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Light and Temperature
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
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
PHOTOMORPHOGENESIS
 Plant SENSES the RATIO of Pr to Pfr which influences
HORMONES and stimulates a RESPONSE
 PHOTOMORPHOGENESIS - Growth and development
in response to light

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SEED GERMINATION
BRANCHING and STEM ELONGATION – ETIOLATION
LEAF MOVEMENTS
ANTHOCYANIN PRODUCTION
FLOWERING and PHOTOPERIODISM
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
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.
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%)
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
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
PHOTOMORPHOGENESIS
 PHOTOPERIODISM
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
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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 GROWTH @ 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
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
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
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
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
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)
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
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


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
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
WINTER INJURIES
 WINTER DESICCATION
 DRYING out of TISSUES
 PREVENTION:
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
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
WATER when ground thawed
MULCHING to retain moisture
WINDBREAKS to decrease
transpiration
ANTI – DESICCANTS sprays reduce
transpiration for a few days, good for
transplanting
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
WINTER INJURIES
 FROST HEAVING (roots)
 PREVENTION:


MULCHING
Better DRAINAGE
 ONCE HAPPENS - PRESS plants
DOWN into ground
 FREEZING of CONTAINER
PLANTS (roots)
 PREVENTION:


GROUP together
HEAL into MULCH
WINTER INJURIES
 ICE DAMAGE
 SNOW DAMAGE

PREVENTION:
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

STAKE or PROP small
trees and shrubs
Proper PRUNING and
THINNING
SLOW GROWING TREES
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
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
SUMMER INJURIES
 WATER and HEAT STRESS
 SUMMER SUNSCALD
SUMMER INJURIES
 WATER and HEAT STRESS
 SUMMER SUNSCALD
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PREVENTION

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Adequate WATER in soil
MISTING plants