苹果果实糖积累特性与品质形成的关系

以'富士'和'国光'苹果为研究对象,对其果实发育过程中糖含量及其代谢关键酶活性的变化进行测定分析,以揭示糖分积累代谢特性对果实品质形成的影响.结果表明:(1)'富士'和'国光'均为己糖积累型果实, '富士'果实以积累果糖最多,果糖/葡萄糖(F/G)值为1.56,而'国光'以积累葡萄糖最多,F/G值仅为0.68;蔗糖在两品种中含量和所占比例均很低,在近成熟期'富士'高于'国光'.(2)'富士'果实蔗糖磷酸合成酶(SPS)和蔗糖合成酶(SS)活性均随果实糖的累积量增加而显著升高,酸性转化酶(AI)活性也渐趋升高,而中性转化酶(NI)活性波动不大,且其糖累积与AI和SPS活性相关性最大,而与NI相关性不大,SS的作用主要表现在发育后期;在 '国光'果实糖积累过程中SPS起主导作用,SS和NI的作用主要表现在发育前期,而AI的作用不大.(3)'富士'和'国光'果实淀粉含量变化趋势相同,在淀粉积累高峰之后,'富士'果实淀粉降解速度更快,其淀粉含量迅速下降且低于'国光',此时其相应淀粉酶活性也高于'国光'.研究发现,'富士'和'国光'果实糖积累和淀粉代谢均存在显著差异,从而直接或间接地影响着果实糖代谢过程,进而导致果实品质的显著差异.     

‘嘎拉’苹果果实品质的电学特性研究

以'嘎拉'苹果果实为材料,在0.1～100 kHz频率范围内,利用平行板电极系统研究了果实采后成熟衰老过程中的电学特性,并对电学参数与果实品质的关系进行了分析.结果表明:随测定频率的增加,'嘎拉'苹果果实的复阻抗(Z)、并联等效电阻(Rp)、并联等效电感(Lp)和并联等效电容(Cp)均逐渐下降,而电导率(σ)却逐渐上升;0.1 kHz是'嘎拉'苹果果实电学特性检测的特征频率;并联等效电阻在0.1 kHz时与果肉硬度呈极显著正相关(r=0.986**)、与可滴定酸含量呈显著正相关(r=0.934*),可作为标志果肉硬度和可滴定酸含量的敏感电参数.研究发现,在特征频率下,并联等效电阻可以作为辨别'嘎拉'苹果果实品质变化的特征电参数.     

光质对‘红富士’苹果果实着色的影响

为探明 '红富士'苹果着色机理,试验以'红富士'苹果为试材,应用不同光质的光源对进入着色期的套袋果实进行室内离体补光和田间树冠内膛补光照射处理,对果皮花青苷、果实糖分及相关酶的活性等生理指标进行测定.试验结果表明,红光(R)照射离体套袋'红富士'苹果果实不着色,紫外光UVA(＞320 nm)灼伤果实果皮而变褐色;UVB(280～320 nm)及其组合光源刺激果实PAL酶活性增加,促进糖含量增长,并使果实花青苷大量积累,促进'红富士'苹果着红色.白光对'红富士'苹果果实PAL酶活性、花青苷及糖分含量的增加也有一定促进作用,但不如UVB及其组合光源照射效果好.因此,UVB光源是'红富士'苹果着色的直接外在因子,是直接刺激'红富士'苹果着色的光信号之一.     

苹果不同品种果实原花青素含量及其动态变化

用香草醛-盐酸法测定了苹果(Malus domestica Mill.)5个品种的幼果和成熟果原花青素含量,并对品种‘富士'和‘新红星'果实发育期间原花青素含量的变化动态进行了研究.结果表明,苹果幼果富含原花青素,5个品种含量在8.46～13.90 mg*g-1(FW)之间,以品种‘金冠'最高,‘乔纳金'次之.苹果成熟果实原花青素主要存在于果皮中,含量达4.232～7.307 mg*g-1(FW),果肉中含量为0.525～1.034 mg*g-1(FW),以品种‘新红星'和‘富士'最高.‘富士'和‘新红星'果实发育期间原花青素含量变化动态基本一致,发育早期果皮原花青素含量呈增加趋势,5月底达最高值,之后下降,7月中旬以后基本稳定;果肉原花青素含量一直呈下降趋势,8月中旬以后基本保持稳定.     

水分胁迫对柑橘果皮细胞壁结构与代谢的影响

研究水分胁迫下,盆栽'暗柳橙(Citrus Sinensis Osbeck cv. Anliu)'的果实成熟期果皮细胞壁超微结构、细胞壁物质成分、细胞壁代谢相关酶活性的变化规律及其之间关系.结果表明,在果实发育成熟期,果皮细胞壁代谢相关水解酶果胶酶、纤维素酶、果胶甲酯酶的活性随着水分胁迫的加强而增加,多酚氧化酶活性与果胶酶活性变化趋势相反,果皮细胞壁代谢相关成分离子结合型果胶、共价结合型果胶、半纤维素、纤维素的含量随着水分胁迫的加强而降低,水溶性果胶含量随着水分胁迫的加强而增加,果皮细胞壁超微结构随着水分胁迫的加强而加速解体.     

桃果实成熟前后细胞壁成分和降解酶活性的变化及其与果实硬度的关系

比较桃品种‘双久红’和‘川中岛白桃’果实成熟前后20 d内果肉硬度、细胞壁成分和细胞壁降解酶活性变化的结果表明,桃果实成熟5 d后,‘双久红’桃果实的硬度、纤维素含量和原果胶含量均极显著高于‘川中岛白桃’:从成熟前15 d开始,‘双久红’的水溶性果胶含量、多聚半乳糖醛酸酶活性和纤维素酶活性均极显著低于‘川中岛白桃’;整个成熟期间,‘双久红’的果胶甲酯酶活性明显低于‘川中岛白桃’。相关分析表明,果实硬度与原果胶、纤维素含量呈极显著正相关,而与可溶性果胶含量、多聚半乳糖醛酸酶活性和纤维素酶活性呈极显著负相关。     

橄榄果实发育过程中细胞壁物质和相关酶活性变化

为了解橄榄(Canarium album)果实质地差异形成的原因,以鲜食型橄榄‘清榄1号’和加工型橄榄‘长营’为材料,对果实发育过程中细胞壁物质含量和相关酶活性进行了测定。结果表明,随着橄榄果实的成熟,‘清榄1号’较‘长营’维持较高的果胶甲酯酶(PME)活性,促进了果胶的水解,离子型果胶(ISP)含量较高而共价型果胶(CSP)含量较低。2个橄榄品种纤维素含量均较高,‘清榄1号’果实的半纤维素含量低于‘长营’。‘清榄1号’木质素含量低于‘长营’,较高的苯丙氨酸解氨酶(PAL)和过氧化物酶(POD)活性促进了木质素含量的增加。因此,ISP、CSP、半纤维素和木质素含量的不同可能是2个橄榄品种果实质地差异形成的原因。     

苹果炭疽叶枯病病原学研究

炭疽叶枯病菌能够侵染苹果叶片造成病叶早期干枯、脱落,侵染果实引起坏死性斑点。该病害近年来在我国一些苹果产区被发现,并有迅速蔓延的趋势。对采自河南和陕西的苹果炭疽叶枯病的病原菌进行了形态学、培养特性、致病性及分子系统发育研究,明确了引起该病害的病原为果生刺盘孢Colletotrichum fructicola和隐秘刺盘孢C.aenigma。经致病性测定,证明C.fructicola和C.aenigma对嘎拉、秦冠、金冠、粉红女士、太平洋玫瑰、金世纪、蜜脆等以金冠为亲本的品种叶片致病;在有伤接种时,C.fructicola和C.aenigma对嘎拉、金冠、秦冠、太平洋玫瑰、新红星、富士等品种果实具有致病性;在无伤接种时,C.fructicola对嘎拉、金冠果实致病,C.aenigma对嘎拉果实致病。研究结果表明,C.fructicola和C.aenigma对不同品种叶片和果实的致病性都存在明显的分化现象。     

草酸复合剂对苹果清洗效果及生理特征的影响

以'红富士'苹果为试材,研究了以草酸(OA)为主剂,二氧化氯(ClO2)、氯化钠(NaCl)等为辅剂的清洗剂(10.0 g·L-1 +10.0 g·L-1 NaCl+9 mg·kg-1 OA ClO2+0.02%吐温-20)对果实的清洗效果及采后生理的影响.结果表明:草酸复合清洗剂对'红富士'苹果表面的农药、重金属、菌落的去除率分别达76.39%～83.24%、62.48%～91.29%和80.64%;在(0±1)℃冷藏条件下,草酸复合清洗剂能显著抑制'红富士'苹果呼吸作用和乙烯释放,延缓二者跃变高峰的出现,同时提高了果实超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性,有效抑制果实丙二醛(MDA)含量和相对膜透性的升高,从而降低膜脂过氧化程度.研究发现,草酸复合清洗剂既能有效清除苹果表面农药、重金属残留和菌落,又能调控果实的呼吸作用和活性氧代谢等过程来明显延缓采后果实的衰老.     

香蕉果实成熟软化过程中细胞壁物质的变化

系统研究了香蕉果实软化过程中细胞壁物质―醇不溶性固形物(AIS)以及3种不同性质的果胶物质:水溶性果胶(WSP)、酸溶性果胶(HP)和碱溶性果胶(OHP)含量的变化。结果表明:随果实的成熟软化,AIS的含量不断降低,且在呼吸跃变时急剧降低;WSP的含量不断增加,HP和OHP的含量不断减少,且均表现出在早期变化量少,在果实硬度迅速降低时变化明显。该研究进一步证明细胞壁物质的变化是导致香蕉果实软化的主要原因。     

In vivo and in vitro swelling of cell walls during fruit ripening

Swelling properties of the cell walls of nine temperate fruit species, selected for their different ripening and textural characteristics, were studied during ripening. Cell wall swelling was examined in intact fruit using microscopy techniques and in vitro, using cell wall material isolated from fruit tissue. In fruit which ripened to a soft melting texture (persimmon, avocado, blackberry, strawberry, plum), wall swelling was pronounced, particularly in vitro. In-vivo swelling was marked only in avocado and blackberry. Fruit which ripened to a crisp, fracturable texture [apple (two cultivars), nashi pear, watermelon] did not show either in-vivo or in-vitro swelling of the cell wall. There was a correlation between swelling and the degree of pectin solubilisation, suggesting that wall swelling occurred as a result of changes to the viscoelastic properties of the cell wall during pectin solubilisation. Chemical and enzymatic removal of pectin from kiwifruit cell wall material supported the idea that swelling is associated with movement of water into voids left in the cellulose-hemicellulose network by the solubilised pectin. However, the results also suggested that swelling in vivo was more complex than this, and that the physicochemical changes which led to swelling included other elements of cell wall modification involving the site and mechanism of pectin solubilisation and-or the cellulose-xyloglucan complex. Received: 28 January 1997 / accepted: 11 March 1997     

间歇低温胁迫对桃果实细胞壁代谢的影响

桃果实在成熟过程中细胞壁干物质不断减少,随着共价结合果胶质和离子结合果胶质减少,水溶性果胶质明显增加,纤维素也逐渐减少,但半纤维素含量变化较小.低温胁迫造成果胶质和纤维素的降解过程受阻,从而造成较高分子量果胶质的积累,果汁粘度升高.中途加温则能促进果胶质和纤维素的增溶和解聚,引导细胞进行与果实成熟有关的细胞壁代谢.14C-蔗糖标记试验表明,在细胞壁不断降解的同时,也进行着合成.在果实成熟的启动阶段,细胞壁的合成能力加强.果实衰老过程与细胞壁合成减少有着直接的联系.受到低温伤害的果实细胞壁物质含量高于正常果实的原因,并不是其合成水平的升高,而是其降解的减慢.     

草莓果实发育成熟过程中糖苷酶和纤维素酶活性及细胞壁组成变化

以丰香和红丰草莓为试材,对果实发育成熟过程中细胞壁水解酶活性和细胞壁成份变化进行了研究．结果表明：半乳糖苷酶和α-甘露糖苷酶活性随草莓果实成熟而提高,葡萄糖苷酶活性不随草莓果实成熟而提高．随着果实发育成熟,纤维素酶活性、果胶酶活性不断提高．果实中未检测到内切多聚半乳糖醛酸酶活性,外切多聚半乳糖醛酸酶活性变化不随果实成熟软化而提高．随果实发育成熟,细胞壁中可溶性果胶和半纤维素增加,而离子结合果胶和共价结合果胶及纤维素减少．     

Ripening-related changes in raspberry cell wall composition and structure

Cell walls were prepared from the fruit of two cultivars of raspberry at three stages of ripening; green, white and red (ripe). The cultivars. Glen Clova and Glen Prosen, are subjectively classified, at harvest by growers, as soft and firm fruit, respectively. The cell walls were analysed for neutral sugar composition, uronic acid content, degree of methyl esterification, lignin and ferulic acid-derived dehydrodimers. Solid-state 31C NMR and diffuse reflectance infrared (DRIFT) spectra were acquired for the cell wall residues. For both cultivars the progression from green to white produced minimal changes, save for a reduction in pectin. NMR analyses indicated that the solubilized pectin was acetylated. Progression to the red (ripe) stage, in both cultivars, was accompanied by a reduction in the ordered cellulose and a dramatic reduction in pectin content and the degree of methyl-esterification. Significantly, the softer fruit (Glen Clova) exhibited greater reductions in both parameters, implicating increased pectin hydrolysis, as one of the main factors contributing to the difference in firmness between the cultivars. A relative increase in cell wall-associated protein was seen at the red stage. The nature and function of the protein(s) are, as yet unknown.     

Papaya Fruit Softening: Role of Hydrolases

Papaya (Carica papaya L.) cultivars show a wide variation in fruit softening rates, a character that determines fruit quality and shelf life, and thought to be the result of cell wall degradation. The activity of pectin methylesterase, β-galactosidase, endoglucanase, endoxylanase and xylosidase were correlated with normal softening, though no relationship was found between polygalacturonase activity and softening. When softening was modified by 1-MCP treatment, a delay occurred before the normal increase in activities of all cell wall activities except endoxylanase which was completely suppressed. Significant cell wall mass loss occurred in the mesocarp tissue during normal softening, but did not occur to the same extent following 1-MCP treatment. During normal softening, pectin polysaccharides and loosely bound matrix polysaccharides were solubilized and the release of xylosyl and galactosyl residues occurred. Cell wall changes in galactosyl residues after 1-MCP treatment were comparable to those of untreated fruit but 1-MCP treated fruit did not soften completely. The changes in the cell wall fractions containing xylosyl residues in 1-MCP treated fruit showed less solubilization and a higher association of xylosyl residues with the pectic polysaccharides. The results indicated that normal modification of cell wall xylosyl components during ripening did not occur following 1-MCP treatment at the color-break stage, this was associated with the failure of these fruit to fully soften and a selective suppression of endoxylanase activity. The results support a role for endoxylanase in normal papaya fruit softening and its suppression by 1-MCP lead to a failure to fully soften. Normal papaya ripening related softening was dependent upon the expression and activity of endoglucanase, β-galactosidase and endoxylanase.     

Tracking cell wall changes in wine and table grapes undergoing Botrytis cinerea infection using glycan microarrays

Background and AimsThe necrotrophic fungus Botrytis cinerea infects a broad range of fruit crops including domesticated grapevine Vitis vinifera cultivars. Damage caused by this pathogen is severely detrimental to the table and wine grape industries and results in substantial crop losses worldwide. The apoplast and cell wall interface is an important setting where many plant–pathogen interactions take place and where some defence-related messenger molecules are generated. Limited studies have investigated changes in grape cell wall composition upon infection with B. cinerea, with much being inferred from studies on other fruit crops.MethodsIn this study, comprehensive microarray polymer profiling in combination with monosaccharide compositional analysis was applied for the first time to investigate cell wall compositional changes in the berries of wine (Sauvignon Blanc and Cabernet Sauvignon) and table (Dauphine and Barlinka) grape cultivars during Botrytis infection and tissue maceration. This was used in conjunction with scanning electron microscopy (SEM) and X-ray computed tomography (CT) to characterize infection progression.Key ResultsGrapes infected at veraison did not develop visible infection symptoms, whereas grapes inoculated at the post-veraison and ripe stages showed evidence of significant tissue degradation. The latter was characterized by a reduction in signals for pectin epitopes in the berry cell walls, implying the degradation of pectin polymers. The table grape cultivars showed more severe infection symptoms, and corresponding pectin depolymerization, compared with wine grape cultivars. In both grape types, hemicellulose layers were largely unaffected, as was the arabinogalactan protein content, whereas in moderate to severely infected table grape cultivars, evidence of extensin epitope deposition was present.ConclusionsSpecific changes in the grape cell wall compositional profiles appear to correlate with fungal disease susceptibility. Cell wall factors important in influencing resistance may include pectin methylesterification profiles, as well as extensin reorganization.     

Down-regulation of POLYGALACTURONASE 1 alters firmness, tensile strength and water loss in apple (Malus x domestica) fruit

ABSTRACT: BACKGROUND: While there is now a significant body of research correlating apple (Malus x domestica) fruit softening with the cell wall hydrolase ENDO-POLYGALACTURONASE1 (PG1), there is currently no direct evidence of its function. This study examined the effect of down regulation of PG1 expression in 'Royal Gala' apples, a cultivar that typically has high levels of PG1, and softens during fruit ripening. RESULTS: PG1-suppressed 'Royal Gala' apples harvested from multiple seasons were firmer than controls after ripening, and intercellular adhesion was higher. Cell wall analyses indicated changes in yield and composition of pectin, and a higher molecular weight distribution of CDTA-soluble pectin. Structural analyses revealed more ruptured cells and free juice in pulled apart sections, suggesting improved integrity of intercellular connections and consequent cell rupture due to failure of the primary cell walls under stress. PG1-suppression also had reduced expansion of cells in the hypodermis of ripe apples, resulting in more densely packed cells in this layer. This change in morphology appears to be linked with reduced transpirational water loss in the fruit. CONCLUSIONS: These findings confirm PG1's role in apple fruit softening and suggests that this is achieved in part by reducing cellular adhesion. This is consistent with previous studies in shown in strawberry but not in tomato. In apple PG1 also appears influence other fruit texture characters such as juiciness and water loss.     

Changes in the distribution of cell wall polysaccharides in early fruit pericarp and ovule, from fruit set to early fruit development, in tomato (Solanum lycopersicum)

During fruit development in tomato (Solanum lycopersicum), cell proliferation and rapid cell expansion occur after pollination. Cell wall synthesis, alteration, and degradation play important roles during early fruit formation, but cell wall composition and the extent of cell wall synthesis/degradation are poorly understood. In this study, we used immunolocalization with a range of specific monoclonal antibodies to examine the changes in cell wall composition during early fruit development in tomato. In exploring early fruit development, the ?1 day post-anthesis (DPA) ovary and fruits at 1, 3, and 5 DPA were sampled. Paraffin sections were prepared for staining and immunolabeling. The 5 DPA fruit showed rapid growth in size and an increase in both methyl-esterified pectin and de-methyl-esterified pectin content in the pericarp, suggesting rapid synthesis and de-methyl esterification of pectin during this growth period. Labeling of pectic arabinan with LM6 antibody and galactan with LM5 antibody revealed abundant amounts of both, with unique distribution patterns in the ovule and premature pericarp. These results suggest the presence of rapid pectin metabolism during the early stages of fruit development and indicate a unique distribution of pectic galactan and arabinan within the ovule, where they may be involved in embryogenesis.     

Uronic Acid products release from enzymically active cell wall from tomato fruit and its dependency on enzyme quantity and distribution

Isolated cell wall from tomato (Lycopersicon esculentum Mill. cv Rutgers) fruit released polymeric (degree of polymerization [DP] > 8), oligomeric, and monomeric uronic acids in a reaction mediated by bound polygalacturonase (PG) (EC 3.2.1.15). Wall autolytic capacity increased with ripening, reflecting increased levels of bound PG; however, characteristic oligomeric and monomeric products were recovered from all wall isolates exhibiting net pectin release. The capacity of wall from fruit at early ripening (breaker, turning) to generate oligomeric and monomeric uronic acids was attributed to the nonuniform ripening pattern of the tomato fruit and, consequently, a locally dense distribution of enzyme in wall originating from those fruit portions at more temporally advanced stages of ripening. Artificial autolytically active wall, prepared by permitting solubilized PG to bind to enzymically inactive wall from maturegreen fruit, released products which were similar in size characteristics to those recovered from active wall isolates. Extraction of wall-bound PG using high concentrations of NaCl (1.2 molar) did not attenuate subsequent autolytic activity but greatly suppressed the production of oligomeric and monomeric products. An examination of water-soluble uronic acids recovered from ripe pericarp tissue disclosed the presence of polymeric and monomeric uronic acids but only trace quantities of oligomers. The significance in autolytic reactions of enzyme quantity and distribution and their possible relevance to in vivo pectin degradation will be discussed.     

Cell wall polysaccharides are specifically involved in the exclusion of aluminum from the rice root apex

Rice (Oryza sativa) is the most aluminum (Al)-resistant crop species among the small-grain cereals, but the mechanisms responsible for this trait are still unclear. Using two rice cultivars differing in Al resistance, rice sp. japonica 'Nipponbare' (an Al-resistant cultivar) and rice sp. indica 'Zhefu802' (an Al-sensitive cultivar), it was found that Al content in the root apex (0-10 mm) was significantly lower in Al-resistant 'Nipponbare' than in sensitive 'Zhefu802', with more of the Al localized to cell walls in 'Zhefu802', indicating that an Al exclusion mechanism is operating in 'Nipponbare'. However, neither organic acid efflux nor changes in rhizosphere pH appear to be responsible for the Al exclusion. Interestingly, cell wall polysaccharides (pectin, hemicellulose 1, and hemicellulose 2) in the root apex were found to be significantly higher in 'Zhefu802' than in 'Nipponbare' in the absence of Al, and Al exposure increased root apex hemicellulose content more significantly in 'Zhefu802'. Root tip cell wall pectin methylesterase (PME) activity was constitutively higher in 'Zhefu802' than in 'Nipponbare', although Al treatment resulted in increased PME activity in both cultivars. Immunolocalization of pectins showed a higher proportion of demethylated pectins in 'Zhefu802', indicating a higher proportion of free pectic acid residues in the cell walls of 'Zhefu802' root tips. Al adsorption and desorption kinetics of root tip cell walls also indicated that more Al was adsorbed and bound Al was retained more tightly in 'Zhefu802', which was consistent with Al content, PME activity, and pectin demethylesterification results. These responses were specific to Al compared with other metals (CdCl(2), LaCl(3), and CuCl(2)), and the ability of the cell wall to adsorb these metals was also not related to levels of cell wall pectins. All of these results suggest that cell wall polysaccharides may play an important role in excluding Al specifically from the rice root apex.