Plant structure and growth KEY CONCEPT Plants are developmentally plastic organs are formed in response to environmental cues Plant structure and growth The three basic plant organs Stems Leaves Roots Plant structure and growth Stems Contain vascular tissue Specialized for support and transport Node part of stem where leaves or other lateral organs attach Internode region between two nodes Plant structure and growth Stems Apical bud tip of shoot where growth and organ differentiation occur Axillary bud Upper surface of leaf stem junction has these can make shoots but most are dormant Apical dominance Plant structure and growth Roots Specialized for anchorage water scavenging and mineral uptake Non photosynthetic needs sugars transported from shoot system Plant structure and growth Roots Many dicots use a taproot Many monocots and seedless vascular plants do not Embyronic root dies adventitious roots form instead Plant structure and growth Roots Absorption of water and minerals is largely exclusive to the tips of root hairs single cells which project from roots Root hairs are short lived not used for anchorage Plant structure and growth Leaves Blade the solar colllector Petiole joins blade to stem at internode Most often specialized for photosynthesis Plant structure and growth Leaf types Simple single leaf per blade Compound 1 leaflet per blade Doubly compound secondary leaflets How to tell Look for axillary bud Plant structure and growth Organs can be extensively specialized here are root examples Plant structure and growth Organs can be extensively specialized here are stem examples Plant structure and growth Organs can be extensively specialized here are leaf examples Plant structure and growth Dermal tissue Outer surfaces On most leaves and stems covered with waxy cuticle In herbaceous plants non woody dermal tissue is one cell layer thick epidermis In woody plants dermal tissue is multiple cell layers the periderm Plant structure and growth Vascular tissue Xylem Phloem Typically located in center of stems Arrangement of vascular tissues differ between monocots and dicots Plant structure and growth Ground Tissue Everything else Pith Inside vascular tissue Cortex Outside of vascular tissue Includes many different specializations photosynthesis storage support Plant structure and growth The Plant Cell what s different Chloroplast Large central vacuole Cell wall Plasmodesmata Plant structure and growth Two types of cell walls Primary Common to all plant cells Relatively thin and flexible generally not lignified Secondary Laid down later in some cell types thick and stiff highly lignified Plant structure and growth Specialized plant cell types 1 Parenchyma the typical plant cell No secondary wall Large central vacuole at maturity Ground tissue Often photosynthetic Relatively undifferentiated Often totipotent Plant structure and growth Specialized plant cell types 2 Collenchyma Often found in strands just below epidermis Ground tissue Thicker primary wall but no secondary wall Flexible not rigid support Support without growth restraint Living at maturity Plant structure and growth Specialized plant cell types 3 Sclerenchyma Rigid support cells with secondary cell walls Ground tissue Often dead at maturity Can form fiber cells or sclerids Plant structure and growth Specialized plant cell types 4 Tracheids Conduct water in xylem of all vascular plants Vascular tissue Dead at maturity Thick lignified secondary cell walls Thin hard tubes to allow water flow Pits enable water movement from cell to cell Plant structure and growth Specialized plant cell types 5 Vessel elements Occur mostly in flowering plants Part of Xylem Vascular tissue Dead at maturity lignified secondary cell walls Wider thinner walls compared to tracheids Connected end to end to make true pipes Perforation plates allow water to flow from cell to cell Plant structure and growth Specialized plant cell types Vessel elements and tracheids co exist in the xylem of most angiosperms Plant structure and growth Specialized plant cell types 6 Sieve tube elements Form the water conducting paths in phloem of angiosperms Vascular tissue Alive at maturity but no nucleus ribosomes vacuoles or cytoskeleton a bag of cytoplasm Like vessel elements linked up end to end to form little pipes Sieve plates allow water flow between cells Plant structure and growth Specialized plant cell types 7 Companion cells Each sieve tube element has a neighboring companion cell Vascular tissue A complete cell with a nucleus ribosomes etc Densely connected to seive tube element via multiple plasmodesmata Functions in sugar loading and unloading Plant structure and growth Specialized plant cell types 8 Trichomes Dermal tissue Spiky hair like outgrowths Secrete oils provide physical barrier against insects Plant structure and growth Multicellular development is drastically different between plants and animals 1 Plants have Indeterminate growth Growth in size continuously throughout lifetime Plant structure and growth Multicellular development is drastically different between plants and animals 2 Plants produce organs in response to the environment Development is plastic organs and tissues represent responses to environment Plant structure and growth Plant cells and thus tissues organs are continuously produced by meristems Active cell division Meristem properties Undifferentiated cells stem cells Cells are small unexpanded Products of cell division either differentiate or remain meristematic Plant structure and growth Apical meristems Generate primary growth Growth in length Shoot apical meristem Dominant over others Responsible for vertical growth Axillary bud meristems Found above petiole node junctions Subordinate to SAM Root apical meristems Increase root length Plant structure and growth Apical meristems Primary growth produces the three major tissues dermal ground vascular Plant structure and growth Primary growth in roots Cell division zone has root apical meristem at the core Plant structure and growth Primary growth in roots Elongation zone Most root growth is the result of elongation not cell division Plant structure and growth Primary growth in roots Differentiation zone Cells take on their final form Plant structure and growth Primary growth in roots Root cap Protects meristem during growth secretes slime Plant structure and growth Primary growth in roots Root hairs Specialized epidermal cells Responsible for almost all water and mineral