THE SUSCEPTIBILITY OF THE PLANT CELL TO VIRUS DISEASE

A number of spraying experiments showed that the virus cannot enter a plant unless some of the cells are injured. It is not essential that such injury should be brought about in the presence of the virus. The chances of infection fall off rapidly in the first few minutes after injury, but infection occurs occasionally as long as half an hour after the cell is damaged.
Inoculations by micropipette into single cells of the host plant yielded only about one-tenth of the expected number of infections. This suggests differences in the susceptibility of the cells to virus attack.     

The Effect of Divalent Cations on Aggregation of Dictyostelium discoideum

Following the initiation of development, amoebae of Dictyostelium discoideum aggregate chemotactically toward cyclic AMP (cAMP). Adenyl cyclase, cAMP phosphodiesterase, and cAMP binding sites all increase 20–40 fold during the first few hours of development. It has been shown that addition of 1 mM EDTA and 5 mM MgCl₂ accelerates the aggregation process. Likewise, the calcium ionophore, A23187, leads to precocious aggregation while 4 × 10⁻⁵ M progesterone considerably delays it These treatments have now been shown to result in increased accumulation of adenyl cyclase in the case of EDTA and Mg²⁺ or the ionophore and greatly decreased accumulation in the case of the steroid.
Treatment with EDTA and Mg²⁺ or the ionophore has been shown not only to accelerate aggregation in wild-type amoebae but to overcome complete blocks to aggregation in certain mutant strains. We have found that addition of Mn²⁺ will also permit aggregation of mutant cells otherwise unable to aggregate. This divalent ion, unlike EDTA and Mg²⁺ or the ionophore, was shown to directly stimulate adenyl cyclase. Calcium ions were also found to affect the enzyme such that at Ca²⁺ concentrations found within the cells the great majority of the activity is inhibited. Manganese ions can overcome the inhibition by Ca²⁺.
These findings show that conditions which stimulate aggregation result in increased activity of adenyl cyclase either by increased accumulation of the enzyme or by increased activity of the available enzyme, and support the proposed central role of adenyl cyclase in aggregation.     

A systematic review of randomised clinical trials of Tripterygium wilfordii for rheumatoid arthritis.

Tripterygium wilfordii is a Chinese herb with immunosuppressive effects and an established history of use in the treatment of rheumatoid arthritis (RA). We have carried out a systematic review of randomised clinical trials (RCTs) which assess the effectiveness of T. wilfordii in this indication. We included only randomised and controlled studies which tested the effectiveness of T. wilfordii monopreparations in the treatment of RA. Studies in any language were included. A search of five electronic databases from inception to February 2005 identified 18 articles which could potentially meet our inclusion criteria. Only 16 of these could be retrieved from the scientific literature and after reading these in full, only two unique RCTs meeting our inclusion criteria were identified. Both indicated that T. wilfordii has beneficial effects on the symptoms of RA. However, the literature indicates that T. wilfordii is associated with serious adverse events which make the risk-benefit analysis for this herb unfavourable. Therefore, we cannot recommend its use.