低分子量有机酸对红壤无机态磷转化及酸度的影响

以鄂南、赣北两红壤样品为材料,加入不同有机酸并经室温培养后,测定不同P组分、pH及活性Al含量的变化。结果表明,供试有机酸均使土壤Ca2－P含量增高,增幅大小依次为柠檬酸＞苹果酸＞琥珀酸＞乙酸;2种土壤的Ca8－P和Ca10－P含量无明显变化规律,Fe-P、Al-P和O－P含量有所下降,除乙酸处理的土壤pH值无显著变化外,其它有机酸的加入使pH下降0．65－1．96;有机酸引起活性Al量增多,除乙酸处理的变化较小外,其它有机酸或混合物的加入使土壤中0．02mol.L^-1CaCl2提取Al增加4．7－50．3倍,1mol.L^-1提取Al增加4．0－67．3倍。可见,有机酸具有双重作用,既增加P的有效性,又增加土壤酸度和Al毒。     

Effects of Low-Molecular-Weight Organic Acids on Gadolinium Accumulation and Transportation in Tomato Plants

Effects of low-molecular-weight organic acids on the accumulation and transportation of gadolinium (Gd) in tomato plants were studied under hydroponic condition. The results indicated that changes of organic acids occurred in the processes of Gd accumulation and transportation in tomato plants which were treated with extraneous Gd solutions. Malic, citric, and succinic acids contributed to both Gd accumulation in roots and transportation in xylem vessels. When Gd was unloaded from the xylem to the leaf cells, formic, lactic, citric, and succinic acids played important roles in Gd accumulation in leaves. When tomato plants were cultured in the uptake solution of Gd-containing malic, citric, or succinic acid for 48 h, the succinic acid in roots and leaves and the malic acid in xylem saps both increased obviously. From the results above, we can conclude that succinic acid had the most important role in Gd accumulation in tomato roots and leaves, while malic acid transported Gd via xylem vessels more effectively.     

Aluminum Tolerance in Wheat (Triticum aestivum L.) (II. Aluminum-Stimulated Excretion of Malic Acid from Root Apices)

We investigated the role of organic acids in conferring Al tolerance in near-isogenic wheat (Triticum aestivum L.) lines differing in Al tolerance at the Al tolerance locus (Alt1). Addition of Al to nutrient solutions stimulated excretion of malic and succinic acids from roots of wheat seedlings, and Al-tolerant genotypes excreted 5- to 10-fold more malic acid than Al-sensitive genotypes. Malic acid excretion was detectable after 15 min of exposure to 200 [mu]M Al, and the amount excreted increased linearly over 24 h. The amount of malic acid excreted was dependent on the external Al concentration, and excretion was stimulated by as little as 10 [mu]M Al. Malic acid added to nutrient solutions was able to protect Al-sensitive seedlings from normally phytotoxic Al concentrations. Root apices (terminal 3-5 mm of root) were the primary source of the malic acid excreted. Root apices of Al-tolerant and Al-sensitive seedlings contained similar amounts of malic acid before and after a 2-h exposure to 200 [mu]M Al. During this treatment, Al-tolerant seedlings excreted about four times the total amount of malic acid initially present within root apices, indicating that continual synthesis of malic acid was occurring. Malic acid excretion was specifically stimulated by Al, and neither La, Fe, nor the absence of Pi was able to elicit this response. There was a consistent correlation of Al tolerance with high rates of malic acid excretion stimulated by Al in a population of seedlings segregating for Al tolerance. These data are consistent with the hypothesis that the Alt1 locus in wheat encodes an Al tolerance mechanism based on Al-stimulated excretion of malic acid.     

一株嗜松青霉JP-NJ4的解磷特性

【目的】土壤中磷素供应不足是造成马尾松林地力衰退的原因之一。本研究对前期从马尾松根际土样中分离筛选出的一株解磷能力较强的嗜松青霉JP-NJ4的解无机磷及解有机磷能力进行探讨。【方法】探究嗜松青霉JP-NJ4对4种无机磷源及2种有机磷源的降解能力,并对其分泌的有机酸和酶类进行测定,对其解磷特性进行初步分析。【结果】表明JP-NJ4菌株可在4种不同无机磷源的培养基中生长,其中对磷酸钙[Ca3(PO4)2]的解磷效果最好,对4种磷源的解磷能力大小为:磷酸钙磷酸铝磷酸氢钙磷酸铁;其分泌的有机酸种类主要为葡萄糖酸、草酸及丙二酸;JP-NJ4菌株的磷酸酶活性较高,并具有一定的植酸酶活性;同时对草甘膦具有较好的生物降解功能,降解率达49.6%。【结论】嗜松青霉JP-NJ4解磷能力受磷源的结构组成影响,且解磷能力与发酵液pH值呈负相关关系;该菌株分泌的葡萄糖酸和草酸对磷酸钙及磷酸铝的溶解效果较明显。本研究供试菌株嗜松青霉JP-NJ4具有良好的解磷功能,在作为林业生物菌肥方面具有极大的应用潜力。     

Aluminum resistance in two cultivars of Zea mays L.: Root exudation of organic acids and influence of phosphorus nutrition

Root exudation of organic acids as Al-chelating compounds and P nutrition have been suggested to play a major role in Al-resistance in higher plants. Effects of Al exposure on maize plant growth, and organic acid root content and root exudation under various levels of P nutrition were examined. Sikuani, a Colombian maize cultivar tolerant to acid soils with high Al saturation, and Corso, a Swiss cultivar, were grown in sterile hydroponic conditions for 21 days. Al-caused inhibition of root growth was lower in Sikuani than in Corso. Al effect on plant growth was decreased with increasing P content in roots. Al content in roots increased with increasing P content and was higher in Sikuani than in Corso. When exposed to Al, the contents in root apices as well as the root exudation of citric and malic acids in Corso and citric, malic and succinic acids in Sikuani increased, and were higher in Sikuani than in Corso. Increased PEP carboxylase (PEPC) activity in root apices after Al exposure partially explained the variations of organic acid content in the roots. These Al-induced changes in PEPC activity, organic acid content and exudation were reduced in plants supplied with higher P concentrations during the 21 days prior to treatment. Increased secretion of organic acids after exposure to Al appeared to be specific to Al and was not totally explained by increased root content in organic acids.     

Organic acids production byStreptomyces spp. isolated from soil,rhizosphere and mycorrhizosphere of pine (Pinus sylvestris L.)

Summary The streptomycetes studied released into the medium the following organic acids: pyruvic, α-ketoglutaric, lactic, malic (or citric), succinic and oxalic. Soil streptomycetes produced more α-ketoglutaric-, lactic- and succinic acid than the root zone microorganisms. Mean indices of the total production of organic acids were in the following order: soil>rhizosphere>mycorrhizosphere. Amounts of pyruvic acid excreted by the soil streptomycetes were inversely proportional to their biomass, whereas those of α-ketoglutaric acid were directly proportional to dry weight. Small repeatability of the results of α-keto acids determinations in these organisms was stated.     

缺磷白羽扇豆排根与非排根区根尖分泌有机酸的比较

采用根系分泌有机酸原位收集方法及高效液相色谱技术分析了供磷及缺磷后不同时间白羽扇豆(LupinusalbusL .)非排根区根尖和排根分泌有机酸的种类和数量 ,以及相应的根尖、排根组织 ,茎木质部、韧皮部汁液中有机酸含量的变化。结果表明 :(1)缺磷能够诱导白羽扇豆根系产生大量排根 ,根系的有机酸分泌量也明显增加。 (2 )无论在供磷或缺磷条件下 ,排根与非排根区根尖组织中的有机酸种类相同 ,但排根主要分泌柠檬酸和苹果酸 ,而非排根区根尖主要分泌苹果酸和乙酸。 (3)缺磷后非排根区根尖分泌苹果酸的量增加 ,至第 17天达到高峰 ;排根开始分泌柠檬酸的时间相对较晚。缺磷后排根分泌柠檬酸的量随缺磷时间的延长不断增加。 (4 )在缺磷的排根与非排根区根尖组织和茎木质部伤流液中含有大量柠檬酸和苹果酸 ,但在茎韧皮部汁液中则几乎检测不到这两种有机酸。上述结果表明 ,尽管排根和非排根区根尖组织中的有机酸种类相同 ,但它们向外分泌的有机酸种类不同。缺磷后排根及非排根区根尖增加向外分泌的有机酸主要在根中合成     

Continuous secretion of organic acids is related to aluminium resistance during relatively long‐term exposure to aluminium stress

Secretion of organic acid has been suggested to be one of the mechanisms for Al resistance in short‐term experiments. In the present study, relatively long‐term response of roots to Al stress was investigated in terms of organic acid secretion. Eight plant cultivars belonging to 5 species that exhibited differential sensitivity to Al were used. Ten days of intermittent exposure to Al (one day in 0.5 m M CaCl₂ containing 50 µ M AlCl₃ at pH 4.5, alternating with one day in nutrient solution without Al) inhibited root growth by 65% in an Al‐sensitive cultivar of wheat ( Triticum aestivum L. Scout 66) and by 25‐50% in two cultivars of oilseed rape ( Brassica napus L. 94008 and H166), two cultivars of oat ( Avena sativa L. Tochiyutaka and Heoats), and an Al‐tolerant cultivar of wheat (Atlas 66). However, root growth was hardly affected by the same treatment in buckwheat ( Fagopyrum esculentum Moench Jianxi) and radish ( Raphanus sativus L. Guangxi). Organic acids were monitored during the first 6 h of each day of Al treatment, and both the kind and amount of organic acids secreted were found to differ among different species. Roots of buckwheat secreted oxalic acid, those of wheat exuded malic acid, while those of rapeseed, oats, and radish secreted both citric and malic acids. Three different patterns in response to relatively long‐term treatment of Al were found in terms of total amount of organic acids secreted: (1) the amount secreted was very low during the treatment (wheat cv. Scout 66, oat), (2) the amount gradually decreased with duration of treatment (wheat cv. Atlas 66, oilseed rape), and (3) the amount maintained at a high level during the whole period of Al treatment (buckwheat and radish). Combined with the results of growth inhibition, it is suggested that the continuous secretion of organic acids at a high level is related to high Al resistance.     

Genotypic variability in phosphorus solubilizing activity of root exudates by pigeonpea grown in low-nutrient environments

A pot experiment confirmed that pigeonpea could efficiently utilize various sources of phosphorus (P) (aluminium phosphate, iron phosphate and apatite), irrespective of genotype. A qualitative assay method for iron (Fe)-P solubilizing activity showed that root exudates collected from P-deficient pigeonpea contained Fe-P solubilizing substances and that they were released mainly from root tips. Citric, malic, malonic, succinic and piscidic acids were identified in root exudates. Citric and piscidic acids release from roots was increased by low-P treatment in all the genotypes tested. The release rates of citric and piscidic acids were affected by the P concentration of shoots rather than that of roots. The pigeonpea roots released approximately 5–100 times more piscidic acid than citric acid depending on P stress status, plant age and genotype. When organic acids were added to Alfisols, citric acid was most capable of mobilizing P from the soil, followed by piscidic acid and malic acid. No correlation was found between genotypic variability in the release rates of citric and piscidic acids from the roots under low-P treatment at hydroponic culture and in the growth and P uptake of plants on Alfisols. Although citric and piscidic acids released from pigeonpea roots may play a partial role in solubilizing unavailable insoluble P in soils, the releases were thought to be an unsatisfactory strategy for explaining genotypic variation in low P availability of pigeonpea.     

Quantitative evaluation of the role of organic acid exudation in the mobilization of rock phosphate by rape

Phosphorus-deficient rape plants appear to acidify part of their rhizosphere by exuding malic and citric acid. A simulation model was used to evaluate the effect of measured exudation rates on phosphate uptake from Mali rock phosphate. The model used was one on nutrient uptake, extended to include both the effect of ion uptake and exudation on rhizosphere pH and the effect of rhizosphere pH on the solubilization of rock phosphate. Only the youngest zones of the root system were assumed to exude organic acids. The transport of protons released by organic acids was described by mass flow and diffusion. An experimentally determined relation was used describing pH and phosphate concentration in the soil solution as a function of total soil acid concentration. Model parameters were determined in experiments on organic acid exudation and on the uptake of phosphate by rape from a mixture of quartz sand and rock phosphate. Results based on simulation calculations indicated that the exudation rates measured in rape plants deficient in phosphorus can provide the roots with more phosphate than is actually taken up. Presence of root hairs enhanced the effect of organic acid exudation on calculated phosphate uptake. However, increase of root hair length without exudation as an alternative strategy to increase phosphate uptake from rock phosphate appeared to be less effective than exudation of organic acids. It was concluded that organic acid exudation is a highly effective strategy to increase phosphate uptake from rock phosphate, and that it unlikely that other rhizosphere processes play an important role in rock phosphate mobilization by rape.     

Application of melatonin and PGPR alleviates thiamethoxam induced toxicity by regulating the TCA cycle in Brassica juncea L

Thiamethoxam, a broad spectrum, neonicotinoid insecticide, is used on various crops including Brassica juncea L. to protect from intruding insects such as leaf-hoppers, aphids, thrips and white-flies. Exposure to thiamethoxam causes acute malady such as tumour development, cell apoptosis, liver damage and neurotoxicity. Melatonin is entailed in umpteen developmental processes of plants, including stress responses. The pleiotropic effects of melatonin in modulating plant growth validate it’s imperative contribution as multi-regulatory substance. Exiguous information is known about the role of Pseudomonas putida in improving plant growth under thiamethoxam stress. Taking these aspects into consideration the contemporary study investigates the role of melatonin and Pseudomonas putida strain MTCC 3315 in alleviating the thiamethoxam induced toxicity in B. juncea plant. Fourier Transform Infrared Spectroscopy (FTIR) analysis uncloaked that thiamethoxam induced stress primarily affects the protein content of plant as compared to lipids, carbohydrates and cell wall components. Organic acid profiling of the treated samples carried-out by High-Performance Liquid Chromatography (HPLC), reported an upregulation in the level of organic acids, malic acid (110%), citric acid (170%), succinic acid (81%), fumaric acid (40%) and ascorbic acid (55%) in thiamethoxam treated plants compared to the investigational untreated plants. The melatonin treated seedlings grown under thiamethoxam stress, exhibit increased level of malic acid, citric acid, succinic acid, fumaric acid and ascorbic acid by 81%, 0.94%, 11%, 21% and 6% respectively. Further, thiamethoxam stressed plants inoculated with Pseudomonas putida showed stupendous up-regulation by 161% (malic acid), by 14% (citric acid), by 33% (succinic acid), by 30% (fumaric acid), by 100% (oxalic acid) respectively. Lastly, the combinatorial application of melatonin and Pseudomonas putida resulted in prodigious upsurge of malic acid by 165%, succinic acid by 69%, fumaric acid by 42% respectively in contrast to distinct melatonin and Pseudomonas putida treatments. The accumulation of organic acids ascertains the defence against thiamethoxam stress and corresponds to meet the energy generation requirement to skirmish thiamethoxam mediated abiotic stress in Brassica juncea plant.     

Characterization of Root Exudates at Different Growth Stages of Ten Rice (Oryza sativa L.) Cultivars

Abstract: Plant root exudates play important roles in the rhizosphere. We tested three media (nutrient solution, deionized water and CaSO₄ solution) for three periods of time (2, 4 and 6 h) for collecting root exudates of soil‐grown rice plants. Nutrient culture solution created complications in the analyses of exudates for total organic C (TOC) by the wet digestion method and of organic acids by HPLC due to the interference by its components. Deionized water excluded such interference in analytical analyses but affected the turgor of root cells; roots of four widely different rice cultivars excreted 20 to 60 % more TOC in deionized water than in 0.01 M CaSO₄. Furthermore, the proportion of carbohydrates in TOC was also enhanced. Calcium sulfate solution maintained the osmotic environment for root cells and did not interfere in analytical procedures. Collection for 2 h avoided under‐estimation of TOC and its components exuded by rice roots, which occurred during prolonged exposure. By placing plants in 0.01 M CaSO₄ for 2 h, root exudates of soil‐grown traditional, tall rice cultivars (Dular, B40 and Intan), high‐yielding dwarf cultivars (IR72, IR52, IR64 and PSBRc 20), new plant type cultivars (IR65598 and IR65600) and a hybrid (Magat) were collected at seedling, panicle initiation, flowering and maturity and characterized for TOC and organic acids. The exudation rates were, in general, lowest at seedling stage, increased until flowering but decreased at maturity. Among organic acids, malic acid showed the highest concentration followed by tartaric, succinic, citric and lactic acids. With advancing plant growth, exudation of organic acids substituted exudation of sugars. Root and shoot biomass were positively correlated with carbon exudation suggesting that it is driven by plant biomass. As root exudates provide substrates for methanogenesis in rice fields, large variations in root exudation by cultivars and at different growth stages could greatly influence CH₄ emissions. Therefore, the use of high‐yielding cultivars with lowest root excretions, for example IR65598 and IR65600, would mediate low exudate‐induced CH₄ production. The screening of exciting rice cultivars and breeding of new cultivars with low exudation rates could offer an important option for mitigation of CH₄ emission from rice agriculture to the atmosphere.     

紫色小白菜有机酸的提取优化及UPLC定量分析

为建立一种紫色小白菜中精准的有机酸提取及定性定量分析方法。本研究在单因素试验的基础上,采用Box-Behnken的中心组合试验设计原理,设计响应面试验优化紫色小白菜有机酸的提取工艺。结果表明,紫色小白菜有机酸提取的最优工艺参数为:乙醇浓度73%,料液比1∶21,超声时间11 min,超声温度70℃。通过超高效液相色谱法(ultra performance liquid chromatography,UPLC)对紫色小白菜叶片和叶柄部位有机酸进行定性定量分析,检测出苹果酸、柠檬酸、丙二酸、琥珀酸和酒石酸,其中苹果酸含量最高,分别为15.968、5.019 mg/g;其次为柠檬酸,分别为9.293、1.385 mg/g。定性定量结果表明,紫色小白菜叶片及叶柄部位含有丰富有机酸类物质,叶片部位苹果酸、柠檬酸、丙二酸、酒石酸含量均高于叶柄部位,而琥珀酸含量较低。     

枇杷果肉有机酸组分及有机酸在果实内的分布

用高效离子交换色谱（HPIC）测定了枇杷（Eriobotrya japonica Lindk）18个品种（小毛枇杷、夹脚、卓南1号、解放钟、富阳、森尾早生、华宝2号、香钟10号、白花、土肥、多宝2号、乌躬白、洛阳青、茂木、早钟6号、白梨、塘头4号和长红3号）的成熟果肉和2个品种（解放钟和早钟6号果）成熟果实不同组织有机酸含量。结果表明,成熟果肉中均含有苹果酸、奎尼酸、柠檬酸、异柠檬酸、α-酮戊二酸、富马酸、草酰乙酸、酒石酸8种有机酸,有的还含有微量的阿魏酸、顺乌头酸和B一香豆酸。大多数品种果肉中苹果酸含量最高,平均含量为4399mg kg^-1 FW,占总酸的62．7％;其次是奎尼酸,其平均含量为2042mgkg—FW,占总酸的29．1％。品种之间可滴定酸和有机酸含量差异很大。通过对果肉可滴定酸进行聚类分析,可把18个枇杷品种分为五个组群：极高酸（小毛枇杷）、高酸（夹脚、卓南1号、解放钟和富阳）、中酸（森尾早生、华宝2号、香钟10号、白花、土肥和多宝2号）、低酸（乌躬白、洛阳青、茂木和早钟6号）和极低酸（白梨、塘头4号和长红3号）。解放钟和早钟6号果肉和果皮的总酸含量及可滴定酸均无显著差异,但果皮和果肉的总酸含量和可滴定酸均大大高于种子。相似于果肉,果皮和种子的主要有机酸也是苹果酸和奎尼酸。果皮中苹果酸含量远高于奎尼酸,但种子中苹果酸含量比奎尼酸稍低。此外,种子中苹果酸和奎尼酸比果肉和果皮中的低得多。     

Carboxylate composition of root exudates does not relate consistently to a crop species' ability to use phosphorus from aluminium, iron or calcium phosphate sources

* The relationship between carboxylate release from roots and the ability of the species to utilize phosphorus from sparingly soluble forms was studied by comparing Triticum aestivum, Brassica napus, Cicer arietinum, Pisum sativum, Lupinus albus, Lupinus angustifolius and Lupinus cosentinii. * Plants were grown in sand and supplied with 40 mg P kg(-1) in the sparingly soluble forms AlPO(4), FePO(4) or Ca(5)OH(PO(4))(3), or as soluble KH(2)PO(4); control plants received no P. * The ability to utilize sparingly soluble forms of P differed between forms of P supplied and species. Pisum sativum and C. arietinum did not access AlPO(4) or FePO(4) despite releasing carboxylates into the rhizosphere. * Species accessed different forms of sparingly soluble P, but no species was superior in accessing all forms. We conclude that a single trait cannot explain access to different forms of sparingly soluble P, and hypothesize that in addition to carboxylates, rhizosphere pH and root morphology are key factors.     

THE RELATION OF COLD RESISTANCE TO THE STATUS OF PHOSPHORUS AND CERTAIN METABOLITES IN RED-OSIER DOGWOOD (CORNUS STOLONIFERA MICHX.)

The process of cold acclimation in the winter hardy woody shrubCornus stolonifera Michx. was studied in relation to changesin phosphorus status and certain metabolites. Plants were coldacclimated effectively under controlled conditions which combinedshortening photoperiods and freezing temperatures. Metabolicchanges under these conditions were similar to those which occurnaturally in autumn. There was an extremely close relationshipbetween cold resistance and the status of phosphorus; i.e. ashardiness increased inorganic P decreased and acid soluble boundP and total organic P increased. Starch decreased during acclimationwhile the simpler carbohydrates increased. These included glucose,sucrose, fructose, raffinose, melibiose, xylose, and stachyosein decreasing order of occurrence. Proteins increased whilefree amino acids generally decreased. The non-volatile organicacids in decreasing quantitative order included malic, succinic,quinic, tartaric, citric, and shikimic acids. Of these onlyshikimic acid increased during hardening. These biochemicalchanges are discussed in reference to current theories of coldacclimation in plants. (Received June 18, 1966; )     

Hormonal Regulation of Organic and Phosphoric Acid Release by Barley Aleurone Layers and Scutella

The release of acid from the aleurone layer and scutellum of barley (Hordeum vulgare L. cv Himalaya) was investigated. Aleurone layers isolated from mature barley grains acidify the external medium by releasing organic and phosphoric acids. Gibberellic acid and abscisic acid stimulate acid release 2-fold over control tissue incubated in 10 mM CACl2. Gibberellic acid causes medium acidification by stimulating the release of phosphoric and citric acids, whereas abscisic acid stimulates the release of malic acid. The accumulation of these acids in the incubation medium buffers the medium against changes in pH, particularly between pH 4 and 5. The amounts of amino acids that accumulate in the medium are low (2-12 nmol/layer) compared to other organic and phosphoric acids (100-500 nmol/layer). The scutellum does not play a major role in medium acidification but participates in the uptake of organic acids. The organic acid composition of the starchy endosperm changes after 3 d of imbibition; malic, succinic, and lactic acids decrease, whereas citric and phosphoric acids remain unchanged or increase. These results indicate that during postgerminative growth, the acidity of the starchy endosperm is maintained by acid production by the aleurone layer.     

Citrate, Malate, and Succinate Concentration in Exudates from P-Sufficient and P-Stressed Medicago sativa L. Seedlings

Under certain stress conditions roots exude organic molecules, which may facilitate the uptake of nutrients. The objective of this research was to identify and measure the effect of low P upon the exudation of organic acids by roots of alfalfa (Medicago sativa L.) seedlings. Surface-sterilized alfalfa seeds were grown aseptically in sterile sand using an apparatus specially designed for the addition of ±P nutrient solutions and for the collection of root exudates. Citric, malic, and succinic acids were detected in the root exudates of 24-day-old alfalfa seedlings. Citrate exudation from the roots of P-stressed alfalfa was 182% that of plants receiving a complete nutrient solution. The increased release of citrate may provide a mechanism by which P-stressed plants enhance the availability of P in the rhizosphere.     

Esterification Rates of Main Organic Acids in Wines

The esterification rates (ratio of the concentration of an acid in the neutral ethyl ester form to total concentration of the acid) of main organic acids in wines were determined to study the extent of ethyl ester formation of organic acids. The esterification rates ranged from zero to 24.6%. The averaged values of table wines were from 6 to 16% for acetic and lactic acid, from 0.3 to 3.6% for succinic and malic acid, and from zero to 0.1% for tartaric acid. Sherries had higher esterification rates, about 1.6 to 6 times larger, than table wines. It was found that storage time and temperature influence the formation of ethyl esters, and it was suggested that the aging period required for the ester equilibrium is about one year for acetic and lactic acid, and more than two years for succinic, malic and tartaric acid. The possibility and the procedure to control wine quality during the aging process were discussed.     

Effects of Various Levels of CO(2) on the Induction of Crassulacean Acid Metabolism in Portulacaria afra (L.) Jacq

In response to water stress, Portulacaria afra (L.) Jacq. (Portulacaceae) shifts its photosynthetic carbon metabolism from the Calvin-Benson cycle for CO₂ fixation (C₃) photosynthesis or Crassulacean acid metabolism (CAM)-cycling, during which organic acids fluctuate with a C₃-type of gas exchange, to CAM. During the CAM induction, various attributes of CAM appear, such as stomatal closure during the day, increase in diurnal fluctuation of organic acids, and an increase in phosphoenolpyruvate carboxylase activity. It was hypothesized that stomatal closure due to water stress may induce changes in internal CO₂ concentration and that these changes in CO₂ could be a factor in CAM induction. Experiments were conducted to test this hypothesis. Well-watered plants and plants from which water was withheld starting at the beginning of the experiment were subjected to low (40 ppm), normal (ca. 330 ppm), and high (950 ppm) CO₂ during the day with normal concentrations of CO₂ during the night for 16 days. In water-stressed and in well-watered plants, CAM induction as ascertained by fluctuation of total titratable acidity, fluctuation of malic acid, stomatal conductance, CO₂ uptake, and phosphoenolpyruvate carboxylase activity, remained unaffected by low, normal, or high CO₂ treatments. In well-watered plants, however, both low and high ambient concentrations of CO₂ tended to reduce organic acid concentrations, low concentrations of CO₂ reducing the organic acids more than high CO₂. It was concluded that exposing the plants to the CO₂ concentrations mentioned had no effect on inducing or reducing the induction of CAM and that the effect of water stress on CAM induction is probably mediated by its effects on biochemical components of leaf metabolism.