Aerobic heat shock activates trehalose synthesis in embryos of Artemia franciscana.

Encysted embryos (cysts) of the brine shrimp, Artemia franciscana, contain large amounts of trehalose which they use as a major substrate for energy metabolism and biosynthesis for development under aerobic conditions at 25 degrees C. When cysts are placed at 42 degrees C (heat shock) these pathways stop, and the cysts re-synthesize the trehalose that was utilized during the previous incubation at 25 degrees C. Glycogen and glycerol, produced from trehalose at 25 degrees C, appear to be substrates for trehalose synthesis during heat shock. Anoxia prevents trehalose synthesis in cysts undergoing heat shock. These results are consistent with the view that trehalose may play a protective role in cells exposed to heat shock, and other environmental insults, in addition to being a storage form of energy and organic carbon for development.     

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     

Complete amino acid sequence of a novel integrin beta subunit (beta 6) identified in epithelial cells using the polymerase chain reaction

The integrin family of adhesion receptors consists of several heterodimeric glycoproteins, each composed of one alpha and one beta subunit. Three different mammalian beta subunits, beta 1, beta 2, and beta 3, have been sequenced, but recent evidence suggests the existence of several others. Amplification of guinea pig airway epithelial cell cDNA with oligonucleotide primers designed to recognize consensus integrin beta subunit sequences led to the identification of a novel partial cDNA sequence. Clones containing portions of this sequence were used to screen cDNA libraries constructed from the human pancreatic carcinoma cell line FG-2 and identified a series of overlapping clones encoding the full-length sequence of the human homologue of this protein. This sequence of 788 amino acids is 43, 38, and 47% identical to the sequences of beta 1, beta 2, and beta 3, respectively. Features shared between this novel protein and the previously sequenced beta subunits include the positions of all 56 cysteine residues in the extracellular domain, the single putative transmembrane domain, and the short putative cytoplasmic domain. However, a unique 11-amino acid extension at the carboxyl terminus, not present in any of the other beta subunits, is suggestive of distinctive interactions with cytoplasmic components. Comparison of the human and guinea pig sequences reveals a high degree (94%) of cross-species conservation. Because this protein is clearly distinct from the two other recently described integrins beta 4 and beta 5, we propose to designate it beta 6.     

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.