1. The AMBIENT ENVIRONMENT
Light and Temperature

2. LIGHT and PHYTOCHROME Pigment PHYTOCHROME Blue-green pigment
Exists in two forms Pr (660 nm) Pfr (730 nm)
Amount of Pr or Pfr in tissues is determined with the type of light present

3. PHYTOCHROME Pr is SYNTHESIZED by the plant and very STABLE
Pfr is NOT STABLE
Slowly reverts back to Pr in the DARK or in SHADE
Highest CONCENTRATIONS found in the MERISTEMATIC TISSUES
Apical meristems
Cambium meristems

4. PHOTOMORPHOGENESIS
Plant SENSES the RATIO of Pr to Pfr which influences HORMONES and stimulates a RESPONSE
PHOTOMORPHOGENESIS - Growth and development in response to light
SEED GERMINATION
BRANCHING and STEM ELONGATION – ETIOLATION
LEAF MOVEMENTS
ANTHOCYANIN PRODUCTION
FLOWERING and PHOTOPERIODISM

5. PHOTOMORPHOGENESIS BRANCHING and STEM ELONGATION
ETIOLATION
Leaves absorb RED & FAR RED light selectively
90% of RED LIGHT absorbed by leaf
~ 2% of FAR RED light absorbed
Higher % of Pr activates GROWTH HORMONES (Gibberelins) allows plant to REACH for light

6. PHOTOMORPHOGENESIS LEAF MOVEMENTS CLOSURE of LEAFLETS at night
Higher % of Pfr increases closure
Cells at attachment points to midrib (pulvini) gain turgor pressure due to water and potassium ions and leaflets open
Loss of turgor leaflets close
PHYTOCHROME thought to affect permeability of the cellular membrane and ion movement across it.

7. PHOTOMORPHOGENESIS ANTHOCYANIN PRODUCTION
During SUNNY DAYS and COLD NIGHTS in fall
Pigments form from high concentrations of SUGARS in CELL
FAR RED light stimulates Anthocyanin production
SHORTENING DAYLIGHT increases more time in FAR RED light (or DARKNESS) which increases more Pr in plant (Pr 97% - Pfr 3%)

8. PHOTOMORPHOGENESIS FLOWERING and PHOTOPERIODISM
PHOTOPERIODISM is the RESPONSE of plants to CHANGING LENGTH of DAYS and NIGHT
DAYLENGTH is important, but plants happen to be more responsive to PERIODS of DARKNESS
% of Pfr which depletes during darkness is primary factor

9. PHOTOMORPHOGENESIS PHOTOPERIODISM is CUMULATIVE
Called CRITICAL DAYLENGTH (CDL) and is species dependent
SHORT DAY – daylength < CDL
LONG DAY - daylength > CDL
DAY NEUTRAL – NOT DAYLENGTH dependent
Also SD or LD plants can be grouped by:
OBLIGATE – must have DAYLENGTH requirement to flower
QUANTITATIVE – plant will FLOWER FASTER or MORE if exposed to proper DAYLENGTH

10. PHOTOMORPHOGENESIS
PHOTOPERIODISM

11. PHOTOMORPHOGENESIS PHOTOPERIODISM related to many PROCESSES
Mostly related to FLOWER INITIATION, but also related to:
FORMATION of STORAGE ORGANS
STEM ELONGATION
FALL COLOR, LEAF AGING, & ABSCISSION
BUD DORMANCY

12. TEMPERATURE
Plants EVOLVED with the earth’s various TEMPERATURE regimes
Limited to 0° – 50° C (32° – 122° F)
@ 0° C (32° F) biological ACTIVITY SLOWS or STOPS
@ > 50° C (122° F) PROTEINS destroyed, PLANT INJURY or DEATH
BEST 10° - 30° C (50° – 85° F)
As TEMPERATURE RISES every 10° GROWTH can increase 1.3 – 5 X’s (2 X’s average)
Growers use this fact to INCREASE or DECREASE GROWTH

13. TEMPERATURE THERMOPERIODICITY
Is the FLUCTUATION of DAY and NIGHT TEMPERATURES
Most plant GROWTH occurs at NIGHT
Plants from GROW BETTER with THERMOPERIODICITY
Important to TEMPERATE CLIMATE plants
Not so important to tropical plants

15. TEMPERATURE VERNALIZATION
The INITIATION of FLOWERING in plants by exposure to EXTENDED COLD PERIODS
CHILLING REQUIREMENTS
ABSOLUTE – specific number of DAYS BELOW a certain TEMPERATURE
QUANTITATIVE – flower EARLIER and MORE with exposure to COLD
Stimulus is perceived in the APICAL MERISTEM
HIGH TEMPS can REVERSE or DEVERNALIZE plants

16. TEMPERATURE
DORMANCY
DORMANCY is state of INACTIVE GROWTH due to INTERNAL and EXTERNAL FACTORS
KEY to SURVIVAL of PERENNIAL plants growing in TEMPERATE or COLD CLIMATES
Plants BREAK DORMANCY when ENVIRONMENTAL CONDITIONS are FAVORABLE for GROWTH and DEVELOPMENT

17. TEMPERATURE
DORMANCY is a gradual process that STARTS as GROWTH TAPERS in SUMMER
TRIGGERED by:
SHORTENING DAYS
LOWER TEMPS
DROUGHT
STEPS to PLANT DORMANCY:
PHOTOSYNTHESIS SLOWS or STOPS
GROWTH STOPS
TRANSLOCATION of FLUIDS reduced
Decreased ENERGY REQUIREMENTS
PROGRESSION through plant
AXILLARY buds >> TERMINAL buds >> BRANCHES >> TRUNK >> BARK last
ROOTS never become truly dormant, they CONTINUE to GROW as long as SOIL TEMPS > 40 degrees

18. TEMPERATURE HARDINESS and ACCLIMATION
HARDINESS - The ability of a DORMANT plant to withstand COLD TEMPS without severe TISSUE DAMAGE
ACCLIMATION - the ability to DEVELOP HARDINESS
DEGREE of HARDINESS changes in RESPONSE to the ENVIRONMENT, and the responsiveness of the plant DEPENDS on it’s GROWTH STAGE (see handout)

19. TEMPERATURE DEGREE of COLD HARDINESS DEPENDS on:
GENETICS of the plant and the HABITAT and CLIMATE it originally ADAPTED to
GROWTH STAGE
FOOD STORED in the plant
LOW RESERVES in the plant will LOWER COLD HARDINESS
Poor nutrition
Heavy foliage, flower, fruit production
Shortened growing period
Excessive forced growth from high N fertilization

20. TEMPERATURE PHYSIOLOGY of ACCLIMATION
The FORMATION of ICE CRYSTALS damages cells
Plant have a variety of WAYS to KEEP SAP from FREEZING
CONVERSION of STARCH to SUGARS in CELLS
Increased VISCOSITY or THICKNESS of CELL CYTOPLASM
ICE CRYSTALS form in the INTERCELLULAR SPACES
DEHYDRATES CELL - draws more water out of cell due to osmosis
Makes content of cell MORE VISCOUS
“SUPERCOOLING” sap
Some plants have the ability to “SUPERCOOL” fluids below the freezing point without freezing their tissues

21. WINTER INJURIES WINTER DESICCATION DRYING out of TISSUES PREVENTION:
WATER when ground thawed
MULCHING to retain moisture
WINDBREAKS to decrease transpiration
ANTI – DESICCANTS sprays reduce transpiration for a few days, good for transplanting

22. WINTER INJURIES FREEZE INJURY
SUDDEN DROP in TEMP or EXTREME TEMP CHANGE
PREVENTION:
MULCH WHOLE plant
SPRAYING ORCHARDS with WATER
As water freezes HEAT is released, continually freezing water protects tissues
@ 32 degrees F

23. WINTER INJURIES FROST HEAVING (roots)
PREVENTION:
MULCHING
Better DRAINAGE
ONCE HAPPENS - PRESS plants DOWN into ground
FREEZING of CONTAINER PLANTS (roots)
GROUP together
HEAL into MULCH

24. WINTER INJURIES ICE DAMAGE SNOW DAMAGE PREVENTION:
STAKE or PROP small trees and shrubs
Proper PRUNING and THINNING
SLOW GROWING TREES

25. WINTER INJURIES BARK SPLITTING or FROST CRACKING
SUDDEN FREEZE before the tree attains HARDINESS causes the BARK to SPLIT along the CAMBIUM LAYER
PREVENTION:
Protect by WRAPPING with burlap, tree guards, white paint
Plant more RESISTANT, THICKER BARK SPECIES
ONCE HAPPENS – WRAP TRUNK or TACK BARK BACK to protect as much cambium and phloem tissue from drying out

26. WINTER INJURIES WINTER SUNSCALD or SW INJURY
Sunny winter day, with a cold nights
Causes bark to deacclimatize and become susceptible to freezing
PREVENTION:
Protect by WRAPPING with burlap, tree guards, white paint
Plant more RESISTANT, THICKER BARK SPECIES

27. SUMMER INJURIES
WATER and HEAT STRESS
SUMMER SUNSCALD

28. SUMMER INJURIES WATER and HEAT STRESS SUMMER SUNSCALD PREVENTION
Adequate WATER in soil
MISTING plants