Yes - By adjusting their pattern of growth and development. In DarkIn Light ???Question?? ? Do plants sense and respond to their environment ?

In Dark ???Question?? ? Plant in dark spends its energy by elongating its stems… to “get out of the dark”

???Question?? ? In the light, leaves grow, roots elongate, and the shoot produces chlorophyll (takes a lot of energy… but it will be photosynthesizing!!) In Light

THOUGHT….. Animals respond to stimuli by changing behaviorAnimals respond to stimuli by changing behavior

Hobby Comment: Plants can’t “move” away from a stimulus, but can change their growth response. Result – plant bodies are more “flexible” in morphology than animals. Plants respond to stimuli by changing growth patternsPlants respond to stimuli by changing growth patterns

Classical Example Phototropism - plant growth response to unilateral light.Phototropism - plant growth response to unilateral light. Observation – plants bend or grow towards the light.Observation – plants bend or grow towards the light.

What mechanism causes this response? Signal Transduction PathwaySignal Transduction Pathway

what is going on with the plant cells?

The tip of the coleoptile senses light

positive phototropism

without the tip, no sense of light

cover the tip, no sense of light

cover the tip with transparent cap, senses light positive phototropism

can’t diffuse down, no sense of light

cells on the dark side - elongate faster than cells on the light

Went Experiments

Plant Hormones Auxins Cytokinins Gibberellins Brassinosteriods Abscisic Acid Ethylene

Promotes cell elongation and growth of stems & roots shoot tip base

Cause of Phototropism - this is how auxin works causes pH to lower enzymes Enzymes called expansins break the H-bonds between cellulose / loosen the cell wall.

this is how auxin works

Monocots can inactivate SYNTHETIC auxins… Eudicots cannot… GREAT BROADLEAF WEED KILLER IN YOUR LAWN!!

Question What is the adaptive value of phototropism ? It tilts the leaves toward the light source for more efficient photosynthesis.

GEOTROPISM Auxin causes:

Promotes cell elongation and growth of stems & meristem regions

Auxin Causes Mimosa Rapid Leaf Movement Auxin causes:

Grape tendrils Auxin causes:

stimulate cell division / mitosis

works together with AUXIN

Promotes growth of root low [cyto] high [auxin]

Promotes growth of shoot high [cyto] high [cyto] low [auxin] low [auxin]

Promotes apical dominance

Promotesanti-aging

Stem elongation

have GA3 lack GA3

have GA3 promotes internode elongation

Fruit growth Extra GA3 No GA3

seed germinatio n

Slows down the dr op pi ng of leaves

promotes seed dormancy

"Stress" hormone produced under unfavorable conditions. Closes stomates quickly "Stress" hormone produced under unfavorable conditions.

Stimulates fruit ripening

fruit ripening One rotten apple DOES spoil the whole bunch!

fruit ripening Put an apple in w/ your green banannas

apoptosis Death of flower after pollination,

apoptosis death of xylem cells, leaves falling off the trees

Flowering Types: 1.Short - Day Plants (long-night plants) 2. Long - Day Plants (short-night plants) 3. Day - Neutral Plants

Night Length Actually controls flowering response, not day length. Proof – experiments show that if you interrupt the dark period, you reset the “clock”.

Short-Day Plants Flower when days are shorter than a critical period (long nights). Ex: Mums Poinsettias

Long-Day Plants Flower when days are longer than a critical period (short nights). Ex: Spinach Iris Lettuce

Day-Neutral Plants Flower whenever they have enough energy. Ex: Roses African Violets

Anatomy of a twig