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IF MORE ultraviolet radiation reaches the surface of the Earth as a
result of the ozone layer getting thinner, it will damage one of the proteins
involved in photosynthesis. Autar Mattoo, a scientist at the US Department
of Agriculture, says that excessive ultraviolet light ‘could have an impact
on plant efficiency that could eventually affect crop yields worldwide’.

The plant protein at risk, known as 32kDA, is one of four proteins involved
in a stage of photosynthesis in plants, known as ‘photo system 2’. Under
normal light, says Mattoo, plants make the protein continually. They then
destroy it during the chemical reactions of photosynthesis.

Mattoo and his colleague, Marvin Edelman of the Weizmann Institute in
Israel, studied 32kDA in duckweed, an aquatic plant. They chose duckweed
because they could raise it in pure water. This meant that the plant was
not affected by minerals in the soil.

Mattoo and Edelman exposed the plant to light at wavelengths ranging
from 280 to 730 nanometres. Visible light spans the range from 450 to 650
nanometres. ‘We found that the protein was degraded at all the wavelengths
we tested,’ says Mattoo, ‘but degradation was highest in the ultraviolet
range, at about 300 nanometres.’

Mattoo and Edelman found that plants exposed to the ultraviolet light
for several hours could not make enough 32kDA to replace the protein that
was destroyed. Asa result, their growth was slowed down. Mattoo says that
if their ‘model’ plant had been a food crop, it would have lost some of
its nutritional value.

Mattoo intends to continue the study of 32kDA in the hope of understanding
the basic mechanisms by which it is created and destroyed. At the same time,
he will study the response of soya beans to ultraviolet stress. ‘Some cultivated
strains of soya beans are resistant to ultraviolet radiation,’ he says.
‘Do they prevent degradation of their protein, or do they compensate by
producing more? No one knows.’

Mattoo believes that if scientists can understand precisely the chemistry
of photo system 2, they might be able to transfer ultraviolet resistance
to sensitive crops.