Transcript root
BOT3015L Biology of Flowering Plants Anatomy Seedlings, Meristems, Stems, and Roots Presentation created by Danielle Sherdan All photos from Raven et al. Biology of Plants except when otherwise noted Today • Review seeds and the life cycle of plants • Seed germination • Roots and root meristem • The three primary tissues • Specialized cells in primary root tissues • Interesting examples of root function and adaptations • Shoot and shoot meristem Life cycles From Outlaw’s lecture series Floral structure Angiosperm life cycle Gametophytes Today From Outlaw’s lecture series Monocot seed development typical monocot (maize) seed with ovary wall (pericarp) Monocots have one cotyledon (scutellum in grasses) that matures during germination Source of nutrition for seed germination: endosperm (compare to dicot) Maize fruit and seed Dicot seed development immature dicot - two cotyledons mature Three tissue systems: Dermal Vascular Cortex or Ground All cells of the primary growth in dicots are part of these three systems and originate at meristems . . . A reminder that endosperm is formed in all angiosperms, but does not persist in dicots. In dicots, cotyledons are the primary source of nutrients for germination. Today • Review seeds and the life cycle of plants • Seed germination • Roots and root meristem • The three primary tissues • Specialized cells in primary root tissues • Interesting examples of root function and adaptations • Shoot and root meristem Seed germination What causes a seed to resume growth? What is growth? Broadly, where do the energy and basic elements required for growth come from? What observations did you make while germinating seeds? Plants-In-Motion Time-lapse videos of plant growth and response Dicot germination and seedling An example of epigeous (epi=above, geo=earth) germination Dicot germination and seedling An example of hypogeous (hypo=below, geo=earth) germination Monocot germination and seedling Today • Review seeds and the life cycle of plants • Seed germination • Roots and root meristem • The three primary tissues • Specialized cells in primary root tissues • Interesting examples of root function and adaptations • Shoot and shoot meristem Root the first structure to emerge from the germinating seed Typical dicot Taproot persists and grows deep into the ground Typical monocot Taproot does not persist and adventitious roots originate from the shoot Notice the high surface volume: area ratio Tap Root vs. Fibrous Root What are the functions of roots? From Outlaw lecture Typical of a dicot Typical of a monocot Organization of the plant body Root apical meristem Meristem = group of perpetually “embryonic” cells Apical = at the tip (of the root, the shoot, including laterals) The rootcap and mucigel protect the root apical meristem as it pushes through the soil Mucigel Today • Review seeds and the life cycle of plants • Seed germination • Roots and root meristem • The three primary tissues • Specialized cells in primary root tissues • Interesting examples of root function and adaptations • Shoot and shoot meristem All cells of primary growth are from one of three primary tissues Diagram of major parts of primary dicot plant body Ground tissue is throughout the plant body Ground tissue of typical dicot root and shoot Root Shoot Buttercup (Ranunculus) Alfalfa (Medicago) All cells are from one of three primary tissues Diagram of major parts of primary dicot plant body Vascular tissue is throughout the plant body Vascular tissue of typical dicot root Root Buttercup (Ranunculus) Vascular tissue of typical dicot shoot Shoot Alfalfa (Medicago) All cells of primary growth are from one of three primary tissues Diagram of major parts of primary dicot plant body Dermal tissue is throughout the plant body Ground tissue of typical dicot root and shoot Root Shoot Buttercup (Ranunculus) Alfalfa (Medicago) Specialized dermal cells in the shoot The structure of the leaf and aspects of stomatal physiology will be topics of study next week Specialized epidermal cells Venus flytrap Today • Review seeds and the life cycle of plants • Seed germination • Roots and root meristem • The three primary tissues • Specialized cells in primary root tissues • Interesting examples of root function and adaptations • Shoot and shoot meristem Root Hairs—a special feature of roots (a) Radish (Raphanus) Bentgrass (Agrostis) Root Hairs—a special feature of roots (b) Cell Elongation Cell Division Root Hairs—a special feature of roots (c) More than with shoots, elongation growth is restricted to very near (~1.5 mm) the root tip; otherwise, elongation would tear off lateral appendages. Root hairs increase surface area. Typical dicot root Root Buttercup (Ranunculus) The endodermis Casparian Strip—a band of hydrophobic material (mostly suberin) that is impregnated in the wall, preventing apoplastic transport. From Outlaw’s lecture The endodermis Pathways for entry into xylem transport: all require that the solute be transported into the symplast (because the apoplast is discontinuous at the endodermis). Then, solutes are excreted into the apoplast interior to the endodermis. Apoplast Symplast From Outlaw’s lecture Typical dicot root Root Buttercup (Ranunculus) Secondary Growth (root) Example cross section of the dicot root in primary growth The cambium (perpetually meristematic layer between xylem and phloem) divides mitotically, producing either: A secondary xylem cell to the inside and a replacement cambial cell. OR A secondary phloem cell to the outside and a Secondary growth rare in monocots replacement cambial cell. From Outlaw’s lecture The pericycle Ordinarily, lateral roots arise in the pericycle. But roots can arise adventitiously, too. (Adventitious simply means arising in an unusual location.) Salix (Salicaceae family) From Outlaw’s lecture Today • Review seeds and the life cycle of plants • Seed germination • Roots and root meristem • The three primary tissues • Specialized cells in primary root tissues • Interesting examples of root function and adaptations • Shoot and shoot meristem Mangrove (a dicot) Support roots in the marsh habitat. From Outlaw’s lecture Interesting Examples Orchid (a monocot) Aerial roots absorb water from the air and have a multi-layered epidermis for protection and reduced water loss Interesting Examples Cross section of root Epidermal layers Flower pot plant (an epiphyte) Interesting Examples Modified leaves form hollow containers that roots grow into and that collect rainwater and debris. Many ants associate with these plants, likely adding to nitrogen supply Today • Review seeds and the life cycle of plants • Seed germination • Roots and root meristem • The three primary tissues • Specialized cells in primary root tissues • Interesting examples of root function and adaptations • Shoot and shoot meristem The shoot What are the functions of the shoot? Primary tissues differently organized in angiosperm shoots Typical of dicots Typical of monocots Primary tissues differently organized in angiosperm shoots Example dicot stem cross section vascular bundles in ring with defined pith and cortex Shoot Alfalfa (Medicago) Primary tissues differently organized in angiosperm shoots Example monocot stem cross section vascular bundles scattered Maize (Zea) Apical Meristems both have the three primary tissues Root Radish (Rafarus) Shoot Lilac (Syringa) Lilac (Syringa) Block Diagram of Typical Shoot Apical Meristem Primary meristems give rise to primary tissues Modified from Outlaw’s lecture Secondary Growth (shoot) Example cross section of the dicot shoot in primary growth The cambium (perpetually meristematic layer between xylem and phloem) divides mitotically, producing either: A secondary xylem cell to the inside and a replacement cambial cell. OR A secondary phloem cell to the outside and a replacement cambial cell. From Outlaw’s lecture The main idea