The Effect of Red Light on the Germination of Lettuce Plants

The Effect of Red Light on the Germination of Lettuce Plants

Abstract

This report describes the findings of an experiment to determine the effect of red light on the germination of lettuce plants. Two hundred seeds were planted, divided between two lettuce varieties; Concept and Waldo. Equal groups of seeds were exposed to four different types of light, which included White light, Red light, Far Red light, and Dark Room (no light). After 24 hours, the seed were observed to determine whether 15 minutes of exposure to red light had a differential effect on seed germination. The findings and relevant discussion are presented.

Introduction

In plants, light produces energy for photosynthesis and provides signals of information that encourage growth and development. One of the numerous benefits sunlight provides is the production of phytochromes, which are imperative to the health and well being of the plant. The phytochrome system works in the apical meristem, which is similar to stem cells used for tissue growth (Campbell, 2009). Phytochrome is the pigment that controls the flowering and growth of many plants. The one-two effect of protein and chromophore make up the parts of the phytochrome, which in turn affects the seed's germination. The chromophore is responsible for the way the seed responds to light for germination to occur. The reaction between different light forms, such as Pr and Pfr, and the length of time that seeds are exposed - and even not exposed - affect seed germination (Kinney, 2003).

The photoreceptor is a phytochrome molecule that is used for the process of red light responses. In the dark grown seedling, the light source form Pr is synthesized making germination possible (Phytochrome Light Regulates Plant Growth and Development, 2006). The Pr absorbs red light which is then converted to the Pfr form. The Pfr form will then instigate a reaction in an active form. To complete the cycle, when the Pfr form absorbs far red light, it is converted back to the Pr form, which is the inactive state. Pfr is required for germination. The responses initiated by the phytochrome system include not only the flowering process but also chloroplast development along with leaf senescence and leaf abscission (Phytochrome Light Regulates Plant Growth and Development, 2006)

The different light sources - red, far red, white and even no light - affects how the seed will react. Nonetheless, it should be noted that white light provides effects of red light and will alter reactions with seed germination (Campbell, 2009). It should also be mentioned that the dark can reverse red light effects and can copy far red light. With this occurrence, a reverse red light reaction can occur (Campbell, 2009).

The purpose of this experiment is to determine the effects of exposure to red light on the germination of lettuce seeds. Therefore, it was hypothesized that if lettuce seeds are exposed to red light for 15 minutes that germination will occur within the first 24 hours after exposure.

Materials and Methods

To answer the research question, an experiment was conducted using 100 Waldo lettuce seeds and 100 Concept lettuce seeds. The seed varieties differ from each other, but the examiner did not know the properties of the seeds. The seeds were planted under similar conditions and were then exposed to four different light treatments; White light, Red light, Far Red light, and Dark Room (no light). After 24 hours, the seedlings were observed to determine which seeds germinated and which did not.

Materials

The materials used to conduct the experiment include the following:

8 Petri Dishes

8 Filter paper discs (cut to size of Petri dish)

8 Sheets of Aluminum foil to cover Petri dish

1 Large dropper

Water to cover seeds in each Petri dish

100 Concept lettuce seeds

100 Waldo lettuce seeds

Red (Pr) light device

Far Red (Prf) device

White light device

Procedures

Seed preparation. To begin the experiment, 8 Petri dishes were lined with filter paper discs. With room lights out, 25 seeds of either Concept or Waldo lettuce seeds were placed in the dishes. One dropper of water was added to each Petri dish and each dish was covered with aluminum foil. Dishes were marked with seed names, date, time, and one of four light sources.

Light treatment. Before covering the dishes, six of the seed dishes were exposed to the different light treatments for a period of 15 minutes. The interval of 15