Crop Growth and Development

1. Vegetative and reproductive development, and senescence

2. Photosynthesis, respiration and assimilation

3. Plant growth regulators

Life Cycles of Flowering Plants

Seed

Embryo Phase

Juvenile Zygote

Annual, Biennial

Seed

Embryo Phase

Juvenile Phase

Zygote

Flower

Juvenile Phase

Adult Phase

Zygote

Senescence

Flower Adult Phase

Axillary buds

Perennial

Reproductive Growth Vegetative Growth

Senescence

Vegetative DevelopmentVegetative Development

What is Vegetative Development?

Vegetative development is thegeneration of leaves, stems androots on a plant.

Phases of Vegetative Development

� Emergence and elongation of roots

� Emergence and development of shoot (leaves, stem, axillary buds)(leaves, stem, axillary buds)

Vegetative Structures

� Leaves

- simple leaf

- compound leaf

� Stems

- contain buds, nodes

- modified stems: tuber (eg. potatoes), rhizome (eg. ginger), bulb (eg. onion),

Simple leaf Compound leaves

pinnate palmate

corm (eg. water chestnut), stolon (eg. grasses, strawberry)

� Roots

- tap root (eg. rubber tree)

- fibrous root (eg. rice, maize, palms, grasses)

- aerial root (eg. orchid)

- adventitious root

- modified roots: tuberous root (eg. sweet potatoes)

De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam,

The Netherlands.

Leaf Anatomy

cuticle

upper epidermis

lower epidermis

spongy mesophyll

cuticle

palisade mesophyll

bundle sheath cellxylem

phloem

stomata guard cell

vascu

lar

bu

nd

le

Vegetative Structures

� Leaves

- simple leaf

- compound leaf

� Stems

- contain buds, nodes

- modified stems: tuber (eg. potatoes), rhizome (eg. ginger), bulb (eg. onion),

Simple leaf Compound leaves

pinnate palmate

corm (eg. water chestnut), stolon (eg. grasses, strawberry)

� Roots

- tap root (eg. rubber tree)

- fibrous root (eg. rice, maize, palms, grasses)

- aerial root (eg. orchid)

- adventitious root

- modified roots: tuberous root (eg. sweet potatoes)

De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam,

The Netherlands.

Vegetative Structures

� Leaves

- simple leaf

- compound leaf

� Stems

- contain buds, nodes

- modified stems: tuber (eg. potatoes), rhizome (eg. ginger), bulb (eg. onion),

Simple leaf Compound leaves

pinnate palmate

corm (eg. water chestnut), stolon (eg. grasses, strawberry)

� Roots

- tap root (eg. rubber tree)

- fibrous root (eg. rice, maize, palms, grasses)

- aerial root (eg. orchid)

- adventitious root

- modified roots: tuberous root (eg. sweet potatoes)

De Hertogh and Le Nard (1993) The Physiology of Flower Bulbs. Elsevier Scientific Publisher. Amsterdam,

The Netherlands.

Reproductive DevelopmentReproductive Development

What is Reproductive Development?

Reproductive development refers to the initiation and development of flowers, fruit and seeds on a plantplant

Phases of Reproductive Development in Flowering Plants

� Flower induction and initiation

� Flower differentiation and development

� Pollination

Fertilization� Fertilization

� Fruit set and seed formation

� Growth and maturation of fruit and seed

� Fruit senescence

Flower Structure

stigma

style

anther

filament

stamen

style

petal

ovule

ovary

sepal

receptacle

pistil

Flower Induction and Initiation

� Photoperiod (daylength)

� Low temperature induction

� Self-induction

Photoperiod

Behaviour of Short-day Plants

Behaviour of Long-day Plants

Light regime

� Long-day plants: only flower under a long daylength (e.g. oat, wheat)

� Short-day plants: only flower under a short daylength or require a certain period of darkness which is uninterrupted by light for flower induction (e.g. soybean, poinsettia, Chrysanthemum morifolium)

� Day-neutral plants: flower induction is not affected by daylength (e.g. grapes, corn, tomato)

24 hours

Light interruption

Critical night length

Vegetative

Flowering

Vegetative

Flowering

Vegetative

Flowering

Low Temperature Induction

� Vernalization is a cold temperature treatment that induces flowering

� Temperature and length of vernalization period vary among species or even cultivars of the same species

� Range of temperatures: 0oC – 10oC

� Examples:

� brussel sprouts

� carrots

� celery

� barley

� oats

� wheat

Self-Induction of Flowering

� Many plants are self-inductive for flowering

� Initiate or form flowers at almost any photoperiod andwithout vernalization

� Start to flower when they reach a certain developmentalstage or maturity

� Examples:

� Garden perennials: roses, carnations, gerbera

� Garden annuals

� Vegetables crops: cucumber, beans, peas, tomatoes

Pollination

� Pollination is the release, transfer and deposition of pollen from an anther to a stigma

� Agents of pollination:

� Animals (insects, birds, snails, bats)

>90% of flowering plants� >90% of flowering plants

� Wind

� Water

Fertilization

� Double fertilization:� One sperm nucleus (1n) + one egg (1n) = zygote (2n)

� One sperm nucleus (1n) + two polar nuclei (1n each) = endosperm (3n)

� Elapsed time between pollination and fertilization� 24 – 48 hours

Pollen grain Three antipodal cells

Pollen tube

Two polar nuclei

Egg cell

Synergid cells

Tube-cell nucleus

Sperm nucleus

Fruit Structure

seed

exocarp

Ovule seed Ovary fruit

mesocarp

endocarp

pericarp

Categories of Fruits� Simple fruits: a single ovary produced by one flower

� Fleshy fruits (the entire pericarp and accessory parts are succulent)� Berry (bananas, grapes, papayas, tomatoes)� Pepo (cucumbers, melons, squashes)� Hesperidium (orange, lemon, lime, grapefruit)

� Dry-fleshy fruits (some parts of pericarp become dry while other parts remain succulent)

� Drupe (peaches, plums, cherries, apricots, olives, almonds)� Pome (apples, pear)

� Dry fruits (the entire pericarp is dry at maturity)� Dehiscent fruits (split to expose seeds at maturity)� Dehiscent fruits (split to expose seeds at maturity)

� Legume or pod (peas, beans)� Capsule (iris, poppy)� Silique (mustard)� Follicle (Delphinium)

� Indehiscent fruits (do not split at maturity)� Achene (sunflower)� Grain or caryopsis (corn, rice, wheat, barley)� Nut (walnut)� Schizocarp (carrots, parsley)� Samara (elm, maple)

� Aggregate fruits: many matured ovaries produced by a single flower which are all fused to a fleshy structure (strawberry, blackberry, raspberry)

� Multiple fruits: cluster of matured ovaries produced by separate flowers which are borne on a fleshy structure (pineapple, mulberries)

SenescenceSenescence

What is Senescence?

� Senescence is a “cellular transdifferentiation or metaplastic process in the course of which plastid structure and function are remodelled” - Thomas et al. (2003)

� Senescence refers to “a decline in age-specific � Senescence refers to “a decline in age-specific survival and reproduction with advancing age” [Roach (1993) Genetica 91: 53-64]

� In the physiological sense, it refers to

…“the orderly degenerative process leading to death of plant parts”

[Roach (1993) Genetica 91: 53-64]

Characteristics of Senescence

� the plasticity of senescenceincreasing plasticity

flowers < fruit < leaf

� Hallmarks of senescence:

Brief life span;

unidirectional

Some temporal

variation

Maximum temporal

variation; often

environmentally controlled

� Hallmarks of senescence:a. morphological changes: nuclear condensation, plasma

membrane blebbing, apoptotic bodiesb. physiological changes: remobilisation of nutrients (senescing

flowers ���� ovary or new flowers)c. molecular changes: degradation of DNA and lipids, activation

of genes related to programmed cell death

End of LectureEnd of Lecture