Effect of some heterocyclic herbicides on CO2 assimilation by spinach chloroplasts

We have studied the inhibitory effect of heterocyclic herbicides simazine, paraquat, pyrazon and amitrole on photosynthetic CO₂ fixation and on the level of intermediates of the CO₂ assimilation cycle in isolated spinach (Spinacia oleracea) chloroplasts, as well as their in vitro activities on ribulose-1,5-bisphosphate carboxylase and fructose-1,6-bisphosphatase. The half inhibitory concentrations (I₅₀) of CO₂ assimilation were about 1 μM for simazine and paraquat, and 10 μM for pyrazon. Amitrole, with an I₅₀ 100 μM, gave only a weak inhibition. In the presence of simazine or pyrazon the triose-phosphates/phosphoglycerate ratio diminished because of a decrease of the triose-phosphates percentage from 47% to 19%, which means an inhibition of the phosphoglycerate reduction step by a low NADPH synthesis. However, there was not a parallel increase of phosphoglycerate, because of collateral pathways leading to phospho-enolpyruvate, amino acids and other non-identified compounds. Paraquat did not give such a decreased ratio, which could be explained as an inhibition of some step of the Calvin cycle later than triose-phosphates by the H₂O₂ formed in a Mehler reaction. Amitrole did not show any effect on the pattern of intermediates. Simazine and pyrazon at 10 μM concentration promote a 20–30% activation of ribulose-1,5-bisphosphate carboxylase activity, whereas paraquat, pyrazon and simazine showed an I₅₀ about 100 μM for the inhibition of the photosynthetic fructose-1,6-bisphosphatase.     

Cortical and Nuclear Events During Cell Division and Resting Cyst Formation in Colpoda inflata

Nuclear and cortical phenomena during dividing and resting cyst formation of Colpoda inflata are described. Cell division forms a cyst and produces two or four tomites. In each tomite, the right oral field results from the proliferation of the anterior extreme of a single kinety, and the left oral field results from the proliferation of four, five, or six somatic kineties. After macronuclear division, each macronuclear mass undergoes a chromatinic extrusion process. During resting cyst formation, the oral infraciliature of the vegetative cell is resorbed. The somatic kineties dispose in a radial way and some pairs of kinetosomes disappear. As in cell division, there is an extrusion process. From these results we conclude that the resting cysts of Colpoda inflata cannot be included in any group of the previous classifications for hypotrich resting cysts. Thus, we propose a new additional group to Walker and Maugel's classification called PKR (partial-kinetosome-resorbing) cysts.     

Enhancement of root hydraulic conductivity by methyl jasmonate and the role of calcium and abscisic acid in this process

The role of jasmonic acid in the induction of stomatal closure is well known. However, its role in regulating root hydraulic conductivity (L) has not yet been explored. The objectives of the present research were to evaluate how JA regulates L and how calcium and abscisic acid (ABA) could be involved in such regulation. We found that exogenous methyl jasmonate (MeJA) increased L of Phaseolus vulgaris, Solanum lycopersicum and Arabidopsis thaliana roots. Tomato plants defective in JA biosynthesis had lower values of L than wild‐type plants, and that L was restored by addition of MeJA. The increase of L by MeJA was accompanied by an increase of the phosphorylation state of the aquaporin PIP2. We observed that MeJA addition increased the concentration of cytosolic calcium and that calcium channel blockers inhibited the rise of L caused by MeJA. Treatment with fluoridone, an inhibitor of ABA biosynthesis, partially inhibited the increase of L caused by MeJA, and tomato plants defective in ABA biosynthesis increased their L after application of MeJA. It is concluded that JA enhances L and that this enhancement is linked to calcium and ABA dependent and independent signalling pathways.     

A unifying study of phenotypic and molecular genetic variability in natural populations of Anadenanthera colubrina var. cebil from Yungas and Paranaense biogeographic provinces in Argentina

Anadenanthera colubrina var. cebil is a discontinuously distributed native tree species in South American subtropical forests. Thirteen quantitative traits and eight nuclear microsatellite loci were examined in individuals from two biogeographic provinces of Argentina to determine the number and composition of genetically distinguishable groups of individuals and explore possible spatial patterns of the phenotypic and genetic variability. Means of reproductive traits were higher in the Yungas than in the Paranaense biogeographic province, whereas five out of eight nonreproductive quantitative traits showed higher mean values in the latter. Variance coefficients were moderate, and there were significant differences between and within provinces. Three clusters were defined based on spatial model for cluster membership for quantitative traits. One cluster grouped the individuals from the Paranaense biogeographic province whereas the individuals from the Yungas biogeographic province grouped regarding its population of origin. Parameters of molecular genetic variability showed higher values in the Yungas than in the Paranaense biogeographic province. Observed heterozygosity was lower than expected heterozygosity in both biogeographic provinces, indicating an excess of homozygosity. The homozygosity test by Watterson and the exact test by Slatkin suggested diversifying selection for locus Ac41.1. Bayesian clustering spatial model for microsatellites loci data were performed for both all loci and for all loci excluding locus Ac41.1. In both analyses two clusters were inferred. Analysis of molecular variance revealed similar results for all genotypes and for all genotypes defined excluding locus Ac41.1. Most of the total variance is attributable to genetic variation within clusters. The presence of homogeneous clusters was detected for both the phenotypic and molecular genetic variability. Two Bayesian clustering analyses were performed according to molecular genetic data, and two clusters were inferred. Individuals were assigned to their provinces of origin. Genetic molecular variation was higher in the populations of the Yungas biogeographic province which translates into highly qualified populations for conservation. Populations from the Paranaense biogeographic province showed the highest mean value of number of seeds per fruit making them valuable as well with regard to the exploitation of management strategies as a means to recover the impacted areas where these populations are located.     

Symbionts of societies that fission: mites as guests or parasites of army ants

• 1 Recently, Hughes et al. (Trends in Ecology & Evolution, 23 , 672–677, 2008) have theorised that symbionts of large, long‐lived, homeostatic, and well defended social insect colonies should mostly be of low virulence. If the symbionts are rare, i.e. few workers are co‐infected, competition between symbionts should be minimal and they should be selected to avoid over‐exploiting their hosts.
• 2 Here we analyse the mites that occur on Eciton burchellii army ant workers and note that our findings are consistent with the predictions from evolutionary theory.
• 3 The mites were species diverse but rare; only 5% of the 3146 workers we examined from 20 army ant colonies had mites. Only one worker was co‐infected by mites of different species and the one relatively common parasitic mite (Rettenmeyerius carli) was limited to only two individuals per ant.
• 4 We also showed that certain mites are more common on workers in nomadic rather than statary army ant colonies and that different worker castes differed in their infestation patterns.
• 5 We suggest that the three traits E. burchellii and honey bees (Apis mellifera) have in common (queens with very high mating frequencies, propagation by colony fission, and low number of parasites among the mite species they host) are associated with one another. Colonies that fission are likely to inherit symbionts and multiple mating will promote genetic diversity within colonies, which may help to limit the abundance of deleterious mites.
• 6 We conclude that most of the symbiotic mites found on workers of the army ant E. burchellii are probably relatively harmless guests, exploiting their hosts for phoresis or, for example, to use their waste deposits.