Responses in Flowering Plants Tropisms and Growth Regulators

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Responses in Flowering Plants Tropisms and Growth Regulators

Responses in Flowering Plants Tropisms and Growth Regulators

Factors affecting plant growth External ◦ ◦ ◦ ◦ Temperature Light intensity Day length

Factors affecting plant growth External ◦ ◦ ◦ ◦ Temperature Light intensity Day length Water Carbon dioxide concentration p. H Gravity Internal ◦ ◦ factors Growth promoters (auxins) Growth inhibitors (e. g. Ethylene, abscisic acid)

Tropisms A stimulus is a change in the environment of a cell or organisms

Tropisms A stimulus is a change in the environment of a cell or organisms that results in a response A response is a change in the cell or organism as a result of it receiving a stimulus Plants often change their growth in response to a stimulus A tropism is a growth response of a plant to an external stimulus

Types of Tropisms Tropism Definition Phototropism Plant growth response to light Geotropism Plant growth

Types of Tropisms Tropism Definition Phototropism Plant growth response to light Geotropism Plant growth to gravity Chemotropism Plant growth response to chemicals Thigmotropism Plant growth response to touch Hydrotropism Plant growth response to water

Positive and Negative Tropisms Positive growth tropism is towards the stimulus Negative growth tropism

Positive and Negative Tropisms Positive growth tropism is towards the stimulus Negative growth tropism is away from the stimulus

Positive and Negative Tropisms Stems positively phototropic negatively geotropic this ensures the leaves get

Positive and Negative Tropisms Stems positively phototropic negatively geotropic this ensures the leaves get more light Roots negatively phototropic positively geotropic and hydrotropic this ensures the roots grow down into the soil and towards water

Pollen Tube - Chemotropism Pollen tubes are positively chemotropic to chemicals released by the

Pollen Tube - Chemotropism Pollen tubes are positively chemotropic to chemicals released by the ovule They are also positively hydrotropic

Positive thigmotropism Tendrils of climbing plants (e. g. Ivy) positively thigmotropic

Positive thigmotropism Tendrils of climbing plants (e. g. Ivy) positively thigmotropic

Plant Growth Regulators A growth regulator is a chemical that controls the growth of

Plant Growth Regulators A growth regulator is a chemical that controls the growth of a plant. They are produced in the meristem transported to other parts of the plant usually carried in the phloem (active transport) often act on parts of the plant that are some distance from the site of production (plant hormones)

Auxins Plant Growth Promoter Produced in meristem, young leaves and seeds Functions and effects

Auxins Plant Growth Promoter Produced in meristem, young leaves and seeds Functions and effects ◦ ◦ ◦ ◦ stem elongation root growth fruit development phototropism apical dominance (inhibits side branching) development of cells’ shape and structure stimulates cell growth, elongation and division

Giberellins and Cytokinins Plant Growth Promoters Giberellins stem elongation germination Cytokinins cell division cell

Giberellins and Cytokinins Plant Growth Promoters Giberellins stem elongation germination Cytokinins cell division cell differentiation lateral bud growth

Combined Effect Many growth process are influenced by a number of growth regulators Auxin

Combined Effect Many growth process are influenced by a number of growth regulators Auxin and Gibberellins promote stem growth, elongation Auxin and Cytokinin: Auxin promotes apical dominance and inhibits lateral bud growth at high concentrations Cytokinin promotes lateral bud growth When auxin is used in combination with cytokinin, apical dominance is broken, and the auxin promotes cell division generally (= growth)

Ethylene Gaseous plant growth regulator Often an inhibitor Produced in ripe fruit and decaying

Ethylene Gaseous plant growth regulator Often an inhibitor Produced in ripe fruit and decaying leaves Causes fruit ripening, and leaf fall Also causes production of more ethylene Over-rips fruit causes surrounding fruit to ripen more quickly “one rotten apple rots the barrel”

Commercial use of Plant Growth Regulators Ethylene Fruit ripening Gibberellin Seedless fruit Auxin Rooting

Commercial use of Plant Growth Regulators Ethylene Fruit ripening Gibberellin Seedless fruit Auxin Rooting powder, herbicide (e. g. 2, 4 -D) Cytokinin Micropropagation Plant tissue culture

Mechanism of a Plant Response - Phototropism In unilateral light, auxin is produced in

Mechanism of a Plant Response - Phototropism In unilateral light, auxin is produced in the apical meristem Auxin moves down the stem Auxin also moves laterally to the shaded side of the stem Increased concentration on the shaded side causes cell elongation Auxin on the illuminated side degenerates The shaded side of the stem elongates. Unequal growth causes the stem to bend towards the light

Mechanism of Phototropism Unilateral light Increased auxin concentration on shaded side Increased cell elongation

Mechanism of Phototropism Unilateral light Increased auxin concentration on shaded side Increased cell elongation on shaded side Lateral movement of auxin from the illuminated side

Phototropism in Unilateral Light

Phototropism in Unilateral Light

Plant Adaptations for Protection Adaptations Anatomical Chemical

Plant Adaptations for Protection Adaptations Anatomical Chemical

Anatomical A physical barrier consisting of epidermis or bark protects plants, these layers prevent

Anatomical A physical barrier consisting of epidermis or bark protects plants, these layers prevent the entry of pathogens and reduce water loss from the plant. Sometimes a protective cuticle is also present. In some plants the epidermis cells are adapted to form thorns e. g. roses or stinging hairs e. g. nettles. A water shortage in plants causes the guard cells to shrivel, this closes the stomata and reduces any further water loss.

Chemical Excessive heat denatures plant enzymes, many plants can form special heat-shock proteins when

Chemical Excessive heat denatures plant enzymes, many plants can form special heat-shock proteins when temperatures exceed 40 ºC, these proteins surround other proteins especially enzymes and help to keep their shape. Sometimes when infected by micro-organisms the plant may produce stress proteins (phytoalexins) which may: Damage micro-organisms by attacking their walls. Stimulate the formation of specialised plant cell walls that prevent the spread of the micro-organisms. Stimulate nearby plant cells to respond to the microorganisms.