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Nickel: plants gotta have it.

The Agricultural Research Service (ARS) this month designated nickel an essential micronutrient for all higher plants. This is the first time in 38 years that an element has won such a distinction.

Until recently, physiologists had few clues to the metal's vital role, says plant nutritionist Ross M. Welch. Indeed, his team at the ARS Plant, Soil and Nutrition Laboratory in Ithaca, N.Y., found that viable seeds carry enough nickel to sustain a plant throughout life. Establishing nickel's function therefore required studying second- and third-generation progeny of plant fed no nickel.

What caused anyone to look? Australian researchers had shown that the enzyme urease requires nickel in order to function. Present in most plants, urease breaks down urea, liberating the nitrogen present in this end product of protein decomposition. Welch's group decided to investigate whether plants fed nitrogen sources other than urea still need urease.

In 1983, the Ithaca researchers showed that legumes do need urease; four years later, they found that cereal grains do too. The cereal finding was somewhat surprising, Welch says, because plant physiologist had never seen urea -- or active urease -- in grains. The reason, it now turns out, is that their urease worked so quickly that urea never had a chance to accumulate.

The ARS team has since demonstrated nickel's vital role in other plants and has identified functions beyond the liberation of nitrogen. For instance, says Welch, "we showed that nickel is required for iron absorption in plants."

In order to germinate, seeds need nickel concentrations of somewhere between 10 and 100 parts per billion, Welch says. Plants grown without additional nickel will gradually dilute this initial store to a level that becomes critical at about the time they mature and begin reproductive growth, the ARS scientists find.
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Author:Raloff, Janet
Publication:Science News
Article Type:Brief Article
Date:Apr 25, 1992
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