Plant Reproductive Growth PDF - Agriculture Science 111.3 2024

Agriculture Science 111.3 PLANT SCIENCES LABORATORY 3 2024 Plant Reproductive Growth Learning Objectives  Differentiate between pollination and fertilization.  List the structures of a typical dicot flower.  List the s...

Agriculture Science 111.3 PLANT SCIENCES LABORATORY 3 2024 Plant Reproductive Growth Learning Objectives  Differentiate between pollination and fertilization.  List the structures of a typical dicot flower.  List the structures of a typical cereal flower.  List the structures that make up a spikelet.  List the male and female structures of a flower.  Describe the whorled arrangement in a single complete flower and list the collective term for the structures contained in each whorl.  Differentiate between a monoecious, dioecious and synoecious plant.  Differentiate between a perfect flower and an imperfect flower.  Differentiate between a complete flower and an incomplete flower.  Describe monocot and dicot fruit structures. Key Terms and Concepts achene fertilization nectary rachis androecium filament ovary receptacle anther flag leaf ovule sepal anthesis floret palea silique Asteraceae flower panicle spike Brassicaceae glume pedicel spikelet calyx gynoecium peduncle stamen capitulum hull perfect flower staminate flowers carpel imperfect flower petal stigma complete flower incomplete flower pistil style corolla indehiscent fruit pistillate flowers synoecious dehiscence inflorescence pollination whorl dehiscent fruit legume polygamous dioecious lemma raceme Fabaceae monoecious rachilla 1  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 3 2024 General information on reproductive growth  In reproductive growth, the shoot apical meristem (SAM) switches from initiating only vegetative organs/structures (leaves, stems), and starts producing flowering structures.  Flowering structures or the inflorescence are made up portions of the stem plus the flowering units. An inflorescence is any flowering system consisting of one or more units.  In some plants, all vegetative growth ceases once flowering begins – this is referred to as determinate growth habit.  In other plants, vegetative growth continues even once flowering begins – this is indeterminate growth habit. o An indeterminate plant grows and produces flowers and fruit until it is killed by an external factor. General information about flowers  Flowers are a means of sexual reproduction. o The female reproductive organs of a flower are known as the pistil/carpel.  The pistil consists of a stigma, style and ovary. o The male reproductive organs of a flower are known as the stamens.  The stamen consists of an anther and a filament.  Dehiscence is the opening of a plant structure that facilitates dispersal of its contents. o Each unique plant structure dehisces in a predetermined way.  Pollen is shed by dehiscence.  The process of an anther shedding its contents is known as anthesis.  The pericarp of dehiscent fruits splits open and releases seeds.  Pollination is the transfer of pollen from the anther to the sticky receptive area of the stigma.  Fertilization occurs when sperm cells from the pollen grain reach the egg cell inside the ovule and fuse with it. o Viable pollen grains (found on the anthers) contain the male sperm cells that will fertilize the female egg cell inside an ovule. Parts of the flower A “typical” flower has four distinct sets of floral organs/structures namely the sepals, petals, stamens, carpels/pistils arranged in whorls (i.e. floral organs form in concentric rings).  Outer ring of sepals forms first.  Petals – next ring inward form second.  Stamens – third ring inward form next.  Middle ring of carpels/pistils forms last. Sepals  Outermost whorl  Collective term for sepals is calyx  Often green, leaf-like structures  Function: cover and protect the flower bud 2  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 3 2024 Petals  Next whorl inside the sepals  Collective term for petals is corolla Stamens  When present these male floral organs are located in the whorl immediately inside the petals  Androecium is the collective term for the stamen(s)  Each stamen consists of a stalk called a filament  The pollen bearing part of the stamen at the apex of the filament is called the anther Carpel/Pistil  The inside whorl or central part of a flower; they are the female floral organs  Gynoecium is the collective term for the carpel(s)/pistil(s) which are made up of the stigma, style and ovary  The style connects the upper and basal portion of the carpel/pistil  The upper portion of the carpel/pistil that receives the pollen is the stigma, which is connected by the style to the enlarged basal portion of the carpel/pistil known as the ovary The receptacle of a flower is the expanded region to which the floral parts are attached. Flower Types  If a flower has all four types of floral organs present (sepals, petals, stamens and pistil) the flower is said to be complete  If a flower is missing any one of the whorls of floral organs, the flower is said to be incomplete  The reproductive organs of a flower (stamens and pistil) are considered the essential parts, and if both are present the flower is said to be perfect  If either is absent, the flower is termed imperfect  A single plant with both staminate and pistillate flowers on the same plant is referred to as monoecious (mono/ecious = one house) o A staminate flower is an imperfect (unisexual) flower containing stamens but no functional pistil. o A pistillate flower is an imperfect female flower. They have one or more pistils, but no stamens.  When staminate and pistillate flowers occur on separate plants the plant is referred to as dioecious (dio/ecious = two houses)  When a single plant has all perfect flowers it is referred to as synoecious (syno/ecious = housed together)  A single plant with a mixture of imperfect and perfect flowers is referred to as polygamous Flowering of Cereal Crops Inflorescences in the grass family are composed of individual units called spikelets. A spikelet consists of two glumes enclosing one or more florets. 1. Working our way through a spikelet from the outside inward, we find first a pair of glumes. o Glumes are bracts, which enclose the spikelet. o Glumes may be large and papery as in oats, or very small and relatively 3  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 3 2024 inconspicuous as in barley. 2. Within the pair of glumes we find at least one, but possibly many florets (small flowers) depending on the species of grass. o Wheat has many florets/pair of glumes. o Barley has one floret/pair of glumes. o In a wheat spikelet that has many florets the main access of a spikelet bearing the florets is called a rachilla. 3. Each floret has two bracts (the lemma and the palea) that enclose the actual sexual parts of the flower. o If the lemma and palea remain around the ripened grain produced by this flower, they form the hull … as in hulled barley and oat. o However, through thousands of years of agricultural selection, in most modern types of wheat the lemma and palea grow brittle and fall off when dry … so this grain is free of hulls when ripe. 4. The ovary, the main female part of the cereal flower, occupies most of the space enclosed within the lemma and palea. o At the upper end of the ovary are two feathery stigmas, which will emerge from between these two bracts to receive pollen at the appropriate time. 5. The male parts of the cereal flower emerge flower from between the lemma and palea. o A grass floret typically has three stamens. 6. Inside the ovary is a single embryonic seed called an ovule. o Once pollinated, the ovule grows to form a seed that entirely fills the ovary chamber. o In grasses the seed will grow to so completely fill the ovary cavity that the seed’s coat (testa) will fuse to the inside of the ovary wall (pericarp) making these two layers essentially inseparable. o The resulting fruit is a caryopsis - a dry, single-seeded fruit with the testa fused to the pericarp. Pollination of Cereal Crops Although only 10 % of flowering plants are wind pollinated, this category includes many of the most important food crops (corn, cereal crops, rice). Flower adaptations for wind pollination include:  flowers clustered at the top of the plant  abundant pollen Inflorescence Types Spike Inflorescence  An elongate inflorescence with sessile spikelet/flower attachment (i.e. the spikelets/flower are attached directly rachis).  The rachis is the central stalk running through the inflorescence and is attached at its base to the peduncle.  Wheat, barley and rye are examples of a spike. 4  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 3 2024 Raceme  A raceme has flowers along a central rachis (main stem) with individual flowers joined to it by tiny secondary stems called pedicels.  The flowers on the raceme will open and mature from the bottom, upward.  A raceme is an unbranched inflorescence.  Canola plants produce flowers arranged in racemes. Panicle Inflorescence  In a panicle inflorescence, branches emerge from the central rachis, and spikelets/flowers are attached to these branches by means of small stalks called pedicels. o There are two series of branches that make up a panicle, main branches from the rachis, and secondary smaller branches (pedicels) joining these primary branches to the spikelets.  Oats grass is an example of a panicle. Umbels  Simple umbel – a large number of pedicels arise from the same point on the peduncle (onions and common geranium).  Compound or double umbel – many small umbels are clustered at the top of a peduncle to form a single large umbel (dill and other members of the family Apiaceae). Capitulum  A capitulum has many small flowers attached to a common receptacle.  Very frequently the capitulum will resemble one very large flower, when in reality it is composed of hundreds or thousands of very small flowers that together form a large flower.  Asteraceae (sunflower/aster) family always produce flower heads (inflorescence) called a capitulum. Corymb  a flat-topped or round-topped inflorescence; pedicels vary in length Insect Pollination  Dicot flowers are adapted to either self- or cross-pollination and have evolved in ways to facilitate this process.  90% of flowering plants, including most dicots are insect pollinated.  Adaptations of dicot flowers to attract insects includes: o large flowers with showy colors o nectaries = gland secreting structures usually present at the base of a flower o flower shape and flower scent Fruit Development  Pollination and fertilization must be successful for a harvestable seed to develop.  The fertilized ovule is known as an embryo. The embryo develops into the seed and the ovary develops into a fruit. 5  Agriculture Science 111.3 PLANT SCIENCES LABORATORY 3 2024 o This embryo develops into a seed, and the surrounding ovary develops into a fruit – this fruit may be a pod, a berry, a fleshy fruit like an apple, peach, or cucumber. In grasses the fruit type is a caryopsis.  In the particular case of grasses, the seed inside the ovary grew to so-completely fill the ovary chamber that the testa (seed coat) pressed tightly against and fused with the pericarp (ovary wall).  The fusion of the ovary wall with the seed coat makes it easy to mistake a grain for a simple seed, but because that seed is enclosed within a ripened ovary wall, the entire structure is actually a simple dry fruit known as a caryopsis.  A caryopsis is the fruit found only in the grass family (Poaceae).  A caryopsis is defined as a dry single seeded fruit with the pericarp (ovary wall) fused to the testa (seed coat). Dicot Fruit Structures Legume  A legume is composed of a single carpel. o A legume dehisces along two sutures at maturity o Found in Fabaceae (pea family) o Pulse crops belong to the pea family Silique  A silique is composed of two carpels.  A silique dehisces along two sutures.  Fruit is divided lengthwise by a false septum.  The structure is longer than it is broad  Found in Brassicaceae(mustard family) Achene  An achene is a one-seeded fruit.  The pericarp is easily separated from the seed coat  Found in Asteraceae (sunflower/aster family). Seed Dispersal is the Primary Function of Botanical Fruits Botanical fruit structures are categorized as either dehiscent or indehiscent. Dehiscent Fruits  The pericarp splits open at maturity and releases the seeds it contains. o Legume and silique are examples of dehiscent fruits o The seed is the unit of dispersal Indehiscent Fruits  The pericarp does not split open at maturity; the seeds remain enclosed within pericarp tissue o Achene and caryopsis are examples of indehiscent fruits o The fruit is the unit of dispersal 6