Plant Growth Regulators – Genetic Factors

Plant Growth Regulators

Introduction

Plants require light, water, oxygen, minerals and other nutrients for their growth and development. Plants also depend on certain organic compounds to signal, regulate and control the growth of plants. These are called Plant Growth Regulators or Plant Growth Hormones. 

Explanation

Characteristics of Plant Growth Regulators 

Plants growth hormones or plant growth regulators exhibit the following characteristics: 

• Differentiation and elongation of cells. 
• Formation of leaves, flowers, and stems. 
• Wilting of leaves. 
• Ripening of fruit. 
• Seed dormancy, etc. 

Types of Plant Growth Regulators 

Plant growth hormones or regulators are of the following types: 

• Plant Growth Promoters 
• Plant Growth Inhibitors 

Auxins 

Auxins cause elongation in cells. They are present at the tip of shoots. When exposed to light, auxins move down the stem and causes it to elongate.  

Functions of Auxins 

1. Facilitate flowering in plants. 

2. Involved in the initiation of roots in stem cuttings. 

3. Prevention of dropping of leaves and fruits at early stages. 

4. Regulate xylem differentiation and assists in cell division. 

5. Auxins are widely used as herbicides to kill dicot weeds. 

6. Used to produce fruit without preceding fertilization. 

Gibberellins 

Gibberellins, just like auxins, promote cell division and elongation in plant shoots. They can cause elongation in stem right before flowering (called bolting) which can help the flower raise up to pollinators. It is used commercially to stimulate seed germination and control fruit development. 

Functions of Gibberellins  

• Delay senescence in fruits 
• Involved in leaf expansion 
• Break bud and seed dormancy 
• Promote bolting in cabbages and beet 

• Facilitate elongation of fruits such as apples and enhance their shape 

Cytokinins 

Cytokinins stimulate cell division and mesophyll growth. They are mostly concentrated in endosperm tissue and young fruit. Cytokinins are used in tissue cultures to allow the production of many new plants genetically identical. 

Functions of Cytokinins 

• Breaks bud and seed dormancy 

• Promotes the growth of the lateral bud 
• Promotes cell division and apical dominance 
• They are used to keep flowers fresh for a longer time 
• Used in tissue culture to induce cell division in mature tissue 

Plant Growth Inhibitors 

Abscisc acid – This growth inhibitor is synthesized within the stem, leaves, fruits, and seeds of the plants. 

Ethylene – Has a significant role in fruit ripening. Affects the color, texture and sugar content of fruits. Ethylene can be applied externally to cause rapid ripening of fruits.