Assessment of Calanus finmarchicus growth and dormancy using the aminoacyl-tRNA synthetases method

We obtained growth rates of the copepod Calanus finmarchicusat different locations across the North Atlantic between May1998 and June 2004. Animals were incubated for 2–9 daysand fed either with natural food assemblages or with culturedalgae. During this period, we measured both somatic weight-specificgrowth rates (measured as protein change) and aminoacyl-tRNAsynthetases (AARS) activity. We found a highly significant relationshipbetween AARS activity and growth in protein content (R² = 0.55,P < 0.001). Significant AARS activity also occurred whengrowth was negative, the relationship predicting an AARS activitylevel of 8.33 nmPPi·mg protein^–1·h^–1when somatic growth is zero. This is because AARS activity isexpected even when growth is negative, owing to the continuedprotein turnover in the cells. The AARS method allowed for thefirst time the study of protein metabolism in overwinteringC. finmarchicus. Our study results showed that overwinteringcopepods had significantly lower values of AARS activity thannon-diapausing animals (t = –3.51, P < 0.002). TheAARS method opens the possibility to better understand physiologydynamics of deep-water organisms (e.g. the beginning and endof diapause).     

A global assessment of mesozooplankton respiration in the ocean

Published data on the biomass and specific respiration ratesof mesozooplankton in the oceans across all latitudes were combinedto assess their community respiration on a global basis. Mesozooplanktonbiomass was higher in boreal/anti-boreal and polar waters, intermediatein equatorial waters and lowest in the subtropical gyres. Specificrespiration rates were the highest in equatorial waters anddecreased rapidly poleward. Global community respiration ofmesozooplankton in the upper 200 m of the oceans integratedover all latitudes was 10.4 ± 3.7 (SE) Gt C year^–1(n = 838). Below the epipelagic zone, mesozooplankton respirationliving in the mesopelagic (200–1000 m) and bathypelagic(below 1000 m) zones was estimated as 2.2 ± 0.4 (n =57) and 0.40 ± 0.2 (n = 12) Gt C year^–1, respectively.Thus, global depth-integrated mesozooplankton respiration was13.0 ± 4.2 Gt C year^–1 (17–32% of globalprimary production), which is 3–8-fold higher than thevalues assigned to mesozooplankton respiration in recent estimatesof total respiration in the ocean. Thus, it appears that mesozooplanktonrepresent a major, but neglected component of the carbon cyclein the ocean.     

Aminoacyl-tRNA synthetases activity as a growth index in zooplankton

A simple method for the assay of aminoacyl-tRNA synthetases(AARS) activity was modified for application in planktonic crustaceansas an index of somatic growth. The cladoceran Daphnia magnawas cultured in the laboratory and its AARS activity measuredwithout substrate addition. The relationship between the enzymeactivities of animals of similar age and individual biomassgrowing at different rates was tested. A significant relationshipwas found between AARS activity and somatic growth in termsof both protein and dry weight.     

Diversity of bacterial endophytes in roots of Mexican husk tomato plants (Physalis ixocarpa) and their detection in the rhizosphere

Endophytic bacterial diversity was estimated in Mexican husk tomato plant roots by amplified rDNA restriction analysis and sequence homology comparison of the 16S rDNA genes. Sixteen operational taxonomic units from the 16S rDNA root library were identified based on sequence analysis, including the classes Gammaproteobacteria, Betaproteobacteria, Actinobacteria, and Bacilli. The predominant genera were Stenotrophomonas (21.9%), Microbacterium (17.1%), Burkholderia (14.3%), Bacillus (14.3%), and Pseudomonas (10.5%). In a 16S rDNA gene library of the same plant species' rhizosphere, only common soil bacteria, including Stenotrophomonas, Burkholderia, Bacillus, and Pseudomonas, were detected. We suggest that the endophytic bacterial diversity within the roots of Mexican husk tomato plants is a subset of the rhizosphere bacterial population, dominated by a few genera.     

Gradients of mesozooplankton biomass and ETS activity in the wind-shear area as evidence of an island mass effect in the Canary Island waters

Mesozooplankton biomass (displacement volume and proteins) andelectron transport system (ETS) activity have been studied aroundGran Canaria (Canary Islands) in the wind-shear field of theisland. Twenty-seven samples were taken after a period of strongnorth trade winds (>5 m s^–1) Biomass and ETS gradientswere observed on the island shelf close to the wind-shear field,at the boundary between the turbulent and calm waters in thewake of the island. Biomass gradient values were about threetimes higher than those found off the island shelf and twiceas high as those to the north of the island. ETS activity, ona volume basis, shows a similar result, which is not observedfor the specific activity. The development of gradients andtheir relation to an island mass effect are discussed. Significantdifferences were found between the values obtained along anoceanic transect to the south of the Archipelago and in thecoastal waters around Gran Canaria.