Development of Rice Seedlings under Salt Stress
Kevin Lehner Department of Biology, Duke University [email protected] Twitter: @krlehner
Introduction: Salinity of soils has a tremendous negative effect on crop productivity. Asian rice (Oryza sativa), a crop that contributes over 20% of the world’s calories, is highly sensitive to this stress. There are two aims/parts to this lesson activity. The first is to allow students to examine germination and early development in rice, a monocotyledon (monocot) plant. In the second part, students observe and quantify the effects of salt concentration on rice seedling growth.
Standards Addressed:
NC Essential Science Standards: 6.L.1.1 Summarize the basic structures and functions of flowering plants required for survival, reproduction, and defense. 6.L.2.3 Summarize how the abiotic factors (such as temperature, water, sunlight, and soil quality) of biomes (freshwater, marine, forest, grasslands, desert, Tundra) affect the ability of organisms to grow, survive and/or create their own food through photosynthesis. 8.L.4.2 Explain the relationship between genetic variation and an organism’s ability to adapt to its environment.
Common Core Math Standards: Summarize and describe distributions.
Next Generation Science Standards: Interactions, Energy, and Dynamics Relationships in Ecosystems
Appropriate Grade Levels: 6-8
Group Size: 2-4
Setting: Indoors
Time of Lesson: Three sessions, 30 minutes each
Resources Needed for Students (contact me and I can help to provide!): Small, clear plastic cups (around 9 ounce) Marker Quikrete play sand (50 lb bag) $4 at Lowes Miracle-Gro all-purpose plant food (granules, 1.5 lb box) $6 at Lowes De-ionized water Sodium Chloride (NaCl) Tweezers Rice seeds (Azucena and Bala, provided upon request) Grow light (optional)
Lesson Activity:
Background: See attached
Step-by-Step Instructions:
Period One (30 minutes): 1. Break students into groups of 4. Each group should receive two cups and four each of Azucena and Bala rice seeds.
2. Students should remove the outer husk of the seeds and place four Azucena and four Bala seeds in each cup (marked Azucena and Bala, respectively).
3. Have students describe the differences between Azucena and Bala seeds (shape, size). Note: Rice with the husk removed is called brown rice. White rice has been further processed.
4. Add de-ionized water to bottom of cups to cover seeds (around 1 inch)
5. Move cups to closed drawer (or box) and leave at room temperature for three days.
Period Two (30-40 minutes): 1. Remove germinated seeds from dark and put in light.
2. Prepare solutions for growth (No salt: Add 1/4 teaspoon of MiracleGro to 4 liters of de-ionized water) (Salt: Add ¼ teaspoon of MiracleGro AND 70.1 grams of NaCl to 4 liters of de-ionized water-this is 300 millimolar (mM) salt)
3. For each group, fill 4 cups half-way with play sand. Mark the cups as: Azucena-No Salt, Azucena-Salt, Bala-No Salt, Bala-Salt
4. Have students look at the germinated seeds. Can they tell which part is the root and which is the shoot? How do they know? Are there any differences between Azucena and Bala at this stage? 5. Add No Salt and Salt solutions to the sand-filled cups until the liquid just covers the sand. Transplant seedlings (with tweezers) to appropriate cups so that root is buried and seed is just covered. Add more growth solution if necessary.
6. Put seedlings in brightly lit window. Add supplemental light during school hours if possible.
7. Let plants grow for 2-3 weeks, adding additional growth solution as needed.
8. Ask students about predictions for growth. Ask about how a plant (or other organism – humans!) would deal with increase salt concentration.
Period Three (Optional Data Analysis, 30-40 minutes): 1. Carefully remove plants and measure the length of the shoot and root system. If there is time, count the number of roots for each plant.
2. Graph these data for the entire class on the board. Was there any effect of the increased salt concentration on any of the traits that were measured? If so, was there a different effect on Azucena vs. Bala (I don’t know the answer to this…)? If there was no effect, ask why. Was the salt concentration too low? Are both of these varieties especially tolerant of high salt?
3. Wrap up with ideas more experiments. More concentrations? Different varieties? More??? Background: Development of Rice Seedlings under Salt Stress
Asian rice (Oryza sativa) is a widely consumed crop plant, contributing over 20% of the calories consumed on the planet. With this in mind, it is critically important to understand the effect that different kinds of environmental stress has on the development of rice. Anatomy: Rice, like other cereals such as corn and wheat, is a monocotyledon (monocot) plant. Some characteristics of monocots are shown below in a comparison with dicotyledon (dicot) plants (such as beans, tomatoes, and most ornamental flowers).
In germinating rice plants, the coleoptile and radicle emerge first. The coleoptile is a transparent sheath that protects the first leaf. The radicle is the first root to appear. Both of these structures are present in the embryo. Plant Varieties: This lesson uses two different varieties of rice, Azucena and Bala. These come from the two major subspecies of rice, japonica and indica. Japonica and indica rice are thought to have been domesticated nearly 10,000 years ago. Azucena is a japonica variety from the Philippines. Bala is an indica variety from eastern India. Salt Stress: Across the globe, land available for crop cultivation is lost due to increased soil salinity. Causes of soil salinity are natural (weathering of minerals) and human- accelerated (runoff, irrigation, or seawater encroachment). High soil salinity can affect all aspects of plant growth. With this in mind, there is a need to breed crop varieties that are resistant to salt stress. Mechanisms by which plants cope with increased salt concentrations are shown below. Hide (in cell)
Pump out
Hide (in plant)
Block
www.irri.org
For more information, see: www.knowledgebank.irri.org/ricebreedingcourse/Breeding_for_salt_tolerance.htm An Example: In 2011, a devastating earthquake and tsunami hit the northeastern coast of Japan. In addition to the tremendous loss of life, and the nuclear crisis that ensued, many thousands of acres of rice-growing land were flooded with salt water. While much of this land has been largely desalinated, effects of increased salt concentration in the soil on crop productivity remain. In response, plant breeders have attempted to develop new salt-tolerant varieties. For more information: www.nytimes.com/2012/04/23/business/global/rice-farmers-seek-to-save-their- crops-from-salt.html Teacher Evaluation of Lesson Plan
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Please return this form to: Kevin Lehner, Duke University Department of Biology, Box 90338, Durham, NC 27708 or email it to [email protected]