Plant Growth

Plant GrowthHormone Function andTropismsWhether they are involved in primary or secondary growth, all plant cells and tissues arise from three primary meristems*: protoderm ground meristem procambiumPrimary Meristems*Meristem: plant tissue that remains embryonic as long as the plant lives, allowing for indeterminate growth Specialized Tissues in PlantsPlant GrowthMeristems tissues responsible for growth Undifferentiated cellsApical MeristemProduce growth increased lengthDifferentiationCells will assume roles in the plantFlower DevelopmentStarts in the meristem

3Growth Hormones (Regulation)Plants produce chemical substances called hormones that inhibit or promote growth.Common plant hormones are.InhibitorsCytokininsGibberellinsAuxinsCytokinins

Hormones that work with auxins to stimulate cell division.GibberellinsHormones that stimulate cell elongation, premature flowering, and breaking of dormancy.

Auxins

Hormones that speed plant growth by stimulating cell enlargement.

TropismsA tropism is a growth response involving bending or curving of a plant part toward or away from an external stimulus that determines the direction of movementResponse toward the stimulus is positive, and response away from the stimulus is negative9PhototropismPhototropism is the growth of stems of plants toward light - it is probably the best known of the plant tropisms - phototropism is caused by elongation of the cells on the shaded part of the plant - so that entire plant bends or curves toward the lightThis growth pattern is caused by the hormone auxin - auxin migrates to the shaded part of the plant and stimulates increased cell growth and elongation on the shaded part of the plant 10

11GravitropismGravitropism is a response to gravity - if a seedling is placed on its side, the root will curve to grow downward and the shoot will curve to grow upwardAuxin may play a role in the response of shoots12

Gravitropism in plants13Thigmotropism Thigmotropism is response to touch or contact with a solid object - this is most commonly seen in tendrils, modified leaves or stems depending on the species. the tendrils wrap around any object they come in contact with and so enable the plant to cling and climb. 14

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