In the context of infectious diseases in mollusc and shrimp aquaculture, research must be focused on diagnosis for zoosanitary controls but also on obtaining resistant animals. This last strategy ...depends heavily on the development of knowledge about marine invertebrate immunology. With the establishment of purification protocols for the main invertebrate pathogens, progress has been made in the study of host-pathogen interactions at cellular and molecular levels and in identifying immune effectors involved in the destruction of pathogens. Recent information on molluscs and crustaceans is presented, concerning both hemocyte studies and cellular defence functions and humoral effectors, with special reference to their application to selection of pathogen-resistant animals. With this aim, research prospects will essentially be devoted to the identification and characterization of immune genes, either specific or heterologous, which could be candidates for mollusc and shrimp genetic transformation.
•Ensiling and sample conditioning have an effect on in situ degradation of maize.•Ensiling maize increased in situ degradability of dry matter and starch.•Ensiling maize decreased in situ ...degradability of cell walls (aNDF).•Grinding dried samples at 4mm limits starch losses during in situ degradation.
High-production ruminants are commonly fed maize silage, which makes accurate evaluation of its nutritive value a key economic issue. However, evaluations of the rate and extent of ruminal degradation of starch and cell wall fractions from maize silage carry uncertainty due to the lack of a standardized method. Here, we investigated the effects of ensiling and sample conditioning on in situ-measured degradation of maize forage. Eight series of maize samples (two hybrids×two maturity stages×two methods of conservation non-ensiled or fresh and ensiled) were nylon-bagged in three conditionings: dried and ground to 1mm (D1), dried and ground to 4mm (D4), frozen and coarse-ground (FG). Disappearance of dry matter (DM), starch and fibre (aNDF) was measured in situ in cow rumen after different incubation times (2, 4, 8, 16, 24, 48 and 96h). Effects of ensiling, sample conditioning, genotype, maturity and their interactions on DM, starch and aNDF degradation were analyzed using the SAS MIXED procedure. Effective dry matter degradability (ED4DM) was significantly higher (P<0.001) in silage than in fresh maize due to a significantly higher rapidly degradable fraction (a) (P<0.001). Effective starch degradability (ED6Starch) followed the same trend due to a higher silage degradation rate (P<0.01). Conversely, effective aNDF degradability (ED2aNDF) was lower in silage (P<0.001) than fresh maize due to the longer lag-time to degradation (P<0.001) and lower hemicellulose ((aNDF−ADF)/aNDF) fraction in silage. Effective DM degradability was higher (P<0.001) for D1 samples than D4 and FG samples, mainly due to the higher rapidly degradable fraction (a) (P<0.001) in D1 than D4 or FG samples. In relation to high degradation rate, starch degradability was significantly higher (P<0.001) in FG than D1 and D4 samples, whereas aNDF degradation was lowest in the FG samples. This study shows that ensiling maize increases starch degradability and decreases aNDF degradability compared to fresh plant. Alongside conservation method, fine-grinding samples (as D1) led to high losses through the pores of the nylon bags, and these losses were correlated with high starch degradability, whereas coarse grinding (as FG) led to low aNDF degradability, probably due to insufficiently reduced particle sizes. In conclusion, using ensiled samples dried and ground to 4mm (D4) emerges as the appropriate method for in situ studies of starch-rich forages used as silages.
The study of carbohydrate metabolism in perennial ryegrass (Lolium perenne L. cv. Bravo) during the first 48 h of regrowth showed that fructans from elongating leaf bases were hydrolysed first ...whereas fructans in mature leaf sheaths were degraded only after a lag of 1.5 h. In elongating leaf bases, the decline in fructan content occurred not only in the differentiation zone (30—60 mm from the leaf base), but also in the growth zone. Unlike other soluble carbohydrates, the net deposition rate of fructose remained positive and even rose during the first day following defoliation. The activity of fructan exohydrolase (FEH; EC 3.2.1.80) was maximal in the differentiation zone before defoliation and increased in all segments, but peaked in the growth zone after defoliation. These data strongly indicate that fructans stored in the leaf growth zone were hydrolysed and recycled in that zone to sustain the refoliation immediately after defoliation. Despite the depletion of carbohydrates, leaves of defoliated plants elongated at a significantly higher rate than those of undefoliated plants, during the first 10 h of regrowth. This can be partly attributed to the transient increase in water and nitrate deposition rate. The results are discussed in relation to defoliation tolerance.
This work assessed the central carbohydrate metabolism of actively photosynthesizing leaf blades of a C3 grass (Lolium perenne L.). The study used dynamic C-13 labelling of plants growing in ...continuous light with contrasting supplies of nitrogen ('low N' and 'high N') and mathematical analysis of the tracer data with a four-pool compartmental model to estimate rates of: (i) sucrose synthesis from current assimilation; (ii) sucrose export/use; (iii) sucrose hydrolysis (to glucose and fructose) and resynthesis; and (iv) fructan synthesis and sucrose resynthesis from fructan metabolism. The contents of sucrose, fructan, glucose, and fructose were almost constant in both treatments. Labelling demonstrated that all carbohydrate pools were turned over. This indicated a system in metabolic steady state with equal rates of synthesis and degradation/consumption of the individual pools. Fructan content was enhanced by nitrogen deficiency (55 and 26% of dry mass at low and high N, respectively). Sucrose content was lower in nitrogen-deficient leaves (2.7 versus 6.7%). Glucose and fructose contents were always low (< 1.5%). Interconversions between sucrose, glucose, and fructose were rapid (with half-lives of individual pools ranging between 0.3 and 0.8 h). Futile cycling of sucrose through sucrose hydrolysis (67 and 56% of sucrose at low and high N, respectively) and fructan metabolism (19 and 20%, respectively) was substantial but seemed to have no detrimental effect on the relative growth rate and carbon-use efficiency of these plants. The main effect of nitrogen deficiency on carbohydrate metabolism was to increase the half-life of the fructan pool from 27 to 62 h and to effectively double its size.
We undertook the characterization of an actin gene and its proximal promoter in the oyster
Crassostrea gigas. A complete actin cDNA was identified, sequenced and its amino acid sequence deduced. ...Comparative analysis showed a high homology with actin of other species and that this gene is closer to the cytoplasmic form of actins than to the muscle type. A probe derived from the 5′-untranslated region of the cDNA was then used to isolate the actin gene from a genomic library. The gene was sequenced and shown to contain a single 643 bp intron. A 1670 bp fragment upstream from the open reading frame was isolated and sequenced. This upstream region displays typical features of actins such as a serum response element (CarG box). This fragment was cloned into the promoterless vector pGL3-basic and the resulting construct was transfected into cells of dissociated oyster heart primary cultures. Its capacity to express the luciferase in this in vitro homologous system was monitored and showed high expression levels. This is the first complete actin sequence reported so far for the oyster
C. gigas and its promoter is the first available among bivalves.
Timothy (Phleum pratense L.) is an important grass forage used for pasture, hay, and silage in regions with cool and humid growth seasons. One of the factors affecting the nutritive value of this ...grass is the concentration of non-structural carbohydrates (NSC), mainly represented by fructans. NSC concentration depends on multiple factors, making it hardly predictable. To provide a better understanding of NSC metabolism in timothy, the effects of maturity stage and nitrogen (N) fertilization level on biomass, NSC and N-compound concentrations were investigated in the tissues used for forage (leaf blades and stems surrounded by leaf sheaths) of hydroponically grown plants. Moreover, activities and relative expression level of enzymes involved in fructan metabolism were measured in the same tissues. Forage biomass was not altered by the fertilization level but was strongly modified by the stage of development. It increased from vegetative to heading stages while leaf-to-stem biomass ratio decreased. Total NSC concentration, which was not altered by N fertilization level, increased between heading and anthesis due to an accumulation of fructans in leaf blades. Fructan metabolizing enzyme activities (fructosyltransferase—FT and fructan exohydrolase—FEH) were not or only slightly altered by both maturity stage and N fertilization level. Conversely, the relative transcript levels of genes coding for enzymes involved in fructan metabolism were modified by N supply (PpFT1 and Pp6-FEH1) or maturity stage (PpFT2). The relative transcript level of PpFT1 was the highest in low N plants while that of Pp6-FEH1 was the highest in high N plants. Morevoer, transcript level of PpFT1 was negatively correlated with nitrate concentration while that of PpFT2 was positively correlated with sucrose concentration. This distinct regulation of the two genes coding for 6-sucrose:fructan fructosyltransferase (6-SFT) may allow a fine adequation of C allocation towards fructan synthesis in response to carbon and N availability. Contrary to fructans, starch content increased in low N plants, suggesting different regulatory mechanisms and/or sensitivity of starch and fructan metabolism in relation to the N status.
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