Meta-analysis reveals that pollinator functional diversity and abundance enhance crop pollination and yield.

How insects promote crop pollination remains poorly understood in terms of the contribution of functional trait differences between species. We used meta-analyses to test for correlations between community abundance, species richness and functional trait metrics with oilseed rape yield, a globally important crop. While overall abundance is consistently important in predicting yield, functional divergence between species traits also showed a positive correlation. This result supports the complementarity hypothesis that pollination function is maintained by non-overlapping trait distributions. In artificially constructed communities (mesocosms), species richness is positively correlated with yield, although this effect is not seen under field conditions. As traits of the dominant species do not predict yield above that attributed to the effect of abundance alone, we find no evidence in support of the mass ratio hypothesis. Management practices increasing not just pollinator abundance, but also functional divergence, could benefit oilseed rape agriculture.

DNA elimination and its relation to quantities in the macronucleus of Tetrahymena.

The macronucleus of Tetrahymena contains a large number of DNA molecules of subchromosomal size. They belong to about 270 species each one occurring at an average number of 45 copies. Macronuclei divide unequally and nothing is known of segregation control. This and the elimination and degradation of DNA during macronuclear amitosis make the clonal stability of macronuclei a problem of qualitative and quantitative control on a subchromosomal level. We studied the contribution of DNA elimination to the quantitative composition of the macronucleus cytophotometrically in single cells of different strains. This was done under standard conditions and under conditions known to influence the amount of macronuclear DNA. The following results were found: Elimination of DNA occurs at almost every division. The size of the elimination body is highly variable but still positively correlated with the macronuclear DNA content. In T. thermophila the amount of eliminated DNA is 2.5% of the G2 content and is not dependent on the growth state. It varies with species, amounting to as much as 8% in T. pigmentosa. During conditions which increase the macronuclear DNA content, very little DNA is eliminated. On the other hand, large amounts are eliminated under other conditions causing the macronuclear DNA content to decrease. DNA to be eliminated at division is synthesized at the same time as bulk DNA. We developed a computer program which helps us study the effects of DNA elimination and unequal divisions upon the copy numbers of subchromosomal DNA classes.(ABSTRACT TRUNCATED AT 250 WORDS)

A characterization of Tetrahymena mRNA by in vitro translation: The effects of culture growth on the recruitment of poly (A)(+) and poly (A)(-) RNA.

Messenger RNA was extracted from exponentially growing and from stationary cultures of Tetrahymena thermophila. It was separated into polyadenylated and non-polyadenylated fractions which were used as templates in a rabbit reticulocyte protein synthesizing system. The translated proteins were analysed by one and by two dimensional electrophoresis. Our experiments were intended to answer the question to which extent the abundance and the specificity of mRNA facilitates or accompanies the passage of cells through one culture growth cycle. As illustrated by the identification of 113 proteins very few differences between translated messages accompany the transition to the stationary phase, the most obvious feature being a change in the intracellular location of translation activities. These data are discussed with special reference to the prevailing occupation of Tetrahymena which is biomass production.

The energy budget of Tetrahymena and the material fluxes into and out of the adenylate pool.

The material budget of the adenylate pool deals with all processes which physically establish and maintain this pool, while the energy budget is concerned with the intracompartmental ATP recycling. Both budgets were analysed in Tetrahymena thermophila exposed to various energy and material demands. Some of the general conclusions are: at a maximum growth rate the overall ATP consumption during one cell cycle is 10(-10) mol ATP; the contribution of osmoregulation and ciliary motion to the budget is about 1% each; at zero net growth, energy is consumed because of a continuous recycling of matter between the monomer and the polymer compartment. The rate of ATP production is about 1000-fold greater than the rate of adenylate monomer influx. The residence time of adenylate monomers within the pool is about 30 min, but for ATP molecules it is only 2 sec.

A population-kinetical approach to RNA formation and degradation in growing and in resting cells.

Labelled RNA was extracted from growing and stationary cultures of the ciliate Tetrahymena and was separated chromatographically into poly(A)- and no poly(A)-containing fractions. A new method was used to derive from the data (cpm/A260, and tD, doubling time of RNA) absolute values of three growth terms which fully describe the population kinetics of RNA molecules: the rates of transcription, decay, and net growth. At all times the messenger RNA (mRNA) content of Tetrahymena was the result of a self-regulating equilibrium between synthesis and decay. The rates of transcription and of degradation of mRNA and ribosomal RNA (rRNA) were found to be controlled independently, but decay was dominant in establishing the growth-specific quantities per cell. In the stationary phase about 94% of all poly(A)-RNA molecules and about 50% of all mRNA molecules were kinetically silent. The remaining portions were transcribed with high rates, but also degraded immediately. During the culture growth cycle the rate of rRNA net growth responded positively to the cellular rRNA content suggesting an autocatalytic effect of rRNA on the rate of its accumulation.

The evaluation of initial rates in the presence of background noise.

A three-parameter model was used to test a curvilinear regression for its gamma-intercept. It was applied in the kinetic analysis of a model reaction and of real experiments. The model reaction consisted of a dialysis experiment with increasing amounts of background added at t0. In the presence of this background, initial rates of solute exchange were determined precisely enough to be in agreement with Fick's law of diffusion. The biological experiments were concerned with the saturation kinetics of the acid-soluble radioactivity of cells exposed to 3H-labelled amino acids. Two models of regression were applied, facilitated and physical diffusion, both consistent with the assumption of a substantial amount of background. This background was assumed to be caused by adsorption of 3H-labelled amino acids to cell-surface proteins. Without further consideration it caused a systematic overestimation of the initial rates.

A feedback control of cell cycle parameters in Tetrahymena.

Protein and RNA contents of individual cells were measured cytophotometrically and related to the duration of individual generation times. Constant amounts of RNA per cell at division, and generation time-dependent protein contents, resulted in generation time-specific RNA/protein ratios. Experimental reduction of these ratios by inhibition of RNA synthesis stimulated premature macronuclear S phases.