Pr Pfr biological activity.
- Absorbs at a peak of 666 nm.
- It is the form synthesized in seedlings grown in the dark.
- When Pr absorbs red light, it is converted to the Pfr form.
- The Pfr form:
- Absorbs at a peak of 730 nm.
- The Pfr form is the active form that initiates biological responses.
- When Pfr absorbs far red light, it is converted to the Pr form.
- An intense elongation usually characterizes seedlings that are cultivated in the dark, as the internodes become extremely long. The shoots are yellowish since nearly no chlorophyll is produced. A plant development that is impaired by the absence of light is called etiolation.
Results
Table 1: The effect of light on Stem elongation in bean seedlings.
Data from Table 1 shows, when taking standard errors into account, epicotyl length is not significantly affected whether the seedlings were grown in the light or the dark. On the other hand, measurements of hypocotyl length differ greatly. This may be primarily due to internode and hypocotyl elongation in etoliated plants which are grown in the dark.
Table 2: The effect of light on Leaf Expansion in bean seedlings.
Analysis of data from Table 2 illustrates that the seedlings grown in light have more than 200% longer blade lengths on average compared to those grown in he dark, and almost 300% longer petioles.
Figure 1: A physical comparison of light grown and dark grown seedlings.
The two diagrams in Figure 1 illustrate the physical differences in light and dark grown seedlings. The seedling grown in the dark produced yellow leaves due to the inability to make chlorophyll without light. They are long and thin, as though they have been growing as fast as possible to seek out light. The plant grown in the light shows to be much greener, shorter and have a thicker stem in comparison to the dark grown one.
Discussion
Analysis of the above data and observation of the physical attributes of plants grown both in the dark and in the light illustrates that light does play a major role in the growth and development of plants.
Photosynthesis is a vital process in plants. They capture light energy and use it to form carbohydrates and oxygen from carbon dioxide and water. This is a light dependent reaction, which cannot proceed in the absence of light, therefore having repercussions on those plants that are to grow and develop in the dark.
Data from Table 1 illustrates that epicotyl length is not significantly affected whether the seedlings were grown in the light or the dark. On the other hand, measurements of hypocotyl length differ greatly. This may be primarily due to internode and hypocotyl elongation in etoliated plants which are grown in the dark.
Etoliation is the intense elongation that usually characterises seedlings that are cultivated in the dark, as the internodes become extremely long. The shoots are a yellow colour since nearly no chlorophyll is produced.
Table 2 suggests that light may play a vital role in the size and length of the blades and petioles of the seedlings. Larger petioles and blades were observed in the plants that were grown in the presence of light. This may be due to light playing a role in activating certain plant hormones responsible for cell elongation and division.
REFERENCES
PLANTS RESPOND TO THEIR ENVIRONMENT
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K.Mudie, J.Brotherton (1992) New Core Biology, Rigby Heinemann, Victoria. pp 84.
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Campbell (2000) Biology. pp 767-769
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Starr,Taggart (2001) Biology: The unity and Diversity of Life. Ninth Edition. Brooks/Cole, California. pp 552.
- http://www.urbanext.uiuc.edu/hortihints.htm
Plants and Light (1995).
- http://www.mobot.org/jwcross/duckweed/phytochrome.htm
Phytochrome (1999)
