The Hertz Corporation

About: The Hertz Corporation is a based out in . It is known for research contribution in the topics: Population & Soil water. The organization has 9562 authors who have published 11044 publications receiving 447929 citations. The organization is also known as: Hertz Rental Car & Hertz Rent-a-Car.

Long term water stress inactivates Rubisco in subterranean clover

Abstract: In long-term field experiments, during consecutive years, microswards of subterranean clover were irrigated to minimise water deficits or subjected to progressively increasing drought over 30 days. Both leaf water potential and relative water content steadily decreased during the experiments. Plants affected by drought grew more slowly and photosynthesis was decreased. Photosynthetic rate (A) and Rubisco were analysed in relation to midday water potentials and relative water contents. The difference in A between droughted and irrigated plants increased progressively, in part as a result of decreased stomatal conductance and CO2 concentration within leaf (Ci). However, A-Ci curves suggest that the photosynthetic capacity in plants experiencing long-term stress was reduced by 50% when compared with irrigated plants. Drought decreased both the initial and the total Rubisco activity per unit area in a similar way but did not reduce the amount of Rubisco protein per unit leaf area. Thus, the specific activity of Rubisco, rather than its activation state, decreased suggesting that under water stress the active sites were blocked by inhibitors.

Pharmacological characterization of human recombinant melatonin mt1 and MT2 receptors

Abstract: We have pharmacologically characterized recombinant human mt1 and MT2 receptors, stably expressed in Chinese hamster ovary cells (CHO-mt1 and CHO-MT2), by measurement of [3H]-melatonin binding and forskolin-stimulated cyclic AMP (cAMP) production. [3H]-melatonin bound to mt1 and MT2 receptors with pKD values of 9.89 and 9.56 and Bmax values of 1.20 and 0.82 pmol mg−1 protein, respectively. Whilst most melatonin receptor agonists had similar affinities for mt1 and MT2 receptors, a number of putative antagonists had substantially higher affinities for MT2 receptors, including luzindole (11 fold), GR128107 (23 fold) and 4-P-PDOT (61 fold). In both CHO-mt1 and CHO-MT2 cells, melatonin inhibited forskolin-stimulated accumulation of cyclic AMP in a concentration-dependent manner (pIC50 9.53 and 9.74, respectively) causing 83 and 64% inhibition of cyclic AMP production at 100 nM, respectively. The potencies of a range of melatonin receptor agonists were determined. At MT2 receptors, melatonin, 2-iodomelatonin and 6-chloromelatonin were essentially equipotent, whilst at the mt1 receptor these agonists gave the rank order of potency of 2-iodomelatonin>melatonin>6-chloromelatonin. In both CHO-mt1 and CHO-MT2 cells, melatonin-induced inhibition of forskolin-stimulated cyclic AMP production was antagonized in a concentration-dependent manner by the melatonin receptor antagonist luzindole, with pA2 values of 5.75 and 7.64, respectively. Melatonin-mediated responses were abolished by pre-treatment of cells with pertussis toxin, consistent with activation of Gi/Go G-proteins. This is the first report of the use of [3H]-melatonin for the characterization of recombinant mt1 and MT2 receptors. Our results demonstrate that these receptor subtypes have distinct pharmacological profiles. British Journal of Pharmacology (2000) 129, 877–886; doi:10.1038/sj.bjp.0703130