Effect of salinity on growth, pigmentation, N2 fixation and alkaline phosphatase activity of cultured Trichodesmium sp

Trichodesmium sp. isolated from the Great Barrier Reef lagoon was cultured in artificial seawater media containing a range of salinities. Trichodesmium sp. actively grew over a wide range of salinities (22 to 43 psu) and hence can be classed as euryhaline. Maximum growth occurred with salinities in the range 33 to 37 psu. Chl a content and alkaline phosphatase activity were found to increase with salinity over the range 22 to 43 psu, but the N-2 fixation rate was reduced at salinities below and above the range for maximum growth. Growth in media exhibiting maximum growth was characterised by well-dispersed cultures of filaments, while significant aggregations of filaments formed in other media. It is proposed that the tendency for Trichodesmium filaments to aggregate in media with salinities outside the range for maximum growth is an opportunistic response to a deficiency of cellular nitrogen, which results from the reduced N-2 fixation rates, and the aggregation occurs in order to enhance the uptake of combined N released within the aggregates and/or the N-2 fixation within the aggregates.

Factors affecting N2 fixation by the cyanobacterium Trichodesmium sp. GBRTRLI101

Various factors affecting N-2 fixation of a cultured strain of Trichodesmium sp. (GBRTRLI101) from the Great Barrier Reef Lagoon were investigated. The diurnal pattern of N2 fixation demonstrated that it was primarily light-induced although fixation continued to occur for at least 1 h in the dark in samples that had been actively fixing N-2. N-2 fixation was dependent on the light intensity and stimulated more by white light when compared with blue, green, yellow and red light whereas rates of N-2 fixation decreased most under red light. Inorganic phosphorous concentrations in the lower range of treatments up to 1.2 muM significantly stimulated N-2 fixation and further additions promoted little or no increase in N-2 fixation. Organic phosphorous (Na-glycerophosphate) also stimulated N-2 fixation rates. Added combined nitrogen (NH4+, NO3-, urea) of 10 muM did not inhibit N-2 fixation in short-term studies (first generation), however it was depressed in the long-term studies (fifth generation). (C) 2003 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.

Simultaneous fixation using glutaraldehyde and osmium tetroxide or potassium ferricyanide-reduced osmium for the preservation of monogenean flatworms: An assessment for Merizocotyle icopae

Simultaneous fixation was investigated for a marine organism: the monogenean flatworm ectoparasite Merizocotyle icopae. Four protocols for primary fixation were compared: 3% glutaraldehyde alone in OAM cacodylate buffer for a minimum of 2 hours; 1% glutaraldehyde in combination with 1% osmium tetroxide, both in 0.1M cacodylate buffer, until tissues darkened (5-20 minutes); 1% glutaraldehyde in OAM cacodylate buffer in combination with 0.5% potassium ferricyanide-reduced osmium until tissues darkened (5-20 minutes); 1% glutaraldehyde in combination with 1% osmium tetroxide, both in 0.1M cacodylate buffer, for 30 minutes. The study confirms that the standard method for transmission electron microscopic fixation (first listed protocol) routinely applied to platyhelminths is optimal for ultrastructural preservation, but some simultaneous fixation methods (second and third listed protocols) are acceptable when rapid immobilization is needed. Scanning electron microscopic preparations may be improved using simultaneous primary fixation. (C) 2004 Wilcy-Liss, Inc.

Effects of phosphorus on the growth and nitrogen fixation rates of Lyngbya majuscula: implications for management in Moreton Bay, Queensland

Significant acetylene reduction and therefore N-2 fixation was observed for Lyngbya majuscula only during dark periods, which suggests that oxygenic photosynthesis and N-2 fixation are incompatible processes for this species. Results from a series of batch and continuous-flow-culture reactor studies showed that the specific growth rate and N-2 fixation rate of L, majuscula increased with phosphate (P-PO4) concentration up to a maximum value and thereafter remained constant. The P-PO4 concentrations corresponding to the maximum N-2 fixation and maximum growth rates were -0.27 and -0.18 muM respectively and these values are denoted as the saturation values for N-2 fixation and growth respectively. Regular monitoring studies in Moreton Bay, Queensland, show that concentrations Of P-PO4 generally exceed these saturation values over a large portion of the Bay and therefore, the growth of the bloom-forming L, majuscula is potentially maximised throughout much of the Bay by the elevated P-PO4 concentrations. Results from other studies suggest that the elevated P-PO4 concentrations in the Bay can be largely attributed to discharges from waste-water treatment plants (WWTPs), and thus it is proposed that the control of the growth of L. majuscula in Moreton Bay will require a significant reduction in the P load from the WWTP discharges. If the current strategy of N load reduction for these discharges is maintained in the absence of substantial P load reduction, it is hypothesised that the growth of L, majuscula and other diazotrophs in Moreton Bay will increase in the future.

The effect of timing and severity of water deficit on growth, development, yield accumulation and nitrogen fixation of mungbean

Mungbean (Vigna radiata L.), as a dryland grain legume, is exposed to varying timing and severity of water deficit, which results in variability in grain yield, nitrogen accumulation and grain quality. In this field study, mungbean crops were exposed to varying timing and severity of water deficit in order to examine: (1) contribution of the second flush of pods to final grain yield with variable timing of relief from water deficit, (2) the sensitivity to water deficit of the accumulation of biomass and nitrogen (N) and its partitioning to grain, and (3) how the timing of water deficit affects the pattern of harvest index (HI) increase through pod filling. The results showed that the contribution of the second flush to final yield is highly variable (1-56%) and can be considerable, especially where mid-season stress is relieved at early pod filling. The capacity to produce a second flush of pods did not compensate fully for yield reduction due to water stress. Relief from mid-season stress also resulted in continued leaf production, N-2 fixation and vegetative biomass accumulation during pod filling. Despite the wide variation in the degree of change in vegetative biomass and N during pod filling, there were strong relationships between grain yield and net-above-ground biomass at maturity, and grain N and above-ground N at maturity. Only in the extreme situations were HI and nitrogen HI affected noticeably. In those treatments where there was a large second flush of pods, there was a pronounced biphasic pattern to pod number production, with HI also progressing through two distinct phases of increase separated by a plateau. The proportion of grain yield contributed to by biomass produced before pod filling varied from 0 to 61% with the contribution greatest under terminal water deficit. There was a larger effect of water deficit on N accumulation, and hence N-2 fixation, than on biomass accumulation. The study confirmed the applicability of a number of long-standing physiological concepts to the analysis of the effect of water deficit on mungbean, but also highlighted the difficulty of accounting for timing effects of water deficit where second flushes of pods alter canopy development, biomass and yield accumulation, and N dynamics. Crown Copyright (C) 2003 Published by Elsevier B.V. All rights reserved.