Temperature Effects on Radish (Raphanus sativus) Root Development
Several studies have been conducted to establish how temperature, seed germination, and root growth are related. Because temperature plays a main role in many growth processes, we decided to focus on how it affected root growth. Radish (Raphanus sativus) seeds were chosen due to their ability to produce a distinct bulbous tuber, and their relatively short growing time. Three test groups were placed under different temperature conditions. There was one “control” group, one “hot” group, and one “cold” group. All test groups were placed in metal trays and set on a cycle of 12 hours of light exposure and12 hours of dark exposure. Each group was monitored and given the appropriate amount of water to maintain moist soil. The radishes were removed from their soil and root lengths were measured. We then ran a two-tailed t-test to determine if there was a significant difference between groups. We found that there was no difference between hot and control groups, but that a significant difference did exist between the cold and hot/control groups. This is most likely because the radishes used are grown in the summer and are not accustomed to the colder temperatures.
The relationship between temperature, seed germination, and root growth has been established through studies dating back to the 1800’s. Almost all studies have been conducted with a constant temperature for 24 hours a day (Reddick 1917). A 12 hour cycle was chosen to reinforce the strong diurnal rhythms that are shown in most dicots (Yazdanbakhsh and Fisahn 2011). The majority of plant root growth occurs during dark periods and exposure to different temperatures during this period has been shown to produce the greatest response (Yazdanbakhsh and Fisahn 2011). Percentage of water within a seed greatly affects seed germination (Waggoner 1971). As percentage of water increases seed germination time also increases. While radish seeds with a water content of four percent germinate within two days, a seed that contained eighteen percent water will not germinate after seven days (Waggoner 1971). Waggoner (1971) also proved that seeds are heat resistant if internal water content is approximately one percent. Water content of soil also influences seed germination. Seeds exposed to high temperatures had greater survival when kept in moist soil (Elegy 1990). Most plants have an optimum temperature that will elicit the fastest germination time. For citrus seeds, this optimum germination temperature existed between 31-35°C (Camps et al 1932). Temperatures outside this optimum may retard seed germination. Seedling germination from natural weed species was reduced by 90 percent when the maximum soil temperature reached 61°C (Melander 2005). In another study it was determined that seed germination did not occur below 20°C or above 40°C (Egley 1990). The relationship between extreme temperatures and seed germination was also confirmed in an experiment on cabbage plants (Fusarium conglutinans) by Reddick (1917). Seeds that were kept at extreme temperatures did not germinate. Extreme temperatures have been shown to have a greater effect on initiating germination compared to later developmental processes (Dell’Aquila 2005).
Our experiment was conducted at Tennessee Technological University Cookeville in a biology lab room. The room was kept at a constant temperature of 21°C. Study organisms were radish (Raphanus sativus) seeds. Seeds were grown indoors near a west facing window in plastic starter pots. Pots were placed into metal trays for the duration of the study. Growth time for the radish seeds was five weeks. A fluorescent light provided artificial sunlight for this study. To ensure seed germination, extreme temperatures were avoided and seeds were moistened with 20 ml of lukewarm water every night before temperature treatment. We used seeds with equal water contents and...
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