Tropisms

Tropisms, first published by two Japanese scientists in 1992, are a directed growth response due to outside stimulus. Phototropism (directed growth in response to light) and gravitropism (directed growth in response to gravity) were the basis of the lecture. John Z. Kiss, from Miami University, studies these behaviors in Arabidopsis.
There are difference response to light and gravity due to the different parts of the plant. Stems grow towards the light (positive phototropism) and away from gravity (negative gravitropism). Roots grow away from the light (negative phototropism) and toward gravity (positive gravitropism).
There were also differences in the direction in which the plants grew in response to different colored lights. In blue light, the plants grow like they would in white light. However, in red light, the plants grew in the opposite direction than expected: the roots grew towards the light and the stems grow at random.
This interesting phenomenon caught Dr. Kiss’s eyes, that he has been studying the phytochrome, a pigment in plants that are light sensitive and controls the germination of flowers and seeds (MSN Encarta 2005). His many experiments with the phytochrome has also led him deeper into the wonders of tropism, that his latest experiment is going to be done up in space! This experiment is based on gravitropism along with phototropism. He is experimenting the effects of microgravity and light to answer the fundamentals of plant biology.

For more information, visit his site:
http://www.cas.muohio.edu/botany/bot/jzk.html

Reference:
MSN Encarta 2005 http://encarta.msn.com/encnet/features/dictionary/DictionaryResults.aspx?refid=1861725945

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