Light

effects of light on plant morphology

• light direction
• intensity
• wavelength

depicts relative response of a process to different wavelengths (graph)

• -control hypocotyl elongation
• -control stomatal opening
• -control phototropism

• -pigments that regulate many of a plant's responses to light throughout its life
• -seed germination
• -shade avoidance

• -what those are
• -blue part
• -upper part
• -ball part

• the quality of light
• -shaded plants receive more far-red than red light

the phytochrome ratio shifts in favor of Pr when a tree is shaded

• •Cycles that are about 24 hours long and are governed by an internal “clock”
• •Can be entrained to exactly 24 hours by the day/night cycle
• •The clock may depend on synthesis of a protein regulated through feedback control and may be common to all eukaryotes

sunrise and sunset providing the biological clock with environmental cues

the relative lengths of night and day, is the environmental stimulus plants use most often to detect the time of year

a physiological response to photoperiod

–Flower when light period is shorter than a critical threshold

–Flower when a light period is longer than a certain number of hours

–Flowering is controlled by plant maturity, not photoperiod

critical night length sets a minimum number of hours of darkness

critical night length sets a maximum number of hours of darkness

• –Discovered in Arabidopsis thaliana
• –FLC activation inhibits flowering
• –MADS box gene
• –Controls vernalization
• –Epigenetic control regulates the gene
• •Cold exposure reduces expression

the flowering signal 

• response to gravity
• -roots show positive gravitropism
• -shoots show negative

• –specialized plastids containing dense starch grains
• •Some mutants that lack statoliths are still capable of gravitropism
• •Dense organelles, in addition to starch granules, may contribute to gravity detection

refers to changes in form that result from mechanical disturbance

• Reduce transpiration by closing stomata
• •Slow leaf growth
• •Reduce exposed surface area
• •Growth of shallow roots is inhibited
• •Deeper roots continue to grow

•Enzymatic destruction of root cortex cells creates air tubes that help plants survive oxygen deprivation during flooding

• •Plants use defense systems to deter herbivory, prevent infection, and combat pathogens
• •Plants counter excessive herbivory with physical defenses such as thorns and chemical defenses such as distasteful or toxic compounds
• •Some plants even “recruit” predatory animals that help defend against specific herbivores

Bitter, poisonous, cause diarrhea, interfere in the Citric acid cycle, intoxication and other harmful effects

• –Nitrogen compounds (e.g. strychnine, morphine)
• –Terpenoids (citronella, menthol, camphor)
• –Phenolics (cannabinoids, lignin)

volatile chemicals to warn other plants of the same species

expression of genes involved in plant defenses