Jamal Y. Ayad

Overexpression of the transcription factor HvSNAC1 improves drought tolerance in barley ( Hordeum vulgare L.)

NAC proteins constitute a family of plant-specific transcription factors that are involved in many plant cellular processes including responses to abiotic stress. In this study, a cDNA clone encoding the HvSNAC1 transcription factor was isolated from drought-stressed barley using a bioinformatics approach based on amino acid sequence data of the stress-related SNAC1 protein from rice. Phylogenetic analysis of the deduced amino acid sequence of HvSNAC1 showed that this protein belongs to the stress clade of NAC proteins that include SNAC1 and TaNAC2. Expression analysis indicated that the HvSNAC1 gene is strongly induced by different abiotic stresses including drought. Overexpression of HvSNAC1 in barley under the control of a constitutive promoter produced plants that grew normally under well-watered conditions when compared with wild-type plants. Transgenic barley plants overexpressing HvSNAC1 showed higher drought tolerance at different growth stages when compared with wild-type plants. In addition, the constitutive overexpression of HvSNAC1 resulted in improved water status, photosynthetic activity and reduced water loss rate when compared with wild-type plants under drought conditions. Furthermore, the transgenic plants also showed significantly improved productivity, as reflected by the increase in biological yield over the wild-type plants under severe field drought conditions. In conclusion, the HvSNAC1 gene could be a useful tool for improving barley productivity under field drought conditions without impairment in growth under normal field conditions.

Over-expression of SlSHN1 gene improves drought tolerance by increasing cuticular wax accumulation in tomato.

Increasing cuticular wax accumulation in plants has been associated with improving drought tolerance in plants. In this study, a cDNA clone encoding the SlSHN1 transcription factor, the closest ortholog to WIN/SHN1 gene in Arabidopsis, was isolated from tomato plant. Expression analysis of SlSHN1 indicated that it is induced in response to drought conditions. The over-expression of SlSHN1 in tomato under the control of the constitutive CaMV 35S promoter produced plants that showed mild growth retardation phenotype with shiny and dark green leaves. Scanning electron microscopy showed that the over-expression of SlSHN1 in tomato resulted in higher cuticular wax deposition on leaf epidermial tissue when compared to non-transformed plants. Expression analysis in transgenic lines over-expressing SlSHN1 indicated that several wax-related synthesis genes were induced. Transgenic tomato plants over-expressing SlSHN1 showed higher drought tolerance when compared with wild type plants; this was reflected in delayed wilting of transgenic lines, improved water status and reduced water loss rate when compared with wild type plants. In conclusion, the SlSHN1 gene can modulate wax accumulation and could be utilized to enhance drought tolerance in tomato plant.

GROWTH, NUTRIENT ACQUISITION, AND PHYSIOLOGICAL RESPONSES OF HYDROPONIC GROWN TOMATO TO SODIUM CHLORIDE SALT INDUCED STRESS

□ Growth and nutrient acquisition of tomato (Lycopersicon esculentum L.) cv ‘Amani’ were studied under induced salt stress in Hoaglands solution. The plants were treated for 37 days with salinity induced by incorporating different concentrations [0.0 (control), 50, 100, 150, or 200 mM] of sodium chloride (NaCl) to the nutrient solution. Slight reduction was obtained in growth represented by (shoot length and number, leaf number, and dry weight) when seedlings were directly exposed to NaCl stress from 0.0 to 100 mM. At higher concentrations (150 or 200 mM), growth parameters were adversely affected and seedlings died thereafter. Elevated salinity significantly reduced crude protein and fiber in shoots and roots. Tomato shoot and root contents of potassium (K), iron (Fe), and ash were reduced significantly in response to increased levels of salinity. Tissue contents of sodium (Na) and chloride (Cl) increased with elevated salinity treatments.

Molecular and Field Comparison of Selected Barley Cultivars for Drought Tolerance

A field experiment was conducted using five most-planted barley (Hordeum vulgare L.) cultivars in Jordan — a country with 90% of its total land area receiving an annual rainfall of less than 200 mm. The objective of this study was to determine the response of these five cultivars evaluated under drought-stressed (DS) and non-stressed (NS) environments and to investigate polymorphism of 10 candidate genes for drought response. Drought susceptibility index (DSI) was used to rank cultivars according to their performance. Biological and grain yield for all cultivars was lower in DS compared with NS. Reduction in biological yield caused by drought stress ranged from 19% for ‘Mutah’ to 45% for ‘Rum’ cultivar. The least affected by drought stress was ‘Mutah’ with 13% percent reduction (PR) in grain yield. DSI for grain yield ranged from 0.33 for ‘Mutah’ to 1.41 for ‘Rum’. Depending on PR and DSI for biological and grain yield, ‘Mutah’ was the most tolerant cultivar. However, no clear differences were detected among cultivars for the tested genes. The use of this tolerant and improved genotype should be maximized in breeding and genetic studies to identify, map, and pyramid new drought-tolerance genes and to enhance sustainable farming systems.

Particle Size of Volcanic Tuff Improves Shoot Growth and Flower Quality of Asiatic Hybrid Lily Using Soilless Culture

Soilless substrates enhance growing environment, nutrient content, and water quality in the growing medium. The objective of this study was to assess the influence of substrate particle size on growth and flower quality (flower number and length per plant) of two asiatic hybrid lily (Lilium ·elegans) cultivars Fangio and Ercolano. Plants were grown in 12-L pot under greenhouse conditions. Five grades of particle-size substrate, consisting of granulated volcanic material (tuff) were used as treatments. These sizes were 0 to 2, 0 to 4, 0 to 8, 2 to 4, and 4 to 8 mm. Fertigation was applied daily. Plant morphology, physiology, and flower quality were determined during flowering stage. Treatments of 2 to 4and 4 to 8-mm tuff had lower water holding capacity (WHC), bulk density, electrical conductivity (EC), and pH compared with 0 to 2and 0 to 4-mm tuff. In addition, plant height, leaf area, and flower quality of ‘Fangio’ were higher compared with ‘Ercolano’. Chlorophyll content and fluorescence were similar among all treatments. Leaf fresh weight, leaf area, shoot dry weight, root dry weight, and flower quality were higher in sizes of 0 to 4-, 2 to 4-, and 4 to 8-mm than 0 to 2-mm tuff, especially those from ‘Fangio’. The 0 to 4-mm substrate had an optimal and consistent flower quality results in both cultivars when compared with other tuff sizes. Overall, the results presented here suggest that using 0 to 4-mm tuff substrate holds promise for improving growth and flower quality of asiatic hybrid lily grown under soilless culture.

Composition of soilless substrates affect the physiology and fruit quality of two strawberry (Fragaria × ananassa Duch.) cultivars

Abstract Leaf-level physiology, yield, and fruit quality of two strawberry (Fragaria × ananassa Duch.) cultivars, “BG4.370” and “Splendor” grown in five growing substrates were assessed. Substrate ratios were T1: tuff (0–4 mm), T2: cocopeat + perlite 4:1, T3: peatmoss + perlite 4:1, T4: tuff + cocopeat 4:1, and T5: tuff + peatmoss 4:1. Strawberry parameters were greatly affected by substrate composition but not cultivars. Plants grown in cocopeat + perlite 4:1 had the highest photosynthesis, transpiration, radical scavenging activity, and fruit firmness while those grown in peatmoss + perlite 4:1 had the highest yield, total phenolics and nitrate concentration compared to other substrates. Given that peat-based growing substrate has raised concerns over the environmental impacts such as, a reduction of wet-lands and loss of soil organic carbon, the lower environmental impact and higher fruit quality grown on cocopeat justifies the use of cocopeat as an alternative substrate to peatmoss.