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Plant Growth & Development (Plant Hormones (Cytokinins (promote cell…
Plant Growth & Development
Plant Hormones
Auxins
group of compounds that stimulate the elongation of plant cells.
Auxins produced by the apical meristem create an effect called apical dominance, in which plant growth is mostly upward with few or no side branches.
The effects of auxins depend on its concentration and location.
Cytokinins
promote cell division and differentiation.
promote cell division by stimulating the production of the proteins needed for mitosis and cytokinesis.
delay the ageing of leaves and fruits
the presence of other hormones, especially auxins, influences the effects of cytokinesis.
Gibberellins
produced in the apical meristem
transported in the vascular tissue
stimulate plant growth by changing the plant's cell walls, stop dormancy in seeds, and can reverse genetic dwarfism in plants
promote the growth of taller, stronger plants and plants that flower early.
Ethylene
only known gaseous hormone, and is in the tissue of ripening fruits, dying leaves, and flowers.
can diffuse through the spaces between cells.
weakens the cell walls of unripe fruit and breaks down complex carbohydrates into simple sugars
Abscisic Acid
synthesized in mature green leaves, fruits, and root caps
generally inhibits growth
inhibits the growth of buds in plant stems and blocks the intake of carbon dioxide by controlling the opening and closing of leaf stomata.
blocks the action of growth-promoting hormones.
Plant Responses to Environmental Stimuli
Nastic response
plant's movement in response to a stimulus that is not associated with the direction of stimulus
not a growth response, is reversible, and can be repeated
Tropic Responses
Gravitropism
growth response to gravity. Stem exhibits a negative gravitropism when it grows upward, pushing against gravity
Thigmotropism
growth response to mechanical stimuli. Ex: vines twisting around nearby structure.
Phototropism
growth response to light caused by an unequal distribution of auxin. The stem curves in the direction of light
Other Factors Affecting Plant Growth
Nutrients
Some nutrients play key functions for the plants. Macronutrients are nutrients needed in relatively large amounts. Micronutrients are needed in much smaller amounts
Soil pH
Most plants grow well within a very narrow range of pH values. Most plants thrive in soils ranging from pH 6 to 7