Published Research in Journal: Plant and Soil - PLANT SOIL, vol. 332, no. 1, pp. 147-162, 2010 Enhancement of morphological, anatomical and physiological characteristics of seedlings of the mangrove Avicennia marina inoculated with a native phosphate-solubilizing isolate of Oceanobacillus picturae under greenhouse conditions Khaled A. El-Tarabily, Tarek Youssef One hundred and twenty-nine rock phosphate (RP) solubilizing bacteria were isolated from the mangrove Avicennia marina rhizosphere sediment deficient in available phosphorus (P), in the United Arab Emirates (UAE). Among these isolates, an outstanding isolate of Oceanobacillus picturae grown in Pikovskaya s liquid medium amended with RP, caused the highest percentage of RP solubilization (97%), the most pronounced drop in the medium ph and produced a variety of organic acids, as well as acid and alkaline phosphatases. Greenhouse experiments were carried out to investigate the effect of sediment inoculation with O. picturae (Op) with or without RP amendment on the growth, nutrient uptake, conducting tissue and photosynthetic gas exchange characteristics of mangrove seedlings. The application of Op to sediments amended with RP significantly promoted the growth of roots and shoots of seedlings compared with those grown in sediment amended with RP only. O. picturae significantly increased available sediment P, decreased sediment ph, positively enhanced nutrient uptake parameters in roots and shoots, increased stem circumference, number of xylem vessels, mean xylem diameter, and the hydraulically weighted xylem vessel diameter, compared with plants grown in non-inoculated sediment amended with only RP. Mechanistic analysis of A:Ci response curves (Assimilation versus sub-stomatal CO2 concentration) showed that photosynthetic gas exchange characteristics were significantly enhanced by Op + RP treatment compared with RP alone or control treatment. The maximal Rubisco-catalyzed carboxylation velocity (V c,max), increased by more than two fold in plants treated with RP + Op, over the control. Application of Op + RP greatly increased the maximal electron transport rate values (J max) by 185%, over the control plants. In addition, the triose phosphate utilization rate (V TPU) increased three fold in plants treated with RP + Op over the control. To the best of our knowledge, this is the first published report of Op from mangrove sediments and also the first report of this organism as a phosphate-solubilizing bacterium. These results have clearly shown that Op has the potential to be applied as an effective and economical treatment in association with RP amendment for mangrove reforestation programs in arid environments such as those found in the UAE.
Published Research in Journal: Orl-journal for Oto-rhino-laryngology and Its Related Specialties - ORL-J OTO-RHINO-LARYNGOL, vol. 72, no. 2, pp. 119-123, 2010 Utilization of CO2 Laser for Temporal Fascia Graft Welding in Myringoplasty: An Experimental Study on Guinea Pigs Tarek Fouad Youssef, Mohamed Rifaat Ahmed, Ahmed Nazmi Kassab An experimental study was undertaken to investigate the use of a CO2 laser welding technique in myringoplasty. Albumin solder was used to fix a temporal fascia graft via an overlay transcanal approach. The results of the operative procedure were assessed by microscopic and histopathologic examination over an interval of 1, 2, 3 and 4 weeks postoperatively. Materials and Methods: Forty-eight adult guinea pigs were divided into two groups after permanent perforation of the tympanic membrane was created: laser-assisted myringoplasty group and surgical myringoplasty group. Laser beam power was 0.4 W, pulse duration 0.75 s, pulse interval 0.1 s and spot size 250 μm. Each experimental group was further subdivided into four subgroups of 6 animals each. Histological and microscopic findings of the tympanic membrane for both groups after 1, 2, 3, and 4 weeks were compared. Results: Microscopic examination of the tympanic membrane showed high success rate in the laser-assisted myringoplasty group compared to the control group. Histological evaluation for the tympanic membrane showed complete repair of the tympanic membrane in the laser-assisted myringoplasty group. Conclusion: Laser-assisted myringoplasty using CO2 might be a promising new method in surgical myringoplasty.
Published Research in Journal of Plant Growth Regulation - J PLANT GROWTH REGUL, vol. 27, no. 1, pp. 1-9, 2008 Mechanisms of Enhancing Photosynthetic Gas Exchange in Date Palm Seedlings ( Phoenix dactylifera L.) under Salinity Stress by a 5-Aminolevulinic Acid-based Fertilizer Tarek Youssef, Mohamed A. Awad Photosynthetic gas exchange characteristics, salt uptake, pigment contents, and electrolyte leakage were examined in date palm seedlings (Phoenix dactylifera L.) subject to seawater treatments at 1-, 15-, and 30-mS cm 1 salinity levels in the presence or absence of 0.08% ALA-based (5-aminolevulinic acidbased) functional fertilizer commercially known as Pentakeep-v. Date palm seedlings accumulated significant amounts of Na+ in the foliage with increasing salinity, about a threefold increase in the accumulated Na+ between the control and 30-mS cm 1salinity treatment. Electrolyte leakage indicated a significant reduction in membrane integrity as salinity increased. A strong linear correlation was observed between the chlorophyll (chl) a/b ratio and assimilation rate throughout salinity treatments. The slope (b) and the correlation coefficient between the chl a/b ratio and assimilation suggested that salinity reduced assimilation predominantly via the reduction in chlorophyll a contents (r 2 = 0.885 and b = 1.77, P < 0.05). Plants treated with Pentakeep-v showed a similar response with increasing salinity but at higher levels of both chl a/b ratios and assimilation rates. Mechanistic analysis of A:Ci response curves showed that photosynthetic gas exchange in seedlings of the date palm was significantly reduced with increasing salinity due to gas phase limitation (S L) as evident by stomatal conductance (g s) values. Salinity did not induce any change in the carboxylation efficiency of the rubisco enzyme (Vc,max), or in the rate of electrons supplied by the electron transport system for ribulose 1,5-bisphosphate (RuBP) regeneration (Jmax). Accelerated carbon loss through respiration has significantly contributed to the described reduction in assimilation and increased CO2 compensation point (Γ). Only at the 30-mS cm 1 salinity level did treatment with Pentakeep-v reduce Na+ accumulation in the leaves, and caused a reduction in K+ selective uptake, leading to a concomitant reduction in K+/Na+ ratios. Pentakeep-v significantly improved chl a contents in all treatments, which was subsequently reflected in total chlorophyll and chl a/b ratios. The non-gas-phase components of the photosynthetic process (biochemical factors limiting gas exchange) were significantly improved by Pentakeep-v applications. Specifically, Pentakeep-v enhanced the biochemical efficiency of carbon fixation (Vc,max) and the rate of electron transport required for RuBP regeneration (Jmax) by 37.4% and 17.8%, respectively, over untreated plants at a salinity level of 15 ms cm 1. In addition, Pentakeep-v reduced S L to values similar to those of control plants (9.07%) and lowered CO2 compensation points by reducing respiratory CO2 loss, with increasing salinity to 30 ms cm 1. We, therefore, conclude that the ALA-based fertilizer Pentakeep-v improves salt tolerance in date palm seedlings by increasing photosynthetic assimilation. The latter is mediated via boosting light-harvesting capabilities of the treated plants by increasing chl a content and by reducing stomatal limitation to photosynthetic gas exchange.
Published Research in Journal: Aquatic Botany - AQUAT BOT, vol. 87, no. 4, pp. 292-298, 2007 Stomatal, biochemical and morphological factors limiting photosynthetic gas exchange in the mangrove associate Hibiscus tiliaceus under saline and arid environment Tarek Youssef The effect of salinity on leaf area and the relative accumulation of Na+ and K+ in leaves of the mangrove associate Hibiscus tiliaceus were investigated. Photosynthetic gas exchange characteristics were also examined under arid and non-arid leaf conditions at 0, 10, 20 and 30 substrate salinity. At salinities 40, plants showed complete defoliation followed by 100% mortality within 1 week. Salinities 30 were negatively correlated with the total leaf area per plant (r2=0.94). The reduction in the total plant leaf area is attributed to the reduction in the area of individual leaves (r2=0.94). Selective uptake of K+ over Na+ declined sharply with increasing salinity, where K+/Na+ ratio was reduced from 6.37 to 0.69 in plants treated with 0 and 30, respectively. Under non-arid leaf condition, increasing salinity from 0 to 30 has significantly reduced the values of the intrinsic components of photosynthesis Vc,max (from 50.4 to 18.4μmolm 2s-1), Jmax (from 118.0 to 33.8μmol photonsm 2s 1), and VTPU (from 6.90 to 2.30μmolm 2s 1), while stomatal limitation to gas phase conductance (SL) increased from 14.6 to 38.4%. Water use efficiency (WUE) has subsequently doubled from 3.20 for the control plants to 8.93 for 30 treatment. Under arid leaf conditions, the stomatal factor (SL) was more limiting to photosynthesis than its biochemical components (73.4 to 26.6%, respectively, at 30 ). It is concluded that salinity causes a drastic decline in photosynthetic gas exchange in H. tiliaceus leaves through its intrinsic and stomatal components, and that the apparent phenotypic plasticity represented by the leaf area modulation is unlikely to be the mechanism by which H. tiliaceus avoids salt stress.
Published Research in Journal: Environmental Pollution - ENVIRON POLLUT, vol. 116, no. 2, pp. 215-223, 2002 Salt secretion and stomatal behaviour in Avicennia marina seedlings fumigated with the volatile fraction of light Arabian crude oil T Youssef, A Ghanem Seedlings of the salt secreting mangrove Avicennia marina were exposed to fumes of the volatile fraction of light Arabian crude oil (VFCO) under controlled conditions. Rates of salt secretion were determined in leaves fumigated for 0, 3, and 6 h under four different salinity levels (10, 20, 30, and 40 ppt). Studying the effect of these fumigation periods on stomatal resistance and transpiration was restricted to one salinity level (20 ppt). Opposite to salinity, increasing the fumigation period significantly reduced both salt secretion and transpiration with a significant increase in the stomatal resistance to gas diffusion. During the first day of recovery from fumigation stress, different stomatal oscillation patterns were observed in the treated plants. The amplitude of the oscillations increased with the duration of fumigation, as did the time required for stomatal recovery. Seedlings fumigated for 3 h started to recover within 48 h, while full recovery in seedlings fumigated for 6 h required almost twice that period. The apparent recovery process was evident in the damping off of the amplitude of stomatal oscillations during the measurements period. Data presented herein show that the exposure of mangrove seedlings to VFCO disturbs the normal functions of two major structures in the leaves, i.e. the stomata and the salt glands. The ecophysiological significance of these results was discussed in relation to previous studies.