Chapter 35 Plant Structure, Growth, and Development

1. Chapter 35Plant Structure, Growth, and Development Shannon Nugent Austin Wetterau Erin Strong

2. Anatomy of a Plant • 3 Basic Organs: • Roots, Stems, Leaves • Absorb water from below and CO2 from above • Root system and Shoot System • Both depend on each other • Roots starve without photosynthesis • Shoot system depends on water and minerals absorbed

3. Roots • Multicellular organ acting as an anchor, absorbs nutrients, and stores carbs • Most gymnosperms or eudicots have a Taproot - main root • Lateral roots - roots linked to main taproot • Monocots - many small roots (fibrous root system)

4. Stems • Stem - an organ consisting of system of nodes where leaves attach with internodes • Axillary bud - in angle of stem and leaf (branch) • Apical bud - developing leaves • Buds describe dormancy • Possible Food storage and asexual reproduction

5. Leaves • Main photosynthetic organ • Monocots - parallel major veins • Eudicots - branched network of veins • Help taxonomists diversify many different plants

6. 35.2 • Intermediate growth - most plants grow continuously • Plant life cycle: Annual, Biennial, Perennial • Meristems make intermediate growth possible • Initials - sources of new • Derivatives - new cells from meristem

8. 35.3 • Growth of Roots • Primary growth produces the Primary plant body: parts of roots and shoot systems produced by apical meristems • Tip of root is covered by the root cap: protects apical meristem  during primary growth • zone of cell division includes apical meristem & 3 primary meristems (protoderm, procambrium, & ground)

9. 35.3 cont. • Growth occurs in 3 stages: • zone of cell division (where new root cells are produced)- • zone of elongation: root cells elongate • -zone of differentiation: zone of maturation, become distinct cell types • Primary growth produces epidermis, ground tissue, and vascular tissue

11. 35.3 cont. • Growth of Shoots • vascular tissue runs through stem in strands called vascular bundles • dicots = vascular bundles in ring, pith inside ring, cortex outside • monocots = vascular bundles scattered through ground tissue • Leaves develop from Leaf primordia: projections along side of apical meristem

12. 35.3 cont. • Tissue Organization • Epidermis has stomata: tiny pores controlled by guard cells that allow gas exchange • Ground tissue is located in the mesophyll • Vascular tissue contains xylem and phloem

14. 35.4 • Secondary growth occurs in stems and roots of woody plants • Secondary Plant Body: tissues produced by vascular cambium and cork cambium- • vascular cambium: cylinder of meristematic cells that forms secondary vascular tissue, increases vascular flow and support for shoots • cork cambium: produces a tough, thick covering that protect the stem from water loss and invasion • Primary and secondary growth occur simultaneously

15. 35.4 cont. • Vascular Cambium and Secondary Vascular Tissue • As meristematic cells divide, they increase circumference of vascular cambium and add layers of secondary xylem (wood) to its interior and secondary phloem to exterior • Some parts of vascular cambium are elongated & other parts are shortened and produce vascular rays: radial files of cells that connect the secondary xylem with secondary phloem

16. 35.4 cont. • A year’s growth appears as a distinct ring in tree trunks and roots • Heartwood= old layers of secondary xylem that no longer transport water and minerals • Sapwood= newest, outer layers of secondary xylem, transports xylem sap

17. 35.4 cont. • Cork Cambium & Production of Periderm • During secondary growth, epidermis is falls off and is replaced by two tissues produced by the first cork cambium • Cork tissue functions as a barrier that protects stem/root from water loss, physical damage, and pathogens • Periderm: consists of cork cambium plus the layers of cells it produces • Lenticels: dot the periderm and enable living cells within a woody stem or root to exchange gases with outside air • Bark: all tissues external to vascular cambium • Components of bark = secondary phloem, most recent periderm, and old layers of periderm

18. 35.5- Growth, Morphogenesis, and Differentiation Produce the Plant Body • Scientists believe that if they identify each gene’s function in a plant, they can discover a blue print of how plants develop

19. 35.5 cont. • GROWTH • When cell numbers increase, cell divisions in meristems increase the potential for growth • Most increase in growth comes from cell expansion or elongation

20. 35.5 cont. • Preprophase band • Concentrated ring of microtubules. Disappears before metaphase, but predicts the future plan for cell division • Water uptake accounts for 90% of plant cell expansion • Vacuoles fill quickly from the water uptake & take up a lot of space in cells, letting the plant grow rapidly

21. 35.5 cont. • Enzymes weaken the cross-links in cell wall, letting it expand as water diffuses into the vacuole by osmosis • Morphogenesis must occur for plant to develop properly • Cells must be organized into multicellular arrangements of tissues and organs

22. 35.5 cont. • Pattern formation- Development of specific structures in specific locations • Positional information is communicated by signals that continuously indicate to every cell its location in the developing structure • Ex. Hormones, proteins, mRNAs provide positional info.

23. 35.5 cont. • Critical step in morphogenesis is proper establishment of axial polarity • Morphogenesis is under the control of homeotic genes (master regulatory genes that over see major events in development)

24. 35.5 cont. • Cellular differentiation depends on the control of gene expression • Positional information is important to all stages of development (growth, morphogenesis, and differentiation) • Phase changes- When internal or environmental changes cause a plant to switch from developing one part to another