Plant Growth

Phases of plant growth Dormancy:Dormancy: –Period of inactivity. Often environmentally regulated –Ex: Winter or drought In Vermont, most plants go dormant by October and remain dormant through AprilIn Vermont, most plants go dormant by October and remain dormant through April –Length of dormancy- depends on your geographic location and the plant species

Phases of plant growth Two phases of dormancy:Two phases of dormancy: –1.) Rest period - plant will NOT grow even if given a favorable environment! October to JanuaryOctober to January –2.) Dormant yet reactive - plant will grow if given a favorable environment February to AprilFebruary to April

Phases of plant growth Why important?Why important? –If you try and force cut stems into flower, you must wait until they have completed their rest phase –Temperate plants need a dormancy period or they will die (important for bonsai/penjing)

Forsythia

Crabapples

Phases of plant growth Vegetative phaseVegetative phase –Food resources directed at production of leaves, stems and roots –Juvenile phase- part of the vegetative phase where reproduction cannot be induced Reproductive phaseReproductive phase –Sugars and starches are stored –The plant flowers, produces seeds & fruit

Phases of plant growth Senescence:Senescence: –Rapid or gradual cycle until death –In hardy perennials, only the above-ground portion senescences (roots/crown remain alive) –In woody trees and shrubs, only the leaves and fruit senescence each year

Sedum

Phases of plant growth Vegetative/Reproductive cycles are regulated by:Vegetative/Reproductive cycles are regulated by: –Age/maturity of the plant –Carbohydrate/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 becoming reproductive (flowering)Too much nitrogen fertilizer can prevent a plant from becoming reproductive (flowering)

Cells Cytology = the study of cellsCytology = the study of cells Cell wallCell wall –Polysaccharides = long chains of simple sugars like glucose Cellulose ( unbranched polymer of several 1000 glucose molecules)Cellulose ( unbranched polymer of several 1000 glucose molecules) Hemicellulose (branched chain)Hemicellulose (branched chain) –Combustible –Directly indigestible by mammals (lack enzyme to break bonds between glucose units) »Ruminants (animals with special bacteria in stomach)

Robert Hookes light microscope 1665

Cells –Lignin = 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 = gel Water-solubleWater-soluble