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Chapter 6: Plant Life Cycle: Fruits and Seeds (Representative Edible…
Chapter 6: Plant Life Cycle: Fruits and Seeds
Fruit Types
Aggregate and Multiple Fruits
aggregate fruit
:
a fruit derived from a single flower with several separate ovaries; example: blackberry
separate carpels/ovaries ripen at the same time
multiple fruit
:
a fruit derived from the fusion of the ovaries of several flowers in an inflorescence; example: pineapple
fruits are unique aspects of sexual reproduction in angiosperms, protect the enclosed seeds and aid in their dispersal
pericarp
:
the fruit wall that develops from the ovary wall
composed of three layers
exocarp
:
outermost layer in the pericarp (fruit wall)
mesocarp
:
middle layer in the pericarp (fruit wall)
endocarp
:
innermost layer of the pericarp (fruit wall)
thickness/distinctiveness between three layers varies among fruit type
Simple Fruits
Simple Fleshy Fruit
fleshy fruit
:
fruit in which the cells of the pericarp are alive at maturity
when ripe, pericarp often soft and juicy
seed dispersal accomplished when animals eat fruit
common types of fleshy fruit
berry
:
simple, one- to many-seeded, fleshy fruit with thin exocarp; example: tomato
has a thin exocarp, a soft fleshy mesocarp, and an endocarp enclosing one to many seeds
hesperidium
:
simple, fleshy fruit with leathery exocarp; example: any citrus fruit
a berry with a tough, leathery rind
accessory fruit
:
type of fruit in which most or part of the fruit is derived from tissue other than the ovary of a flower
pepo
:
fleshy fruit with a tough outer rind that is composed of both receptacle tissue and exocarp, such as cucumber, pumpkin, and melon
a specialized berry with a tough outer rind (consisting of both receptacle tissue and exocarp), with a fleshy mesocarp and endocarp
pome
:
a simple fleshy fruit; the outer portion formed by floral parts that surrounded the ovary; examples: apple and pear
most of the fleshy part develops from enlarged base of perianth that has fused to ovary wall
drupe
:
simple, fleshy fruit with the seed enclosed in a hard endocarp (pit); example: cherry
thin exocarp, fleshy mesocarp, and hard/stony endocarp that encases the seeds
Simple Dry Fruits
dry fruits fall into two categories
dehiscent fruit
:
fruit that splits open at maturity, facilitating seed dispersal
Dry Dehiscent Fruits
three common types of dehiscent fruits, all characterized by the way in which they open
follicle
:
single, dry, dehiscent fruit that splits along one seam; example: milkweed
legume
:
simple, dry, dehiscent fruit that splits along two seams, a pod; member of the Fabaceae; a type of bean or pea
capsule
:
simple, dry, dehiscent fruit that opens along three or more seams or pores; example: cotton
most common dehiscent fruit
indehiscent fruit
:
dry fruit that does not split open on maturity
examples of dry indehiscent fruits
achene
:
simple, dry, indehiscent fruit with seed attached to pericarp at only a single point
one-seeded fruit in which pericarp is free from seed
samara
:
a simple, dry indehiscent fruit with the pericarp bearing winglike outgrowths; winged fruit of maple
usually described as modified achenes
grain
:
single, dry indehiscent fruit of a single seed that is fused to the ovary wall
single-seeded fruits in which pericarp is fused to seed coat
caryopsis
:
simple, dry, indehiscent fruit with a single seed that is fused to the ovary wall; also called a grain; example: wheat
nut
:
a one-seeded, dry, indehiscent fruit with a hard pericarp
dry fruit
:
fruit in which the cells of the pericarp are dry (dead) at maturity
pericarp of dry fruits may be tough/woody or thin/papery
usually contain more than one seed
seed dispersal often aided by wind
simple fruit
:
a fruit that develops from a single ovary
derived from ovary of single carpel or several fused carpels
described as fleshy or dry
Seed Structure and Germination
Dicot Seeds
dicot seeds usually have two cotyledons that are attached to/enclose embryonic plant
cotyledons often large and fleshy and occupy greatest part of dicot seed and have absorbed nutrients from endosperm
endosperm in many dicot seeds either lacking or reduced
example is the garden bean
thin, membranous seed coat (aka testa) encloses the seed
seed coat
:
the outer layer of a seed that is developed from the integuments of the ovule; the testa
testa
:
seed coat
hilum and micropyle are visible on surface of testa
hilum
:
scar on a seed indicating where it was attached to the ovary
micropyle
:
the opening in an ovule through which the pollen tube enters during fertilization
if seed coat is removed, two large food-storing cotyledons are easily seen/separated
sheltered between the cotyledons is embryo axis, consisting of the epicotyl, the hypocotyl, and he radicle
epicotyl
:
portion of the shoot of an angiosperm embryo or seedling above the cotyledons
develops into the shoot (stems and leaves) of the seedling and typically bears embryonic leaves within the seed
hypocotyl
:
region of stem in a plant embryo that is below the cotyledons
radicle
:
the embryonic root found in the seed
Monocot Seeds
monocots have a single, thin cotyledon that transfers food from endosperm to embryo
example is the corn kernel
grain is a fruit in which the seed coat of the single seed is fused to the pericarp
differs from garden bean since corn kernel has extensive endosperm that occupies much of the volume of seed
small embryo has only single cotyledon (aka scutellum)
scutellum
:
the single cotyledon in grass seeds
seeds in grass family have other differences, such as presence of coleoptile (sheath that surrounds the epicotyl) and a coleorhiza
coleoptile
:
sheath surrounding the embryonic shoot of monocotyledons
coleorhiza
:
sheath surrounding the radicle (embryonic root) of monocotyledons
Seed Germination and Development
when seeds germinate, first structure to emerge is the radicle, which continues to grow and provides the primary root
enables developing seedling to absorb water
shoot emerges next
in garden beans, hypocotyl elongates and breaks through soil in arch that protects the epicotyl tip with its embryonic leaves
in most dicots, the cotyledons are carried aboveground with the expanding hypocotyl, but in some they remain belowground
soon after tissues of seedling emerge from underground and are exposed to sunlight, develop chlorophyll and begin to photosynthesize
exposure to sunlight triggers the hypocotyl to straighten into an erect position
seed develops from the fertilized ovule and includes an embryonic plant and some form of nutritive tissue within a seed coat
differences between dicots and monocots apparent in seeds, names refer to number of seed leaves (or cotyledons) present in seed
cotyledon
:
seed leaf in the seed and seedling
Representative Edible Fruits
Tomatoes
botanically fruits, but declared vegetables by the government
cultivar
:
abbreviation for the cultivated variety of a plant
there are over 500 cultivars in the tomato species
commercial tomatoes have been bred for efficient mechanical harvesting, transportability, and long shelf life, not necessarily taste
also developed as a determinate habit, which are shorter, bushier, and more compact
identified 13 species of tomatoes and four closely related species from wild populations
most of the characteristics associated with domesticated tomato are result of mutations in just 30 out of the 35,000 genes in the tomato
the gene fasciated doubles fruit size by increasing the number of locules, compartments in the ovary containing the seeds
domestication brought genes producing more sugars and acids, making the domesticated tomato more flavorful
Apples
the blossoms of the apple tree are five-serous flowers (containing five sepals, five petals, numerous stamens, and a five-carpeled ovary), usually pollinated by bees
not grown with seeds today, since cannot tell what genes the seeds have and most will not develop into valuable varieties
most apple trees produced by grafting, a form of asexual reproduction or cloning in which stem cuttings/buds from desirable cultivar are joined to the base of a second tree
grafting
:
the union of a part of one plant, the scion, to the root or stock of another plant
scion
:
a small twig or bud that is grafted to a stock
will become the upper/top portion of the new tree
rootstock
:
root system to which a scion or upper portion of a woody plant is grafted; also known as a stock
stock
:
the rooted part of a plant to which the scion is grafted
the root system of the grafting combination
apple is a pome, a single fleshy fruit with accessory tissue
core is a five-carpeled ovary with seeds
ovary wall is visible as a fine, brownish like, endocarp is prominent as parchmentlike material around the seeds
skin and flesh of apple develop from the receptacle and base of the perianth
Oranges and Grapefruit
both part of citrus family (Rutaceae)
botanically, citrus fruit is a hesperidium, characterized by its thick rind, which has many oil glands
fragrant oils attract animals for fruit and seed dispersal
within the fruit, individual carpels are filled with many one-celled juice sacs
Chestnuts
product of a genus native to temperate regions of eastern NA, southern Europe, northern Africa, and Asia
one of the most useful trees to native people in NA
high tannin content of wood made it resistant to decay
usually, three nuts (one-seeded fruits with a stony pericarp) are borne in spiny bur or husk that splits open at maturity
each nut produced by single female flower, which is borne in cluster of three
cluster is subtended by an involucre, a collection of bracts that develop into the spiny bur as the fruits nature
trees are monoecious, with staminate flowers born in long, slender catkins on same individual
disease affected trees in early 20th c, infected the trunk of the tree but not the roots
today, young saplings can reach 4-6 meters before they succumb to disease
Exotic Fruits
includes apples, oranges, peaches, bananas, watermelons, pineapples, which had origins in faraway places
in US, cultivation of kiwi mainly in northern CA
cherimoya may be seen more frequently in near future
tree fruit native to uplands of Peru and Ecuador
atemoya is new hybrid and more tolerant of environmental conditions
Carambola recently introduced to NA, native to Malaysia (star fruit)
durians are major fruit throughout Southeast Asia
trees produce melon-sized fruits that have thick green rind and are covered with stout spines
inside, five compartments with smooth, creamy white pump surrounding the seeds
smell similar to rotten eggs because of presence of sulfur compounds
created odorless variety recently
The Influence of Hormones on Plant Reproductive Cycles
many phases of plant cycle are influenced by hormones, act as chemical messengers that are effective at very low concentrations
produced in one part of organism and affect another part
major types of plant hormones
auxins
:
a class of plant hormones that influences cell elongation and is involved in many stages of growth and development
Darwins studied phototropism (growth toward the light) and suggested response was due to “influence” produced in top of coleoptile that moved to growing area
several decades later, Went discovered that “influence” was actually chemical compound, named it auxin
produced in apical meristems and other actively growing plant parts, including young leaves, flowers, fruits, and pollen tubes
also involved in many stages of growth and development
promote elongation of young stems and coleoptiles by stimulating cell elongation
inhibit lateral bud development and promote apical dominance, producing a plant with a main stem and limited branching
stimulate adventitious root initiation and are involved in growth responses to gravity (gravitropism)
regulate fruit development
produced by pollen tube as it grows through style and by embryo and endosperm in developing seeds
synthetic auxins do not occur naturally in plants but are often more effective in stimulating plant responses
have no effect on flowering except in pineapple, which can be applied to promote uniform flowering by stimulating ethylene formation
apples, oranges, and grapefruit can be sprayed to prevent premature development of abscission layers (separation zones) and the resulting fruit drop
gibberellins
:
a class of plant hormones involved in many stages of growth and development, especially stem elongation and seed germination
promote stem elongation of dwarf plants by stimulating internode elongation
promote speed germination of some plants by substituting for an environmental trigger
can stimulate flowering in biennials during first year, instead of the rosette (tight cluster of leaves) typically produced in first year
rosette typically occurs on stems with very short internodes, which expand and produce flowering in the second year (bolting)
cytokinins
:
a class of plant hormones that promote growth by stimulating cell division
stimulate cell division and differentiation of plant organs
along with auxins, necessary as ingredient in media for tissue culture of plant cells
delay senescence in detached plant parts
areas remain green and healthy while surrounding tissues age and die
used commercially to maintain freshness of cut flowers
abscisic acid
:
a plant hormone that promotes dormancy and is associated with water balance by causing stomatal closure
inhibitor hormone that promotes dormancy in seeds and buds
involved in regulating water balance in plants by causing stomata to close
in well-watered plants, concentrations in leaves are very low, but increases in drought, which results in stomatal closure, which causes transpiration rates to decrease dramatically
ethylene
:
gaseous plant hormone involved in fruit ripening and other aspects of plant growth and development
unusual because it is a gas
can be produced in all parts of plant, but especially in roots, the shoot apical meristem, senescing (aging) flowers, and ripening fruit
high levels of auxin stimulate ethylene production
promotes flowering in a few species, such as the pineapple
stimulated by auxin, with promotes uniform flowering
most dramatic effects are on fruit ripening
stimulates fruit softening, the conversion of starch to sugars, and production of volatile compounds that impart aromas and flavor in many types of fruit
typically accompanied by peak in cellular respiration of fruit
used to produce ripe fruits throughout winter
picked early and exposed to conditions that inhibit ethylene production and then, when ready for sale, exposed to small amount of ethylene, then producing its own
sometimes considered stress hormone because produced in wounded or infected tissues and flooded plants
of more than 350,000 known species of angiosperms, only small percentage produce fruits that have been utilized by humans