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Jason: What you need to know about selenium 2010, 7-45.

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Iron-stressed sugar beets were resupplied with ferrous salts and ferric EDTA and the transport of iron into leaves was monitored with time. After 24 hours of iron resupply, leaf iron concentrations increased 11-fold whether iron was resupplied as ferrous sulfate or ferric EDTA. There was a substantial increase in leaf iron during the first two hours with the maximum rate of accumulation occurring during the first six hours after resupply began. The massive transport of iron into leaves following iron resupply was associated with iron movement into interveinal areas as well as into petioles and veins. The results suggest that the phenomenon of enhanced iron uptake by iron-stressed plants occurs even when the ferric to ferrous reduction step at the root is bypassed. INTRODUCTIONIt is well known that when iron is resupplied to ironstressed plants of several species, iron uptake and transport is

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Cobalt treatment of iron-stressed sugar beet plants resulted in leaf cobalt concentrations nearly three times as high as in cobalt-treated control plants. When iron-stressed plants were treated with cobalt and iron together, cobalt was transported into leaves in preference to iron. The transport system in iron-stressed sugar beet appears to be relatively specific for iron and cobalt because iron-stressed plants supplied with manganese, zinc, and copper did not transport these elements in similarly enhanced amounts. Measurements of metal contents of chloroplasts isolated nonaqueously showed that both cobalt and iron were readily transported into chloroplasts (and therefore the leaf symplast) within 48 h. The implications of these results on the mechanism of iron transport across the root plasmalemma are discussed.

The 1989 and 1990 economic summits in Paris and Houston, as well as the 1992 Rio Summit, suggest a growing global commitment to protect the environment. In this context, it is important to understand the causes of conflict among states over environmental issues as well as the factors that inhibit or facilitate dispute resolution. To that end, a number of theoretical frameworks attempt to explain the outcome of pollution-related conflicts. Four of these frameworks are assessed here for their relevance in understanding the conflict between Canada and the United States over acid rain controls and its eventual resolution. A meta-regimes analysis predicts the range of possible outcomes consistent with prevailing political and economic norms and principles. An interest-based explanation predicts the initial bargaining positions of the two countries and the decade-long intransigence to agreement within the United States. An epistemic community analysis identifies the importance of both the knowledge base and issue-area experts. Negotiations analysis, which addresses the dynamics among many of the foregoing factors, also ensures that the potential influence of all affected stakeholders is included, and incorporates nonobvious issue linkages. As the acid rain case demonstrates, each of the frameworks provides partial insights. To understand the whole it is useful to integrate the frameworks.

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