9.3 Plant growth Flashcards
Plant life spans
Determined genetically
- annuals: cucumber, carrot
- biannuals: 1st year germinating, roots, 2nd year stems, leaves, flowers, fruits - cellery
- perennials: live 2+ years - trees
Plant anatomy
Leaf anatomy
Apical vs lateral meristem growth
Explain meristem cells
Meristems: tissues in a plant consisting of undifferentiated cells capable of indeterminate growth (allow plants to regrow structures/ form entirely new plants)
- apical: shoot/root - primary growth - leaves/flowers
- lateral: at cambium - secondary growth - production of bark
Explain auxin and apical dominance
Auxins - growth hormones in shoots/roots- trasnported by PIN3 proteins - absorbed by auxin efflux pumps
Produced by shoot apical meristem - promotes growth in shoot appex but prevents in lateral (auxillary) buds - apical dominance - ensures plant growth towards light
Explain tropisms
Tropism - growth or turning movement of an plant in response to a directional external stimulus
Both regulates by auxin
Phototropism - shoots, light receptors regulate distribution of auxin - growth where auxin - positive photostropism
Gravitropism (geotropism) - roots, auxin accumulates at the lower part of roots - dark side of root becomes shorter - negative phototropism
Explain micropropagation
Micropropagation - technique used to produce large numbers of identical plants (clones) from a selected stock plant
- undifferentiated shoot apex selected from a stock plant and sterilised
- tissue sample - explant - grown on a sterile nutrient agar gel
- explant is treated with growth hormones (e.g. auxins) to stimulate shoot and root development
- growing shoots continuously divided + separated - new samples (multiplication phase)
- root and shoot are developed, the cloned plant can be transferred to soil
Adv:
- fast
- takes up less space
- virus free
- save rare species
- genetically identical
Disadv:
- labs needed
- high costs
- skilled workers
Explain apical growth
- Growth - combination of cell enlargement and mitosis in shoots and roots - regulated by auxins
- Differentiation - variety of stem tissues/ structures + leaves/flowers
- in stem - at nodes - axillary (lateral) buds - new branching shoots - leaves and flowers
Auxins in shoots vs roots
In shoots: promotes growth - cell elongation, auxin activates proton pumps - decrease pH - cellulose fibres loosen + auxin activates expression of expansins - increases elastciity of cell wall - influx of water - into vacuole - cell increases in size => increase in cell size helps bend towards the sun - more sunlight
In roots: inhibits elongation, cells become smaller
Plant hormones and their function
Auxins: primary growth by elongation and mitosis
Promote apical dominance – whereby the apex grows while - lateral buds remain undeveloped
Auxin concentrations - response to directional stimuli - tropisms
Cytokinins: promote cytokinesis and ensure roots and shoots grow at equal rates
- promotes secondary growth (thickening) and help to control the rate of branching by a plant, involved in stimulating the growth of fruit
Gibberellins: triggers germination in dormant seeds (initiates plant growth), causes stem elongation by promoting cell elongation and mitosis
Ethylene: gas which acts as a plant hormone - stimulates maturation and ageing (senescence)
- responsible for ripening of fruit (auxins + gibberellins promote fruit growth but inhibit ripening)
- contributes to the loss of leaves (abscission) and the death of flowers
Abscisic Acid (ABA): inhibit plant growth and development
- promotes the death of leaves (abscission) and is responsible for seed dormancy
- initiates stress responses in plants (like winter dormancy in deciduous plants)
- controls the closing of stomata - regulates transpiration
