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Solanum lycopersicum, tomato

● Taxonomy

● Brief facts

● Tomato flower anatomy

● Developmental stages (Life cycle)

● Tomato fruit anatomy

● References

● Appendix: Tomato reproductive developmental landmarks (Xiao H. et al. (2008))

cellular organisms - Eukaryota - Viridiplantae - Streptophyta - Streptophytina - Embryophyta - Bryophyta - Moss Superclass V - Bryopsida - Funariidae - Funariales - Funariaceae - Physcomitrella - Physcomitrella

patens

Brief facts

● Together with eggplants, potatoes, and peppers it belongs to the Solanaceae (nightshade) family. Tomato is short-lived perennial usually grown as annual plant.

● The tomato is native to Central, South, and southern North America. The Incas and Aztecs began cultivating tomato plants as early as 700 A.D. In the mid-1500s, Spanish conquistadors carried tomato seeds back to Europe, where they gained popularity as a food item in Italy, Spain and Portugal. Thomas Jefferson was one of the first Americans to grow tomatoes at his Virginia home. By 1812, tomatoes were embraced by Louisiana and Maine cooks.

● The tomato is one of the most commonly grown fresh market vegetables. Tomato farm can harvest as much as 19,000-25,000 pound (10-13 tons) per acre. Harvesting tomatoes is very labor intensive. Cultivation, handling, and marketing costs combined can run as high as $4,500 per acre. However, because of high market demands, farming of tomatoes can be quite profitable.

● There are two types of tomatoes: determinate and indeterminate. Determinate tomatoes grow to a certain height, then flower and set their fruit within a short time. "Celebrity" is popular cultivar of determinate tomato. Indeterminate tomatoes continue to grow and produce flowers and fruits until killed by first frost or senesce naturally. The harvest from indeterminate varieties often extends over 2 or 3 months (this is why they are very good for home gardening). Yields are generally heavier than from determinate types. The plants need to be supported by stakes, cages, or trellises. One of popular cultivars of indeterminate varieties is "Better boy".

● Tomatoes' varieties (more than 4,000) are commonly divided into these categories:

❍ Cherry: sweet small round tomatoes, usually eaten whole in salads ("Small Fry", "Super Sweet 100" cultivars)

❍ Plum: pear-shaped, meaty, multi-purpose tomatoes, eaten fresh or processed ("Roma" cultivars)

❍ Slicing: round or globe-shaped, multi-purpose tomatoes ("Celebrity", "Better Boy" cultivars)

❍ Beefsteak: round, juicy, ideal for sandwiches ("Big Beef" cultivar)

❍ Heirloom: old varieties of tomatoes whose seeds were passed from generation to generation; they are not hybrids like many modern tomatoes cultivars; they are popular because many gardeners believe that they have better flavor; they come in all shapes (often quite irregular), colors and sizes

❍ Yellow/Orange: sweet tomatoes rich in vitamin C and potassium but lacking lycopene ("Jubilee", "Lemon boy", respectively)

● The FDA found no credible evidence to support an association between lycopene intake or consumption of tomato and a reduced risk of lung, colorectal, breast, ovarian, or endometrial cancer. The FDA found very limited evidence to support association between tomato consumption and reduced risk of prostate, ovarian, gastric, and pancreatic cancers.

● One cup of chopped tomato contains about 32 calories (3 calories from fat). Tomatoes are valued for their vitamin and antioxidant content.

Tomato flower

Developmental stages (life cycle)

Life Cycle Stages

Tomato is a short-lived perennial, grown as an annual (5-6 months).

● seed stage MeSH

❍ dormant seed

❍ germination MeSH

under optimal conditions seed

germination (emergence of radicle) takes

from 5 to 10 days

● vegetative vegetative stage (from emergence until

the first flower) takes about 10-12 weeks

❍ seedling MeSH

the seedling can be transplanted to the

field 3 to 6 weeks after sowing

● reproductive

❍ flowering a period between floral initiation and

production of mature flower; this process

takes about 2 weeks; during this period

number of carpels and shape of the fruit

are determined;

● fruit development

❍ fruit set at fruit set, flower petals and anthers

senesce and fall away and a pea-sized

green fruit appears; from this point it

takes typically 40-50 days for fruits to be

harvestable

❍ developing fruit the fruit is of light green color and very

firm; an intensive cell division takes place

but overall fruit's growth is relatively

slow; takes about 2-3 weeks

❍ green fruit the fruit is still green; its growth

accelerated by cell expansion rather than

the cell division; cells enlarge up to 20-

fold; this period takes about 3-5 weeks;

fruit almost reached its final size and is

changing colors

❍ breaker stage rapid chemical and structural changes

that determine fruit aroma, color,

texture, etc. begin; fruit just started to

change coloration; tannish-yellow, pink,

or red occupies no more than 10 percent

of the surface of the fruit

❍ turning stage from 10 to 30 percent of surface of the

fruit is tannish-yellow, pink, or red

❍ pink stage from 30 to 60 percent of the surface of

the fruit, in aggregate, shows pink or red

color

❍ light red stage

from 60 to 90 percent of the surface, in

the aggregate, shows pinkish-red or red

color

❍ ripe more than 90 percent of the fruit reached

its final coloration; typically it is uniform

bright red or orange color; unusually for

plants, the ripe tomato fruit accumulates

large amount of carotenoid lycopene, as

the pattern of gene expression occurring

in green fruit during the fruit ripening

Tomato fruit

● Botanically, the tomato is a berry (a simple fruit produced from a single ovary). However, in 1893, the U.S. Supreme Court declared it as a vegetable.

● Ovary is superior (is above the attachment of the petals, sepals and stamens, and is free from the receptacle) and with 2-9 compartments. Mostly self- but partly cross-pollinated. Bees and bumblebees are most important pollinators.

● The tomato fruit is ripening by climacteric mechanism (as opposed to non-climacteric). Climacteric ripening is accompanied by a peak in respiration

and a concomitant burst of ethylene (important phytohormone). Exposure to exogenous ethylene accelerates ripening of green tomatoes. Other examples of climacteric fruits are apple, grape, banana, strawberries. Fruit ripening culminates in dramatic changes in color, texture, flavor, and aroma of the fruit flesh. Chloroplasts are transformed into chromoplasts, chlorophyll is degraded and carotenoids accumulate.

● The characteristic pigmentation of red tomato fruit is due to the deposition of lycopene, the predominant carotenoid found in tomato fruit, and beta-carotene, which are associated with the change from green to red as chloroplasts are transformed to chromoplasts.

● The characteristic flavor of tomato fruits results from the volatile compounds produced within the fruit during the ripening. Over 400 volatile compounds are found in tomato fruit. Among them seven are the most important contributors to the aroma: hexanal, hexenal, hexenol, 3-methylbutanal, 3-methylbutanol, methylnitrobutane, and isobutylthiazole.

● Although fruit-bearing crop species are taxonomically diverse, they share a common feature: fruit from domesticated species often are considerably larger than their wild progenitors. For example, the putative wild ancestor of the cultivated tomato bears fruit that contains only two locules and weighs just a few grams. By contrast, a single fruit of a modern cultivated tomato may contain many locules and weigh up to 1 kg, a nearly 1000-fold increase in weight.

References

PubMed articles

● Tanksley SD. The genetic, developmental, and molecular bases of fruit size and shape variation in tomato. Plant Cell. 2004;16 Suppl:S181-9. Epub 2004 May 6. PMID: 15131251

● Bramley PM. Regulation of carotenoid formation during tomato fruit ripening and development. J Exp Bot. 2002 Oct;53(377):2107-13. PMID: 12324534

● Kavanaugh CJ, Trumbo PR, Ellwood KC. The U.S. Food and Drug Administration's evidence-based review for qualified health claims: tomatoes, lycopene, and cancer. J

Natl Cancer Inst. 2007 Jul 18 PMID: 17623802

● Alexander L, Grierson D. Ethylene biosynthesis and action in tomato: a model for climacteric fruit ripening. J Exp Bot. 2002 Oct;53(377):2039-55. PMID: 12324528

Websites

● Wikipedia: Tomato

● Organic tomato production by Diver S., Kuepper G., and Born H. (ATTRA). 1999 (.pdf)

● Agrodok 17: Cultivation of tomato: production, processing and marketing by Naika S et al., 2005 (.pdf)

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Appendix

Xiao H, Radovich C, Welty N, Hsu J, Li D, Meulia T, van der Knaap E. Integration of tomato reproductive developmental landmarks and expression profiles, and the effect of SUN on fruit shape. BMC Plant Biol. 2009 May 7;9:49. PMID: 19422692

Flower Development Landmarks

(The timing of the landmarks described by Buzgo et al (2004) in S. pimpinellifolium accession LA1589)

Flower

Development

Landmarks

Days after

flower

initiation in

tomato

Perianth organs Ovary and ovule Stamen and pollen

(1) Inflorescence

formation and

flower initiation

1

Flattened

inflorescence apex

becomes dome-

shaped.

(2) Initiation of

outermost perianth

organs

2

Emergence of

sepal primordia in

a helical pattern.

(3) Initiation of

inner perianth

organs.

4

Simultaneous

emergence of

petal primordia in

alternating

positions to the

sepals. Sepals

overlay the floral

meristem

(4) Stamen initiation 5 Sepals and petals

elongate.

Simultaneous initiation

of stamen primordia.

(5) Carpel initiation 6 Petals start curling

over the stamens. Carpel primordia arise.

7

Central column that will

form the locular cavities

arise.

Central column that will

form the locular cavities

arise.

6) Microsporangia

initiation 8

Central column continues

to elongate. Carpels fuse

at the apex of the ovary.

Style initiation. Initiation

of placental development.

Primary pariety cells

develop into

endothecium, middle

layers and tapetum.

Sporogenous layers

visible.

(7) Ovule initiation 9

Ovule primordia begin to

emerge from the

placenta.

The two lobes of the

anther and the locule are

distinguishable,

microsporocyte and

tapetal cells are

distinguishable.

Binucleate tapetal cells.

(8) Male meiosis 10

Microsporogenesis.

Microsporocytes or

microspore mother cells

undergo meiosis I and II

and forming tetrads.

(9) Female meiosis 11

Megasporogenesis.

Megaspore mother cell

(meiocyte or

megasporocyte) is

visible. Meiosis I. The

nucellus is small resulting

in a tenui-nucellate ovule.

12 Petals grow to the

top of sepals.

The single integument

begins to grow over the

nucellus resulting in

unitegmic ovules.

Callose wall surrounding

the tetrads degrades

releasing the

microspores. Tapetum

starts degenerating.

13 Petals emerge

from the sepals.

Petals emerge from the

sepals.

Free microspores are

being incased in a thick

polysaccharide wall;

tapetum degenerated.

14 Onset of sepal

opening.

Megagametogenesis and

development of the

embryo sac.

Microspores come

vacuolated, and begins

asymmetric mitosis.

15 Bi-cellular pollen grain.

16 Bi-cellular pollen grain.

The vegetative cell and

generative cell are well

distinguishable.

(10) Anthesis 19 Petal opening.

Fruit developmental landmarks

(Timing of the fruit landmarks in S. pimpinellifolium LA1589)

Fruit Development

Landmarks Days post anthesis

Fruit growth (Gillaspy et

al 1993) Embryo/seed development

(1) Anthesis 0 Mature ovary, phase I.

Mature gametes. Pollen is

shed, which will land on the

stigma and germinate. Pollen

tubes growth through the

style.

(2) Fertilization 1 - 2 End of phase I, beginning

of phase II.

Fusion of sperm and egg

nuclei.

(3) 4–16 Cell Stage Embryo 3 - 6

Phase II and III, cell

division and elongation

stage.

First embryo divisions.

(4) Globular Stage Embryo 6 - 10 Phase III, cell expansion

stage. Globular embryo.

(5) Heart Stage Embryo 10 - 12 Phase III, cell expansion

stage.

Heart Stage embryo lasts

approximately one day and

occurs 10–12 dpa.

(6) Torpedo Stage Embryo 13 - 16 Phase III, continued fruit

enlargement.

Torpedo Stage embryo lasts

approximately one day and

occurs 13–16 dpa.

(7) Coiled Stage Embryo 20 Phase III, continued fruit

enlargement.

Cotyledon expansion and

curl as they elongate.

Embryo appears physically

mature, but the seed is not

yet viable.

20 - 28 Seed maturation period.

(8) Seed germination 29 - 31

The fruit has reached the

mature green stage. Fruit

becomes sensitive to

ethylene.

Seeds are becoming viable

for germination.

(9) Fruit ripening 33 - 40

Ripening starts at the onset

of the breaker stage.

Changes in pigmentation

are visible.

After ripening of seed.

(10) Ripe Fruit 40 Red ripe stage of tomato.

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