In the course of long-term studies the workers of our institute have found some phenomena, which make it possible to compare the growth response of different maize genotypes to temperature. We would like to propose demonstration experiments to assess the temperature response of elongating cells of different genotypes in teaching upper grade students.
Maize seedlings grown in cuvettes on filter paper soaked with tap water are taken for comparison. The cuvette should be lightproof and tightly closed from above with a plastic lightproof cap.
The procedure of growing initial seedlings starts by placing presoaked seeds on filter paper dampened by tap water. The cuvette containing these seeds is kept at room temperature for germination to start. In two days the seedling roots are marked with India ink at two points at a distance of 2 and 4 cm from the root tip. No less than 30 seedlings should be used in each treatment. It is the root segment between these two marks that contain elongating cells. The seedlings are divided into two groups, placed into two cuvettes on filter paper dampened with tap water and covered with caps. The first cuvette is kept at room temperature and the other one is put into a household refrigerator (+8 - +10 C). The distance between the two marked points is measured at regular intervals. The seedlings growing at room temperature are measured every hour for 6-8 hours until ceasing growth of the marked region. The seedlings growing in the refrigerator should be measured every 12-24 hour for 2-4 days also until ceasing growth of the marked region. These measurements, the number of which should be not less than three, are easy to perform with construction paper. The average growth rate expressed in mm/hr is calculated for all seedlings in each treatment using the distance between the marks.
Thus, by determining growth rates of the marked region in these two treatments one can compare the root growth response to the effect of low temperature. The correlation between growth rate and temperature can then be compared in different varieties of maize. We have observed a genotype dependent 6-12-fold difference in reduction of rootgrowth rate response. A similar experiment can also be used to demonstrate genotype responses to the effect of other environmental factors (high temperature, salt and drought resistance, etc.).
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