Endogenous Cytokinins and the Breaking of Dormancy and Apical Dominance in Potato Tubers

Cytokinins are present in all parts of potato tubers, and areequally distributed between the apical, lateral, and internodaltissue when dormant. However, the breaking of dormancy coincidedwith a rapid increase in the free base cytokinin levels in theapical buds and the tissue adjacent to it. These high levelsof cytokinin in the apical tissue were maintained while apicaldominance was displayed. Once apical dominance was overcomethe cytokinin levels in the lateral buds and the tissue adjacentto them were similar to the levels in the apical regions. Thepresent evidence suggests that cytokinin glucosides are transportedto the meristematic regions of the tubers where they are hydrolysedto their free bases. Amounts of free bases in excess of thoserequired for growth are apparently again converted to storageforms (particularly zeatin glucoside) in the meristematic regionsof the tubers and in the sprouts.     

Tuberization in Potato at High Temperatures: Gibberellin Content and Transport from Buds

Warm temperatures (35°C day/30°C night) which inhibittuberization in potato (Solanum tuberosum L., cv. Sebago) increasedgibberellin activity in crude extracts from buds, but not frommature leaves, as determined by the lettuce hypocotyl bioassay.Changes in the growth of tubers and stolons indicate the occurrenceof basipetal movement of GA₃ applied to the terminal bud ora mature leaf. ¹⁴C labelling from GA₃ or mevalonic acid injectedjust below the terminal bud was recovered in the lower shoot,stolons and tubers, but the amount transported was greater atcool temperatures (20/15°C). It is concluded that high temperaturespromote the synthesis of gibberellin in the buds rather thantransport to the stolons. Solanum tuberosum L., potato, tuberization, gibberellin     

Role of Endogenous Abscisic Acid in Potato Microtuber Dormancy

Potato (Solanum tuberosum L. cv Russet Burbank) microtubers generated in vitro from single-node explants contained substantial amounts (approximately 250 pmol/g fresh weight) of free abscisic acid (ABA) and were completely dormant for a minimum of 12 weeks. Microtubers that developed in the presence of 10 [mu]M fluridone (FLD) contained considerably reduced amounts (approximately 5-25 pmol/g fresh weight) of free ABA and exhibited a precocious loss of dormancy. Inclusion of exogenous racemic ABA in the FLD-containing medium suppressed the premature sprouting of these microtubers in a dose-dependent manner. At a concentration of 50 [mu]M, exogenous ABA restored internal ABA levels to control values and completely inhibited FLD-induced precocious sprouting. Exogenous jasmonic acid was ineffective in suppressing FLD-induced sprouting. Application of FLD to preformed, fully dormant microtubers also resulted in a reduction in internal ABA content and precocious sprouting. These results indicate that endogenous ABA is essential for the induction and maintenance of potato microtuber dormancy.     

Changes of Abscisic Acid and Gibberellin Contents during the Release of Dormancy in Winter Buds of Populus tomentosa Carr.

Changes of abscisie acid (ABA) and gibberellin (GA3) contents during the release of dormancy in winter bud of Populus tomentosa Carr. were determinedwith GC. After leaf fall in autumn, content of ABA in the bud was 888.0 μg/kg. fr.wt. Obvious decrease in ABA content was observed during the bud released from dormancy. The bud kept in room temperature opened about two months earlier thanthat under natural condition; and the rate of decrease of ABA content in these budwas also more rapid. The ABA contents of buds with similar outer appearance werecompared, either the bud from outside under natural condition or under room temperature, they were similar, although time of their occurrence was quite different, withalmost a difference of about two months. From this fact it has been assumed that thereis a close relationship between the release of dormancy and the decrease in ABA content. Another fact was noticed before Dec. 6, no GA3 could be detected in the dormantbud. From Jan. 9 and thereafter, GA3 content increased gradually and reached itsmaximum (20 μg/kg. fr.wt) by Mar. 19, the bud was inflated. GA3 decreased again as the bud was opened, it seems to be that the process of releasing dormancy in bud mightbe promoted by GA3.     

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 Viruses Y and A in Tubers by Enzyme-Linked Immunosorbent Assay after Natural and Artificial Break of Dormancy

The effects of natural and artificial break of dormancy on the detection of potato viruses Y (PVY) and A (PVA) in tubers of field-grown potato cultivars with primary and secondary infections were studied by enzyme-linked immunosorbent assay (ELISA). Both viruses were at low concentration and unevenly distributed in dormant -tubers. Four to six weeks after treatment with Rindite, maximum concentrations of PVY and PVA were detected at both tuber ends with generally higher values at the rose end than at the heel end. Slower and smaller virus increase and a retarded and/or limited virus translocation were observed in treated tubers of resistant cultivars. Consequently, detectability of PVY and PVA was higher in tubers of susceptible cultivars than in those of the resistant ones. Detection of both viruses was very difficult and unreliable in tubers after natural break of dormancy. The very low concentration of PVY and PVA in dormant tubers and their drastic multiplication in Rindite- treated tubers appear to be characteristic of potyviruses and are unique among the major potato viruses.     

杜仲形成层休眠机理

对杜仲 (EucommiaulmoidesOliv .)一年生枝条休眠中的芽和维管形成层的结构和蛋白质含量进行了研究 ,探讨了杜仲不同休眠期转化的生理生化机理。结果证实了杜仲树的休眠期包括 2个被动休眠期和一个生理休眠期。在生理休眠期 ,无论用外源IAA处理 ,还是给予适当的温度和光照 ,形成层都不能恢复活动。而且 ,雌株进入各个休眠阶段的时间都比雄株早。树皮中的蛋白质含量在第一被动休眠期间 (Q1)显著地逐步增高 (P <0 .0 1) ,进入生理休眠期 (R)后 ,急剧降低 ,但第二被动休眠期 (Q2 )开始后又显著升高 (P <0 .0 1)。杜仲雌雄株树皮中的蛋白质含量变化趋势基本一致 ,但雄株发生变化的时间比雌株早。SDS_PAGE电泳结果表明 ,在Q1 R Q2的转变期出现一11.8kD的特异蛋白条带。此特异蛋白条带可能与形成层休眠期中各阶段的转变调节有关。     

杜仲形成层休眠机理

对杜仲(Eucommia ulmoides Oliv.)一年生枝条休眠中的芽和维管形成层的结构和蛋白质含量进行了研究,探讨了杜仲不同休眠期转化的生理生化机理.结果证实了杜仲树的休眠期包括2个被动休眠期和一个生理休眠期.在生理休眠期,无论用外源IAA处理,还是给予适当的温度和光照,形成层都不能恢复活动.而且,雌株进入各个休眠阶段的时间都比雄株早.树皮中的蛋白质含量在第一被动休眠期间(Q1)显著地逐步增高(P<0.01),进入生理休眠期(R)后,急剧降低,但第二被动休眠期(Q2)开始后又显著升高(P<0.01).杜仲雌雄株树皮中的蛋白质含量变化趋势基本一致,但雄株发生变化的时间比雌株早.SDS-PAGE电泳结果表明,在Q1-R-Q2的转变期出现一11.8 kD的特异蛋白条带.此特异蛋白条带可能与形成层休眠期中各阶段的转变调节有关.     

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     

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)     

Regulation of Bud Rest in Tubers of Potato, Solanum tuberosum L: VI. Biochemical Changes Induced in Excised Potato Buds by Gibberellic Acid

The rest period of the potato tuber was studied in relation to certain biochemical changes that are induced by gibberellic acid (GA₃). The concentration of reducing sugars in excised plugs with buds treated with 10⁻⁴m GA₃ decreased in the first 4 hours after treatment and then rapidly increased up to 70 hours. The pattern in control buds was similar, but the changes occurred more slowly. The response to GA₃ is temperature-dependent and is not limited to any particular tissue of the tuber. The concentration of reducing sugars in excised buds increased proportionally to the log of the concentration of GA₃ in a range from 10⁻⁸ to 10⁻⁴m. At 10⁻³m, GA₃ slightly inhibited production of reducing sugars. Malonate inhibits the initial decrease and the subsequent increase in reducing sugars in control buds, but not the increase induced by GA₃.     

Levels and Aggregation of Ribosomes during Dormancy and Dormancy Break of Peach Flower Buds

The level of ribosomes and their aggregation state (monosomes-polysomes) have been investigated in relation to dormancy in peach flower buds (Prunus persica). The ribosomes were analysed by a linear sucrose gradient. The ribosomal content hardly changes in the bud before dormancy and until dormancy breaks; on the other hand after this period there is a remarkable increase in the ribosomal level strictly related to the increase in bud weight. The ribosomal content reaches the highest value at flowering. During dormancy break the largest portion of ribosomes is localized in flower primordia, not in scales. Polysomes, which are always present in buds, remain constant during dormancy (35%), increase at dormancy breaking, reaching the highest level at flowering.     

Cell Cycling and the Fate of Potato Buds

The cell cycling characteristics of the regions of the apicalmeristems of underground shoots and buds of Solanum tuberosumL. were investigated by stathmokinesis and labelling. The apicaldomes of orthotropic shoots produce cells at twice the elementalrate of those of stolons, and their youngest leaf primordiaat twelve times the rate. Changing the fate of stolons so thatthey will become orthotropic by decapitating the tuber sproutsthat bear them results within 24 h in a general increase incell production especially in the leaf primordia. Axillary buds on tuber sprouts induced to become precursorsof orthotropic shoots instead of stolons undergo a spectacularincrease in cell division within 24 h in all regions, especiallyin the primordia and bud anlagen where the rate increases 20-foldor more. The summit is slower to react than other regions, but,by 24 h, its rate of cell division increases 11-fold and itis contributing 14 cells per day to the flanks from its 80 cells. In all the axillary buds the rate of mitosis in the summit ishalf that of the flanks of the apical dome, but, in both stolonsand orthotropic underground shoots, the rate is higher in thesummit than in the flanks or rib meristem. The results are discussed in relation to what is known of cellcycling changes after floral evocation. Solanum tuberosum L., potato, fate, cell division, apical meristem, stathmokinesis     

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.