Development of Teaching Material Using Dwarf Sunflower plants for Understanding the Effect of Gibberellin on Stem Elongation

Abstract

Seedlings of the dwarf sunflower ‘konatsu’ were approximately 20% as tall as the tall ‘kagayaki’ type 12 days after seeding. However, when gibberellic acid (GA) (1.0×10^–4 M GA₃) was applied 5 days after seeding, the dwarf sunflower seedlings became elongated, up to twice as tall as the control plants. The dwarf sunflower seedlings treated with GA elongated at the rate of 7.6 mm/day, while the elongation rate of the tall ones was 8.0 mm/day. That is, the dwarf sunflower seedlings could recover their height through the GA treatment. Based on these results, we developed a lesson in which students sprayed a dose of gibberellic acid solution on sunflower seedlings and measured the elongation of the seedlings for one week. The students plotted a graph of the seedling elongation and compared the heights of the tall sunflower seedlings with those of the dwarf ones, and also compared the height of the GA treated seedlings with those of the untreated ones with the aid of a worksheet. To clearly evaluate our lesson, the achievement tests of students’ understanding of the plant hormone GA and the plant’s morphology were carried out before and after the lesson. They revealed that the students’ correct answers on the relationship between gibberellin and height of the seedlings increased from 57% to 86%. Furthermore, approximately 95% of the students stated that their interest in the mechanism of the plant growth was aroused. Asking them about the comprehensive approach to the resolution of the relationship between plant growth and GA, some students proposed a quantificational experiment using endogenous GA contents and other students offered a comparison of the participant plants’ genes. These replies suggested that they came to consider the difference in the GA contents as well as variations in genes among the sunflower varieties.