PLANT RESPONSES ADAPTATIONS PLANT GROWTH DEVELOPMENT 1 3

PLANT RESPONSES & ADAPTATIONS

PLANT GROWTH & DEVELOPMENT 1. 3 STAGES OF PLANT DEVELOPMENT (SIMILAR TO ANIMAL DEVELOPMENT) MITOSIS DIFFERENTIATION GROWTH 2. MERISTEM – AREAS OF RAPID CELL DIVISION (MITOSIS) A) APICAL MERISTEM (TIPS OF SHOOTS & ROOTS) PRIMARY GROWTH TISSUES – INCREASES LENGTH OF ROOTS & SHOOTS B) LATERAL MERISTEM/CAMBIUM (FOUND IN TRUNKS & STEMS) SECONDARY GROWTH TISSUES – INCREASES WIDTH/DIAMETER 3. AFTER NEW CELLS ARE PRODUCED BY APICAL & LATERAL MERISTEMS, THEIR LOCATION WILL DETERMINE SPECIALIZATION (DIFFERENTIATION) INTO DERMAL, GROUND, OR VASCULAR TISSUES, FOLLOWED BY ELONGATION OF CELLS RESULTING IN GROWTH

APICAL MERISTEMS

PLANT EMBRYOS 1. EPICOTYL: REGION OF SHOOT ABOVE COTYLEDON 2. HYPOCOTYL: REGION OF SHOOT BELOW COTYLEDON 3. PLUMULE: 1 ST FOLIAGE LEAVES 4. COTYLEDONS: GREEN & CARRY ON PHOTOSYNTHESIS, BUT MOSTLY THE STORED FOOD IN THE COTYLEDON THAT THE YOUNG DEVELOPING PLANT USES. **IN MONOCOTS (CORN, GRASSES, BAMBOO) THE COTYLEDONS STAY WITHING THE SEED COAT IN THE SOIL.

Hormone Action on Plants Section 25 -1 Hormone-producing cells Movement of hormone Target cells

AUXINS (APICAL MERISTEMS) YOUNG LEAVES, GROWING SEEDS, DEVELOPING FRUIT • ALSO CALLED IAA (INDOLEACITIC ACID) • REACTS TO LIGHT AND GRAVITY VERTICAL GROWTH IN ROOTS: • DECREASE IN AUXIN = INCREASE IN ROOT ELONGATION • INCREASE IN AUXIN = DECREASE IN ROOT ELONGATION BRANCHES: APICAL DOMINANCE • TERMINAL (APICAL) BUD PRESENT = DECREASE IN LATERAL BRANCHES • TERMINAL (APICAL) BUD REMOVED = INCREASE IN LATERAL BRANCHES

Section 25 -1 Apical Dominance Apical meristem Lateral buds Auxins produced in the apical meristem inhibit the growth of lateral buds. Apical meristem removed Without the inhibiting effect of auxins from the apicial meristem, lateral buds produce many branches.

Auxins and Phototropism Section 25 -1 High concentration of auxin Low concentration of auxin Control Tip removed Opaque cap Clear cap Opaque shied over base

AUXINS & HORIZONTAL ROOT GROWTH (GRAVITY) INCREASE AUXIN ON BOTTOM SIDE OF ROOT = INCREASE GROWTH ON TOP SIDE & DECREASE GROWTH ON BOTTOM SIDE (ROOT BENDS DOWN) • AUXINS CAN PROMOTE ROOT GROWTH ON STEMS AND LEAVES (CUTTINGS); CAN • CAUSE FRUIT GROWTH & SEEDLESS FRUIT • AUXIN CONCENTRATION HAS OPPOSITE EFFECT IN STEMS (LIGHT), CAUSING INCREASE IN GROWTH, COMPARED TO ROOTS (GRAVITY), CAUSING DECREASE IN GROWTH • SYNTHETIC AUXINS – (SELECTIVE OVERGROWTH) – 2, 4 -D HERBICIDE – WEED KILLER (WILL NOT HARM GRASS) – 2, 4, 5 -T LEAF DEFOLIANT (AGENT ORANGE)

GIBBERELLINS (APICAL MERISTEMS) INCREASE IN GIBBERELLINS = INCREASE IN ELONGATION OF MATURE STEMS’ CELLS – CAUSES PLANT TO GROW ABNORMALLY TALL & SPINDLY (NO SUPPORT)

CYTOKININS (APICAL MERISTEMS/FRUIT) INCREASE IN CYTOKININ = INCREASE IN CELL DIVISION (MITOSIS) IN ROOTS & SHOOT TIPS • • SEED – INCREASE SPROUTING FRUIT – INCREASE FORMATION INCREASE IN CYTOKININ = INCREASE IN LATERAL BRANCH GROWTH; DECREASE IN LATERAL ROOT GROWTH

ABSCISIC ACID (LEAF) • PROMOTES DORMANCY OF BUDS & SEEDS • PROTECTS AGAINST TEMPERATURE EXTREMES AND H 2 O LOSS – “STRESS HORMONE” • CAUSES LEAF STOMATES TO CLOSE

ETHYLENE GAS (FRUIT) • PROMOTES FRUIT RIPENING AND AGING OF TISSUE (WILL HELP CAUSE LEAVES, FLOWERS, AND FRUIT TO DROP) • CO 2 CAN BE USED WITH “GREEN FRUIT” FOR STORAGE TO PREVENT FRUIT RIPENING – THEN TREATED WITH ETHYLENE GAS TO SPEED RIPENING • AUXINS AND ETHYLENE GAS SEEM TO OFFSET EACH OTHER – DECREASE AUXIN = INCREASE ETHYLENE (MATURE) – INCREASE AUXIN = DECREASE ETHYLENE (YOUNG)

Photoperiodism and Flowering Section 25 -2 Short-Day Plant Midnight Noon Long Day Midnight Noon Short Day Midnight Noon Interrupted Night Long-Day Plant

PHOTOPERIODISM

PHYTOCHROMES – LIGHT SENSITIVE PIGMENT PRODUCTS IN PLANTS – USED TO MEASURE “DARKNESS” REMAINS INACTIVE AS LONG AS PLANT IS IN DARK ACTIVE- FORMED DURING DAY OR LIGHT RAPID REACTION SLOW REACTION

HELIOTROPISM (PHOTOTROPISM) – RESPONSE OF LEAVES & STEMS TO LIGHT

GEOTROPISM (GRAVITROPISM)

THIGMOTROPISM (+STEM/-LEAF)

RESEARCH ON PHOTOPERIODISM

BOYSEN-JENSEN CONT. PROVED: 1. A CHEMICAL WAS CARRIED FROM THE TIP TO THE LOWER PART OF A STEM 2. LIGHT INHIBITED THIS CHEMICAL

F. W. WENT 1. 2. 3. EXTRACTED SUBSTANCE (AUXIN) & ISOLATED IT- FOUND 2 X THE AMOUNT OF THIS SUBSTANCE ON THE “AGAR BLOCK” SIDE AUXIN: CAUSES CELL ELONGATION, INCREASING CELL LENGTH ON ONE SIDE OF STEM (WHEN EXPOSED TO LIGHT) LIGHT INHIBITS THE TRANSPORT OF AUXIN DOWN THE PLANT STEM

RESEARCH ON PHOTOPERIODISM **DARWINS DEMONSTRATED THAT THE PHOTOTROPIC RESPONSE WAS DEPENDENT UPON LIGHT STRIKING THE TIP OF THE PLANT STEM.