Reda E. A. Moghaieb

Potassium deficiency affects water status and photosynthetic rate of the vegetative sink in green house tomato prior to its effects on source activity

The potassium requirement of green house tomatoes is very high for vegetative growth and fruit production. Potassium deficiency in plants takes long time for expression of visible symptoms. The objective of this study is to detect the deficiency early during the vegetative growth and define the roles of aquaporin and K-channel transporters in the process of regulation of water status and source-sink relationship. The tomato plants were grown hydroponically inside green house of Hiroshima University, Japan and subjected to different levels of K in the rooting medium. Potassium deficiency stress decreased photosynthesis, expansion and transport of ¹⁴C assimilates of the source leaf, but the effects became evident only after diameter expansion of the growing stem (sink) was down-regulated. The depression of stem diameter expansion is assumed to be associated with the suppression of water supply more than photosynthate supply to the organ. The stem diameter expansion is parameterized by root water uptake and leaf transpiration rates. The application of aquaporin inhibitor (AgNO₃) decreased leaf water potential, stem expansion and root hydraulic conductance within minutes of application. Similar results were obtained for application of the K-channel inhibitors. These observations suggested a close relationship between stem diameter expansion and activities of aquaporins and K-channel transporters in roots. The deficiency of potassium might have reduced aquaporin activity, consequently suppressing root hydraulic conductance and water supply to the growing stem for diameter expansion and leaf for transpiration. We conclude that close coupling between aquaporins and K-channel transporters in water uptake of roots is responsible for regulation of stem diameter dynamics of green house tomato plants.

Effect of salinity stress on photosynthesis and vegetative sink in tobacco plants

Abstract The effects of salinity stress on vegetative growth in tobacco (Nicotiana tabacum) plants were examined in terms of the source–sink relationship. The effect of salinity stress on plant growth was continuously measured using a micromorphometric technique under greenhouse conditions. This technique is less cumbersome and more precise than conventional techniques used to measure plant growth under salinity conditions. The effect of salinity stress on photosynthetic rate, 13C partitioning and sugar and Na+ concentrations was also measured. Salinity stress was imposed by irrigating the plants with NaCl solution at 50 and 100 mmol L−1. Stem diameters of the control plants started to decrease around 07:00 am and reached a minimum at 03:00 pm. Salinity stress did not change the diurnal pattern of stem diameter dynamics, but increased the amplitude of daytime shrinking, and consequently stem growth estimated by the difference in stem diameter at night was inhibited. The effect of salinity stress on stems, a major sink, appeared within a few hours of treatment, whereas the effects on photosynthetic rate were observed after a lag period of 3–4 days of salt application. Salinity stress also reduced 13C export rate, but increased leaf sugar concentration and Na concentration in all plant parts. These results suggest that salinity impairs sink activity earlier than source activity. Based on the results of this study, the utilization of micromorphometric techniques for early diagnosis of growth in salt-prone environments is recommended.

Genetic transformation of mature embryos of bread (T. aestivum) and pasta (T. durum) wheat genotypes

The objective of the present study is to develop an efficient protocol for regeneration of transgenic wheat plants using Agrobacterium- mediated transformation of mature embryos of hexaploid bread wheat (Triticum aestivum) and tetraploid pasta wheat (Triticum durum). The data indicated that embryogenic calli were formed within 7 days in the presence of 2 mgl-1 2,4-D. Adventitious shoots emerged from the embryonic calli in the presence of 2 mgl-1 BA. Shoot regeneration frequency varied between wheat cultivars according to their genetic background differences. Regeneration frequency was higher in the cultivar Gemmiza 10 (95 %) compared with the other cultivars tested. Mature embryos derived callus of the cultivars Gemmiza 10 and Gemmiza 9 were co-cultivated with A. tumefaciens strain LBA4404 harboring a binary vector pBI-121 containing the neomycin phosphotransferase-II gene (npt-II). The resulted putative transgenic plantlets were able to grow on kanamycin containing medium. A successful integration of the transgene was confirmed by analyzing the T0 plantlets using Southern hybridization and PCR amplification. The gus gene expression can be detected only in the transgenic plants. The reported protocol is reproducible and can be used to regenerate transgenic wheat plants expressing the genes present in A. tumifaciens binary vectors.

Transgenic rice plants expressing cry1Ia5 gene are resistant to stem borer (Chilo agamemnon)

The stem borer, Chilo agamemnon Bles., is the most serious insect pest in rice fields of the Egyptian Nile Delta. To induce rice plant resistance to Chilo agamemnon, the cry1Ia5 gene was introduced to rice plants (Oryza sativa L.). The integration of the cry1Ia5 gene into the plant genome was confirmed using PCR and Southern blot analyses. The obtained plantlets were transferred to the greenhouse until seeds were collected. Northern blot analysis of the T1 plants confirmed the expression of the cry1Ia5 gene. The insecticidal activity of the transgenic plants against the rice stem borer Chilo agamemnon were tested. The third larval instars were fed on stem cuts from three transgenic lines (L1, L2 and L3) as well as cuts from the control (gfp-transgenic) plants for one week and the mortality percentage was daily recorded. Transgenic line-3 showed the highest mortality percentage after one day (50%) followed by L2 (25%) then L1 (0%). Two days post treatment the mortality percentage increased to 70, 45 and 25% for transgenic lines 1, 2 and 3 respectively. Mortality of 100% was recorded four days post treatment, while those fed on the gfp-transgenic rice (control) showed 0% mortality. Thus, transgenic plants showed high resistance to stem borers and can serve as a novel genetic resource in breeding programs. Transgenic plants expressing BT protein were normal in phenotype with as good seed setting as the nontransgenic control plants.

Salt tolerance in two gramineae sp. Panicum maximum and Eleusine coracana: Glycinebetaine accumulation and expression of betaine aldehyde dehydrogenase mRNA

Two gramineae species, Panicum maximum and Eleusine coracana, were exposed to salinity stress and leaf water status, solute concentrations in cell sap, levels of betaine aldehyde dehydrogenase (BADH) and BADH mRNA were measured. Panicum maximum was able to maintain a high turgor and high relative water content at low leaf water potentials, and this was associated with the greater capacity for osmotic adjustment. Major osmotica in Panicum maximum leaves were Na+, Cl-, sugar and glycinebetaine, and these solutes were increased by salinity. Na+ and glycinebetaine concentrations in Eleusine coracana leaves also were increased by salt stress, but these solutes were in significantly lower concentrations than those measured in Panicum maximum. BADH enzyme activity and BADH mRNA levels in Panicum maximum leaves were both increased by salt stress, and their expression coincided with the observed betaine accumulation. Although the addition of abscisic acid (ABA) to leaf disks of Panicum maximum plants also increased BADH mRNA levels, these were smaller than those observed in NaCl treated leaves.

Molecular markers associated with salt tolerance in Egyptian wheats

Salinity affects plant growth by the osmotic stress of the salt around the roots, as well as by toxicity caused by excessive accumulation of salt in leaves. In the present study, seven common ( Triticum aestivum ) and two durum ( T. turgidum ssp. Durum) wheat genotypes were subjected to salt stress for 2 weeks. Salt stress decreased leaf osmotic potential in all cultivars. The difference in osmotic adjustment between the cultivars was correlated with the concentrations of minerals examined such as Na + and K + . The salt tolerance in the T. aestivum cultivar Gemmiza 10 and in T. durum cultivars Sohag and Beni Sweif was due to higher ability to maintain osmotic potential of the cells than the other cultivars by increase in osmoticum concentration under salt stress. The genetic variation and relationships among different wheat genotypes with different responses to salt stress were also investigated by RAPD and SSR analyses. 82 out of 118 RAPD markers detected were polymorphic (69.5%) and 42 out of 59 SSR alleles were polymorphic (71%), and can be considered as useful markers for the wheat cultivars tested. 18 random amplified polymorphic DNAs (RAPD) markers and 13 simple sequence repeats (SSR) markers generated were found to be genotype-specific. Seven markers distinguished the cultivar Beni Sweif, six markers for the cultivar Sohag and two markers for the cultivar Gemmiza 10. These markers can be verified as being genetic markers associated with salt tolerance in the three wheat genotypes and help in marker-assisted selection breeding program. Key words : Osmotic adjustment, RAPD and SSR marker, salt tolerance, wheat genomes.

Molecular identification and genetic diversity among Photorhabdus and Xenorhabdus isolates

Five bacterial strains were isolated from the hemocoel of the greater wax moth larvae (Galleria mellonella) infected with the entomopathogenic nematodes: Heterorhabditis bacteriophora HP88, Heterorhabditis indicus RM1 and Heterorhabditis sp (S1), Steinernema abbasi and Steinernema sp. (S II). Strains were identified as Photorhabdus luminescens HRM1, P. luminescens HS1, P. luminescens HP88, Xenorhabdus indica and X. nematophila ATTC19061 using 16S rDNA sequence analysis. To reveal the genetic diversity among these strains, three molecular markers (RAPD, ISSR and SRAP) were employed. RAPD analysis showed 73.8 and 54.5 polymorphism percentages for the Photorhabdus and Xenorhabdus strains, respectively. ISSR analysis resulted in 70.1 and 75.2 polymorphism percentages among the Photorhabdus and Xenorhabdus strains, respectively. The SRAP analysis indicated that 75.6 and 61.2% genetic polymorphism was detected among Photorhabdus and Xenorhabdus strains, respectively. The cluster analysis grouped the three Photorhabdus strains together in one cluster and the two Xenorhabdus strains together in another cluster indicating the phylogenetic relationships among them. The genotype-specific markers detected from the three molecular markers (RAPD, ISSR and SRAP) were sufficient to distinguish between the different bacterial strains tested and can be used in the future IBM program that could be built on the use of these strains.