The AMBIENT ENVIRONMENT 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 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

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 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: 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) GROUP together HEAL into MULCH

WINTER INJURIES ICE DAMAGE SNOW DAMAGE PREVENTION: 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 PREVENTION Adequate WATER in soil MISTING plants