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Control Systems in Plants

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Presentation on theme: "Control Systems in Plants"— Presentation transcript:

1 Control Systems in Plants
Chapter 22 Control Systems in Plants

2 22.1 Hormones Charles and Francis Darwin Plant tip experiments

3 Auxins Promote plant growth Produced in apical meristem of shoots
Cell elongation Auxin builds up on shaded side Elongation on shaded side causes plant to bend toward light Stimulate secondary growth Secreted by seeds to stimulate development of ovary to fruit Farmers use this to grow seedless plants

4 Cytokinins Stimulate cell division
Produced in embryos, roots, and fruits Slow aging of flowers and fruits Affected by auxins High levels of auxins inhibits branching Travels from terminal bud Bushier plant = “pinch back”

5 Gibberellins Stimulate growth of stems
Cell division and elongation(similar to auxins) With auxins, influence fruit development Promotes seed germination

6 Abscisic Acid (ABA) Halts primary and secondary growth Stress hormone
Promotes dormancy during winter or drought More likely to survive when it becomes dormant Stress hormone Dehydration - ABA causes stomata to close

7 Ethylene Stimulates fruit ripening Promote “leaf drop”
Adaptation helps trees from drying out in the winter High ethylene; low auxins - cooler temps and shorter days

8 22.2 Plant Response Tropisms: growth responses that cause parts of a plant to grow slowly toward or away from a stimulus Rapid plant movements Plants can respond quickly to touch to avoid being eaten Leaf folding

9 Thigmotropism Change in plant growth due to touch Climbing plants
Tendrils coil and grasp objects Mechanical stress Bend to avoid damage Leaf folding

10 Phototropism Growth of a plant part toward or away from light
Light on a shoot tip Protein with light-absorbing molecule Signals molecules that affect auxin transport Auxin lengthens shade side

11 Gravitropism Response to gravity
Seedling’s shoot grows upward, root downward Hypothesis: gravity pulls organelles to low points of cells Uneven distribution may signal cells to move auxins

12 Drought Causes wilting and reduces photosynthesis Succulents (cacti)
Respond by conserving water Succulents (cacti) Thick cuticle and fleshy stems Spines instead of leaves Arctic Plants Small leaves and low to the ground Reduce transpiration

13 Flooding Overwatered plants can suffocate Plants in wet areas
Lack of oxygen spaces in soil Plants in wet areas Mangroves Roots partially above ground to provide oxygen Release ethylene Some cells die to form air tubes

14 Salt Stress Too much salt; lose water to soil through osmosis
halophytes: salt-tolerant plants Salt glands Pump out salt across leaf epidermis Rain washes salt away Pickleweed Excess salt to stems; shed stems

15 Disease Defense Epidermis - barrier to pathogens Chemicals
Pathogens cross by wounds or stomata Chemicals Antimicrobial Signal lignin production- seals off invader Ability to recognize and attack certain pathogens

16 22.3 Light and Seasons circadian rhythm: biological cycle that occurs about every 24 hours Daily signals; light Plants produce flowers during different times of the year based on day/night length

17 Photoperiodism Ability to use lengths of day to time seasonal activities short-day plants: flower in fall or winter when darkness is a certain length Long-day plants: flower in spring or summer when days are longer Spinach, irises day-neutral plant: flowers when it reaches a certain stage of maturity Dandelions, tomatoes, rice Florists can change this by flashing light in the night

18 Phytochromes Pigment proteins that detect sunrise and sunset
Sunrise= red light Change to active form that triggers responses Sunset - change back to inactive form

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