Growth In Nutrient Solution Research Articles

Study of the effect of consortia of PGPR on the growth of Trichosanthes cucumerina in a hydroponic system

Hydroponics is the method of growing plants using soil-less cultivation systems. Plant growth-promoting bacteria are the rhizosphere bacteria that help plant growth and suppress plant diseases. In this study, we have isolated PGPR from the hydroponic systems and tested the efficacy of a consortium on the growth of Trichosanthes cucumerina. Ten organisms were isolated from a pre-set hydroponic system, of which three were selected based on their plant growth-promoting abilities. The isolated strains were identified as Chryseobacterium jejuense, Pseudomonas oryzihabitans and Sphingomonas paucimobilis. These isolates produced high levels of indole-3-acetic acid as well as other plant growth-promoting factors such as cellulase, pectinase, and siderophore production. All three isolates showed biofilm formation and growth in nutrient solutions with high EC values, indicating their ability to adhere to plant root surfaces and survive in nutrient solutions to promote plant growth. A consortium of these organisms used in the deep-water hydroponic system of T. cucumerina showed a significant increase in the number of leaves and root mass compared to control plants. Since these PGPR isolates exhibited multiple traits beneficial to the host plant, it has opened new possibilities for commercial application of these isolates in the hydroponic systems.

Electrical properties of plant root cell plasma membrane influence the alleviation of Al and Cu phytotoxicity by Ca and Mg cations.

Although it is known that cations such as calcium (Ca) and magnesium (Mg) can alleviate metal toxicity in plants, much uncertainty remains regarding the mechanisms by which this alleviation occurs. In this study, three plant species, cowpea (Vigna unguiculata. cv. White Caloona), soybean (Glycine max. cv. Bunya), and wheat (Triticum. cv. Axe), were used to examine growth in nutrient solutions containing a series of cations (Ca and Mg) and toxicants (Al and Cu). The addition of Ca and Mg increased Al3+ activities that induced 50% plant root elongation rate decline (EC50) from 4.0, 4.2, 0.34 to 31, 22, 9.4 for cowpea, soybean, wheat respectively. However, when expressed as the Al3+ activity at the root-cell plasma membrane (PM) surface, the addition of Ca and Mg increased Al sensitivity. In regression models, plant root elongation rate (RER) had higher R2 values with Al3+ activity at the PM than with Al3+ activity in the bulk solutions (0.60, 0.58, 0.93 for cowpea, soybean, wheat respectively). For Cu, the addition of Ca and Mg alleviated its phytotoxicity when expressed as the Cu2+ activity in the bulk-phase solutions for both cowpea and wheat. However, in soybean, the addition of Mg did not alter Cu toxicity when expressed as the Cu2+ bulk activity. Generally, the metal activity at the outer PM surface of the root cells is a better predictor for their phytotoxicity than the activity in bulk solution (R2=0.80, 0.80, 0.87 for cowpea, soybean, wheat respectively). These results supported the concept that the strength of alleviation of Ca and Mg cations depends on both the plant species and the toxicants that they alleviate. The different mechanisms should be fully considered in relevant assessments of trace metal toxicity in plants.

Shoot nutrient contents and vegetative melon plants growth at different pH levels of the nutrient solution

Melon plants development are determined by nutrient availability in the nutrient solution which is markedly influenced by the solution pH. The objective of this work was to evaluate the effects of hydroponic nutrient solution pH on growth and mineral content of melon plants. The plants were growth in nutrient solution at five pH levels (4, 5, 6, 7 and 8) in a completely randomized design with three replicates. At 40 days after transplanting were evaluated shoot and roots fresh and dry weight as well as the root volume. Leaf nutrients contents was also determined. It was concluded that it is essential to keep the nutrient solution pH at 6.0 in order to obtain plants with high leaf number, fresh and dry root mass, root volume and iron and zinc contents in the leaves.

Quantitative Nutrient Management Reduces Nitrate Accumulation in Hydroponic Butterhead Lettuces Grown under Artificial Lighting

To reduce nitrate concentrations in vegetables grown under artificial lighting, we determined nitrate accumulation under various conditions of nitrate availability. Butterhead lettuce plants were grown with nutrient solutions of various concentrations, which were maintained according to electrical conductivity (EC) throughout the cultivation period. Under these conditions, growth in nutrient solutions with lower EC led to slight decreases in nitrate concentrations in leaves, but also decreased fresh and dry weights of shoots, leading to the risk of a yield loss under EC control management (ECM). By contrast, when total nitrate requirement was supplied only at the start of cultivation, nitrate concentrations in leaves were decreased significantly with only slightly reduced plant growth. Hence, marketable-sized butterhead lettuces with lower nitrate concentrations can be produced by supplying total nitrate requirements in the nutrient solution at the start of cultivation.

Biochar, a potential hydroponic growth substrate, enhances the nutritional status and growth of leafy vegetables

A hydroponics system developed using a nutrient film technique was used to evaluate the effectiveness of rice husk biochar (RB) alone or in combination with perlite (PL) as substrates for increasing the growth of leafy vegetables compared with that of PL. Seedlings of cabbage, dill, mallow, red lettuce, and tatsoi were grown hydroponically in PL, RB, and PL + RB (1:1 ratio of PL to RB, v/v) substrates for a 30-d under optimal environmental conditions in a greenhouse. Shoot length and fresh/dry masses of cabbage, dill, and red lettuce plants grown in RB substrate were decreased by 49% on average compared to those plants grown in PL substrate. In contrast, PL + RB substrate led to approximately 2-fold increases in shoot length, number of leaves, and fresh/dry masses of leafy vegetable plants compared with those grown in PL substrate. Foliar nutritional composition (Ca, Mg, K, Na, Mn, Fe, and Zn) and nitrogen status (SPAD index) of plants grown in PL + RB and PL substrates suggested the presence of optimal growth conditions for ensuring optimum yield with high quality. In addition, RB substrate contributed to respective increases of 1.2–3.5-fold in leaf K, Mg, Mn, and Zn contents in most vegetable plants compared with those grown in PL substrate. The RB alone or in combination with PL substrates decreased algal growth in the nutrient solutions as confirmed by scanning electron micrographs of microalgae on the RB surface. The results also indicated that use of PL + RB hydroponic substrate could be an alternative and effective technology for the better management of unwanted algal growth in nutrient solutions and high production of leafy vegetables.

Laboratory-scale production and purification of the iron chelator rhizoferrin: a novel Fe supplier to plants

Rhizopus arrhizus was grown in an iron-free nutrient solution growth medium. Mass production of the siderophores was achieved in a short time by continuous growth of the fungi: after the secretion of the siderophores into the growth medium the spent medium was collected and replaced by a fresh medium while the fungus mat was kept in the flask. The medium exchange was repeated several times and the optimal time for the collection of the siderophore was found to be when the fungus was fully developed, usually about 3 days after the exchange. It was found that it is feasible to grow the fungi continuously for five growth periods, after which the fungus culture becomes too old and collapses.The siderophore was isolated and cleaned from the spent medium using a series of columns on an FPLC at room temperature. Additional tests were used to verify the existence of the siderophore in the solution. The concentrations of rhizoferrin in the various fractions was measured using an exchange reaction between the siderophore and that of an added chelate solution (CAS) while employing a series of dilutions of the CAS.For a precise analytical determination of the siderophore rhizoferrin, Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTICR-MS) was used to validated that the siderophore is indeed rhizoferrin which has been structurally identified earlier.

Establishment of New Split-root System by Grafting.

A new split-root system was used to simulate non-uniform salt, drought or nutrient deficiency stress in the root zone, in which the root system was divided into two or more equal portions. Here, we established a split-root system by grafting of cotton seedlings. In contrast to the conventional split-root, the main roots of the new system remained intact, which provided a better system for studying cotton response to unequal treatment in the root zone. The new system was suitable for plant growth in nutrient solution and the two root systems can fully be immerged in the nutrient solution.

Autotoxic effect of ginsenoside extrats on growth of American ginseng in different medium

Ginsenosides are the abundant secondary metabolites in American ginseng (Panax quinquefolium), it could be released into soil through root exudation and decomposition during plant growth. This study determined ginsenoside contents in American ginseng cultivated soil by HPLC. Three ginsenosides, Rb1, Rb2 and Rd, were detected in the rhizosphere soil of 3-4 years old American ginseng cultivated in Huairou District, Beijing, and their contents were 0.80-3.19 mg x kg(-1). Correspondingly, the contents of the three ginsenosides in soil solution were 4-16 mg x L(-1) at field water-holding capacity of 20%. According to the field soil test data, we designed the concentration of ginsenosides for bioassays (0.2-125 mg x L(-1) in solution or 0.2-125 mg x kg(-1) in soil). The results showed that radicle lengths of American ginseng were reduced by 6%-23% in solution containing 0.2-125 mg x L(-1) ginsenoside extract, and a significant difference was observed at concentration of 125 mg x L(-1) (P < 0.05). The shoot lengths of American ginseng were not significantly inhibited by 0.2-125 mg x L(-1) ginsenosides extractions. After 20 days of growth in nutrient solution amended with 25 mg x L(-1) ginsenosides extraction, plant height of 3-year-old American ginseng seedling was decreased by 28% compared to the control, and the biomass of aerial parts was also reduced by 50% (P < 0.05). However, the growth of newly-grown fibrous root was not significantly inhibited. Comparatively, when American ginseng embryos were cultivated into sterile or non-sterile soil, neither radicle lengths nor shoot lengths were significantly affected by 0.2-125 mg x kg(-1) ginsenoside extracts. In conclusion, ginsenosides showed autotoxic effect on growth of American ginseng radicle and adult seedling, however, this effect was weakened in field soil.

Nutrition, dry matter accumulation and partitioning and phosphorus use efficiency of potato grown at different phosphorus levels in nutrient solution

High rates of phosphate fertilizers are applied to potato (Solanum tuberosum L.), which may cause antagonistic interactions with other nutrients and limit crop yields when over-supplied. The purpose of this study was to evaluate the influence of phosphorus (P) levels in nutrient solution on P use efficiency, nutritional status and dry matter (DM) accumulation and partitioning of potato plants cv. Ágata. The experiment was carried out in a greenhouse, arranged in a completely randomized block design with four replications. Treatments consisted of seven P levels in nutrient solution (0, 2, 4, 8, 16, 31, and 48 mg L-1). Plants were harvested after 28 days of growth in nutrient solution, and separated in roots, stems and leaves for evaluations. The treatment effects were analyzed by regression analysis. Phosphorus levels of up to 8 mg L-1 increased the root and shoot DM accumulation, but drastically decreased the root/shoot ratio of potato cv. Ágata. Higher P availability increased P concentration, accumulation and absorption efficiency, but decreased P use efficiency. Higher P levels increased the N, P, Mg, Fe, and Mn concentrations in roots considerably and decreased K, S, Cu, and Zn concentrations. In shoot biomass, N, P, K, and Ca concentrations were significantly increased by P applied in solution, unlike Mg and Cu concentrations. Although higher P levels (&gt; 8 mg L-1) in nutrient solution increased P concentration, accumulation and absorption efficiency, the DM accumulation and partitioning of potato cv. Ágata were not affected.

Nitrogen nutrition of young triticale plants grown under aluminium stress

stress Ana Maria Domingues1, 2 1Tropical Research Institute, Department of Natural Sciences / Instituto de Investigacao Cientifica Tropical, Departamento de Ciencias Naturais Tapada da Ajuda – PAIAT, 3 rd floor/ 3o piso Apartado 3014, 1301-901 Lisboa Codex PORTUGAL 2Centro de Estudos da Macaronesia / Center for Macaronesian Studies, University of Madeira, Campus Penteada, 9000-390 Funchal - PORTUGAL E-mail: dam.portugal@hotmail.com ABSTRACT Triticale has proven to be a tolerant crop in many places around the globe, under extreme climatic and edaphic conditions, particularly in Al-toxic soils. To suffice the growing food demand of the world population, one of the most important goal is the sustainable increase of cereal production avoiding the anthropogenic pollution, often air and groundwater contamination by volatilization and leaching of N compounds. The effects of enhanced ammonia proportion in relation to nitrate nutrition in hydroponics, with or without Al, were investigated on the short-term growth of triticale plants. Three days old plants of the Al-tolerant genotype TTE 9203 were submitted to 0 or 370 mM Al and received different NO3-/ NH4+ ratios with the four proportions 15:1, 8:1, 3:1 and 1:1 (with fixed total N concentration at 3.2 mM in all treatments). In relation to the corresponding control solutions, 370 mM Al induced important decreases in root length, ranging from 75.3 % to 47.3 %, reductions in fresh weight from 80 % to 60 % in roots, and from 89 % to 71 % in shoots, depending on the NO3-/ NH4+ ratio. A decrease in NO3- net uptake was shown by plants in the presence of Al. The most detrimental Al effect for young plant growth in nutrient solutions was observed with the 15:1 NO3-/ NH4+ ratio, which induced the highest reductions of length of the main root (52.7 % reduction relative to control) and of root biomass fresh weight (40.6 %) in four days of treatment. By the contrary, the plants grown in the 8:1 ratio solution with Al suffered the smallest reductions of root length (24.7 % in 370 mM Al treatment relative to control) and of root biomass fresh weight (20.3 %). Taken together the results indicate that NH4+ can alleviate Al toxicity in triticale and point out the ideal NO3-/ NH4+ proportion of 8:1 as the best for these young plants growth and N use efficiency, under acidic and Al toxic condition. Some economical and ecological advantages of NH4+- N sources use in plant fertilization are discussed.

Association and Linkage Analysis of Aluminum Tolerance Genes in Maize

BackgroundAluminum (Al) toxicity is a major worldwide constraint to crop productivity on acidic soils. Al becomes soluble at low pH, inhibiting root growth and severely reducing yields. Maize is an important staple food and commodity crop in acidic soil regions, especially in South America and Africa where these soils are very common. Al exclusion and intracellular tolerance have been suggested as two important mechanisms for Al tolerance in maize, but little is known about the underlying genetics.MethodologyAn association panel of 282 diverse maize inbred lines and three F2 linkage populations with approximately 200 individuals each were used to study genetic variation in this complex trait. Al tolerance was measured as net root growth in nutrient solution under Al stress, which exhibited a wide range of variation between lines. Comparative and physiological genomics-based approaches were used to select 21 candidate genes for evaluation by association analysis.ConclusionsSix candidate genes had significant results from association analysis, but only four were confirmed by linkage analysis as putatively contributing to Al tolerance: Zea mays AltSB like (ZmASL), Zea mays aluminum-activated malate transporter2 (ALMT2), S-adenosyl-L-homocysteinase (SAHH), and Malic Enzyme (ME). These four candidate genes are high priority subjects for follow-up biochemical and physiological studies on the mechanisms of Al tolerance in maize. Immediately, elite haplotype-specific molecular markers can be developed for these four genes and used for efficient marker-assisted selection of superior alleles in Al tolerance maize breeding programs.

Chromium‐ and copper‐induced inhibition of photosynthesis in Euglena gracilis analysed on the single‐cell level by fluorescence kinetic microscopy

Here, we investigated effects of copper (Cu) and chromium (Cr) toxicity on two contrasting strains of Euglena gracilis, with and without chloroplasts, grown in culture media promoting either phototrophic or heterotrophic growth. This led to insights into Cr/Cu toxicity mechanisms and into the regulation of phototrophic vs heterotrophic metabolism. Our data strongly suggest that in Cu(2+) and Cr(6+) stressed Euglena photosynthesis is the primary target of damage. In the applied light conditions, this was mainly damage to the photosystem II reaction centre, as shown by single-cell measurements of photochemical fluorescence quenching. Respiration and photosynthetic dark reactions were less sensitive. The malfunctioning photosynthesis enhanced production of reactive oxygen species (mainly superoxide), leading to elevated amounts of carotenoid degradation products. At higher metal concentrations in chloroplast-containing cells, but not white cells, this oxidative stress resulted in increased respiratory oxygen uptake, likely by damage to mitochondria. During growth in nutrient solution promoting heterotrophic metabolism, the cells were able to repair the metal-induced damage to photosynthesis, moderating the inhibition of photochemistry. Growth in medium forcing the cells into photosynthesis increased the investment in photosynthetic pigments. Comparison of the two Euglena strains surprisingly showed that the previously metal-resistant strain lost this resistance during culture.

Purification, properties and specificity of a NDP kinase from Alyssum murale grown under Ni 2+ toxicity

During the growth of Alyssum murale, a nickel accumulator plant, three root peptides chains of 55, 18 and 16kDa undergo phosphorylation. The intensity of the phosphorylated bands decreased in the course of growth in nutrient solution supplied with 0.5mM Ni(2+). In the shoot only two phosphorylated peptide chains with a size of 18 and 16kDa were detected. These two shoot peptides disappeared on the 19th day of growth in Ni(2+)-exposed plants, while the root peptide of 16kDa continued to be present in less intensity. This peptide was identified as the catalytic subunit of nucleoside diphosphate kinase (NDP kinase: E.C. 2.7.4.6) and was named NDPK-B. The enzyme was purified by means of ammonium sulphate precipitation, DEAE-sepharose and hydroxyapatite column chromatography. NDPK-B was thermostable, displayed a molecular mass of 103,000 and was comprised of six catalytic subunits. The autophosphorylated enzyme displayed an isoelectric point (pI) of 6.5. The NDPK-B autophosphorylation activity was metal-dependent. With regard to the transfer reaction, NDPK-B exhibited the following properties: (a) the enzyme had an optimum pH of 7.6; (b) it was capable of using both (gamma-(32)P) ATP and (gamma-(32)P) GTP as phosphate donors and of using all the available NDPs except dCDP as phosphate acceptors; (c) its activity using NDPs as substrates was metal dependent; (d) in the presence of (gamma-(32)P) GTP as the phosphate donor, it phosphorylated exclusively ADP when a mixture of NDPs was added in the reaction mixture; and, (e) ADP had a very low K(m) value towards 8.4nM. This high affinity towards ADP suggests that the enzyme may play a crucial function in the formation of the amount of ATP necessary for Alyssum murale to survive Ni(2+) stress.

Influence of calcium, magnesium, sodium, potassium and pH on copper toxicity to barley ( Hordeum vulgare)

The extent to which Ca 2+, Mg 2+, Na +, K + ions and pH independently influence copper toxicity to barley ( Hordeum vulgare) was assessed by measuring root growth in nutrient solutions. Increased Ca 2+ activity resulted in a sixfold decrease in EC 5 0 Cu 2 + values, while a positive relationship between the cation activity and the EC50 was expected. Increased Mg 2+ activity resulted in a twofold increase in EC 5 0 Cu 2 + values. Na +, K + and H + activities did not significantly affect Cu 2+ toxicity. The obtained results indicated that competition for binding sites between Cu 2+ and cations such as Ca 2+, Mg 2+, Na +, K + and H + is not an important factor in determining Cu 2+ toxicity to H. vulgare. However, the EC50s could, with one exception, be predicted within a factor three based on the free Cu 2+ activity, indicating that the free Cu 2+ activity cannot only be used to predict metal toxicity to aquatic, but also to terrestrial organisms.

Possible Involvement of Cytokinin in Nitrate-mediated Root Growth in Maize

Response of root system architecture to nutrient availability in soils is an essential way for plants to adapt to soil environments. Nitrate can affect root development either as a result of changes in the external concentration, or through changes in the internal nutrient status of the plant. Nevertheless, less is known about the physiological mechanisms. In the present study, two maize (Zea mays L.) inbred lines (478 and Wu312) were used to study a possible role of cytokinin in nitrate-mediated root growth in nutrient solutions. Root elongation of 478 was more sensitive to high nitrate supply than that of Wu312. Medium high nitrate (5 mM) inhibited root elongation in 478, while, root elongation in Wu312 was only inhibited at high NO 3 − supply (20 mM). Under high nitrate supply, the root elongation zone in 478 became swollen and the site of lateral root elongation was close towards the root tip. Both of the phenomena are typical of root growth induced by exogenous cytokinin treatments. Correspondingly, zeatin and zeatin nucleotide (Z + ZR) concentrations were increased at higher nitrate supply in 478, whereas they were constant in Wu312. Furthermore, exogenous cytokinin 6-benzylaminopurine (6-BA) completely reversed the stimulatory effect of low nitrate on root elongation. Therefore, it is supposed that the inhibitory effect of high concentration of nitrate on root elongation is, at least in part, mediated by increased cytokinin level in roots. High nitrate supply may have negative influences on root apex activity by affecting cytokinin metabolism so that root apical dominance is weakened and, therefore, root elongation is suppressed and lateral roots grow closer to the root apex. Nitrate suppressed lateral root elongation in Wu312 at concentration higher than 5 mM. In 478, however, this phenomenon was not significant even at 20 mM nitrate. Although exogenous 6-BA (20 nM) could suppress lateral root elongation as well, the inhibitory effect of high NO 3 − concentration of nitrate on lateral root growth cannot be explained by changes in endogenous cytokinin alone.

New Sources of Aluminum Tolerance in South African Maize

Laboratory nutrient culture techniques were used to screen maize (Zea mays L.) genotypes, including commercial cultivars as well as seed collected from traditional farmers located in various parts of the province KwaZulu-Natal, Republic of South Africa, for aluminum (Al) tolerance. Tolerance was assessed after 10 days’ growth in nutrient solutions on the basis of measurements involving Al-induced (0; 100 µM) changes in primary root growth and a loss of root apical dominance. Among the commercial cultivars Al tolerance decreased in the order Sc 602, Sr 52, Snk 2665, Kalahari Early Pearl, Ls 8501, Pan 6479, Zm 521, Sc 709. The commercial maize cultivars all had lower levels of Al tolerance to that observed in the better adapted seed collected from traditional sources (Khum, Mbon, Aj) which indicated that the fixation of important Al tolerance genes has occurred in some maize populations in response to external environmental conditions. Not all the seed from traditional sources proved to be Al tolerant (Mak, Emb, Msomi). Large intervarietal differences in root development (length and mass) were also identified. No meaningful relationships existed between Al tolerance and root development (size of root system) or between plant performance in solutions containing Al and leaf chemical contents.

Autotoxicity of root exudates from strawberry in hydroponic culture

SummaryThe effects of exudates from strawberry roots on the growth of strawberries in hydroponic culture were investigated. Vegetative and reproductive growth in nutrient solution without activated charcoal (–AC) was lower than with AC (+AC). The root exudates adsorbed by the AC were extracted and analysed in a gas chromatograph coupled to mass spectrometer (GC-MS). The compounds identified included lactic, benzoic, succinic, adipic and p-hydroxybenzoic acids. The allelopathic potential of these compounds were evaluated on strawberry plantlets. The results indicated that benzoic acid significantly inhibited the fresh weights of shoots, the dry weights of shoots and roots, and the maximum root length, at all concentrations tested. These results suggest that root exudates from strawberry plants may cause growth inhibition, and that the greatest inhibition was caused by benzoic acid.

Avaliação de nove linhagens de milho em cruzamentos dialélicos quanto à tolerância ao alumínio

Avaliaram-se nove linhagens endogâmicas de milho e seus cruzamentos quanto à tolerância ao alumínio (Al), em um dialelo incompleto. Foram utilizados os índices fenotípicos de comprimento relativo de raiz seminal (CRRS), comprimento líquido de raiz seminal (CLRS) e coloração por hematoxilina, determinados após sete dias de crescimento em solução nutritiva contendo 222 mimoles L-1 de Al. Os resultados dos cruzamentos dialélicos demonstraram que os efeitos aditivos foram mais importantes que os efeitos não-aditivos para os três índices avaliados. As linhagens L13, L724, L723 e L16 seriam as mais indicadas para a obtenção de híbridos visando tolerância ao Al, por apresentarem os melhores valores de capacidade geral de combinação e por participarem dos cruzamentos de melhor capacidade específica de combinação. Uma correlação de 0,76 foi observada entre os índices CLRS e a coloração por hematoxilina, de 0,63 entre CLRS e CRRS e de 0,27 entre CRRS e coloração por hematoxilina. A coloração por hematoxilina demonstrou ser uma valiosa ferramenta para programas de melhoramento de milho que visam a seleção de genótipos com maior tolerância ao alumínio.

低酸素条件下の根のエタノール，乳酸およびリンゴ酸代謝と細胞液ｐＨにおけるトマトとキュウリ間の差異

Plant growth in nutrient solution with a low dissolved oxygen concentration (DO) of 1 ppm is greatly inhibited in tomato (Lycopersicon esculentum Mill.), but almost normal in cucumber (Cucumis sativus L.)(Guo·Tachibana, 1997). To elucidate the mechanisms for the high tolerance of cucumber to root-zone hypoxia, the metabolisms of ethanol, lactate and malate, and the cell sap pH in intact and excised roots under hypoxia were compared between tomato 'Hausu-Momotaro' and cucumber 'Sharp I'. In intact roots of tomato, concentrations of ethanol and lactate as well as the activity of alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH) were markedly increased on exposure to 1 ppm DO for 3 and 6 days compared to 4 ppm DO. Similar results were obtained with excised tomato roots incubated at 0, 1, and 4 ppm DOs for 24 and 48 hr. Concentrations of malate decreased at low DOs in both intact and excised tomato roots. Contrarily, in cucumber the increase in ethanol concentrations and ADH activity at low DOs was slight in intact roots and did not occur in excised roots. Lactate concentrations and LDH activity did not increase in both types of hypoxic roots, except that excised roots incubated at 0 ppm DO exhibited a slight increase in lactate concentrations but to a much lesser extent than tomato roots. On the other hand, malate concentrations were greatly increased in both intact and excised roots at 1 ppm DO ; excised roots, incubated at 0 ppm DO, showed no increase in malate concentrations. The cell sap pH of intact tomato roots grown 3 days at 1 ppm DO fell from 5.70 to 5.51 and that at 0 ppm DO to 5.22. However, in intact cucumber roots it did not change significantly at 1 ppm DO and arose markedly from 5.98 to 6.33 after 3 days at 0 ppm DO. The results strongly suggest that the metabolic properties of roots to stimulate synthesis of malate in response to low O2 in the root tissue and consequently prevent cytoplasmic acidosis because of lactate accumulation are responsible for the high tolerance of cucumber to root-zone hypoxia.

Screening soya beans [Glycine max (L.) Merill] for calcium efficiency by root growth in low-Ca nutrient solution

There are severe soil constraints for agriculture in many tropical regions of the world. Acidity and low levels of calcium are examples of them in the Brazilian Cerrados (Savannahs). They may prevent deep root growth of cultivated plants, exposing them to moisture stress during dry spells. This study aimed to develop a technique for screening soya bean varieties tolerant to low calcium based on root growth in nutrient solution. The results have shown varietal differences for tolerance to low-Ca stress. The method of screening for response to low-Ca is quick, non-destructive and can be employed in genetic studies and breeding programmes for efficient calcium utilisation by soya beans. It is expected that improved varieties for this character will lead to yield stability and contribute to develop sustainable farming systems in the savannahs.