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Understanding aluminum toxicity in plants.

Leon Kochian spends his days looking a gift horse in the mouth.

For years, farmers have struggled with acid soils in which overabundance of soluble aluminum has spelled death to crops. And when a particular type of maize or sorghum or wheat seemed able to tolerate the excess aluminum, the farmers gratefully accepted that crop as a gift of nature and didn't ask a lot of seemingly unanswerable questions.

Kochian, a plant physiologist at the U.S. Plant, Soil, and Nutrition Laboratory at Ithaca, New York, on the other hand, has enough questions to make up for everyone else. He wants to know why certain plants can put up with aluminum toxicity and to find out what's happening to the ones that can't. The answers will be important to a lot of people.

"Up to 70 percent of the world's potentially arable soils are acidic, including regions in the eastern United States and large areas in Asia, Africa, and South America," says Kochian. Aluminum toxicity is the primary problem limiting agricultural production in these acid soils."

That's because aluminum is one of the most prevalent minerals in the Earth's crust. High acidity in soil can render that aluminum soluble - forming with water a potion that is deadly to growing plants.

While lime can be added to soil to neutralize some of the troublemaking acid, that's a luxury" many Third World farmers can neither obtain nor afford. Even when lime is a feasible expenditure, it's hard to place deep in the soil. So excess aluminum might still lurk below the limed zone, down where thirsty roots wander in the summer.

It's those groping roots that engross Kochian and his coworkers these days. Their studies have revealed the root tip is the plant's Achilles' heel when it comes to aluminum.

"In experiments, we exposed the entire root system - except the tip - to a solution containing a toxic level of aluminum, and the roots grew just fine," Kochian recalls. "But when we exposed just the root tip to the same solution, growth was inhibited in about 2 hours."

In comparisons of aluminumtolerant and nontolerant plants, uptake into the root tip of elements such as potassium and chlorine was not hindered in either group of plants when aluminum levels were high. But calcium uptake was a different story.

"We found aluminum inhibits calcium uptake almost immediately in aluminum-sensitive plants," Kochian notes. "But we saw a much smaller effect on calcium uptake in aluminumtolerant plants."

Calcium is an essential plant nutrient and plays an important role in regulating many diverse cell functions, Kochian adds.

"Our goal is to develop more aluminum-tolerant crop plants," he concludes. "As we leam what's happening in aluminum toxicity and find out what's different in the tolerant plants, we can better look for ways to develop or transfer that tolerance to other plants."
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Title Annotation:research of acid soils
Author:Hays, Sandy Miller
Publication:Agricultural Research
Date:Nov 1, 1992
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