Plant Growth

Growth in Animals Animals grow throughout the whole organism many regions & tissues at different rates

Growth in Plants Specific regions of growth: _____________ stem cells: perpetually embryonic tissue regenerate new cells ___________________ growth in length primary growth growth in girth (width) secondary growth

Apical meristems shoot shoot

Root structure & growth protecting the meristem

protecting the meristem Shoot growth Apical bud & primary growth of shoot region of stem growth __________________ “waiting in the wings” protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium Vascular tissue

Growth in woody plants Woody plants grow in height from tip Primary xylem Growth in woody plants Woody plants grow in height from tip primary growth ______________________ Woody plants grow in diameter from sides secondary growth _____________________ makes 2° phloem & 2° xylem makes bark Primary phloem Epidermis Lateral meristems Secondary xylem Primary phloem Primary xylem Secondary phloem Annual growth layers Bark

Secondary growth Secondary growth growth in diameter thickens & strengthens older part of tree ____________________________________ growing ring around tree

Why are early & late growth different? Vascular cambium Phloem produced to the outside Xylem produced to the inside bark phloem cork cambium phloem late vascular cambium early last year’s xylem

Woody stem How old is this tree? cork cambium vascular cambium late early 3 2 1 xylem phloem bark

Tree trunk anatomy tree girdling What does girdling do to a tree? Aaaargh! Murderer! Arborcide! Tree trunk anatomy tree girdling What does girdling do to a tree?

Tree trunk anatomy tree girdling What does girdling do to a tree? Aaaargh! Murderer! Arborcide! Tree trunk anatomy tree girdling What does girdling do to a tree?

Where will the carving be in 50 years?

Plant hormones __________________ and more…

Auxin (IAA) Effects controls cell division & differentiation __________________ growth towards light asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side

Gibberellins Family of hormones Effects over 100 different gibberellins identified Effects stem elongation ____________________ plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

Abscisic acid (ABA) Effects ____________________ high concentrations of abscisic acid germination only after ABA is inactivated or leeched out survival value: seed will germinate only under optimal conditions light, temperature, moisture

One bad apple spoils the whole bunch… Ethylene Hormone gas released by plant cells Effects ____________________ like in Autumn apoptosis One bad apple spoils the whole bunch…

Fruit ripening Adaptation Mechanism hard, tart fruit protects developing seed from herbivores ripe, sweet, soft fruit attracts animals to disperse seed Mechanism triggers ripening process breakdown of cell wall softening conversion of starch to sugar sweetening positive feedback system ethylene triggers ripening ripening stimulates more ethylene production clusters of fruit ripen together

Apoptosis in plants Many events in plants involve apoptosis What is the evolutionary advantage of loss of leaves in autumn? Many events in plants involve apoptosis response to hormones ethylene auxin death of annual plant after flowering senescence differentiation of xylem vessels loss of cytoplasm shedding of autumn leaves The loss of leaves each autumn is an adaptation that keeps deciduous trees from desiccating during winter when the roots cannot absorb water from the frozen ground. Before leaves abscise, many essential elements are salvaged from the dying leaves and are stored in stem parenchyma cells. These nutrients are recycled back to developing leaves the following spring. Fall color is a combination of new red pigments made during autumn and yellow and orange carotenoids that were already present in the leaf but are rendered visible by the breakdown of the dark green chlorophyll in autumn. Photo: Abscission of a maple leaf. Abscission is controlled by a change in the balance of ethylene and auxin. The abscission layer can be seen here as a vertical band at the base of the petiole. After the leaf falls, a protective layer of cork becomes the leaf scar that helps prevent pathogens from invading the plant (LM).

Don’t take this lying down… Ask Questions!! 2007-2008

Apical meristems shoot shoot

Root structure & growth protecting the meristem

protecting the meristem Shoot growth Apical bud & primary growth of shoot region of stem growth __________________ “waiting in the wings” protecting the meristem Young leaf primordium Apical meristem Older leaf primordium Lateral bud primordium Vascular tissue

Growth in woody plants Woody plants grow in height from tip Primary xylem Growth in woody plants Woody plants grow in height from tip primary growth ______________________ Woody plants grow in diameter from sides secondary growth _____________________ makes 2° phloem & 2° xylem makes bark Primary phloem Epidermis Lateral meristems Secondary xylem Primary phloem Primary xylem Secondary phloem Annual growth layers Bark

Why are early & late growth different? Vascular cambium Phloem produced to the outside Xylem produced to the inside bark phloem cork cambium phloem late vascular cambium early last year’s xylem

Woody stem How old is this tree? cork cambium vascular cambium late early 3 2 1 xylem phloem bark

Basic plant anatomy 1

Leaves Function of leaves photosynthesis gas exchange transpiration energy production CHO production gas exchange transpiration simple vs. compound

Parenchyma Parenchyma cells are unspecialized, thin, flexible & carry out many metabolic functions all other cell types in plants develop from parenchyma

Collenchyma Collenchyma cells have thicker primary walls & provide support help support without restraining growth remain alive in maturity the strings in celery stalks are collenchyma

Sclerenchyma Thick, rigid cell wall Cells for support lignin (wood) cannot elongate mostly dead at maturity Cells for support xylem vessels xylem tracheids fibers rope fibers sclereids nutshells seed coats grittiness in pears

Structure–Function again! Vascular tissue vessel elements Xylem move water & minerals up from roots dead cells at functional maturity only cell walls remain need empty pipes to efficiently move H2O transpirational pull vessel element dead cells Aaaah… Structure–Function again! tracheids

Phloem: food-conducting cells carry sugars & nutrients throughout plant sieve tube companion cell sieve plate plasmodesmata living cells

Phloem: food-conducting cells sieve tube elements & companion cells

Vascular tissue in stems dicot monocot trees & shrubs monocot grasses & lilies collect annual rings

Vascular tissue in roots: dicot phloem xylem

Vascular tissue in roots: monocot xylem phloem

Flower Modified shoot with 4 rings of modified leaves sepals petals stamens male carpel female Anther Filament Stamen Stigma Style Ovary Carpel Sepal Petal Ovule sepals petals stamens carpel adaptations through mutations

What is a Cotyledon? Cotyledon: seed leaf in the embryo of an angiosperm that hold food for the developing plant May form a leaf after germination