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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.

Oceanologia

2005

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.

5-Aminolevulinic acid ameliorates salinity-induced metabolic, water-related and biochemical changes in Brassica napus L.

64%

Naeem M. S., Rasheed M., Liu D., Jin Z. L., Ming D. F., Yoneyama K., Takeuchi Y., Zhou W. J.

Acta Physiologiae Plantarum

2011

tom 33

nr 2

A number of studies have established that plant growth and development in oilseed rape (Brassica napus L.) are hampered by salinity stress. Nowadays, researchers have focused on the use of plant growth regulators to increase plant tolerance against salinity. An experiment was performed to evaluate the effects of 5-aminolevulinic acid (ALA, 30 mg l⁻¹) on Brassica napus L. (cv. ‘ZS 758’) plants under NaCl (100, 200 mM) salinity. Data presented here were recorded on two different leaf positions (first and third) to have a better understanding of the ameliorative role of ALA on NaCl-stressed oilseed rape plants. Results have shown that increasing salinity imposed negative impact on relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), whereas enhanced the level of relative conductivity, malondialdehyde (MDA) content, osmolytes (soluble sugar, soluble protein, free amino acid and proline) concentration, reactive oxygen species (ROS), and enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in two different leaf position samples. Foliar application of ALA improved relative growth rate (root and shoot) and leaf water relations (osmotic potential and relative water content), and also triggered the further accumulation of osmolytes (soluble sugar, soluble protein, free amino acid and proline) as well as enzymatic (ascorbate peroxidase, guaiacol peroxidase, catalase and superoxide dismutase) and non-enzymatic (reduced glutathione and ascorbate) antioxidants activity in both leaf samples, whereas decreased the membrane permeability, MDA content and ROS production. Our results also indicate that osmolytes are preferentially accumulated in younger tissues.

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

64%

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.

Ograniczanie wyników

2 Acta Physiologiae Plantarum

1 Oceanologia

3 Rasheed M.

2 Naeem M. S.

1 Ahmed Z. I.

1 Al-Najjar T.

1 Badran M. I.

1 Jilani G.

1 Jin Z. L.

1 Liu D.

1 Manasrah R.

1 Ming D. F.

1 Najeeb U.

1 Shen W.

1 Takeuchi Y.

1 Xu L.

1 Yoneyama K.

1 Zhou W.

1 Zhou W. J.

2 2011

1 2005

Wyniki wyszukiwania

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

5-Aminolevulinic acid ameliorates salinity-induced metabolic, water-related and biochemical changes in Brassica napus L.

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