Physiological and biochemical responses resulting from nitrite accumulation in tomato (Lycopersicon esculentum Mill. cv. Ibiza F1)

The sensitivity of hydroponically cultivated tomato (Lycopersicon esculentum Mill. cv. Ibiza F1) submitted to nitrite treatments (0.25-10mM KNO(2)) for 7d was studied. Increasing nitrite levels in the culture medium led to several disruptions of tomato plants, reflected by reductions of both dry matter per plant, chlorophyll concentrations and the appearance of chlorosis symptoms at the leaf surface. This behaviour was accompanied by stimulation of nitrite, nitrate and ammonia ion accumulation, mainly in roots and old leaves. Higher proteolytic and gaiacol peroxidase (GPX, EC. 1.11.1.7) activities and malonyldialdehyde content were also noted. Protein content of the different plant organs was decreased by nitrite treatment. These physiological and biochemical parameters were chosen as they are stress indicators. Taken together, our data partly explain the harmful effects of nitrite ions, when excessive in the culture medium.     

Annual reproductive cycle,spawning periodicity and sexual maturity of blue runner Caranx crysos (Pisces,Carangidae) from the Gulf of Gabes (Tunisia,Eastern Mediterranean)

From June 2004 to May 2006, the reproductive biology of the blue runner Caranx crysos was studied in the Gulf of Gabes (Southern Tunisia). Of 1668 individuals examined, 777 were females (46.6%) and 891 were males (53.4%). The sex ratio significantly deviated in favour of males (♀:♂ = 0.87 : 1). The difference in the numbers of females and males was significant among size‐classes. However, there was no significant difference between sexes over months and seasons. Monthly changes in the Gonado‐Somatic Index (GSI) showed a rapid increase during summer to very high levels in July (3.51% for males and 2.55% for females) and August (3.47% for males and 2.59% for females) before declining sharply in September (0.58% for females and 0.38% for males). The gametogenesis activity began with a pre‐maturation phase, from 20 May to the first 10 days of July, followed by a pre‐spawning phase, from 20 July to 20 August. From the last 10 days of August to 20 September the gonads were in the ripe and spawning stages. From the end of September to early May, gonads were in the post‐spawning and resting stages. The size at which 50% of the population reached sexual maturity was significantly different in males and females: males attained sexual maturity at fork length FL₅₀ = 210.20, whereas females attained maturity at FL₅₀ = 222.3 mm. Age at maturity was 2.4 years for males and 2.8 years for females.     

A thermoactive uropygial esterase from chicken: purification, characterisation and synthesis of flavour esters

A lipolytic activity was located in the chicken uropygial glands, from which a carboxylesterase (CUE) was purified. Pure CUE has an apparent molecular mass of 50 kDa. The purified esterase displayed its maximal activity (200 U/mg) on short-chain triacylglycerols (tributyrin) at a temperature of 50°C. No significant lipolytic activity was found when medium chain (trioctanoin) or long chain (olive oil) triacylglycerols were used as substrates. The enzyme retained 75% of its maximal activity when incubated during 2h at 50°C. The NH(2)-terminal amino acid sequence showed similarities with the esterase purified recently from turkey pharyngeal tissue. Esterase activity remains stable after its incubation during 30 min in presence of organic solvents such as hexane or butanol. CUE is a serine enzyme since it was inactivated by phenylmethanesulphonyl fluoride (PMSF), a serine-specific inhibitor. The purified enzyme, which tolerates the presence of some organic solvent and a high temperature, can be used in non-aqueous synthesis reactions. Hence, the uropygial esterase immobilised onto CaCO(3) was tested to produce the isoamyl and the butyl acetate (flavour esters). Reactions were performed at 50°C in presence of hexane. High synthesis yields of 91 and 67.8% were obtained for isoamyl and butyl acetate, respectively.     

Hypolipidemic effect of diet supplementation with bacterial levan in cholesterol-fed rats

Levan polysaccharide, a type of fructan, has been shown to have industrial applications as a new industrial gum in the fields of cosmetics, foods like dietary fiber and pharmaceutical goods. The objective of this current study was to investigate the possible hypolipidemic and antioxidative effects of levan in rats fed with a high-cholesterol diet. Animals were allocated into four groups of six rats each: a normal diet group (Control), normal rats received levan (L), a high-cholesterol diet group (Chol) and a high-cholesterol diet with a daily dose of levan equivalent to 5%. Treated hypercholesterolemic rats were administrated with levan in drinking water through oral gavage for 60 days. After the treatment period, the plasma antioxidant enzymes and lipid profiles were determined. Our results show that treatment with levan polysaccharide positively changed plasma antioxidant enzyme activities and lipid profiles (total cholesterol, HDL-cholesterol, LDL-cholesterol and triglycerides) in cholesterol-rats, and thus may have potential hypolipidemic and antioxidant effects. Levan could protect against oxidative stress linked atherosclerosis and decrease the atherogenic index.     

In vitro culture: a simple and efficient way for salt-tolerant grapevine genotype selection

In order to quickly and efficiently evaluate the grapevine's salt tolerance, salinity tests were conducted on some grapevine varieties and rootstocks under in vitro conditions. Plant materials used in the salinity test were propagated using the axillary buds culture method. Single-node shoots were subjected to seven different NaCl concentrations (0, 20, 50, 100, 150, and 200 mM NaCl) in MS medium for 45 days. The different growth parameters analysed were: survival capacity, length of shoot, bud formation, and rooting capacity. Our results showed that salinity reduced in vitro growth and development of grapevine. Proliferation, growth, rooting and viability of explants decreased due to the increase in NaCl concentration. First symptoms of stress (leaves necrosis) appeared after 10 days of treatment with 80 mM NaCl, which may lead to total desiccation. It was determined that severity of salt treatment injury varied depending on the genotype and NaCl concentration. A positive correlation was found between the vigour of plants in saline medium and their faculty to tolerate salt. The most tolerant grapevine genotypes to salt treatment were Sejnene and Asli, followed by the moderately sensitive Saouadi and Sakasly genotypes, and last Razegui, 1103P, 41B, and SO(4), which were particularity sensitive. Thus, grapevine's salt tolerance seems to be linked to the genetic background. To cite this article: L. Hamrouni et al., C. R. Biologies 331 (2008).     

Identification and characterization of "rd22" dehydration responsive gene in grapevine (Vitis vinifera L.)

To identify and isolate genes related to abiotic stresses (salinity and drought) tolerance in grapevine, a candidate gene approach was developed and allowed isolating a full-length cDNA of rd22 gene from the Cabernet Sauvignon variety. The latter, named Vvrd22, is a dehydration-responsive gene that is usually induced by the application of exogenous ABA. Details of the physicochemical parameters and structural properties (molecular mass, secondary structure, conserved domains and motives, putative post-translational modification sites...) of the encoded protein have also been elucidated. The expression study of Vvrd22 was carried out at the berry growth stages and at the level of plant organs and tissues as well as under both drought and salt stresses. The results showed that Vvrd22 is constitutively expressed at a low level in all analyzed tissues. Moreover, salt stress induced Vvrd22 expression, particularly for the tolerant variety (Razegui), contrary to the sensitive one (Syrah), which did not display any expression variation during the stress, which means that Vvrd22 is involved in salt stress response and that its expression level depends on regulatory mechanisms that are efficient only for the tolerant variety. On the other hand, under drought stress, Vvrd22 is induced in an identical manner for both tolerant and sensitive varieties. In addition, stress signal molecules such as ABA (lonely applied or in combination with sucrose) induced Vvrd22 expression, even at a low level. A minimal knowledge about the role and the functionality of this gene is necessary and constitutes a prerequisite condition before starting and including Vvrd22 in any program of improvement of grapevine's abiotic stress tolerance.     

Hemitoxin, the first potassium channel toxin from the venom of the Iranian scorpion Hemiscorpius lepturus

Hemitoxin (HTX) is a new K+ channel blocker isolated from the venom of the Iranian scorpion Hemiscorpius lepturus. It represents only 0.1% of the venom proteins, and displaces [125 I]alpha-dendrotoxin from its site on rat brain synaptosomes with an IC50 value of 16 nm. The amino acid sequence of HTX shows that it is a 35-mer basic peptide with eight cysteine residues, sharing 29-69% sequence identity with other K+ channel toxins, especially with those of the alphaKTX6 family. A homology-based molecular model generated for HTX shows the characteristic alpha/beta-scaffold of scorpion toxins. The pairing of its disulfide bridges, deduced from MS of trypsin-digested peptide, is similar to that of classical four disulfide bridged scorpion toxins (Cys1-Cys5, Cys2-Cys6, Cys3-Cys7 and Cys4-Cys8). Although it shows the highest sequence similarity with maurotoxin, HTX displays different affinities for Kv1 channel subtypes. It blocks rat Kv1.1, Kv1.2 and Kv1.3 channels expressed in Xenopus oocytes with IC50 values of 13, 16 and 2 nM, respectively. As previous studies have shown the critical role played by the beta-sheet in Kv1.3 blockers, we suggest that Arg231 is also important for Kv1.3 versus Kv1.2 HTX positive discrimination. This article gives information on the structure-function relationships of Kv1.2 and Kv1.3 inhibitors targeting developing peptidic inhibitors for the rational design of new toxins targeting given K+ channels with high selectivity.