Sucrose-Induced Accumulation of beta-Amylase Occurs Concomitant with the Accumulation of Starch and Sporamin in Leaf-Petiole Cuttings of Sweet Potato

β-Amylase of sweet potato (Ipomoea batatas L.), which constitutes about 5% of the total soluble protein of the tuberous root, is absent or is present in only small amounts in organs other than the tuberous roots of the normal, field-grown plants. However, when leaf-petiole cuttings from such plants were supplied with a solution that contained sucrose, the accumulation of β-amylase was induced in both leaf and petiole portions of the explants. The sucrose-induced accumulation of β-amylase in leaf-petiole cuttings occurred concomitant with the accumulation of starch and of sporamin, the most abundant storage protein of the tuberous root. The accumulation of β-amylase, of sporamin and of starch in the petioles showed similar dependence on the concentration of sucrose, and a 6% solution of sucrose gave the highest levels of induction when assayed after 7 days of treatment. The induction of mRNAs for β-amylase and sporamin in the petiole could be detected after 6 hours of treatment with sucrose, and the accumulation of β-amylase and sporamin polypeptides, as well as that of starch, continued for a further 3 weeks. In addition to sucrose, glucose or fructose, but not mannitol or sorbitol, also induced the accumulation of β-amylase and sporamin, suggesting that metabolic effects of sucrose are important in the mechanism of this induction. Treatment of leaf-petiole cuttings with water under continuous light, but not in darkness, also caused the accumulation of small amounts of these components in the petioles, probably as a result of the endogenous supply of sucrose by photosynthesis. These results suggest that the expression of the gene for β-amylase is under metabolic control which is coupled with the expression of sink function of cells in the sweet potato.     

Spatial Patterns of Sucrose-Inducible and Polygalacturonic Acid-Inducible Expression of Genes That Encode Sporamin and r{beta}-Amylase in Sweet Potato

Two major proteins of tuberous roots of sweet potato, sporaminand rß-amylase, were detected in storage parenchymacells, which contain a large amount of starch. In both the leavesand petioles of sweet potato, the sucrose-induced accumulationof mRNAs for sporamin and rß-amylase, and of starchoccurred in a wide variety of cells, first in cells within andaround the vascular tissue and then in various cells distalto them, with the exception of epidermal cells. In the mesophyllcells of leaves treated with sucrose, the accumulation of largenumbers of well-developed starch granules occurred in the preexistingchloroplasts. These results, together with the previous observationthat the sucrose-induced accumulation of sporamin, of rß-amylaseand of starch occurs with similar dependency on the concentrationof sucrose, suggest that an excess supply of sugars to varioustypes of cell triggers a cellular transition that induces thesimultaneous accumulation of these reserve materials that arenormally present in tuberous roots. Accumulation of mRNAs forsporamin and rß-amylase, but not the accumulationof starch, in leaves and petioles can be also induced when leaf-petiolecuttings are supplied with low concentrations of polygalacturonicacid (PGA) at their cut edges. The spatial patterns of accumulationof mRNAs for sporamin and rß-amylase in leaves andpetioles after treatment with PGA were found to be similar tothose observed upon treatment with sucrose. These results suggestthat most of the cells in leaves and petioles have the capacityto respond to both a carbohydrate metabolic signal and a PGA-derivedsignal that is transmitted by diffusion from the vascular system. ⁴Present address: Department of Molecular Biology, NationalInsustitute of Agrobiological Resources, Tsukuba City, Ibaraki,305 Japan.     

Sucrose-Induced Expression of Genes Coding for the Tuberous Root Storage Protein, Sporamin, of Sweet Potato in Leaves and Petioles

Sporamin, a major tuberous root protein of sweet potato, wasfound to accumulate in large quantities in excised leaves andpetioles when such explants were supplied with high concentrationsof sucrose. Although a small amount of sporamin could be detectedin leaves and petioles treated with 1% or lower concentrationsof sucrose, the maximum level of induction required sucroseat a concentration of 3% or higher. The appearance of sporaminpolypeptides in leaves and petioles treated with 3% sucrosefollowed a lag period of about one day, while a significantamount of sporamin mRNAs was already detectable in petiolesafter one day of treatment with sucrose. Addition of silvernitrate to the medium did not affect the accumulation of sporamin,suggesting that this induction is not due to the effect of ethyleneinduced by wounding of the tissue. The accumulation of sporamincould also be induced by glucose and by fructose, but not byman-nitol, suggesting that changes in carbohydrate and/or energymetabolism in the cell may be involved in the induction. Callustissues obtained by treatment of leaf segments with 1-naphthaleneaceticacid did not accumulate sporamin even though these cells werecultured on agar medium that contained 3% sucrose. However,when callus tissues were allowed to grow after transfer to amedium that contained 6-benzylaminopurine and sucrose, accumulationof large amounts of sporamin was induced. These results suggestthat, while expression of genes coding for sporamin can be inducedin organs other than the tuberous root by a process that doesnot accompany the differentiation of tissue, the induction ofexpression of sporamin genes by sucrose requires that cellsbe competent in some specific, but as yet unidentified, way. (Received August 27, 1990; Accepted November 5, 1990)     

Induction of Furano-terpenoids in Sweet Potato Roots by the Larval Components of the Sweet Potato Weevils

When sweet potato root tissues were infested by the larvae of sweet potato weevil, Cylas formicarius and West Indian sweet potato weevil, Euscepes postfasciatus, furano-terpenoids and coumarins were produced in brown necrotic layer formed during the infestation.

The larval homogenates of both weevils also induced in the tissue the production of furano-terpenoids and coumarins, as well as the formation of necrotic layer. The larval homogenate of sweet potato weevil induced also ethylene formation, the marker of injury in the tissue. Investigations on the furano-terponoid inducing factor demonstrated that the factor was 20 mm KCl-soluble, non-dialyzable, acetone-precipitable, (NH₄)₂SO₄-precipitable, heat-unstable, passing through Sephadex G–25 column without sieving and partially inactivated by pronase, indicating that the factor was a high molecular weight compound, perhaps of a proteinacious property. It is likely that the factor causes injury or death to sweet potato root tissue, leading to the formation of ethylene and necrotic layer, and then to production of furano-terpenoids and coumarins.     

Isolation of the Sweet Potato Weevil Factor Causing Terpene Induction in Sweet Potato Roots

The larval homogenate of sweet potato weevil, Cylas formicarius, induced terpene formation in sweet potato root tissue. We indicated that the terpene-inducing factor of the larvae consisted of high molecular weight component(s) and low molecular weight component(s). The high molecular weight component(s) was heat-unstable and partially inactivated by pronase, indicating proteinacious properties. The low molecular weight components) was heat-stable.     

Transport of a Sweet Potato Storage Protein, Sporamin, to the Vacuole in Yeast Cells

The propeptide of a precursor to sporamin, a storage proteinof sweet potato, is required for targeting of sporamin to thevacuole in transformed tobacco cells (Matsuoka and Nakamura1991). A fusion gene consisting of an inducible GAL 10 promoterand sporamin cDNA was introduced into Saccharomyces cerevisiaeby use either of a multiple-copy plasmid (YEpSAD16) or of asingle-copy plasmid (YCpSAD16) to control the level of expressionof the precursor. Although we could not detect any sporamin-relatedpolypeptides in cells that harbored YCpSAD16, extracts fromcells that harbored YEpSAD16 contained multiple forms of sporaminrelatedpolypeptides: preprosporamin, prosporamin and several polypeptidesthat were smaller than prosporamin. However, YCpSAD16 directedthe accumulation of prosporamin in pep4 mutant yeast cells thatlack vacuolar proteases, andpep4 mutant cells that harboredYEpSAD16 did not contain any sporamin-related polypeptides smallerthan prosporamin. The vacuole fractions isolated from the wild-typeand pep4 mutant cells contained sporamin-related polypeptidessmaller than prosporamin and prosporamin, respectively. Theseand other results suggest that, at a low level of expressionof the precursor, prosporamin is transported to the vacuoleand degraded by vacuolar proteases. A mutant precursor to sporamin,in which the propeptide and the N-terminal region of maturesporamin were replaced by an unrelated sequence of four aminoacid residues, directed the secretion of sporamin to the culturemedium in transformed tobacco cells. However, this mutationdid not affect the transport of sporamin to the vacuole in yeastcells and none of the sporamin-related polypeptides were secretedto the extracellular space. (Received July 16, 1991; Accepted March 25, 1992)     

The Occurrence of Quinic Acid in Sweet Potato Roots

The aroma extract dilution analysis of an extract prepared from pork stock and subsequent experiments led to the identification of 15 aroma-active compounds in the flavor dilution factor range of 64–2048. Omission experiments to select the most aroma-active compounds from the 15 odor compounds suggested acetol, octanoic acid, δ-decalactone, and decanoic acid as the main active compounds contributing to the aroma of pork stock. Aroma recombination, addition, and omission experiments of these four aroma compounds in taste-reconstituted pork stock showed that each compound had an individual aroma profile. A comparison of the overall aroma between this recombined mixture and pork stock showed strong similarity, suggesting that the key aroma compounds had been successfully identified.     

微波消解-FAAS法测定普通甘薯和紫甘薯中的金属元素

采用微波消解法处理普通甘薯和紫甘薯样品,运用火焰原子吸收光谱法测定其中的K、Ca、Mg、Fe、Mn、Zn、Cu 7种对人体有益的金属元素含量。结果表明,普通甘薯和紫甘薯中K、Ca、Fe、Mg元素含量较高,Mn、Zn、Cu元素含量较低,且7种金属元素含量在两者之间存在一定的差异,各元素在紫甘薯中的含量均比普通甘薯中含量高。方法的加标回收率介于98.5%～103.2%,相对标准偏差(RSD)不大于3.14%。可为普通甘薯与紫甘薯的品质评价提供理论参考。     

Isolation and Properties of Acid Phosphatases of Sweet Potato Roots

Acid phosphatase of sweet potato root tissue was found to consist of five components by diethylaminoethyl-cellulose column chromatography, and each component was isolated by the rechromatography. They were not separated by Sephadex G-200 gel filtration. All components hydrolyzed various phosphate compounds including phosphomonoester- and pyrophosphate-linkages. Their optimum pH values were in the range of pH 5 to 6. However, there were observed some differences in optimum pH, Michaelis constant for various substrates and relative maximum velocity among the components.     

Induction of Phytohemagglutinin Activity by Arachidonic Acid in in vitro Potato Plants

Tube-grown potato (Solanum tuberosum L., cv. Nevskii) plants treated with arachidonic acid (AA) were used as a model to study the activity of phytohemagglutinins (PHA) during induction of the plant antiviral defense system. Plant treatment with 10^–8 M AA and also their inoculation with potato viruses X, Y, and M resulted in the increased activity of PHAs in potato shoots. The inducer of antiviral resistance behaved as a modulator of the PHA activity providing for its various levels during the development of viral infection. During the development of AA-induced systemic resistance, the level of phytohemagglutinin activity did not essentially depend on the nature of the viral pathogen. We suggested that the mechanism of AA-induced plant antiviral defense was connected with changes in the PHA activity.     

甘薯油菜素内酯应答基因的克隆和表达分析

为了解甘薯油菜素内酯(brassinosteroids,简称BR)应答基因BES1的功能及其在甘薯不同组织的表达特性,该研究利用甘薯(Ipomoea batatas L.)基因组数据库,筛选保守性较好的BES1基因序列设计引物,以甘薯品种‘广薯87’为模板进行PCR扩增,克隆出甘薯BES1基因(GenBank登录号为MH448304)。该基因长度为2 256 bp,编码322个氨基酸。系统进化树分析结果表明,BES1与番茄、芝麻的亲缘关系最近,其氨基酸序列具有高度保守的N末端结构域和PEST结构域。qRT-PCR分析表明,BES1基因在甘薯膨大期的块根表达量最高,而且受油菜素内酯的诱导表达,油菜素内酯浓度为10μmol/L时表达量最高。该结果为进一步研究甘薯BES1基因的功能奠定了基础,对甘薯的遗传改良与抗逆品种选育具有一定的参考价值。     

Carbohydrate and Metal Analyses of Violet-colored Acid Phosphatase of Sweet Potato

Two malate dehydrogenases (MDH-M1 and MDH-M2) were found in a methanol-using yeast, Candida sp. N-16. MDH-M2 was induced with methanol. These enzymes were purified as electrophoretically and isoelectrophoretically homogeneous proteins. The molecular weights of MDH-M1 and MDH-M2 were estimated to be about 78,000 (homodimer) and 160,000 (homotetramer). Several kinetic properties were significantly different between the two enzymes. The value (2.07) of V_{max(oxaloacetate)}/V_max(malate) and K_cats (555 s^-1 for oxaloacetate, 481 s^-1 for NADH) of MDH-M2 were higher than the ratio (1.37) of V_max and K_cats(241 s^-1 for oxaloacetate, 271 s^-1 for NADH) of MDH-M1, respectively. The activity of MDH-M2 was inhibited by a high concentration of NAD⁺ and the activity of MDH-M1 by oxaloacetate.     

Purification and Properties of a Polygalacturonic Acid Trans-Eliminase Produced by Bacillus pumilus

A strain of Bacillus pumilus produced an extracellular pectic enzyme with polygalacturonic acid as the substrate. This enzyme, with optimal activity at pH 8.0 to 8.5, produced reaction products that strongly absorbed light at 232 nm, indicating the presence of a pectic acid trans-eliminase (PATE). Neither pectin esterase nor polygalacturonase was detected in the cell-free culture fluid. Chromatographic examination of the end products revealed the presence of large quantities of unsaturated oligouronides unlike those found with B. polymyxa. It was found that the PATE was produced extracellularly during the negative logarithmic death phase of the organism. The filtrate from sonically treated cells did not show any activity for PATE or hydrolases for lower oligogalacturonides at any time during the growth cycle. The enzyme was inducible. Pectin, National Formulary (NF) was the best inducer, followed by polygalacturonic acid and galacturonic acid. Enzyme activity was markedly stimulated by calcium and other divalent ions. Copper and cobalt ions were inhibitory. The partially purified enzyme showed no significant activity on pectin containing a high methoxyl content (96% esterified). However, pectin NF with a lower methoxyl content (68% esterified) was attacked to a degree by the partially purified and crude enzyme preparations. The initial rate of PATE activity increased up to 60 C, about 16-fold higher than that observed at room temperature. The activation energy was calculated as 12,183 cal/mole. A protective action of calcium chloride against heat inactivation of the PATE was observed. Degradation of polygalacturonic acid by this enzyme produced several unsaturated oligouronides soon after its addition to the substrate. The major endproduct was thought to be different from that of other known PATE enzymes. Paper chromatographic studies and viscosity measurements disclosed the random cleaving nature of the enzyme an endo-PATE.     

利用甘薯质体同源片段构建多顺反子表达载体

反子定点整合表达载体pSAG,酶切鉴定结果表明所构建的载体符合预期设计.这为后期甘薯质体转化体系的建立和通过质体基因工程手段将更多目的基因导入甘薯进行遗传改良奠定了基础.     

Induction of Polysome Formation in Sweet Potato Root Tissue in Response to Wounding

We determined the effects of yolk water-soluble protein (YSP) on bone resorption. YSP potently suppressed osteoclastogenesis from bone marrow-derived precursor cells driven by tumor necrosis factor-α (TNF-α). YSP (200 μg/ml) abolished the formation of tartarate-resistant acid phosphatase (TRAP)-positive osteoclasts. Furthermore, TNF-α induced TRAP activity was greatly inhibited by YSP (100 μg/ml) treatment. Our results suggest that YSP has therapeutic potential for bone-erosive diseases.     

PEG对甘薯愈伤组织淀粉酶活性的影响

用聚乙二醇 (PEG) 6 0 0 0对甘薯愈伤组织进行处理后观察到其所含淀粉酶的活性变化。这些变化随PEG的浓度不同 ,处理时间长度不同而有显著差异。低浓度的PEG(0 5 %、 1% )处理愈伤组织其淀粉酶活性变化的幅度较小 ;而高浓度 (8% )的PEG处理所引起的淀粉酶活性变化幅度较大 ;这一结果显示了PEG对甘薯愈伤组织淀粉酶的调节作用。     

民族植物学：学科发展动态与展望

对民族植物学的学科发展进行了简要综述。民族植物学自1896年在美国诞生以来,经历了百年漫长的发展过程。民族植物学由早期的描述编目有用植物,已经发展到了实验性、技术性和定量性研究的新阶段;民族植物学的原理与方法已被广泛应用于植物资源的可持续利用、社区发展和生物多样性保护。近代民族植物学的学科发展可归纳为3个特征：(1)研究方法的进展主要表现在由记载编目和描述到实验性、技术性的定量研究和从基础研究到实际应用的发展;(2)研究途径的发展表现在由调查记录、访谈式的被动研究到参与式研究和取证分析;(3)研究地区已由局部区域性研究扩大到全球范围的民族植物学研究,从对原住民和少数民族的民族植物学研究扩展到所有不同文化背景民族的民族植物学研究。特别是发展中国家的民族植物学研究在近半个世纪以来得到迅速发展,并广泛应用于植物资源的管理和生物多样性保护的实际工作中。民族植物学在中国起步较晚,但在过去20年里已从无到有,建立起了我国民族植物学研究的理论框架、内容、方法和途径,将民族植物学从基础描述性研究(调查、记载、编目),推进到应用研究,在植物资源的可持续利用、生物多样性保护、农村发展和山区扶贫等方面取得了若干进展。当前,我国民族植物学研究面临着发展的新机遇和新的挑战,必须紧跟国民经济发展的新形势,投入西部大开发,加强学科建设,推进研究与产业发展的结合,把民族植物学由地区性研究推进到全国性研究,进一步完善中国特色的民族植物学研究体系,积极参与国际合作与交流,对国民经济的持续发展、民族地区的团结稳定和生物多样性保护作出更大的贡献。     

植物脂肪酸去饱和酶及其编码基因研究进展

脂肪酸去饱和酶是催化脂肪酸链特定位置形成双键和产生不饱和脂肪酸的酶类。植物脂肪酸去饱和酶主要有5种(FAD2、FAD3、FAD6、FAD7和FAD8), 可分为ω-3型 (FAD2、FAD6)和ω-6型(FAD3、FAD7、FAD8)两大类。其编码基因(FAD2、FAD3、FAD6、FAD7和FAD8)在植物中一般有多个拷贝。同种基因在不同植物中拷贝数不同, 同一植物中相同基因的不同拷贝间在序列特征、表达调控和功能等方面也存在显著差异。本文根据国内外对脂肪酸去饱和酶基因及编码产物的研究现状, 分别从它们的分类、拷贝数、结构、作用机制、表达调控等方面的研究进展进行了详细的分类阐述。     

植物脂肪酸去饱和酶及其编码基因研究进展

脂肪酸去饱和酶是催化脂肪酸链特定位置形成双键和产生不饱和脂肪酸的酶类。植物脂肪酸去饱和酶主要有5种（FAD2、FAD3、FAD6、FAD7和FAD8）,可分为ω-3型（FAD2、FAD6）和ω-6型（FAD3、FAD7、FAD8）两大类。其编码基因（FAD2、FAD3、FAD6、FAD7和FADS）在植物中一般有多个拷贝。同种基因在不同植物中拷贝数不同,同一植物中相同基因的不同拷贝间在序列特征、表达调控和功能等方面也存在显著差异。本文根据国内外对脂肪酸去饱和酶基因及编码产物的研究现状,分别从它们的分类、拷贝数、结构、作用机制、表达调控等方面的研究进展进行了详细的分类阐述。