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Nutrient flux fuels the summer primary productivity in the oligotrophic waters of the Gulf of Aqaba, Red Sea

100%

Badran M. I. , Rasheed M. , Manasrah R. , Al-Najjar T.

tom 47

nr 1

The thermohaline characteristics of the Gulf of Aqaba, Red Sea, depict a welldefined seasonal pattern of winter mixing from December to April and summer stratification from May to November. This thermohaline structure is a major controlling factor of the nutrient, chlorophyll a and primary productivity seasonal cycles. The nitrate and chlorophyll a concentration records generated down to 200 m at a vertical resolution of 25 m – weekly during 1994, 1995 and every two weeks from April 1997 through to December 2000 – are employed to assess the nitrogen flux across the summer thermocline of the Gulf of Aqaba. The flux calculations are based on a simple diffusion model that incorporates the physical stress eddy diffusivity factor Kz and a biological stress factor k. Both Kz and k are calculated using the Michaelis-Menten equation and the nitrate concentration gradient. The total nitrate flux of the Gulf of Aqaba during the seven summer months (May–November) is estimated at 0.52 moleN m−2. In relation to established primary productivity values (75.5 gC m−2 (May November)−1) and the generated chlorophyll a records, this yields an f fraction of new to total primary production of 0.50. This relatively high f value is discussed with respect to the geophysical characteristics of the Gulf of Aqaba and similar oceanic basins. The remaining 50% is accounted for by cross-sectional flow from the relatively nutrientrich coral reef coastal habitat and rapid recycling, triggered by high irradiance and water temperature.

Ultraviolet-C mediated physiological and ultrastructural alterations in Juncus effusus L. shoots

63%

Najeeb U. , Xu L. , Ahmed Z. I. , Rasheed M. , Jilani G. , Naeem M. S. , Shen W. , Zhou W.

Acta Physiologiae Plantarum

2011

tom 33

nr 2

Increased ultraviolet radiations intruding on the earth pose a serious threat to the unadapted plants. Due to the ecological and economic significance of mat rush (Juncus effusus L.), an in vitro experiment was conducted to unveil the toxic effects of ultraviolet radiation (UV-C) on its physiology and ultrastructure. The basal culm segments of plant were used for in vitro treatments of UV-C with different exposure times (15, 30 and 45 min). The treated segments were first transferred to 1/2 strength MS media and then shifted to soil-perlite mixture for further growth. With increasing exposure time to UV-C, there was significant reduction in plant growth and biomass, and increased activities of antioxidant enzymes. Physiological and ultrastructural alterations were observed in the shoots of UV-treated plants. These plants exhibited significant reduction in chlorophyll contents and noticeable modifications at the ultra-cellular levels. Cell and chloroplast size reduced greatly, and there was appearance of higher amounts of plastoglobuli in chloroplasts resulting in disruption of thylakoid integrity. The functional and ultrastructural alterations in the stressed plants suggest a potential hazard of UV-C radiation on this aquatic flora and thus the ecosystem. The study further explores that UV-C radiations trigger these modifications mainly by damaging the chloroplast.

Butyrylcholinesterase Inhibitory C-Glycoside from Symplocos racemosa

63%

Ahmad V. , Zubair M. , Abbasi M. , Kousar F. , Rasheed M. , Rasool N. , Hussain J. , Nawaz S. , Choudhary M.

2006

tom Vol. 80, nr 3

403-407

The re-investigation of the chemical constituents of Symplocos racemosa Roxb. led to the isolation of one new C-glycoside, symcososide (1) along with one known compound beta-sito-glycoside (2). The structure of the new compound was determined by 1D and 2Dhomonuclear and heteronuclearNMRspectroscopy, chemical evidences, and by comparison with the published data of the closely related compounds. The glycoside 1 displayed in vitro inhibitory activity against butyrylcholinesterase (BChE) enzyme with IC50 value of 21.2 š 0.01 miM.