BIO 335 Seeds and Fruit Lecture PDF

Seeds and Fruit BIO 335 General Botany Seeds Primary function of the seed is to protect the embryo. The embryo is the product of fusion of the sperm and egg. The egg provides the cytoplasm and organelles. Endosperm is triploid and very active. Once formed it will divide...

Seeds and Fruit BIO 335 General Botany Seeds Primary function of the seed is to protect the embryo. The embryo is the product of fusion of the sperm and egg. The egg provides the cytoplasm and organelles. Endosperm is triploid and very active. Once formed it will divide rapidly and go through a coenocytic stage. Endosperm forms via many nuclear divisions and cytoplasmic thickening.  Coconut Seed Endosperm Embryo Embryo Development Embryo forms by both nuclear and cellular divisions. Embryo divides via asymmetrical division. Basal cell and apical cell – polarity. Development of suspensor anchors the embryo. Globular stage is next, the Heart and Torpedo. Based on appearance of embryo in dicots. The look of the monocot embryo is a bit different. The look of the gymnosperm embryo is very much like that of the dicot except that there are many more cotyledons. Dicot Embryogenesis Images are of Arabidopsis Capsella – Sheppard’s Purse Capsella Seeds Embryogenesis in Monocots Monocot Embryogenesis Am. J. Bot. August 2014 vol. 101 no. 8 1259-1274 Seed Types Seeds can be described as albuminous and exalbuminous. The difference is whether there is nutritive material left surrounding the developing embryo. The Castor bean and the corn are albuminous and the Common bean is exalbuminous. Gymnosperm seeds can also be considered albuminous although the nutritive tissue is largely megagametophyte tissue. Dicot Seeds Capsella - albuminous Phaseolus - exalbuminous Dicot Seed Radicle Plumule Monocot Seed Gymnosperm Seed Megagametophyte Embryo Seed Coat (Testa) Sclerids Parenchyma Dormancy There are a number of different dormancy mechanisms, some of them physical, some of the hormonal, etc. Dormancy mechanisms can be overcome with the appropriate scarification methods. Most involve some combination of temperature variation and moisture variation – we often refer to the combination as vernalization. Other mechanisms require some physical disturbance of the testa that can include burning by fire, acid, or physical scraping. Dormancy The ABA/GA response model for dormancy centers on the relative amounts of the phytohormones present in the seed tissue. The balance between the synthesis of one and the degradation of the other can trigger or inhibit the germination response. Germination Seeds germinate in basically the same way. Seed needs to be imbibed to “wake up” the embryo and break dormancy. Germination begins when the embryo starts to respire, which can be easily measured. Embryo will be involved in the digestion of of the endosperm via the release of hydrolytic enzymes. Usually the first visible sign are swelling of the seed and emergence of the radicle as it ruptures the seed coat. Germination Activation of the seed metabolism. Anaerobic respiration at first as well as PPP and Beta- oxidation. Mobilization of enzymes and stored nutrients. Activation of the aleurone in cereals. Exalbuminous dicots use metabolites in cotyledons. Rapid cell division in hypocotyl and epicotyl. Causes the emergence of the radicle. Imbibed bean seed Barley Seed Germination – GA Sensitive Lettuce Seed Germination GA Insensitive Establishment of the Stele Hypogeal Germination Epigeal Germination Dicot Emergence Dicot Emergence Dicot Emergence Monocot Emergence Monocot Emergence Monocot Emergence Conifer Seed Emergence Embryo Cotyledons (seed leaves) The seed of the gymnosperm represents three generations of the life cycle. The seed coat is derived Megagametophyt from the integuments of the e sporophyte (2n), which encases the tissue Seed coat megagametophyte (n), which surrounds the embryo (2n). Fruit Modifications of the ovary or receptacle wall. Most fruit is specialized to facilitate seed dispersal. When fruit forms, the other floral organs wither away. The walls differentiate into three distinct layers. Endocarp – inner most layer surrounds seeds. Mesocarp – middle fleshy layer. Exocarp – outer layer, skin or peel Pericarp – is all of the layers together. Fruit Morphology Fruit Terminology Fruit Terminology True fruit = ovarian tissue only - tomato Accessory = other tissues. – strawberry = receptacle Simple = derived from one ovary from one flower. Compound = aggregate - separate carpels from a single gynoecium fuse together. raspberry Multiple – individual fruits from an inflorescence fuse together. Pineapple / fig. Fleshy = pericarp edible and usually eaten during seed distribution. Dry = pericarp not usually eaten. Dehiscent = break open and release the seeds. Indehiscent = must be cracked open. Fruit Seed Dispersal Many fruit do not open when mature, the simply are eaten or decompose. Dehiscent fruit will rupture on it own, but with some specific patterns. These patterns are used to describe fruit types. Dispersal Consequence of breeding  Fruit ripening Developing fruit pass through a series of programmed stages. Fruit goes through two stages of division and expansion (sometimes called filling). Ripening process is influenced by the gaseous plant growth regulator (hormone) called ethylene. The stages of starch accumulation and decline are influenced by the maturation of the seed. Starech degredation will lead to the accumulation of simple sugars like fructose, Fleshy Fruits Berry Pome Pome Similar to berry by the exocarp is papery, or leathery. Drupe Similar to berry but the endocarp is sclerenchymous (stone fruits) Pepo A fleshy fruit is where the exocarp is tough or hard. The inner layers may not de differentiated. Hesperidium Simple fruit with a thick and leathery exocarp. Hip (Semi-fleshy) Separate carpels enclosed by a fleshy receptable/hypanthium Dry Indehiscent Fruit Caryopsis Simple small indehiscent fruits contains one seed and the testa. The seed fuses with the thin pericarp and ruptures it during germination. Achene Seed Indehiscent fruit like the caryopsis Pericarp but fruit and seed remain distinct. Anthocarp Similar to achene, but perianth and receptacle are fused Samara One seeded fruit with winged outgrowths of the ovary wall. Nut Generally comes from a compound gynoecium Nut with Involucre Chestnuts and Hazelnuts as well. Tryma Nut-like drupe Utricle Single seeded bladders with thin walls. Dry Dehiscent Fruit Legume Loment Silique  Follicle Fruit breaks open on one side Capsule Develops from a compound gynoecium Schizocarp Clock weed Compound Fruit Aggregate Fruit - Druplets Aggregate Fruit - Achene Multiple Fruit - Berry Multiple Fruit - Syconium Figs are best known example and require special pollinators. What is it? Coconut What is it? Cherimoya Cherimoya What is it? Dragon Fruit Dragon Fruit What is it? Banana or Plantain Banana