A rapid bioassay for the detection of photosynthesis inhibitors in water

A modified leaf disc buoyancy procedure for the detection of photosynthesis-inhibiting residues in water is described. The modifications proposed, mainly the presence of sodium hydrogen carbonate in the infiltration solution, increased the sensitivity of the method and reduced the time required. The substituted urea and 1,3,5-triazine herbicides diuron, linuron, monuron, atrazine, ametryn and atraton were detected below 0.7 mg litre^?1 using cucumber (Cucumis sativus L., cv. ‘Dalia’) leaf discs. A concentration as low as 0.09 mg diuron litre^?1 could be detected. Although bean (Phaseolus vulgaris L., cv. ‘Bulgarian’) leaf tissue was less sensitive in this bioassay than cucumber, 0.3 mg diuron litre^?1 could still be detected. The test, being very rapid (less than 30 min per determination) and relatively sensitive, could be used for the detection of photosynthesis inhibitors in recycled water used for irrigation.     

Effect of saline irrigation and water deficit on tuber quality

Summary The effect of salinity and water dificit on the quality of tubers for processing was investigated. Total tuber yield was not affected by the treatments, while the percentage of non-marketable tubers was significantly reduced by high salinity (EC_i=6dS m⁻¹) and by water reduction. Accumulation of dry matter in the tubers was increased by all the treatments, that of proline by salinity only and the content of reducing sugars was increased only by water deficit. The colour of the french fries was similar in tubers from the various treatments.     

Growth,photosynthesis and protein content in cucumber plants as affected by supplied nitrogen form

Cucumber plants were grown hydroponically in three different nutrient solutions to determine the effect of NO₃ ^‐/NH₄ ⁺ ratio on several parameters. Top and root growth, CO₂ fixation, and ion content (K⁺, Ca⁺², NO₃ ^‐) were always lower when urea and ammonium nitrate were the major N source as compared with a Hoagland solution in which nitrate was the major N source. No significant differences were found in total N and protein content among the three nutrient solution treatments.     

Nitrogen-enhanced phytotoxicity to cucumber of low concentrations of EPTC and metolachlor

The impact of nitrogen source on the response of cucumber (Cucumis sativus) seedlings to sub-toxic concentrations (<10⁻⁶ ) of metolachlor and EPTC was studied in nutrient solutions. Nitrogen increased the phytotoxicity of low concentrations of both herbicides. The presence of a relatively high ammonium level (5m ) in solution enhanced growth inhibition (up to 50%), increased total nitrogen (20%) and protein content (26%), and resulted in less K⁺ (50%) and Ca²⁺ (70%) absorption. Under optimal nitrogen nutrition conditions, metolachlor temporarily inhibited plant growth, and both herbicides decreased the protein content in cucumber leaves. The effect of herbicides at the high ammonium level on plant growth was stronger and more long-lasting compared with control growing conditions.     

Characterization of a novel tomato mutant resistant to the weedy parasites <Emphasis Type="Italic">Orobanche</Emphasis> and <Emphasis Type="Italic">Phelipanche</Emphasis> spp.

Orobanche and Phelipanche, commonly known as broomrape, are dicotyledonous holoparasitic flowering plants that cause heavy economic losses in a wide variety of plant species. Breeding for Orobanche resistance is still one of the most effective management strategies for this weed. However, previous efforts to find broomrape-resistant tomato (Solanum lycopersicon) genotypes have been unsuccessful. Here, we report on the isolation and characterization of a fast-neutron-mutagenized M-82 tomato mutant, Sl-ORT1. The Sl-ORT1 mutant showed resistance to Phelipanche aegyptiaca as compared to cultivar M-82; segregation analysis suggested a single recessive ort1 allele. Sl-ORT1 broomrape resistance was reflected in a lower number of broomrapes per plant, reduced P. aegyptiaca fresh weight per plant, and the absence of broomrape’s negative effect on plant host growth and yield. Sl-ORT1 was shown to be resistant to high concentrations of P. aegyptiaca seeds, and to another three broomrape species: Phelipanche ramosa, Orobanche cernua, and Orobanche crenata. Grafting experiments demonstrated that roots, rather than shoots, are necessary for Sl-ORT1 broomrape resistance. In addition, Sl-ORT1 was shown to be resistant to broomrape under field conditions. Since yield parameters are slightly affected by the mutation, this resistance gene should be introduced into tomato varieties with different genetic backgrounds; this newly identified Orobanche-resistant mutant may be further utilized in breeding programs for Orobanche resistance.     

Cloning of a second variant of somatolactin-encoding cDNA from the gilthead seabream Sparus aurata

cDNA clones which include coding sequences of the gilthead seabream (Sparus aurata) somatolactin (SL) have been isolated from a cDNA library prepared from seabream pituitary gland poly (A)⁺ RNA. Flounder – SL cDNA was used as a hybridization probe. The complete nucleotide (nt) sequence of the seabream somatolactin has been determined. The clone encodes a polypeptide of 231 amino acid (aa) residues including 24 amino acid residues of signal peptide. Northern blot hybridization detected one band of approximately 1.8 kb mRNA. By comparing the sequences of this SL cDNA to the one recently published, it is suggested that two variants of the SL exist in seabream. By comparing the sequences of the aa of SL to the deduced aa sequences, it is possible that even a third variant of SL exists in this species.     

All-fish gene constructs for growth hormone gene transfer in fish

In order to develop all-fish expression vectors for microinjection into fertilized fish eggs, we have prepared the following constructs: rainbow trout metallothionein a/b and the gilthead seabream growth hormone cDNA (ptMTa-gbsGHcDNA, ptMTb-gsbGHcDNA), carp β-actin gilthead seabream GH cDNA (pcAβ-gsbGHcDNA). The inducible metallothionein promoters a and b were cloned from rainbow trout, and the constitutive promoter β-actin was isolated from carp. The metallothionein promoters were cloned by using the PCR technique. The tMTa contains 430 bp, while the tMTb contains 260 bp (Hong et al. 1992). These two promoters were introduced to pGEM-3Z containing the GH cDNA of Sparus aurata to form ptMTa-gsbGH and ptMTb-gsbGH, respectively. The carp cytoplasmic β-actin gene was chosen as a source for isolating strong constitutive regulatory sequences. One of these regulatory sequences in pUC118 was ligated to GH cDNA of S. aurata to form the pcAβ-gsbGHcDNA. Expression of the constructs containing the metallothionein promoters was tested in fish cell culture and was found to be induced effectively by zinc. The ptMTa gsb-GH cDNA construct was microinjected into fertilized carp eggs, and integration in the genome of carp was detected in the DNA isolated from fins at the age of two months.

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Résumé Afin de développer des vecteurs d'expression de poisson, entièrement homologues, destinés aux microinjections dans des oeufs fertilisés, les constructions suivantes ont été préparées: promoteurs de la metallothionine, a ou b, de truite arc-en-ciel d'une part, et promoteur de l'actine β de carpe d'autre part, associés à l'ADNc de l'hormone de croissance de daurade royale (ptMTa-gsbGH cDNA, ptMTb-gsbGH cDNA, et pcAβ-gsbGH cDNA). Les promoteurs de la metallothionine ont été clonés en utilisant la technique de la RCP. La tMTa comprend 430 pb. tandis que la tMTb en comprend 260 (Hong et al. 1992). Ces deux promoteurs ont été insérés dans pGEM-3Z qui contenait l'ADNc de GH de Sparus aurata, pour former, respectivement, ptMTa-gsbGH et ptMTb-gsbGH. Le gène de l'actine cytoplasmique β de carpe été choisi comme source d'isolement de séquences régulatrices fortement constitutives. Une de ces séquences régulatrices a été liguée à l'ADNc de GH de S. aurata dans pUC118, pour réaliser la construction pcAβ-gsbGH cDNA. L'expression des constructions contenant les promoteurs de la metallothionine a été tentée dans des cultures de cellules de poisson, où elle a été effectivement induite par le zinc. La construction ptMTa-gsbGH cDNA a été microinjectée dans des oeufs fertilisés de carpe. Son intégration dans le génome de carpe a pu être détectée dans l'ADN isolé à partir de nageoires d'animaux agés de 2 mois.