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Meristematic Region

Author: Janice VanCleave

Growth Zone

Dicots, the popular name for dicotyledons, are one of the two large groups of flowering plants. In dicots the seeds have two cotyledons, which is the leaflike part of the seed containing nutrition for the seed to develop and grow. All types of plants contain areas of rapidly growing tissue, called meristem. The meristem is responsible for growth, both in the length and the width of plant stems.

In this project, you will discover the location of the meristematic region in dicot plant stems responsible for the elongation of the stems. You will discover if there is a change in meristematic growth rate during different times of the day and among different plants. You will determine any effect of light duration on meristematic growth. You will also research how the primary and secondary growth of a plant affects its size.

Getting Started

Purpose: To determine where growth occurs in the stem of a pinto bean plant.

Materials

  • three 9-ounce (270-ml)
  • paper cups
  • potting soil
  • ruler
  • pencil
  • 12 dry pinto beans
  • tap water
  • marking pen

Procedure

  1. Fill each cup with potting soil to within 2 inches (5 cm) from the top.
  2. Use the pencil to punch six or more holes near the bottom of each cup.
  3. Lay four beans on the surface of the soil of each cup.
  4. Cover the beans with about 1 inch (2.5 cm) of soil.
  5. Moisten the soil with water. Keep the soil moist but not wet throughout the experiment.
  6. Allow the seeds to germinate and the seedlings to grow to a height of about 6 inches (15 cm) above the top of each cup. Note: This will take seven or more days.
  7. Select 4 or more of the most healthy looking seedlings.
  8. Use the marking pen to draw a line across the stem of each selected plant level with the lip of the cup. Use this mark as the starting line.
  9. Mark three equal sections on each stem between the cotyledons (the two remaining parts of the seed) and the starting line (see Figure 13.1).
  10. Growth Zone

  11. Mark three equal sections on each stem between the cotyledons and the true leaves at the top of the stem.
  12. Prepare drawings of each plant, numbering each section from 1 to 6, starting at the top of each stem as in Figure 13.1.
  13. Measure and record the starting length of each section in a Stem Growth Data table, such as the one in Table 13.1.
  14. Set the plants near a window with indirect sunlight. Add equal amounts of water to each cup to keep the soil moist but not wet. After seven days, again measure and record the length of each section. Determine any change in the length of each section.

Results

The author's plants showed the greatest elongation in the sections marked 1, only slight changes in the sections marked 2, and no measurable changes in the lower sections marked 3 through 6.

Why?

New plant cells are formed at growing points of actively dividing cells. These growing points are called meristems. The specialized clusters of cells in the meristem produce growth by mitosis. In mitosis, the cell parts duplicate themselves and then divide into two separate cells. With each division at least one of the new cells, called daughter cells, remains meristematic, thus preserving the meristem. The second daughter cell may be meristematic for a time, but eventually forms a specialized cell.

A bean plant is a dicotyledon (dicot), which is one of two groups of flowering plants, characterized by having seeds with two cotyledons. In a dicot, the cotyledons are the two parts of the seed, also called seed leaves, that contain stored nutrients (nourishing materials needed for life and growth of organisms—living things) required for the seed to grow and develop. The stems (part of a plant that supports other plant parts, including leaves, flowers, and fruit) of the bean plants in this experiment have meristems located at the apex (tip) of their stem, which are called apical meristems. Division of apical meristem cells increases the length of the stem, at the top of the stem.

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