1. Internal Factors Affecting Plant Growth
Plant Growth Regulators

2. Plant Hormones Stimulate or inhibit growth
Produced in growing tissue (meristems)
Regulated by environmental conditions

3. Plant Hormones AUXINS primarily promote cell elongation
stimulate apical bud growth, inhibit lateral bud growth
Stimulate ripening of fruit
present in very low quantities, but exert a strong influence
synthetic auxins have many uses, including fruit ripening and herbicides

4. Plant Hormones GIBBERELLINS
promote cell division and elongation in shoots
in some plants, they cause stems to elongate just before plant flowers (raises flower toward pollinators and wind)
dwarf varieties of some plants have a gene mutation which blocks synthesis of gibberellins
Commercially, used to stimulate seed germination

5. Plant Hormones GIBBERELLINS
promote cell division and elongation in shoots
dwarf varieties of some plants have a gene mutation which blocks synthesis of gibberellins
Fig. 4: Arabidopsis mutant with & without gibberellin.

6. Plant Hormones CYTOKININS
stimulate cell division and leaf mesophyll growth
mostly in endosperm tissue and young fruit
commercially, used in the expanding field of biotechnology and in new tissue cultures, which allows the production of many new (genetically altered) plants

7. Plant Hormones CYTOKININS Delays leaf senescence (color change)
Effect of cytokinin application on leaf senescence.

8. Plant Hormones ETHYLENE significant role in fruit ripening
many fruits begin to produce ethylene gas just before fruit ripening
related to both colour change and softening of tissue of ripening fruit
ethylene can be applied externally when they want fruit to ripen

9. Plant Hormones ETHYLENE significant role in fruit ripening
many fruits begin to produce ethylene gas just before fruit ripening

10. Plant Hormones ABSCISIC ACID
important in promoting closure of stomata,
provides resistance to water stress