Light and Temperature

LIGHT and PHYTOCHROMEPigment PHYTOCHROME

Blue-green pigmentExists in two forms Pr (660 nm) Pfr (730 nm)Amount of Pr or Pfr in tissues is determined

with the type of light present

PHYTOCHROMEPr 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

PHOTOMORPHOGENESISPlant 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

PHOTOMORPHOGENESISBRANCHING 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

PHOTOMORPHOGENESISLEAF 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.

PHOTOMORPHOGENESISANTHOCYANIN 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%)

PHOTOMORPHOGENESISFLOWERING 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

PHOTOMORPHOGENESISPHOTOPERIODISM 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

PHOTOMORPHOGENESISPHOTOPERIODISM

PHOTOMORPHOGENESISPHOTOPERIODISM 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

TEMPERATUREPlants EVOLVED with the earth’s various

TEMPERATURE regimesLimited 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

TEMPERATURETHERMOPERIODICITY

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

TEMPERATUREVERNALIZATION

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

TEMPERATUREDORMANCY

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

TEMPERATUREHARDINESS 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)

TEMPERATUREDEGREE 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

TEMPERATUREPHYSIOLOGY 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

WINTER INJURIESWINTER 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

WINTER INJURIESFREEZE 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 INJURIESFROST 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 INJURIESICE DAMAGE

SNOW DAMAGE

PREVENTION: STAKE or PROP small

trees and shrubs Proper PRUNING and

THINNING SLOW GROWING

TREES

WINTER INJURIESBARK 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 INJURIESWINTER SUNSCALD or SW

INJURYSunny winter day, with a cold

nightsCauses 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 INJURIESWATER and HEAT

STRESS

SUMMER SUNSCALD

SUMMER INJURIESWATER and HEAT

STRESS

SUMMER SUNSCALD

PREVENTION Adequate WATER in soil MISTING plants