chemical coordination in plants

growth- an irreversible change in the structure and the development of a cell, tissue or organism.

in plants growth is localised to the apical and lateral meristems

auxin [apical dominance]

they have the ability to induce cell elongation.
the first auxin produced was indole acetic acid [IAA]
it is formed in the apical meristems of root, stems and leaves. they are translocated to the region of elongtion by diffusion.
translocation is basipetal [top to bottom]
they are non specific in their action and an auxin in one species wou

functions

promote cell division along with cytokinins
promote cell elongation
apical dominance- inhibits production of lateral buds
controls geotropic behaviour of shoot & root
delays abscision
promotes growth of fruits.

ex- stem needs higher quantity of auxins for growth, they accumulate on the lower side and in the shadow causing a higher rate of growth on that side accounting for the upward curvature.

however in the roots, the lower accumulation of the auxins has an inhibitting effect. and causes downward curvature.

gibberellins [increase in size between nodes]

they move to all parts of the plant through vascular tissue [basipetal & acropetal]

functions
- they promote cell division
- stimulates cell elongation
- induces parthenocarpic fruit development
- promotes the dormancy of seeds in many species.
- delays leaf senescence

cytokinins

primarily involved in cell growth
they prevent aging
promote auxillary bud & lateral growth.

functions

delay of senescence
breaking seed dormancy in cells
influences growth
promotes growth of lateral buds

ethylene

it is a gaseous hydrocarbon
it is produced by amino acid methionine

functions

induces ripening of fruits
promotes leaf abscision
enhibits elongation but induces enlagement.

abscisic acid “dormin”

it is a very powerful growth inhibitor
it conserves energy and also called a stress hormone
anti gibberellin

functions

stimulates closing of stomata by inhibiting uptake of potassium ions
powerful gibberlin antagonist. induces dormancy
promotes sensescence of leaves.

terms

tropism	movement of plant or plant part in the direction of the stimulus	root is positively geotropic, shoot is negatively geotropic
chemotropism	growth of plant part in the direction of chemical stimulus	pollen tube growth down the style during fertilization
thigmotropism	directional response to touch	climbing tendrils of sweet pea
nastic movements	movements which are neither towards nor away from the stimulus	mimosa pudica
parthenocarpy	production of fruits without fertilisation	seedless oranges are produced with the help of auxins
abscission layer	the structural cause of leaf fall, formation of a layer of cork at the base of the petiole
seed dormancy	the time after maturation which a seed will not germinate despite being provided with all the necessary conditions required for germination
epinasty	the opening up of rolled up leaves & becoming straight	the opening of flowers
sensescence	ageing process
bolting	premature production of flowering stems before the crop is harvested	to mimic a natural method to produce seeds
photoaxis	light induced movents of a single or a few cells towards light	small organisms
photomorphogenisis	light induced plant growth and differenciation	a plant grown in the dark becomes etiolated
photoperiodism	the process of stimulation of a plant to flower by exposure to length of light period	used by farmers to control the length of day and night by artificial lights.