36

key concepts

36.1

Plants Develop in Response to the Environment

36.2

Gibberellins and Auxin Have Diverse Effects but a Similar Mechanism of Action

36.3

Other Plant Hormones Have Diverse Effects

36.4

Photoreceptors Initiate Developmental Responses to Light

A Nobel Prize for a Plant Biologist

In their constant search for ways to help farmers produce more food for a growing population, biologists have developed cereal crops whose physiology allows them to produce more grain per plant (resulting in higher yields). The drawback of this approach is that the sheer weight of the load of seeds may cause the stem to bend over. The problem is made worse when fertilizer added to the soil stimulates plants to grow taller. Harvesting seeds on the ground is very difficult; think of how hard it would be to pick up seeds one by one, when some have already sprouted.

In 1945 the U.S. Army temporarily occupied Japan, which was defeated in World War II. During the war, Japan, an island nation with a limited amount of land suitable for farming, was blockaded and could not import food or other supplies. Food was rationed and many people were hungry, but there were no major famines in Japan during that period. How were the Japanese able to produce enough grain to feed their population? The answer to this question lay in the fields: the Japanese had bred genetic strains of rice and wheat with short, strong stems, growing in thickness rather than height, that could bear high yields of grain without bending over. An agricultural advisor to the occupying American army sent samples of the grains to the United States.

A decade later, the American plant geneticist Norman Borlaug, who was working in Mexico at the time, began making genetic crosses between the Japanese wheat and other varieties that had genes conferring rapid growth, adaptability to varying climates, and resistance to fungal diseases. The results were “semi-dwarf” wheat varieties that gave record yields. The varieties were grown first in Mexico, and later in India and Pakistan during the 1960s. At about the same time and using a similar strategy, scientists in the Philippines developed semi-dwarf rice with equally spectacular results. People who had lived on the edge of starvation now produced enough food. Countries that had relied on food from other countries were now able to grow more than enough grain, and export the surplus. The development of these semi-dwarf grains began what was called the “Green Revolution.” Borlaug was awarded the Nobel Peace Prize for his research on wheat, which is estimated to have saved a billion lives.

How is plant growth controlled, and what changes in growth patterns made the new strains of wheat and rice successful?