Higher Biology Hormonal Control of Growth in Plants -part 2

2 Hormonal Control of Growth 2 By the end of this lesson you should be able to:  Know the name of a 2nd plant growth substance.  Know the effects of GA: o on cells oon stems oon dormancy oin inducing  -amylase in barley grains  Describe practical applications of plant growth substances.

3 Introduction  In the 1920s Japanese rice farmers noticed that some of their rice seedlings started to grow abnormally tall.  It was found that these plants were infected with a fungus which secreted substances.  They called these substances gibberellins.  It is now known that there are more than 70 different types of gibberellin- many of them occurring naturally in plants.

4 Gibberellic Acid (GA)  GA is the most important gibberellin.  GA (like IAA) promotes cell elongation, but only in the stems of plants.  Low concentrations of GA have this effect.  It does this by increasing the length of the internodes (not their number).  GA and internodes GA and internodes  An internode is a space between 2 sets of leaves on a stem.

5 Effect of GA on germination  internal structure of barley grain internal structure of barley grain 1. Copy this diagram and label:  Starchy endosperm  Embryo (young plant)  Aleurone layer  Cotyledon

6 Gibberellic Acid (GA) & Germination  Read pages , “Effect of GA on germinating barley grains” of Torrance, then answer the following questions: 1. What carbohydrate is found in the endosperm? 2. What carbohydrate is required for barley seeds to germinate? 3. What enzyme converts the carbohydrate in the endosperm into the carbohydrate needed for germination?

7 Gibberellic Acid (GA) & Germination Stages in GA action:  Water is absorbed by the seed.  The embryo produces GA which diffuses to the aleurone layer.  GA stimulates the aleurone layer to synthesise and secrete  -amylase into the endosperm.   -amylase breaks down the starch in the endosperm to maltose.  Maltose diffuses into the embryo and is used for respiration.

8 Summary Put the following stages into the correct order: GA is produced by the embryo GA stimulates the aleurone layer cells to synthesise  -amylase  amylase travels to the endosperm GA is transported to the aleurone layer  amylase breaks down starch to maltose GA is produced by the embryo GA is transported to the aleurone layer GA stimulates the aleurone layer cells to synthesise  -amylase  amylase travels to the endosperm  amylase breaks down starch to maltose

9 Gibberellic Acid (GA) & Germination  Insert and complete the “Germination” summary into your notes.

10 Bud Dormancy Read pages on “GA and Bud Dormancy” in Torrance, and then answer the following questions: 1. What is meant by “bud dormancy”? 2. What effect does GA have on dormant buds? 3. When would this effect normally happen?

11 Rooting Powder Read page 255 on “Rooting Powders” in Torrance, and then answer the following questions: 1. What is present in rooting powder? 2. What effect does this have on the roots?

12 Herbicides Read page 256 on “Herbicides” in Torrance, and then answer the following questions: 1. Explain how auxins are used to kill weeds. 2. Explain why auxins can be used as selective weedkillers on lawns.  Insert and complete the “IAA v GA” summary.

13 Practice Questions  Torrance 1. TYK page 259 Q1 and 2 2. AYK pages Q2,3 and 7 3. You will need graph paper for Q2 on page 260!

14 Hormonal Control of Growth 2 Can you do it?  Know the name of a 2nd plant growth substance.  Know the effects of GA: o on cells oon stems oon dormancy oin inducing  -amylase in barley grains  Describe practical applications of plant growth substances.