Plant Growth Regulators Why is the use of plant growth regulators important? Key Questions What are two groups of plant growth regulating compounds? What is the difference between synthetic growth regulators and plant hormones? How do plant hormones control apical dominance? What are the benefits of using plant growth regulators? What are the different types of rooting compounds? How do you use plant growth regulators control the size of flowering plants? What is the impact of growth regulators on turf maintenance companies? When should growth regulators be applied? What are gibberellins and anti-gibberellins? What are the two groups of plant growth regulating compounds? Natural vs. Synthetic Natural- found naturally in plants Synthetic- human made Both groups regulate or influence: Cell division Cell differentiation Root and shoot growth Senescence (plant aging) Promoters vs. Inhibitors Promoters- cause faster growth Inhibitors- reduce growth What is the difference between synthetic growth regulators and plant hormones? Hormones plant produced natural compounds that inhibit or promote plant growth Major classes of plant growth regulators (hormones) are: 1. Auxins 2. Gibberellins 3. Cytokinins 4. Abscisic acid 5. Ethylene Auxins Growth promoting chemicals Promote cell division and cell elongation Primary plant auxin is indoleacetic acid (IAA) Common synthetic forms of auxins are indolebutyric acid (IBA) and naphthaleneacetic acid (NAA) Useful in phototropism, geotropism, apical dominance, and root formation Phototropism- plant growth toward a light source Geotropism- plant growth in response to gravitational forces Apical dominance- terminal buds prevent the development of lateral buds on plant stem Gibberellins Also known as Gibberellic acid or GA Growth promoting chemicals Stimulate stem growth through cell elongation and cell division Commercial supplies obtained from the fungus Gibberella fujikuroi Cytokinins Promote cell division and delay leaf aging Used as a growth promoter in tissue culture Slows the process of senescence (biological aging) by preventing the breakdown of chlorophyll in leaves Abscisic acid (ABA) Only natural plant growth inhibitor Growth inhibitor that closes the stomates of plants under water stress Counteracts the effects of auxins and gibberellins Cycocel and B-Nine are two synthetic ABA type growth inhibitors commonly used Ethylene Gas that forms in tissue undergoing stress Important in the fruit-ripening process and early petal drop of flowers How do plant hormones control apical dominance? Apical dominance Controlled by auxins where the terminal bud inhibits the development of lower lateral buds In greenhouses, we pinch the terminal bud out of a plant so that the plant branches out and becomes bushy Phototropism Controlled by auxins, which is a plant’s response to grow toward light Geotropism Plant growth response to gravity What are the benefits of using plant growth regulators? Benefits Promote and accelerate root formation on cuttings Keep fruit on trees longer to allow further ripening achieved by the application of auxin Thin blossom clusters and increase berry size in grapes- achieved by the application of gibberellic acid Increase size and crispness of stalks of celery- achieved by the application of GA Control the size of plants What are the different types of rooting compounds? Rooting compounds Indoleacetic acid (IAA)- naturally occurring auxin that produces bushy, stunted root systems Indolebutyric acid (IBA)- synthetic form of auxin that produces strong, fibrous root systems Napthaleneacetic acid (NAA)- synthetic form of auxin similar to IBA How do you use plant growth regulators control the size of flowering plants? Leggy Condition when greenhouse plants grow too tall to make desirable flowering potted plants Growth regulators used in producing flowering plants 1. Arest 2. B-nine 3. Cycocel 4. Florel 5. Phosfon 6. IBA and NAA Increase the number of flower buds formed Improve the number of flower buds formed Improve the longevity and quality of cut flowers Control vegetative growth and reduce mowing frequency in turfgrass Reduce or eliminate unwanted sprouts and suckers Reduce pollen, for people with allergies, by eliminating flowers on some trees, which also can control unsightliness and odor caused by falling fruit Control the growth of shrubs and hedges What is the impact of growth regulators on turf maintenance companies? Growth regulators used on turf: 1. Cutless 2. TGR 3. Primo 4. Maintain CF 125 5. De-Cut 6. Retard 7. Slo-Gro 8. Posan Regulators reduce amount of mowing needed Reduces number of mowings per year Reduces labor and machinery costs Growth regulators beneficial to: 1. Lawn care operators 2. Cemetery managers 3. Golf course superintendents When should growth regulators be applied? Timing of application can affect how various regulators do their job & their affect on non-targeted plants Ex. Embark should be applied after spring “green-up but before seedhead emergence Some chemical may be washed away if applied before a rain or watering Be sure to read the label to find out when to apply!!! If a crop is edible, how would application affect harvest date? What are gibberellins and anti-gibberellins? Gibberellins- promote plant growth Anti-gibberellins- counteract the effect of naturally occurring gibberellins Can reduce the rate of growth in shade trees Used be utility companies to control trees that may grow into utility lines How else could anti-gibberellins be used?