Fruit development

Juvenile stage Transitional stage Maturity stage Senescence stage

Pollination Development after fertilization Maturity, ripening and

senescence

Seeds ?????

Seeds are ripened ovules

Fruits ?????Fruits are the ripened ovaries or carpels

that contain the seeds.

Most commonly develop from the ovary wall. “True fruits” – fruit derived from a single ovary “False fruits” - composed of tissues derived from

flower parts other than the ovary or from more than one ovary.

Simple fruits - derived from a single ovary eg. apple and mango

Aggregate fruit - compound fruits where separate ovaries are joined eg. blackberry

Multiple fruit or compound fruit - fruit that develop from the ovaries of many flowers growing in a cluster or into a single structure eg. pineapple

Generally occurs in four phases:1. fruit set2. rapid cell division3. cell expansion 4. ripening/maturation

Transformation of flower to fruit

Pollinationpollen from the anthers (male structures) of a flower is transferred to the stigma (the receptive part of the female structures) of the same or another flower, mediated by abiotic or biotic means

Self- pollination - when the pollen of a flower are deposited on the stigma of the same flower

Cross-pollination - when pollen are deposited on the stigma of another flower of the same species

Without pollination - flowers abort

Wind or other pollinators

Once on the stigma, the pollen grain is stimulated to germinate.

The pollen tube cell grows under the control of the tube nucleus. It grows down the style of the pistil towards the ovules.

Discharge sperm into embryo sac & fertilizing the egg.

Fertilization occurs when that pollen reaches the ovule and starts the beginnings of a new organism

Once the pollen tube nears an ovule, it enters the ovule through its opening or micropyle. It then enters one of the synergids - the cells which are located next to the eggs on the micropyle side of the ovule

Fertilization depends on compatibility between pollen and stigma.

• Without pollination - fruit usually does not develop, and the entire flower withers and falls away.

• If compatibility - substance in the surface of stigma can induce pollen germination and pollen can produce hydrolase to make stigma hydrolysis. The pollen tuber elongates, pass through stigma and fertilizes.

• If incompatibility, - stigmatic papilla will produce tylosis to block the entrance of pollen tuber or/and produce hydrolases (RNAse and protease) to degrade RNA and protein of pollen tuber and kill the pollens in the surface of stigma. ◦ pollen tuber in stigma slowly elongates and does not reach to

embryo sac

Compatibility & incompatibility between pollen & stigma

14

Generative cellTube cell

Stigma

Style

Ovary

Ovule

Carpel

Pollination

Pollen grain

Embryosac

Tube cell

Sperm cells

Tube cellnucleus

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15

Growth of pollen tube

Pollen tube

Double fertilizationRelease of sperm cells

Zygote (2n)

Antipodals

Polar nuclei

Egg cell

Synergids

Endosperm nucleus (3n)

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Physiological changes during pollination & fertilization

1. growing pollen tube increases GA production2. increase auxin production by the style and then the ovary

3. respiration rise

Auxin application can also induce parthenocarpic fruit

Pollen triggers fruit development indicating that positive signals are generated during pollination. If not- the flowers abscise.

auxin which was known to control cell enlargement in plants was thought to be the controlling factor in fruit growth

The presence of auxin in pollen, its production in the style and ovary accompanying pollen tube growth and fertilization, and the resultant stimulation in growth of the ovary

The important role of auxin in this respect is exemplified by a number of fruits that may be produced without pollination but by exogenous auxin application

After double fertilization, the ovule (containing a zygote) develops into a seed (containing an embryo), and the ovary develops into a fruit enclosing the seed(s).

As the embryo develops, the seed store proteins, oils, and starch.

Initially, these nutrients are stored in the endosperm, but later in seed development in many species, stored in cotyledons of the embryo itself.

Seed formation

Rapid cell division - involves all growing parts of the fruit

controlled by the developing seeds where the number of fertilized ovules in a fruit is correlated with both the initial cell division rate and the final size of the fruit

fruits with an uneven distribution of seeds are often lopsided

cytokinin involves in developing embryos and cell division in surrounding tissues

parthenocarpy represents an abnormal situation.

Phases in fruit development

Cell expansion - The rate and duration of cell division varies among fruits and tissues within a fruit

Tissues made up of many small cells at maturity continue dividing while tissues composed of large cells have begun expanding.

Gibberellins are also associated with fruit expansion and removal of the seeds from pea pods inhibited GA biosynthesis in the pericarp.

In general the rate change in fruit size follows two curve patterns.

1. Simple sigmoid curve e.g. peaThe initial growth rate slow in absolute terms, then increasing to steady state and finally decreasing toward maturity. eg tomatoes

2. Double sigmoid curveTwo periods of growth with a period of slow or suspended growth in between eg. peach.

 Cumulative diameter(A) tomato, Sigmoid curve(B) peach, Double sigmoid

Rate of change in diameter over time

Fruit growth curve

Maturation refer to attainment of full size or the size desired for commercial use, even though the fruit may not be ripe.

Ripeningincludes the qualitative changes which occur after the fruit has reached full size eg. firmness.

Fruits must have reached certain stage of maturity before ripening will occur or the cells have possess the necessary mechanisms for ripening.

Involve process in which the biochemistry and physiology of the organ are developmentally altered to influence appearance, texture, flavor, and aroma

SenescenceRelated to ripening – but involve catabolic stage where tissue will damage and the organ dead

1. Limited pollination◦ Types of flower◦ Receptive condition◦ Pollinators 2. Limited nutrients

CHO:N3. Abscission of flowers and young fruits

4. Light5. Rain or drought during flowering

Rain - reduce cross-pollinationDrought – pollen tube grows slow or style wilts

6. TemperatureModerate temperature favor fruit set

Environmental conditions affecting fruit development

1. Water deficient water results in slow growth and small fruit.

superfluous water causes fruit drop and less sweet, less aromatic.

2. Temperature Fruit development is enhanced by greater difference in T between day and night.

3. Light Without enough light, fruit is smaller, low sugar contents and poor color.

4. Mineral nutritionP,K increase fruit and seed and fruit sugar contents.

Physiological & biochemical events during seed development(1) Change in respiration(2) Synthesis and accumulation of storage substance.◦ Starchy seeds: Soluble sugar accumulates at beginning,

and starch increase and reach the highest in the end, while the soluble sugar decreases.

◦ Oil seedsSoluble sugar and starch accumulate at beginning

and then fat accumulates◦ Protein seed

During the ripening carbohydrate contents decrease, amino acid and amide rise at first and decrease in the end, stored protein contents reach up maximum at ripen stage.

（ 3） Plant hormones: Contents and type change from cytokinin—GA—IAA—ABA(4） dehydration

At late ripening stage, water contents of seed decline and resistance of seed to dehydration rise as late embryo abundant protein, ABA and soluble carbohydrates accumulates.

Physiological and biochemical events duringfruit ripening 1. Change in respiratory rate & ethylene production

Climacteric and non climacteric fruits 2. Coloring

Carotenoids and anthocyanins synthesize and accumulate while chlorophylls degrade due to increase in enzyme chlorophylase.

Xanthophyll – yellow colour Carotene – orangeLycopene – red Anthocyanin – red & blue or purple

3. Sweet, good smell and less acid Starch to soluble sugar - increased juiciness and sweetness enzyme amylases to accelerate hydrolysis of starch into

sugar Organic acids are broken down, changes from sour to neutral

hydrolases to help break down organic acids

Papaya fruit expansion and ripening stages for candidate gene expression analysis. A, Color development in fruit flesh of SunUp (top row) and Kapoho (bottom row). B, Expansion size (ES) of developing papaya fruit compared with mature fruit. C, Fruit ripening stages based on change in fruit skin color.

Volatile aromatic compounds increase- detected as an aroma enzymes break down large organic molecules into smaller

molecules that can volatile (evaporate into the air)4. Fruit softening

Result of enzymatic breakdown of the pectins which cement the cell walls together ie. breakdown of cell walls.

Polygalacturonase hydrolyzes bonds in pectins. Methylestarasepectinse – hydrolyse pectin in cell wallCellulose & polysaccharides hydrolysis – degrade cell

wall change of texture/firmness - softer fruitSignificant in berry fruits

5.Waxy cuticle formation to retards dehydration

Climacteric vs

Non-climacteric Fruits

A marked rise in the rate of respiration during ripening. Low respiration rate in maturing fruits followed by a large

increase in respiration during ripening. And after reaching a climacteric peak, the rate of respiration again falls

Production of ethylene increase up to 1000-fold of the basal ethylene level.

Characteristic of climacteric fruits:Requires ethylene for ripeningDramatic increase in ethylene levels during ripening Increased respiration during ripeningContinues to ripen after harvest ie. able to ripen

after being picked

eg. papaya, bananas, cantaloupes, tomatoes

Respiration and ethylene production in climacteric fruits

The rate of respiration remains steady during their ripening.

Characteristic of climacteric fruits:fruit does not ripen after harvest.does not normally require ethylene for ripeninglittle or no increase in ethylene levels during ripeninggive off little or no ethylene gas.ripening does not continue after harvest

ie. once harvested, never ripen furthernormally contain less starch

eg. pineapple, durian, strawberrie, citrus fruit, grape

1. Reduce ethylene level.i. high CO2 level inhibit ethylene production and

respirationii. certain materials which can absorb ethylene eg.

charcoal2. Temperature

Cold storage will reduce rate of respiration . High rate of respiration will shorten storage life

3. Change oxygen concentrationLowering O2 delay ripening

4. Gibberellin delays color development or color changes eg. in orange, lemon

Fruit Abscission occurs in a layer of cells in the pedicel near the point of attachment to the stem of the plantLayer called the abscission zone because this layer will eventually separate and the fruit will drop from the plant.

cells that in cross sectional layer in the pedicel get ethylene signal from the ripening fruit causes new enzymes to be made. The cells "ripen" and pectinases unglue the cells of the abscission zone. When the cells have weak-enough connections, the weight of the fruit will cause it to fall from the plant.