Physiological Changes in Phaseolus vulgaris in Response to Long-term Ozone Exposure

The effects of ozone on Phaseolus vulgaris cv. Lit were investigatedusing open-top chambers (OTCs) ventilated with charcoal andPurafil filtered air (CF treatments), ambient air (NF treatments)and ambient air to which low, medium or high concentrationsof ozone were added (NFL, NFM and NFH). Ozone additions of 8,16 and 23 nl l^–1 were made during phase 1 of the experiment(0–44 d after emergence, DAE), and additions of 15, 30and 47 nl l^–1 were made during phase 2 (45–99 DAE).Ozone was added to the chambers between 1100 and 1800 h GMT,for 3 or 4 consecutive days each week. The seasonal 7-h meanozone concentrations were 8, 21, 27, 33 and 38 nl l^–1in the CF, NF, NFL, NFM and NFH treatments, respectively. No visible symptoms of ozone injury or significant physiologicalchanges were detected in P. vulgaris during phase I of the experiment.In phase 2, the photosynthesis (Pn) and stomatal conductance(gs) of NFH-plants were inhibited by 73% and 86%, respectively,during ozone exposure, and recovered to pre-exposure valueson the following day. These observations were made prior tothe appearance, 60 DAE, of bronze lesions on the leaves of NFH-plants.The photosynthetic capacity and gs of NFH-leaves decreased asthe severity of ozone injury increased. Rates of weight lossfrom excised leaves also increased with increasing ozone injury.Microscopic investigations of the bronzed regions revealed extensivecellular breakdown, including tonoplast and chloroplast enveloperupture, and the aggregation of the cytoplasmic contents towardsone end of the cell. Severely damaged leaves abscised from the plants, resultingin premature canopy senescence in the NFM and NFH treatments.This, coupled with the lower photosynthetic capacity of existingleaves led to 25 % lower yield in the NFH than the NF treatment(P < 0.05). Phaseolus vulgaris, green bean, ozone, symptom development, photosynthesis, cell ultrastructure     

Functional role of phenylacetic acid from metapleural gland secretions in controlling fungal pathogens in evolutionarily derived leaf-cutting ants

Fungus-farming ant colonies vary four to five orders of magnitude in size. They employ compounds from actinomycete bacteria and exocrine glands as antimicrobial agents. Atta colonies have millions of ants and are particularly relevant for understanding hygienic strategies as they have abandoned their ancestors'' prime dependence on antibiotic-based biological control in favour of using metapleural gland (MG) chemical secretions. Atta MGs are unique in synthesizing large quantities of phenylacetic acid (PAA), a known but little investigated antimicrobial agent. We show that particularly the smallest workers greatly reduce germination rates of Escovopsis and Metarhizium spores after actively applying PAA to experimental infection targets in garden fragments and transferring the spores to the ants'' infrabuccal cavities. In vitro assays further indicated that Escovopsis strains isolated from evolutionarily derived leaf-cutting ants are less sensitive to PAA than strains from phylogenetically more basal fungus-farming ants, consistent with the dynamics of an evolutionary arms race between virulence and control for Escovopsis, but not Metarhizium. Atta ants form larger colonies with more extreme caste differentiation relative to other attines, in societies characterized by an almost complete absence of reproductive conflicts. We hypothesize that these changes are associated with unique evolutionary innovations in chemical pest management that appear robust against selection pressure for resistance by specialized mycopathogens.     

Morphometric parameters of neurons in reticular nuclei of the brain stem in kittens

Three types of Golgi-stained neurons were discovered in brain stem reticular nuclei of 30-day-old kittens: sparsely branching reticular neurons, those with densely branching dendritic trees, and giant multipolar neurons (Leontovich's classification). Adopting computerized morphometric techniques enabled 23 different parameters to be measured in cells of these types. The measurements taken from the neuronal groups investigated revealed statistically significant differences between them for most parameters. It was concluded from this that each of the neuronal types distinguished has its own morphological identity (or stability). Characteristics of structural differences and properties of differing cell types in reticular nuclei are discussed in relation to their functional properties.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 399–409, July–August, 1991.     

Relative growth rate correlates negatively with pathogen resistance in radish: the role of plant chemistry

Plant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativus L.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused by Fusarium oxysporum. We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow-growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow-growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow-growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn-over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be involved.     

The cytomegalovirus enhancer: a pan-active control element in transgenic mice.

In an effort to identify widely active positive regulatory elements, we have examined the action of the cytomegalovirus enhancer-promoter in transgenic mice. These elements activated expression in 24 of 28 tissues tested. The greatest expression was observed in the heart, kidney, brain, and testis. Maximum expression further localized to specific cells within the heart and kidney.     

NP7 protects from cell death induced by oxidative stress in neuronal and glial midbrain cultures from parkin null mice

Parkin mutations produce Parkinson’s disease (PD) in humans and nigrostriatal dopamine lesions related to increased free radicals in mice. We examined the effects of NP7, a synthetic, marine derived, free radical scavenger which enters the brain, on H₂O₂ toxicity in cultured neurons and glia from wild-type (WT) and parkin null mice (PK-KO).NP7, 5-10 μM, prevented the H₂O₂ induced apoptosis and necrosis of midbrain neuronal and glial cultures from WT and PK-KO mice. NP7 suppressed microglial activation and the H₂O₂ induced drop-out of dopamine neurons_. Furthermore, NP7 prevented the increased phosphorylation of ERK and AKT induced by H₂O₂. NP7 may be a promising neuroprotector against oxidative stress in PD.