Download basic horticulture – notes

BASIC HORTICULTURE – NOTES
WEEK #11
PLANT GROWTH and DEVELOPMENT
PROJECTS DUE TODAY
EXAM REVIEW TODAY
HANDS-ON DEMONSTRATIONS – help with set up, grade students
PLANT GROWTH and DEVELOPMENT
GROWTH and DEVELOPMENT are separate, but
INTERELATED PROCESSES
 GROWTH – increase in size and weight - measurable
 DEVELOPMENT – differentiation of cells, tissues and
organs
Example: shape of leaf, or fruit, or shape of shrub or tree
2 FACTORS determine GROWTH and DEVELOPMENT
 HEREDITY – GENES in cells
o All CELLS contain a full COMPLIMENT of
GENETIC CODE
o Through PROCESS of DIFFERENTIATION only a
FEW will be EXPRESSED
Example: formation of adventitious roots from stem
tissue
Example: tissue culture or cell totipotency, all genes
there to make a new plant
 ENVIRONMENT
o Lots of factors including - COMPETITION, SOIL,
TEMP, LIGHT, PREDATION by insects, disease,
parasites, etc.
HEREDITY
ENVIRONMENT
INTERNAL
BIOCHEMICAL
&
PHYSICAL
PROCESSES
GROWTH
&
DEVELOPMENT
 HEREDITY provides POTENTIAL
 ENVIRONMENT determines WHAT the plant will do and to
what DEGREE
Example: CHLOROPHYLL
GENES
Produce CHLOROPHYLL
PHOTOSYNTHESIS
LIGHT
&
MINERALS
PHOTOSYNTHESIS
SUGARS
CO2, H2O, LIGHT, TEMP
GROWTH
&
DEVELOPMENT
PLANT HORMONES – PHYTOHORMONES
PHYTOHORMONES are different than animal hormones
 GENERALIZED PRODUCTION sites
 Affect many ORGANS
 INTERACT in COMPLEX WAYS
3 PROPERTIES
 Effective in VERY LOW CONCENTRATIONS (PPM)
 Can be TRANSLOCATED from synthesis to where it acts
 Effect GROWTH and DEVELOPMENT
5 MAJOR PLANT HORMONE GROUPS
 AUXINS
 GIBBERELLINS
 CYTOKININS
 ETHYLENE
 ABSCISSIC ACID
 AUXIN – longest known hormone and the BEST understood
o EFFECT - CELL ELONGATION @ STEM and ROOT
TIPS
o PRODUCED in ACTIVELY GROWING PLANT
PARTS
 Apical meristems of shoots and buds
 young leaves, flowers, fruits, embryos, pollen
o CONCENTRATION
 Too much – inhibitory
 Too little – not enough growth
 OPTIMAL CONCENTRATION – concentration
of hormone that promotes the MAXIMUM
GROWTH
 CONCENTRATION EFFECTS differ in ROOTS
and SHOOTS
o TRANSLOCATION – DOWN, and side to side
 The farther away from tip the lower the
concentration
o TYPES
 IAA – indole 3 acetic acid (natural)
 IPA – indole pyruvic acid (natural)
 NAA – Napthalene acetic acid (synthetic)
 IBA – indole butyric acid (synthetic)
 2, 4, D - (weed killer) toxic in large conc.
 2, 4, 5, T – (weed killer) affects DICOTS
 MCPA - (weed killer)
o AUXIN and PLANT GROWTH
 INHIBITS ABSCISSION of LEAVES,
FLOWERS, & FRUITS
 LEAVES produce AUXIN until triggered to
decrease due to AGE, DROUGHT,
COOLER, SHORTER days
 FLOWERS will drop off if not for the
POLLEN GRAIN and developing
EMBRYO producing AUXIN
 FRUIT will fall off when production of
AUXIN decreases as fruit RIPENS and
MATURES
 STIMULATE ADVENTITIOUS ROOT
GROWTH
 Use IBA or NAA or BOTH for rooting
cuttings
 INHIBITS LATERAL BUD GROWTH through
APICAL DOMINANCE
 Influence lessens as AUXIN travels down
through stem
 Each bud produces it’s own AUXIN
 INHIBIT FLOWER INITIATION
 Flower POLLEN, EMBRYO’S and FRUIT
all produce AUXIN which inhibits more
FLOWER PRODUCTION
 REMOVE SPENT FLOWERS to keep more
flowers coming
 Essential for FRUIT DEVELOPMENT
 Supplied by POLLEN and EMBRYO
 Some PARTHENOCARPIC FRUIT can be
induced by AUXIN application
Example: figs, grapes, okra, strawberries
o Some PARTHENOCARPIC FRUITS
form SPONTANEOUSLY (fruit
produced without fertilization)
Example: Navel oranges, seedless
grapes, bananas (no seeds are formed)
 Responsible for TROPISMS (tropos = turn)
 GROWTH CURVATURE due to differing
ELONGATION of CELLS
 PHOTOTROPISM (show overhead /
handout)
o response to LIGHT in SUN loving
plants (shady plants don’t respond as
much)
o LIGHT causes AUXIN to migrate
from the side closest to the light to the
opposite side
o CELLS on opposite side ELONGATE
more and “TURN” toward the light
 THIGMOTROPISM
o Response to TOUCH
o TOUCH triggers AUXIN to migrate to
opposite side from touch
o CELLS on opposite side ELONGATE
more and “TURN” to the structure
 GEOTROPISM
o Response to GRAVITY
o GROWTH response DIFFERS in
STEM and ROOTS
 STEMS require HIGHER
concentrations to for CELL
ELONGATION
 ROOTS are more sensitive than
STEMS and require very tiny
amounts for CELL
ELONGATION
 ROOTS will be INHIBITED by
the amount of AUXIN that
STEMS need
o AUXIN migrates downward in plant to
LOWER side
o STEM tissue responds by
ELOGATING on the BOTTOM side
and growing UP(negatively geotropic)
o ROOTS respond by being INHIBITED
on the BOTTOM side and growing
DOWN (positively geotropic)
o GIBBERELLINS
 Many kinds of GIBBERELLINS (>100)
 GIBBERELLIC ACID first discovered in
Japan produced by a fungus Gibberella
 EFFECT – CELL ELONGATION @ internodes
 PRODUCED
 In actively growing tissues, ROOTS
 Primarily CHLOROPLASTS of LEAVES
 CONCENTRATION – increased concentrations,
increase growth
 TRANSLOCATION – up and down, and side to
side
 KEY EFFECTS:
 STEM ELOGATION – more than AUXIN
because HIGHER concentrations of GA do
not inhibit GROWTH
Example: sugar cane to increase production of
stems
 DEVELOPMENT and ELOGATION OF
FLOWER STEMS
Example: grape clusters sprayed to loosen up
Induced biennial growth of flower stem
 FRUIT DEVELOPMENT – some species
 FLOWER DEVELOPMENT – some species
 BREAKING DORMANCY in SEEDS and
BUDS
o Application of GA will substitute for
environmental requirements of COLD or
LIGHT (Vernalization and Stratification)
CYTOKININS
 EFFECT – CELL DIVISION and DIFFERENTIATION
 PRODUCED – mainly in ROOT TIPS (meristems), embryos,
and fruits
 CONCENTRATION – in relation to AUXIN
o HIGH CYTOKININ to AUXIN – produces SHOOT
initiation
o LOW CYTOKININ to AUXIN produces ROOT
initiation
Example: CYTOKININS used in tissue culture to
promote SHOOT growth, AUXINS for ROOT growth
AUXINS “root’em” - CYTOKININS “shoot’em”
o MOD to HIGH C & A produces CALLUS
(undifferentiated cells)
 TRANSLOCATION – UP only (xylem), and side to side
 KEY ROLES:
o Promotes SHOOT INITIATION – tissue culture
o Promotes BRANCHING – counteracts AUXINS and
apical dominance
o PREVENTS LEAF AGING and DEATH
 delays degrading of chlorophyll
o BREAKS DORMANCY in light requiring seed
o Development of PISTILLATE FLOWERS
ETHYLENE
 C2H4 – natural product of plant metabolism
o Normally in GASEOUS STATE outside plant
o DISSOLVED in SOLUTION within plant
 AUXIN stimulates ETHYLENE production
 PRODUCED in ACTIVELY GROWING MERISTEMS
o AGING FLOWERS
o RIPENING FRUIT
o GERMINATING SEEDS
 KEY EFFECTS:
o Stimulates FRUIT RIPENING
 FRUIT produces more ETHYLENE which
produces more RIPENING FRUIT which
produces more ETHYLENE
 fruit can be picked GREEN and shipped,
RIPENED with ETHYLENE
Example: bananas, tomatoes, oranges
o Promotes ABSCISSION of ORGANS – LEAVES,
FRUIT
o Plants produce ETHYLENE in response to STRESS
 May be involved in WOUND HEALING and
DISEASE RESISTANCE
ABSCISSIC ACID - ABA
 EFFECT – growth inhibitor related to environmental stress
o COUNTERACTS effects of AUXIN,
GIBBERELLINS, CYTOKININS
 PRODUCTION - synthesized in plastids of mature leaves
o Also ABA biosynthesis of ETHYLENE
 TRANSLOCATION – up and down, side to side
 KEY EFFECTS:
o ABSCISSION of LEAVES and FRUITS (Ethylene
involved more in this process)
o Stimulate AGING
o Stimulate DORMANCY in SEEDS and BUDS
o INHIBITS CELL DIVISION – produces compact
plants
o CLOSING of STOMATA – triggers closing when
water levels low (originates in roots and translocates
up) when plant can’t keep up with transpiration
FLOWERING
MECHANISM for response to LIGHT and INDUCING
FLOWERING is not known
 PHYTOCHROME in leaves senses LIGHT
 Some plants INITIATE FLOWERING in response to
CHANGING LENGTH of LIGHT – PHOTOPERIODISM
 LIGHT induces plant to CHANGE MERISTEMATIC
TISSUE to form FLOWERS
o Once done cannot change back
FLOWERING HORMONE named FLORIGEN
 Evidence for EXISTENCE does exist, but COMPOUND has
not been ISOLATED
 It may be a COMBINATION of HORMONES, therefore not
easy to DETECT
 Can be TRANLOCATED
Example: Cocklebur plant (show overhead)