Plant GrowthPlant Growth

Phases of plant growthPhases of plant growth• Dormancy:Dormancy:

– Period of inactivity. Often environmentally Period of inactivity. Often environmentally regulatedregulated

– Ex: Winter or droughtEx: Winter or drought

• In Vermont, most plants go dormant by In Vermont, most plants go dormant by October and remain dormant through AprilOctober and remain dormant through April– Length of dormancyLength of dormancy- depends on your - depends on your

geographic location and the plant speciesgeographic location and the plant species

Phases of plant growthPhases of plant growth• Two phases of dormancy:Two phases of dormancy:

– 1.) 1.) Rest periodRest period - plant will NOT grow even if - plant will NOT grow even if given a favorable environment!given a favorable environment!

• October to JanuaryOctober to January

– 2.) 2.) Dormant yet reactiveDormant yet reactive - plant will grow if - plant will grow if given a favorable environmentgiven a favorable environment

• February to AprilFebruary to April

Phases of plant growthPhases of plant growth• Why important?Why important?

– If you try and force cut stems into flower, If you try and force cut stems into flower, you must wait until they have completed you must wait until they have completed their “rest” phasetheir “rest” phase

– Temperate plants need a dormancy period Temperate plants need a dormancy period or they will die (important for or they will die (important for bonsai/penjing)bonsai/penjing)

ForsythiaForsythia

CrabapplesCrabapples

Phases of plant growthPhases of plant growth• Vegetative phaseVegetative phase

– Food resources directed at production of leaves, Food resources directed at production of leaves, stems and rootsstems and roots

– Juvenile phase- part of the vegetative phase Juvenile phase- part of the vegetative phase where reproduction cannot be inducedwhere reproduction cannot be induced

• Reproductive phaseReproductive phase– Sugars and starches are storedSugars and starches are stored– The plant flowers, produces seeds & fruitThe plant flowers, produces seeds & fruit

Phases of plant growthPhases of plant growth• Senescence:Senescence:

– Rapid or gradual cycle until deathRapid or gradual cycle until death

– In hardy perennials, only the above-ground In hardy perennials, only the above-ground portion senescences (roots/crown remain alive)portion senescences (roots/crown remain alive)

– In woody trees and shrubs, only the leaves and In woody trees and shrubs, only the leaves and fruit senescence each yearfruit senescence each year

SedumSedum

Phases of plant growthPhases of plant growth• Vegetative/Reproductive cycles are regulated by:Vegetative/Reproductive cycles are regulated by:

– Age/maturity of the plantAge/maturity of the plant

– Carbohydrate/nitrogen balance in the plantCarbohydrate/nitrogen balance in the plant• Carbohydrates come from photosynthesis in leavesCarbohydrates come from photosynthesis in leaves

• Nitrogen is taken up by the rootsNitrogen is taken up by the roots

• Too much nitrogen fertilizer can prevent a plant from Too much nitrogen fertilizer can prevent a plant from becoming reproductive (flowering)becoming reproductive (flowering)

CellsCells• Cytology = the study of cellsCytology = the study of cells

• Cell wallCell wall– Polysaccharides = long chains of simple sugars like Polysaccharides = long chains of simple sugars like

glucoseglucose• Cellulose ( unbranched polymer of several 1000 glucose Cellulose ( unbranched polymer of several 1000 glucose

molecules)molecules)• Hemicellulose (branched chain)Hemicellulose (branched chain)

– CombustibleCombustible– Directly indigestible by mammals (lack enzyme to break bonds Directly indigestible by mammals (lack enzyme to break bonds

between glucose units)between glucose units)» Ruminants (animals with special bacteria in stomach)Ruminants (animals with special bacteria in stomach)

Robert Hooke’s Robert Hooke’s light microscopelight microscope

16651665

CellsCells– Lignin = polymers of phenolic acidLignin = polymers of phenolic acid

• Hardens cellulose walls (lignifies)Hardens cellulose walls (lignifies)

• Resists microbial decompositionResists microbial decomposition

• Causes yellowing in paper (photo-oxidation)Causes yellowing in paper (photo-oxidation)

– Pectin = acidic polysaccharides = gelPectin = acidic polysaccharides = gel• Water-solubleWater-soluble