Photosynthetic Activity of Ripening Tomato Fruit

Gas exchanges, chlorophyll (Chl) a fluorescence and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and phosphoenolpyruvate carboxylase (PEPC) were determined in tomato (Lycopersicon esculentum Mill.) fruits picked at different developmental stages (immature, red-turning, mature, and over-ripe). The fruits did not show signs of CO₂ fixation. However, photochemical activity was detectable and an effective electron transport was observed, the values of Chl fluorescence parameters in green fruits being similar to those determined in the leaves. The RuBPCO activity, which was similar to those recorded in the leaves at the immature stage of the fruit, decreased as the fruit ripened. PEPC activity was always higher than RuBPCO activity.     

番茄果实乙烯释放量的遗传模型分析

本试验选择2个番茄果实乙烯释放量显著不同的番茄品系,通过P_1、P_2、F_1、F_2、B_1和B_2六世代的分析方法,研究了番茄果实乙烯释放量的遗传规律.结果表明:番茄果实乙烯释放量遗传符合1对负向完全显性主基因+加性-显性多基因模型(D-4),主基因效应在B_1、B_2和F_(23)个世代的遗传率分别为36.33%、44.09%和35.14%,多基因效应在B_1、B_2和F_(23)个世代的遗传率分别为54.73%、40.50%和54.88%.     

植物乙烯生物合成过程中活性氧的作用

大量的研究结果表明,活性氧参与植物乙烯生物合成过程具有明显的普遍性,超氧阴离子自由基是参与乙烯生物合成过程的主要活性氧。近年来研究的焦点主要从乙烯生物合成的关键调控酶ACC合酶及ACC氧化酶的酶活性、酶动力学特性、酶蛋白空间结构、酶基因表达水平等方面来阐明活性氧调控植物乙烯生物合成的机制。最新的研究表明：植物在各种正常或应激的生长条件下首先诱导了活性氧产生水平的变化,活性氧在基因或蛋白质水平上影响ACC合酶和ACC氧化酶的活性水平,从而调节乙烯的生物合成。本文首次综述了活性氧影响植物乙烯生物合成过程的最新研究进展,并对活性氧在植物乙烯生物合成中具有诱导与抑制并存的“双重性”作用进行了探讨。     

通过表达ACC脱氨酶基因控制番茄果实的成熟

乙烯在跃变型果实的成熟过程中起着触发呼吸跃变和促进果实成熟的作用。细菌来源的1-氨基环丙烷-1-羧酸(ACC)脱氨酶能降解乙烯的直接前体ACC,从而抑制植物体内乙烯的合成。我们用PCR方法从假单孢杆菌中克隆到ACC脱氨酶基因并通过农杆菌介导的方法将其转入番茄(Lycopersicun esculentum)中。再生植株经Southern blot检测证明,ACC脱氨酶基因已整合到番茄基因组中并稳定表达。转基因番茄果实成熟期的推迟时间与体内乙烯的抑制程度有相关性。转基因番茄植株乙烯的合成降低80%左右,果实在离体条件下可保鲜75d左右。研究ACC脱氢酶基因在植物体内的作用可阐明高等植物体内乙烯的作用机理并为培育耐贮藏果蔬品种打下基础。     

Antioxidant Systems in Ripening Tomato Fruits

Two cultivars of tomato (Lycopersicon esculentum Mill.), Selection-7 (shelf life 7–8 d) and ARTH-3 (shelf life 14–15 d) were analyzed for oxidative stress and the antioxidant enzyme system at different stages of fruit ripening. The results presented here suggest that during the early stages of fruit ripening, efficient antioxidant system protects the tomato fruits against the damaging effect of progressive oxidative stress. At later stages, however, oxidative damage occurs due to decreased activities of the ROS scavenging enzymes.     

Characterisation of the ACC oxidase activity in transgenic auxin overproducing tomato during ripening

As part of our studies on the role of auxin in regulating the ethylenebiosynthesis during fruit ripening, in this paper we describe the functionalproperties of the ACC oxidase activity extracted from transgenic tomato(Lycopersicum esculentum Mill. cv. Ailsa craig)overexpressing the tryptophan monooxygenase or iaaM protein fromAgrobacterium tumefaciens that increases the auxin levels.Maximal activity was recovered by extracting the enzyme at pH 8.0 from fruitspicked three days after the onset of the colour change. The enzyme exhibits ahalf-life of 85 min, two relative maxima at 30 and 38°C, an optimum pH of 7.9 and an apparent Km forACC of 118 M. Our results also show the first evidence of anallosteric type kinetic of the ACC oxidase activity with respect to itscosubstrate ascorbate, with an apparent Km of 12.5mM,estimated as the concentration which gave 50% Vmax.     

Altered Tomato (<Emphasis Type="Italic">Lycopersicon esculentum</Emphasis> Mill.) Fruit Cuticle Biomechanics of a Pleiotropic Non Ripening Mutant

Tomato (Lycopersicon esculentum Mill.) fruit ripening involves multiple metabolic changes resulting in softening and pigmentation. We investigated the mechanics and morphology of the enzymatically isolated cuticular membrane (CM) of cv. Ailsa Craig wild-type (wt) and nonripening mutant (nor) at three developmental stages. Cuticle thickness and degree of cutinization increased significantly from immature to fully ripe fruits for both wt and nor without differences between them. Mechanical characterization was carried out on dry and fully hydrated samples in uni-axial tension to determine their modulus of elasticity, stress, and strain at failure. Corresponding stress-strain diagrams were biphasic and showed yield for virtually all dry CM samples, while that of hydrated CM displayed considerable differences between wt and nor fruits. Concerning the mechanical properties, the CM of wt fruits was characterized by increasing stiffness and strength during fruit growth and maturation in both dry and hydrated states, whereas the CM of nor fruits was significantly less stiff and weaker at full maturity. Hydration generally caused lower moduli of elasticity and strength, while breaking strain was significantly affected only for the CM of ripe nor fruits. This plasticizing effect of water increased towards full maturity for both wt and nor, and may be related to fiber content in the CM matrix and hydration state of the cuticle. Comparative analysis of two additional wild-type tomato cultivars supported the ripening-related stiffening of the CM of Ailsa Craig wt and the altered mechanical properties of the nor mutant, as well as the plasticizing effect of water.     

伤处理和乙烯对桃ACC氧化酶基因表达的影响

桃果实不耐贮运,特别是溶质水蜜桃、珐I大11＿程技术的发展使番茄果实实现延熟保鲜'－'、人f［］也试图通过乙烯合成的关键酶的］i义HNA技术来延长桃果实的贮运期。：ICC氧化酶是乙烯生物合成的关键酶之一,ACC氧化酶4peJL从番茄'、矮牵牛。。。桃卜'、苹果、'等许多植物...     

The Role of Polygalacturonase (PG) in Tomato Fruit Ripening and Effects of Divalent Metal Ions and Ethylene on PG Activity

It has been reported that PG is a key enzyme related to the tomato fruit ripening. In this study tomato fruits were harvested at the mature-green stage and stored at room temperature. The cell ultrastructure of pericarp tissue was observed at different ripening stages, and the effects of treatments with ethylene and calcium on PG activity and fruit ripening were examined. The object of this study is to elucidate the role of PG in regulation of tomato fruit ripening by ethylene and calcium. PG activity, was undetectable at mature-green stage, but it rose rapidly as fruif ripening. The rise in PG activity was coincided with the dechnmg of fruit firmness during ripening of tomato fruits. The observation of cell ultrastructure showed that the most of grana in chloroplast were lost and the mitochondrial cristae decreased as fruit ripening. Striking changes of cell wall structure was most noted, beginning with dissolution of the middle lamella and eventual disruption of primary cell wall. A similar pattern of changes of cell wall and chloroplast have been observed in pericarp tissue treated with PG extract. In fruits treated with calcium and other divalent metal ions atmature-green stage, the lycopene content and PG activity decreased dramatically. Ethylene application enhanced the formation of lycopene and PG activity. The inhibition of Ca2+ on PG ac ivity was removed by ethylene. Based on the above results, it was demonstrated that PG played a major role in ripening of tomato fruits, and suggested that the regulation of fruit ripening by ethylene and Ca2+ was all mediated by PG. PG induced the hydrolysis of cell wall and released the other hydrolytic enzymes, then effected the ripening processes follow up.     

春小麦水分胁迫响应中的ACC、MACC合成及乙烯的释放

水分胁迫使两个抗旱性不同的春小麦 (TriticumaestivumL .)品种“8139”(抗旱性较弱 )和“5 0 4”(抗旱性较强 )叶片ACC和MACC含量于胁迫初期下降后期升高 ,ACC合酶活性持续升高 ,乙烯释放量在 8139中下降而在5 0 4中先大幅升高而后下降。两种作用效果相反的抑制剂MGBG (抑制SAMDC活性 )和AOA (抑制ACC合酶活性 )均明显影响了两品种春小麦叶片以上各指标的变化。结果表明 ,水分胁迫下作物乙烯的释放量并不与其合成直接前体ACC的量成正相关 ;胁迫乙烯在抗性品种中于胁迫初期的升高可能是植物胁迫信号传导的响应之一 ,是一种干旱适应现象 ,可能与作物的干旱忍耐形成有关 ,而MACC具有调节胁迫乙烯释放的特殊生理作用。     

春小麦水分胁迫响应中的ACC、MACC合成及乙烯的释放

水分胁迫使两个抗旱性不同的春小麦 (Triticum aestivum L.) 品种"8139"(抗旱性较弱)和"504"(抗旱性较强)叶片 ACC 和 MACC 含量于胁迫初期下降后期升高,ACC 合酶活性持续升高,乙烯释放量在 8139 中下降而在 504 中先大幅升高而后下降.两种作用效果相反的抑制剂 MGBG (抑制SAMDC 活性)和 AOA (抑制 ACC 合酶活性) 均明显影响了两品种春小麦叶片以上各指标的变化.结果表明,水分胁迫下作物乙烯的释放量并不与其合成直接前体 ACC 的量成正相关;胁迫乙烯在抗性品种中于胁迫初期的升高可能是植物胁迫信号传导的响应之一,是一种干旱适应现象,可能与作物的干旱忍耐形成有关,而 MACC 具有调节胁迫乙烯释放的特殊生理作用.     

Hormonal Regulation of Tomato Fruit Development: A Molecular Perspective

Fruit development is a complex yet tightly regulated process. The developing fruit undergoes phases of cell division and expansion followed by numerous metabolic changes leading to ripening. Plant hormones are known to affect many aspects of fruit growth and development. In addition to the five classic hormones (auxins, gibberellins, cytokinins, abscisic acid and ethylene) a few other growth regulators that play roles in fruit development are now gaining recognition. Exogenous application of various hormones to different stages of developing fruits and endogenous quantifications have highlighted their importance during fruit development. Information acquired through biochemical, genetic and molecular studies is now beginning to reveal the possible mode of hormonal regulation of fruit development at molecular levels. In the present article, we have reviewed studies revealing hormonal control of fruit development using tomato as a model system with emphasis on molecular genetics.     

Azospirillum sp. Promotes Root Hair Development in Tomato Plants through a Mechanism that Involves Ethylene

Tomato seeds were inoculated with the plant growth–promoting rhizobacteria Azospirillum brasilense FT326, and changes in parameters associated with plant growth were evaluated 15 days after inoculation. Azospirilla were localized on roots and within xylematic tissue. An increase in shoot and root fresh weight, main root hair length, and root surface indicated that inoculation with A. brasilense FT 326 resulted in plant growth improvement. The levels of indole-3-acetic acid (IAA) and ethylene, two of the phytohormones related to plant growth, were higher in inoculated plants. Exogenously supplied ethylene mimicked the effect of inoculation, and the addition of an inhibitor of its synthesis or of its physiological activity completely blocked A. brasilense growth promotion. Based on our results, we propose that the process of growth promotion triggered by A. brasilense inoculation involves a signaling pathway that has ethylene as a central, positive regulator.     

番茄ACC合成酶cDNA克隆及其对果实成熟的反义抑制

利用RT—PcR技术克隆了ACC合成酶多基因家族成员之－LE-ACC2编码区约1．7kb的cDNA,经酶切图谱和序列分析鉴定无误后,反向插入到植物表达载体pBin437中,构建了表达Acc合成酶反望RNA的二元载体。经农杆菌途径转化番茄“丽春”品种后,通过PCR检测从抗卡那霉素再生植株中筛选到6株转基因植株,Southern杂交确证了外源基因是以单拷贝插入到番茄染色体中;对果实乙烯释放的测定结果表明转基因番茄果实的乙烯释放量仅为对照的30％左右,在室温下转基因番茄果实采后保存60 d以上仍然没有变红、软化。以上结果表明其反义RNA在转基因番茄中的表达能有效地抑制乙烯的生物合成从而延缓果实成熟,表现出良好的耐储保鲜特性。对转基因植株子一代(T1)的分析结果进一步表明反义ACC合成酶基因以典型的单基因方式传到子代。通过对子二代的分析已初步筛选到一 个耐储藏的转基因番茄纯合品系。