Barley Autotoxicity as Influenced by Varietal and Seasonal Variation

Barley (Hordeum vulgare L.) is widely cultivated in the semi-arid region of Tunisia for grain production and grazing, which often occurs during the same season. We previously demonstrated autotoxic effects of barley among varieties. The present study was conducted to test the effects of barley variety and seasonal variation on the expression of autotoxicity by barley. Four barley varieties were grown in a field experiment over three growing seasons (1999–2000, 2000–01, 2001–02). In the laboratory, germination and seedling growth bioassays were used to assess autotoxicity potential of field-harvested barley. Barley autotoxicity was fully expressed based on inhibition of radicle growth detected in seedling bioassays. Stems were often the most allelopathic plant component. Allelopathic activity of the barley varieties differed across growing seasons suggesting the influence of a seasonal effect due to the extent of water deficit during the dry season and monthly rainfall variability. The results suggest that when planning to integrate barley within cropping sequences, barley producers should carefully select appropriate barley varieties to minimize autotoxicity, which can be more severe under drought conditions.     

Chemical composition and profile characterisation of pumpkin (Cucurbita maxima) seed oil

Seeds of a Tunisian variety (Béjaoui) of pumpkin (Cucurbita maxima) were analysed for their main chemical composition and for their oil properties. Expressed on dry weight basis, seed moisture was 8.46%, whereas contents of proteins, fibre, ash, fat, and total sugars established at 33.92%, 3.97%, 21.97%, 31.57%, and 0.11% respectively. Gas chromatography revealed that the major fatty acids were oleic, linoleic, and palmitic acids (44.11%, 34.77%, and 15.97% respectively). Seed oil was also found to be rich in tocopherols with a predominance of δ-tocopherol (42.27%). The sterol marker β-sisosterol accounted for 39.6% of total sterols contained in seed oil of this variety. Six phenolic acids (protocatechuic, caffeic, syringic, vanillic, p-coumaric and ferulic) were detected, the syringic acid being predominant (7.96 mg/100 g). As a whole, based on its seed oil features, pumpkin may be considered as a valuable source for new multi-purpose products for industrial, cosmetic, and pharmaceutical utilisation.     

Purification and characterization of three trypsin isoforms from viscera of sardinelle (<Emphasis Type="Italic">Sardinella aurita</Emphasis>)

Three trypsin isoforms A, B and C were purified to homogeneity from the viscera of sardinelle (Sardinella aurita). Purification was achieved by ammonium sulfate precipitation (20–70% (w/v)), Sephadex G-100 gel filtration and Mono Q-Sepharose anion-exchange chromatography. The molecular weights of these purified enzymes were estimated to be 28.8 kDa by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). Based on the native PAGE and casein-zymography, each purified trypsin appeared as a single band. Trypsins A and C exhibited the maximal activity at 55°C, while trypsin B at 50°C. All isoforms showed the same optimal pH (pH 9.0) using Nα-benzoyl-dl-arginine-p-nitroanilide (BAPNA) as a substrate. The three trypsins were stable at temperatures below 40°C and over a broad pH range (7.0–11.0). The activities of the three isoforms were strongly inhibited by soybean trypsin inhibitor and phenylmethylsulfonyl fluoride, a serine protease inhibitor, and partially inhibited by ethylenediaminetetraacetic acid, a metalloenzyme inhibitor. Kinetic constants of trypsins A, B and C for BAPNA were evaluated at 25°C and pH 9.0. The values of K _m and k _cat were 0.125, 0.083 and 0.10 mM, and 2.24, 1.21 and 5.76 s⁻¹, respectively. The N-terminal sequences of the first 10 amino acids were “I V G G Y E C Q K Y” for trypsin A and “I V G G Y E A Q S Y” for trypsins B and C. These sequences showed highly homology to other fish trypsins.     

Detection of QTLs for salt tolerance in Asian barley (Hordeum vulgare L.) by association analysis with SNP markers

Two hundred ninety-six Asian barley (Hordeum vulgare L.) accessions were assessed to detect QTLs underlying salt tolerance by association analysis using a 384 single nucleotide polymorphism (SNP) marker system. The experiment was laid out at the seedling stage in a hydroponic solution under control and 250 mM NaCl solution with three replications of four plants each. Salt tolerance was assessed by leaf injury score (LIS) and salt tolerance indices (STIs) of the number of leaves (NL), shoot length (SL), root length (RL), shoot dry weight (SDW) and root dry weight (RDW). LIS was scored from 1 to 5 according to the severity of necrosis and chlorosis observed on leaves. There was a wide variation in salt tolerance among Asian barley accessions. LIS and STI (SDW) were the most suitable traits for screening salt tolerance. Association was estimated between markers and traits to detect QTLs for LIS and STI (SDW). Seven significant QTLs were located on chromosomes 1H (2 QTLs), 2H (2 QTLs), 3H (1 QTL), 4H (1 QTL) and 5H (1 QTL). Five QTLs were associated with LIS and 2 QTLs with STI (SDW). Two QTLs associated with LIS were newly identified on chromosomes 3H and 4H.