Scientists have uncovered new details about the importance of the tips of plant roots in sending signals about the soil environment to the rest of the plant.The scientists hope the information can someday help farmers minimize the effects of environmental stresses like drought and improve control over pests and diseases. The strategy would involve interpreting soil and plant data obtained by precision farming technologies such as remote sensing and yield monitors on combines. Chemical signals sent by plant roots to shoots are already known to include nitrate, a plant nutrient, and hormones such as cytokinins and abscisic acid. But when ARS scientists analyzed the growth patterns of corn root systems, they found that changes in root distribution and architecture could result from the chemical activity in the root tips–sites of cell division. These changes may increase or decrease the volume of soil accessible to the roots for taking up water and nutrients. The scientists found that the growing tips of roots sense soil conditions like availability of water and nutrients as well as soil hardness and temperature. Roots relay signals about these conditions. These signals include fluxes of ions and growth hormones. Shoots respond by regulating production of photosynthetic enzymes and the size of small pores in leaves–which, in turn, affect photosynthesis and water use.

Central Great Plains Research, Akron, CO Robert M. Aiken, (970)345-0519, aiken@gpsr.colostate.edu

Kangaroo rats and their relatives get the credit, say researchers, for more than 90 percent of the Indian ricegrass seeds that sprout and take hold on desert rangeland ecosystems of California, Utah and Nevada. The scientists are studying way to increase the supplies of this native plant, which provides nutritious forage for wildlife and cattle. Wildlife biologists already know that Indian ricegrass seed is a favorite of the furry rodents. But a 4-year ARS study provides useful new details on the role of kangaroo rats, pocket mice and other seed-eating animals in re-seeding Western ranges. On spring and summer nights, a single kangaroo rat may gather hundreds of seeds in its fur-lined cheek pouches, then bury them in shallow hiding places or caches. But the animals often don't return for these tasty meals. They may cache more seeds than they need, fall victim to a predator or to a harsh winter, or simply forget where they put some seeds. In any event, many of the buried seeds sprout the following spring. Unfortunately, the rodents eat ricegrass seeds planted by humans just as readily as those produced within the native ecosystem. But the new study adds to the scientists' ongoing efforts to devise new ways to outwit kangaroo rats and other seed-eaters that steal seeds planted, for example, by machine in costly range re-seeding operations. Ecology of Temperate Desert Rangelands Laboratory, / Reno, NV William S. Longland, (702) 784-6057,longland@scs.unr.edu

A single-cell parasite, Cryptosporidium parvum, has for the first time been found in oysters. An ARS researcher and colleagues with Johns Hopkins University and the National Oceanic and Atmospheric Administration found oocysts–encased eggs–of the protozoan parasite in oysters in six rivers feeding the Chesapeake Bay. Some of the oysters had as many as 4,000 oocysts, many times the human infective dose. The researchers demonstrated that oocysts could develop in mice. This indicates they pose a potential risk to humans who eat raw oysters, although there have been no known cases attributed to oysters. The oocysts don't survive temperatures above 164° F, so cooking shellfish will prevent potential infection. C. parvum protozoa are found in waterways worldwide. If swallowed, they can infect gastrointestinal cells, where they cause cramping and diarrhea and sometimes nausea and vomiting four to 10 days later. Because of the long incubation period, C. parvum is often not connected with these flu-like symptoms. Symptoms range from mild to severe in healthy people and can lead to chronic diarrhea, dehydration and death in people who have a weakened immune system. In 1993, more than 400,000 Milwaukee residents suffered C. parvum infections from contaminated drinking water. Smaller outbreaks have occurred around the country. Immunology and Disease Resistance Laboratory, Beltsville, MD Ronald Fayer, (301) 504-8750, rfayer@ggpl.arsusda.gov

Last Updated: April 29, 1998
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