Drivers of vegetative dormancy across herbaceous perennial plant species

Vegetative dormancy, that is the temporary absence of aboveground growth for ≥ 1 year, is paradoxical, because plants cannot photosynthesise or flower during dormant periods. We test ecological and evolutionary hypotheses for its widespread persistence. We show that dormancy has evolved numerous times. Most species displaying dormancy exhibit life‐history costs of sprouting, and of dormancy. Short‐lived and mycoheterotrophic species have higher proportions of dormant plants than long‐lived species and species with other nutritional modes. Foliage loss is associated with higher future dormancy levels, suggesting that carbon limitation promotes dormancy. Maximum dormancy duration is shorter under higher precipitation and at higher latitudes, the latter suggesting an important role for competition or herbivory. Study length affects estimates of some demographic parameters. Our results identify life historical and environmental drivers of dormancy. We also highlight the evolutionary importance of the little understood costs of sprouting and growth, latitudinal stress gradients and mixed nutritional modes.     

Three binding sites in protein-disulfide isomerase cooperate in collagen prolyl 4-hydroxylase tetramer assembly

Protein-disulfide isomerase (PDI) is a modular polypeptide consisting of four domains, a, b, b', and a'. It is a ubiquitous protein folding catalyst that in addition functions as the beta-subunit in vertebrate collagen prolyl 4-hydroxylase (C-P4H) alpha(2)beta(2) tetramers. We report here that point mutations in the primary peptide substrate binding site in the b' domain of PDI did not inhibit C-P4H assembly. Based on sequence conservation, additional putative binding sites were identified in the a and a' domains. Mutations in these sites significantly reduced C-P4H tetramer assembly, with the a domain mutations generally having the greater effect. When the a or a' domain mutations were combined with the b' domain mutation I272W tetramer assembly was further reduced, and more than 95% of the assembly was abolished when mutations in the three domains were combined. The data indicate that binding sites in three PDI domains, a, b', and a', contribute to efficient C-P4H tetramer assembly. The relative contributions of these sites were found to differ between Caenorhabditis elegans C-P4H alphabeta dimer and human alpha(2)beta(2) tetramer formation.     

Response of zooplankton to nutrient enrichment and fish in shallow lakes: a pan-European mesocosm experiment

1. Responses of zooplankton to nutrient enrichment and fish predation were studied in 1998 and 1999 by carrying out parallel mesocosm experiments in six lakes across Europe. 2. Zooplankton community structure, biomass and responses to nutrient and fish manipulation showed geographical and year‐to‐year differences. Fish had a greater influence than nutrients in regulating zooplankton biomass and especially the relative abundances of different functional groups of zooplankton. When fish reduced the biomass of large crustaceans, there was a complementary increase in the biomasses of smaller crustacean species and rotifers. 3. High abundance of submerged macrophytes provided refuge for zooplankton against fish predation but this refuge effect differed notably in magnitude among sites. 4. Large crustacean grazers (Daphnia, Diaphanosoma, Sida and Simocephalus) were crucial in controlling algal biomass, while smaller crustacean grazers and rotifers were of minor importance. Large grazers were able to control phytoplankton biomass even under hypereutrophic conditions (up to 1600 μg TP L^?1) when grazer biomass was high (>80–90 μg dry mass L^?1) or accounted for >30% of the grazer community. 5. The littoral zooplankton community was less resistant to change following nutrient enrichment in southern Spain, at high temperatures (close to 30 °C), than at lower temperatures (17–23 °C) characterising the other sites. This lower resistance was because of a greater importance of nutrients than zooplankton in controlling algal biomass. 6. Apart from the reduced role of large crustacean grazers at the lowest latitude, no consistent geographical patterns were observed in the responses of zooplankton communities to nutrient and fish manipulation.     

Protein-mediated Selective Enclosure of Early Replicators Inside of Membranous Vesicles: First Step Towards Cell Membranes

Containment in cell membranes is essential for all contemporary life, and apparently even the earliest life forms had to be somehow contained. It has been postulated that random enclosure of replicating molecules inside of spontaneously assembled vesicles would have formed the initial cellular ancestors. However, completely random re-formation or division of such primitive vesicles would have abolished the heritability of their contents, nullifying any selective advantage to them. We propose that the containment of the early replicators in membranous vesicles was adopted only after the invention of genetically encoded proteins, and that selective enclosure of target molecules was mediated by specific proteins. A similar containment process is still utilised by various RNA- and retroviruses to isolate their replication complexes from the host’s intracellular environment. Such selective encapsulation would have protected the replicators against competitor and parasitic sequences, and provided a strong positive selection within the replicator communities.     

Effects of weaning age and formic acid-based feed additives on pigs from weaning to slaughter

Two hundred and forty piglets were used in a 2 x 6 factorial experiment to study the effects of weaning age (26 or 36 d) and four formic acid-based feed additives on the performance of pigs from weaning to slaughter. Either formic acid (F) or a mixture of formic acid, propionic acid, and potassium sorbate (FPS) or a mixture of formic acid, propionic acid, and sodium benzoate (FPB) or formic acid in a diatomaceous earth carrier (FD) were added to the diets of weaned piglets (from weaning to 60 d of age) and growing (18-46 kg) and finishing pigs (46-107 kg) to provide 8, 6, and 6 g acid per kg feed, respectively. The negative control treatment's (C) diets contained no growth promoters, whereas the positive control treatment's weaner and grower diets were supplemented with 40 mg/kg of avilamycin (A). The piglets weaned at the age of 26 and 36 d weighed 7.6 and 10.7 kg at weaning (p < 0.001), and 18.5 and 17.9 kg at the age of 60 d (p > 0.05), respectively. There was a weaning age x feed additive interaction in the weight gain of piglets after weaning (p < 0.05). The weight gain of piglets weaned on day 26 was enhanced by A, FPS, and FD (p < 0.05), and that of piglets weaned on day 36 by A and FPB (p < 0.05). The feed conversion ratio was not affected by weaning ages but was decreased in groups A, F, FBS, and FPB (p < 0.05). The severity of post-weaning diarrhoea was less in groups A, F, FPS, and FD than in C (p < 0.05). In piglets weaned on day 26, faecal water content and the total Escherichia coli count were highest 9 d after weaning. The total E. coli count was reduced only by FD (p < 0.05). Increased faecal water content was characterized by increased faecal Na+ and decreased K+ concentrations. Weaning age did not influence performance or carcass quality in the growing-finishing pigs. Feed additives did not affect weight gain in the growing pigs, but FPS and FPB enhanced weight gain during finishing period and total fattening (p < 0.05). In summary, the pigs' growth performance from weaning to slaughter was not affected by weaning age but it was enhanced by mixtures of formic and propionic acids with small amounts of sorbate or benzoate.     

Effect of polysaccharide structure on mechanical and thermal properties of galactomannan-based films

Films were prepared from guar gum and locust bean gum galactomannans. In addition, enzymatic modification was applied to guar gum to obtain structurally different galactomannans. Cohesive and flexible films were formed from galactomannans plasticized with 20-60% (w/w of polymer) glycerol or sorbitol. Galactomannans with lower galactose content (locust bean gum, modified guar gum) produced films with higher elongation at break and tensile strength. The mechanical properties of films were improved statistically significantly by decreasing the degree of polymerization of guar gum with mannanase treatments (4 h) of 2 and 10 nkat/g, whereas 50 nkat/g produced films with low elongation at break and tensile strength. Galactomannans with approximately 6 galactose units per 10 mannose backbone units resulted in films with 2 peaks in loss modulus spectra, whereas films from galactomannans with approximately 2 galactose groups per 10 mannose units behaved as a single phase in dynamic mechanical analysis.     

Endophytic fungus decreases plant virus infections in meadow ryegrass (Lolium pratense)

We studied the effects of fungal endophyte infection of meadow ryegrass (Lolium pratense=Festuca pratensis) on the frequency of the barley yellow dwarf virus (BYDV). The virus is transferred by aphids, which may be deterred by endophyte-origin alkaloids within the plant. In our experiment, we released viruliferous aphid vectors on endophyte-infected and endophyte-free plants in a common garden. The number of aphids and the percentage of BYDV infections were lower in endophyte-infected plants compared to endophyte-free plants, indicating that endophyte infection may protect meadow ryegrass from BYDV infections.     

Brown adipose tissue functions in humans

Human adults have functionally active BAT. The metabolic function can be reliably measured in vivo using modern imaging modalities (namely PET/CT). Cold seems to be one of the most potent stimulators of BAT metabolic activity but other stimulators (for example insulin) are actively studied. Obesity is related to lower metabolic activity of BAT but it may be reversed after successful weight reduction such as after bariatric surgery. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease.