Plant Growth

Growth in Animals Animals grow throughout the whole organism Many regions & tissues at different rates Growth stops when a certain size or development is reached Called determinate growth.

Growth in Plants Specific regions of growth: meristems Perpetually embryonic tissue Cells can divide indefinitely. Called indeterminate growth.

Growth in Plants regenerate new cells apical shoot meristem growth in length primary growth apical root meristem lateral meristem growth in girth secondary growth

Apical meristems shoot root

Root structure & growth protecting the meristem

protecting the meristem Shoot growth Apical bud & primary growth of shoot Region of stem growth Lengthens the shoot by mitosis and cell division. Tip of shoot = Apex 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 apical meristem Woody plants grow in diameter from sides secondary growth lateral meristems vascular cambium makes 2° phloem & 2° xylem cork cambium 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 cork cambium makes bark growing ring around tree vascular cambium makes xylem & phloem

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

Where will the carving be in 50 years?

PLANT HORMONES A. Are chemical signals that coordinate different parts of an organism. B. Require only minute amounts. C. Produced by 1 part of plant body. D. Transported to another part E. Binds to specific receptor F. Triggers response in target cells and tissues.

Examples of Plant hormones: auxin gibberellins abscisic acid ethylene and more…

Auxin (indole-3 acetic acid or IAA) Effects controls cell division & differentiation phototropism growth towards light asymmetrical distribution of auxin cells on darker side elongate faster than cells on brighter side

Auxin (indole-3 acetic acid or IAA) Effects Apical dominance Prevents axillary buds from growing. These auxins are produced by meristem in shoot apex.

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

Animal vs. Plant Responses Comparing responses to stimuli of plants and animals: A. Animals – Respond to stimuli by changing behavior. 1. Move toward positive stimulus 2. Move away from negative stimulus

B. Plants – Respond to stimuli by: Adjusting growth and development Plants adjusting their directional growth responses to directional external stimuli (such as light or gravity) are called tropisms. Response to light is phototropism. Response to gravity is called gravitropism. Growth toward a stimulus is a positive tropism. Growth away from a stimulus is a negative tropism.

Auxin influences gene expression in phototropism. Light is absorbed by photoreceptor proteins called phototropins. Phototropins change conformation and bind to receptors within the cell. Receptors control specific genes transcribing plasma membrane proteins which transport auxin.