

Potato (Solanum tuberosum L.) tubers are an excellent staple food due to its high nutritional value. When the tuber reaches physiological competence, sprouting proceeds accompanied by changes at mRNA and protein levels. Potato tubers become a source of carbon and energy until sprouts are capable of independent growth. Transcript profiling of sprouts grown under continuous light or dark conditions was performed using the TIGR 10K EST Solanaceae microarray. The profiles analyzed show a core of highly expressed transcripts that are associated to the reactivation of growth. Under light conditions, the photosynthetic machinery was fully activated; the highest up-regulation was observed for the Rubisco activase (RCA), the glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and the Photosystem II 22kDa protein (CP22) genes, among others. On the other hand, sprouts exposed to continuous darkness elongate longer, and after extended darkness, synthesis of chloroplast components was repressed, the expression of proteases was reduced while genes encoding cysteine protease inhibitors (CPIs) and metallocarboxypeptidase inhibitors (MPIs) were strongly induced. Northern blot and RT-PCR analysis confirmed that MPI levels correlated with the length of the dark period; however, CPI expression was strong only after longer periods of darkness, suggesting a feedback loop (regulation mechanism) in response to dark-induced senescence. Prevention of cysteine protease activity in etiolated sprouts exposed to extended darkness could delay senescence until they emerge to light.

Genome characterization of a Potato virus S (PVS) variant from tuber sprouts of Solanum phureja Juz. et Buk

Potato virus S (PVS) is a prevalent virus in potato fields in Colombia and the rest of the world. PVS has been classified into two separate lineages, PVSO (Ordinary) and PVSA (An- dean), which are genetically distinct. In this study, the com- plete genome sequence of a new PVS isolate (PVS_Antioquia) was obtained using High-throughput sequencing (Illumina HiSeq-2000) from tuber sprouts of Solanum phureja (var. Criolla Colombia). The PVS_Antioquia genome comprises 8,483 nt that code for six ORFs: RdRp (223 kDa), TGBp1-3 (25kDa, 12kDa, 7kDa) CP (32.3 kDa) and NABP (11 kDa) and share a high sequence identity with respect to the PVS_RVC (>95%) from Colombia, in contrast to 81 to 82% identity with respect to the PVSA and PVSO isolates from around the world. This genome information was used to design RT-qPCR primers that are specific for the Colombian PVS strains (RVC and Antioquia) which were validated in S. phureja leaf and tuber samples. These primers detected PVS in 80 and 60% of a set of fifteen leaf and tuber samples, respectively, suggesting a high incidence of this virus in the potato crops of Antioquia.

The Involvement of Gibberellins in 1,8-Cineole-Mediated Inhibition of Sprout Growth in Russet Burbank Tubers

The involvement of gibberellins in 1,8-cineole-mediated inhibition of tuber sprout growth was investigated in non-dormant field- and greenhouse-grown tubers of Russet Burbank. Continuous exposure of tubers to cineole in the vapor-phase resulted in a dose-dependent inhibition of sprout growth. Comparative studies using plant bioassay systems whose growth was differentially dependent on cell division, cell elongation, or both demonstrated that cineole had no direct effect on either process. Of the assays used, only cineole-mediated inhibition of etiolated hypocotyl growth mirrored the inhibition of tuber sprout growth which suggested an effect on gibberellin synthesis or action. Both GA19 and GA20 were detected in extracts prepared from control sprouts but only GA19 was found in extracts prepared from cineole treated sprouts. Exogenous GA3, GA20, and GA1 (but not GA19) reversed cineole-mediated sprout growth inhibition. Expression of genes encoding key GA metabolic enzymes was altered by cineole treatment in a manner consistent with diminished endogenous GA content. Collectively, these results suggest that the inhibition of sprout growth by low vapor-phase concentrations of cineole is in part a result of impaired GA biosynthesis resulting in a reduction in bioactive GA content.

Влияние заражения клубней кольцевой гнилью и обработки монойодацетатом натрия совместно с прогреванием на хранение картофеля

В статье обсуждается влияние на проращивание клубней монойодацетата натрия (МИА) совместно с прогреванием (45 °C, 1 ч) в качестве потенциального агента для борьбы с Clavibacter michiganensis ssp. sepedonicus (Cms) перед закладкой картофеля на хранение. В работе использованы клубни картофеля (Solanum tuberosum L.) сорта Лукьяновский. В эксперименте присутствовало четыре варианта обработки клубней, в каждом варианте было 30 клубней. После проведенных обработок клубни помещали в условия овощехранилища на 8 месяцев. Весной подсчитывали количество ростков, измеряли длину проростков у клубней и проводили клубневой анализ. Полученные результаты статистически обрабатывали с использованием пакета программ Excel. Показано, что заражение клубней Cms снижало способность клубней к прорастанию. Обработка МИА и прогревание здоровых клубней картофеля перед закладкой на хранение подавляло прорастание клубней, что полезно для продовольственного картофеля. Результаты клубневого анализа показали, что прогревание снижало общее количество больных клубней примерно на 39 %, клубни были менее поражены кольцевой и бурой гнилями. Обработка МИА также способствовала снижению количества клубней, пораженных бурой и кольцевой гнилями. Обработка клубней МИА совместно с прогреванием снижала общее количество больных клубней, пораженных проволочником и пустотелых, кольцевой и сухой гнилями, а также паршой. Обработка МИА и прогреванием инфицированных клубней картофеля перед закладкой на хранение снимала подавляющий эффект бактерий на прорастание. Полученный результат актуален для обработки семенного картофеля, так как кольцевая гниль является латентным заболеванием.

Antiviral Effect of Ribonuclease from <i>Bacillus pumilus</i> against Phytopathogenic Rna-Viruses

Background: Viruses can cause different diseases in plants. To prevent viral infections, plants are treated with chemical compounds and antiviral agents. Chemical antiviral agents usually have narrow specificity, which limits their wide application. Alternative antiviral strategy is associated with the use of microbial enzymes, which are less toxic and are readily decomposed without accumulation of harmful substances. The aim of this work is to study the effect of Bacillus pumilus ribonuclease on various phytopathogenic viruses with specific focus on the ability of enzyme to eliminate them from plant explants in vitro. Materials and methods: Extracellular ribonuclease of B. pumilus is tested as an antiviral agent. To study the antiviral effect of RNase, depending on concentration and the time of application several plant-virus model systems are used. Virus detection is conducted by serological testing and RT-PCR. Results: Bacillus pumilus ribonuclease possesses antiviral activity against plant Rna-viruses RCMV (red clover mottle virus), PVX (Potato Virus X) and AMV (Alfalfa Mosaic Virus). The maximum inhibitory effect against actively replicating viruses is observed when plants are treated with the enzyme in the concentration of 100 ug/ml prior to infection. In case of local necrosis ribonuclease in the concentration of 1 ug/ml completely inhibits the development of RCMV virus on bean plants. The enzyme is able to penetrate plants and inhibit the development of viral infection, inhibiting effect for untreated surfaces decreased on average for 20%. It is also found that B. pumilus ribonuclease protects apical explants of sprouts of potato tubers from PVM and PVS viruses. Conclusion: B. pumilus ribonuclease possesses antiviral activity against plant Rna-viruses and produces viruses-free plants in the apical meristem culture.

Comparative Effects of Foliar Application of Gibberellic Acid and Benzylaminopurine on Seed Potato Tuber Sprouting and Yield of Resultant Plants

Seed potato tubers planted immediately after harvest is characterized by delayed plant emergence, poor establishment and low yields. Gibberellic acid (GA) and Benzylaminopurine (BA) or their combinations cause dormancy breakage though little information is available on their combined application to dormancy termination. The effects of foliar application of GA and BA on potato tuber sprouting and subsequent yield were studied. Three potato varieties with different tuber dormancy period; ‘Asante’ (short dormancy), Dutch Robyjn (medium dormancy) and ‘Kenya Sifa’ (long dormancy) were planted at National Potato Research Centre, Tigoni and sprayed with a factorial combinations of 0, 50, 100, 300 ppm GA and 0, 50, 75, 100 ppm BA separately and combined at the rate of 1000 lts/ha spray volume towards the end of maturation. The resulting tubers were put in diffuse light storage (DLS) and data on number, length and vigour of sprouts recorded. Sprouted seed tubers were subsequently planted and evaluated for both growth characteristics and yields. The data collected was subjected to analysis of variance and significantly different means were separated using Fisher’s protected least significant difference at p≤0.05. Higher rates of foliar application of GA+BA (300 ppm + 100 ppm) compared with the control (0 + 0) resulted in significant increase insprout length (cm), number of sprout/tuber, sprout vigour (score), and % sprouting from 3.24 to 7.02 and 3.84 to 9.03, 2.04 to 4.45 and 2.07 to 4.8, 1.7 to 3.06 and 1.63 to 3.23, 61.21to 86.67and 63.3 to 83.7 in Asante, 2.94 to 8.03 and 2.8 to 7.99, 1.84 to 5.24 and 1.87 to 4.76, 1.3 to 3.0 and 1.27 to 2.63, 50.61 to 92.7 and 52.7 to 85.7in Dutch Robyjn and 0.79 to 6.43 and 1.32 to 6.99, 0.61 to 3.49 and 0.79 to 3.33, 0.61 to 3.03 and 0.73 to 2.83, 22.12 to 85.76 and 28.3 to83.7 in Kenya Sifa after storage in 2008 and 2009 respectively. A combination of BA and GA resulted in significantly more growth than using only GA or BA alone at the same level. Similarly the subsequent tuber numbers per plant and yield (tons/ha) in resultant plants increased from 7.13 to 12.53 and 24.66 to 32.27, 6.93 to 10.47 and 16.73 to 23.37, and 5.63 to 9.6 and 17.53 to 30.13 in Asante, Dutch Robyjnand Kenya Sifa respectively. Combined application of GA + BA at varied rates can be used to improve sprouting characteristics of seed potato and yield of resultant plants.

Modification of serological techniques and their evaluation for detection of potato viruses in seed certification related activities

Development of alternative serological techniques to ELISA for detection of potato viruses offers advantages for monitoring virus incidence and for seed potato certification systems. Several trials showed that multiplex tissue print immunoassay (TPIA) and dot blot immunoassay (DBIA) might represent fast, practical, and sensitive alternatives for the detection of: Potato leaf roll virus (PLRV), Potato virus S (PVS), Potato virus X (PVX) and Potato virus Y (PVY), from green and/or tuber tissues. In TPIA, the specific precipitation patterns in infected tissues of leaf petioles or stem cross sections, observed with each virus, allowed identification of the specific virus or mixed infections in a single multiplex assay. For detection of PVY in green tissues, DBIA was shown to be over 50 times more sensitive than ELISA. TPIA and ELISA from the tuber stem end or from eyes might be used for rapid detection of PVY and PVS in seed potato tubers without prior germination. PVS was evenly distributed in potato tuber tissue, while PVY was localized in the vascular tissue beneath the epidermis, with irregular distribution along the periphery of the potato tuber. For laboratories in developing countries lacking time and facilities for tests based on tuber germination, monitoring for PVS and PVY using TPIA in tuber tissue may be a suitable alternative to ELISA.

Evaluation of potato mini-tubers dormancy breaking affected by various chemicals, genotype and mini-tuber Size

This work was done in order to evaluation the effect of gibberellic acid to potato mini-tubers dormancy breaking at Seed and Plant Certification and Registration Institute of Karaj (SPCRI) in form of factorial based on randomized completely design in three replication at 2011. Experimental factors were considered chemicals as the first factor in four levels (control, 50 g/lit gibberellic acid, 25 mlit/m3 carbon disulfide, 3% thiourea), potato cultivars as the second factor in two levels (agria and born) and potato mini-tuber size as the third one in four levels (12-20 millimeter, 20-25 millimeter, 25-30 millimeter and 30-35 millimeter). In this experiment characteristics such as sprout length, days to sprouting and days to breaking dormancy were studied. The results of this experiment showed that the main and interactions effects of three factors were affected statistically significant on days to sprouting with probability level of 99%. Sprout length affected by main and interaction effects of experimental factors too. Also dormancy period length showed significant differences about application of chemicals treatments, different seed cultivars and different sizes of potatoes seed noted in 99% probability level. In general it can be stated that application of gibberellic acid left greatest effects among the used chemicals. Also Dormancy period length had greater reduction than other chemicals by application of gibberellic acid. Difference seed cultivars and sizes showed significant differences in their response due to genetic and physiological characteristics. In fact, based on these test’s results can be declared that application of gibberellic acid lead to reduce the time between planting and germination of tubers, to increase sprout length and to reduce the potato seed dormancy period length.

Effects of Production History and Gibberellic Acid on Seed Potatoes

In the present study effects of production history on tuber sprout, root, stem development and crop yield of seed potato cultivars Fambo and Van Gogh were investigated in the High Grade Area of Finland (64.9 N, 25.4 E). The haulms of seed potatoes were destroyed at the time of flowering (50 days after planting, DAP), three weeks after flowering (75 DAP) and as a control the haulm was left to natural death until harvest (95 DAP). The temperature sum accumulation of the seed potatoes was recorded for the growing season and storage period. In addition, the use of plant hormone gibberellic acid (GA) in sprout control was also investigated. The results indicated that cultivar properties had a greater effect on the sprouting and crop yield of seed potatoes than production-phased haulm killing or temperature sum accumulation. Haulm killing carried out at three weeks after flowering (75 DAP) accelerated the emergence of both cultivars significantly compared to killing at 50 DAP or 95 DAP. Gibberellic acid (GA) treatments significantly increased the number of sprouts and at lower concentration (100 mM) GA increased the number of tubers in the cultivar Fambo. Thus, the timing of haulm killing and in the case of Fambo, GA treatment influenced the characteristics of seed potatoes produced in the present study, revealing methods to improve seed potato production in the northern latitudes.

Alelopatia de adubos verdes sobre Cyperus rotundus

The objective of this study was to evaluate the allelopathic effect of soil incorporation of straw of different species of green manure (SGM) on the dry weight of purple nutsedge (Cyperus rotundus). The experiment was conducted at the State University of Mato Grosso do Sul - Unit Aquidauna, sector Plant Science, MS, Brazil. The SGM used were Mucuna aterrima, Mucuna deeringiana and Cajanus cajan and area where the soil remained without vegetation cover and highly infested with C. rotundus (witness). The dry biomass (DB) of the weed emerged plants was quantified at 7, 14, 21 and 28 days after incorporation of vegetation (DAIV) for each 1 m² plot. At 28 DAIV, per plot, the number of purple nutsedge tubers (NT) was counted in a soil volume of 8,000 cm³. Thereafter the tubers were planted in gerboxes filled with sand and placed in a greenhouse type BOD to obtain the percentage of germination of tubers (GT). The DB of the nutsedge increased linearly over the course of the DAIV of SGM biomass where M. aterrima had the highest allelopathic effect on nutsedge, greatly reducing the BS, NT and GT this weed.

Some biological aspects of the weed Lesser celandine (Ranunculus ficaria)

Lesser celandine (Ranunculaceae) is a perennial weed with tuberous root. Tubers are the most important means of reproduction and dispersion of this weed. In recent years, it has spread into wheat fields in Western Iran, mainly in the Lorestan province. A series of experiments were conducted to determine cardinal temperatures and to study the effects of pre-chilling, temperature fluctuations, tuber size, freezing and drying on germination of the tubers, as well as the effect of planting depth on sprouting of the tubers. The results obtained showed that the highest percentage of germination occurred when tubers were stored for more than 2 weeks at 4 or 8 ºC. The optimum temperature for germination differed in large and small tubers (8 and 14oC, respectively). Germination was the highest (almost 100%) at temperature fluctuations of 5-10oC. Germination of the finger-like and small tubers was the highest (95%); however, very small, small, and broken tubers showed the lowest germination percentage. In the freezing experiment, decreasing the temperature and increasing the storage duration decreased the germination of tubers. Increasing the osmotic potential and temperature resulted in decreased tuber germination of Lesser celandine. Lesser celandine could sprout down to 20 cm depth but heat demand for tubers from superficial depth was smaller than for tubers planted at greater depth.

Concerted suppression of all starch branching enzyme genes in barley produces amylose-only starch granules.

BackgroundStarch is stored in higher plants as granules composed of semi-crystalline amylopectin and amorphous amylose. Starch granules provide energy for the plant during dark periods and for germination of seeds and tubers. Dietary starch is also a highly glycemic carbohydrate being degraded to glucose and rapidly absorbed in the small intestine. But a portion of dietary starch, termed “resistant starch” (RS) escapes digestion and reaches the large intestine, where it is fermented by colonic bacteria producing short chain fatty acids (SCFA) which are linked to several health benefits. The RS is preferentially derived from amylose, which can be increased by suppressing amylopectin synthesis by silencing of starch branching enzymes (SBEs). However all the previous works attempting the production of high RS crops resulted in only partly increased amylose-content and/or significant yield loss.ResultsIn this study we invented a new method for silencing of multiple genes. Using a chimeric RNAi hairpin we simultaneously suppressed all genes coding for starch branching enzymes (SBE I, SBE IIa, SBE IIb) in barley (Hordeum vulgare L.), resulting in production of amylose-only starch granules in the endosperm. This trait was segregating 3:1. Amylose-only starch granules were irregularly shaped and showed peculiar thermal properties and crystallinity. Transgenic lines retained high-yield possibly due to a pleiotropic upregualtion of other starch biosynthetic genes compensating the SBEs loss. For gelatinized starch, a very high content of RS (65 %) was observed, which is 2.2-fold higher than control (29%). The amylose-only grains germinated with same frequency as control grains. However, initial growth was delayed in young plants.ConclusionsThis is the first time that pure amylose has been generated with high yield in a living organism. This was achieved by a new method of simultaneous suppression of the entire complement of genes encoding starch branching enzymes. We demonstrate that amylopectin is not essential for starch granule crystallinity and integrity. However the slower initial growth of shoots from amylose-only grains may be due to an important physiological role played by amylopectin ordered crystallinity for rapid starch remobilization explaining the broad conservation in the plant kingdom of the amylopectin structure.

Promoter activity of polypyrimidine tract-binding protein genes of potato responds to environmental cues

Polypyrimidine tract-binding (PTB) proteins are RNA-binding proteins that target specific RNAs for post-transcriptional processing by binding cytosine/uracil motifs. PTBs have established functions in a range of RNA processes including splicing, translation, stability and long-distance transport. Six PTB-like genes identified in potato have been grouped into two clades based on homology to other known plant PTBs. StPTB1 and StPTB6 are closely related to a PTB protein discovered in pumpkin, designated CmRBP50, and contain four canonical RNA-recognition motifs. CmRBP50 is expressed in phloem tissues and functions as the core protein of a phloem-mobile RNA/protein complex. Sequence from the potato genome database was used to clone the upstream sequence of these two PTB genes and analyzed to identify conserved cis-elements. The promoter of StPTB6 was enriched for regulatory elements for light and sucrose induction and defense. Upstream sequence of both PTB genes was fused to β-glucuronidase and monitored in transgenic potato lines. In whole plants, the StPTB1 promoter was most active in leaf veins and petioles, whereas StPTB6 was most active in leaf mesophyll. Both genes are active in new tubers and tuber sprouts. StPTB6 expression was induced in stems and stolon sections in response to sucrose and in leaves or petioles in response to light, heat, drought and mechanical wounding. These results show that CmRBP50-like genes of potato exhibit distinct expression patterns and respond to both developmental and environmental cues.

Ontogeny of the tuber crop Plectranthus edulis (Lamiaceae)

Plectranthus edulis (Lamiaceae) is one of the economically important tuber crops of the genus Plectranthus. It is grown in mid and high altitude areas in parts of Ethiopia. The structure of this plant and its development in time has not been described in detail. Two similar experiments were carried out at Awassa and Wondogenet (Southern Ethiopia) with two cultivars (Lofuwa and Chankua) and 20 harvest dates [from 14 to 280 days after planting (DAP)]. The plants were grown from seed tuber pieces and attained a maximum height of about 1.5 m. Plants produced main stems and primary, secondary and tertiary branches, with primary and secondary branches and their leaves constituting the main part of the canopy. Plant components were the seed tuber pieces, sprouts, main stems, branches, leaves, flowers, fruits, seeds, roots, stolons and tubers. Five, partly overlapping, ontogenetic vegetative phases were observed during one crop cycle: emergence, canopy development, stolon initiation and development, tuber initiation and growth, and a phase of canopy senescence. Stolons were formed on main stems and primary branches and originated below ground or above ground (aerial stolons). Aerial stolons were initiated later than below-ground stolons and were much longer (up to 2.5 m). Tubers usually were produced as a swelling on the tip of the stolon and sometimes as a swelling of the middle part of stolons. Tubers were stem tubers with pairs of ''eyes'' (compound buds) being arranged in the same decussate pattern as the axillary buds on stolons and stems. Tubers of cv. Lofuwa were up to 25 cm in length, those of cv. Chankua up to 20 cm, and both with a diameter of about 2 cm. The tubers in the middle of the stolon were longer than the ones at the tip. After tuber initiation, the total number of tubers increased almost linearly during 12 to 14 weeks, and maximum numbers of tubers were attained around 238 DAP, at crop senescence. Also, the number of smaller tubers (< 10 or 20 g) increased until 238 DAP. In the period of tuber initiation, the average weight per tuber increased up to 20 to 25 g per tuber. The increase in tuber fresh weight with time was therefore realized by an increase in both tuber number and in average weight per tuber. After crop maturity, farmers keep the tubers unharvested in the soil until they need them. This practice dramatically reduces tuber yield and number, because decreases of 36 to 59% were found in total tuber fresh weight and of 18 to 48% in number of tubers when tubers were kept in the soil in the 6 weeks period between 238 and 280 DAP.