2. Plants Transport and Tissue

3. 2005-2006 Transport in plants H 2 O & minerals – transport in xylem – transpiration Sugars – transport in phloem – bulk flow Gas exchange – photosynthesis CO 2 in; O 2 out stomates – respiration O 2 in; CO 2 out roots exchange gases within air spaces in soil Why does over-watering kill a plant?

4. 2005-2006 Transport in plants Physical forces drive transport at different scales – cellular from environment into plant cells transport of H 2 O & solutes into root hairs – short-distance transport from cell to cell loading of sugar from photosynthetic leaves into phloem sieve tubes – long-distance transport transport in xylem & phloem throughout whole plant

5. 2005-2006 Cellular transport Active transport – solutes are moved into plant cells via active transport – central role of proton pumps chemiosmosis proton pumps

6. 2005-2006 Short distance (cell-to-cell) transport Compartmentalized plant cells – cell wall – cell membrane cytosol – vacuole Movement from cell to cell – move through cytosol plasmodesmata junctions connect cytosol of neighboring cells symplast – move through cell wall continuum of cell wall connecting cell to cell apoplast symplast apoplast

7. 2005-2006 Routes from cell to cell Moving water & solutes between cells – transmembrane route repeated crossing of plasma membranes slowest route but offers more control – symplast route move from cell to cell within cytosol – apoplast route move through connected cell wall without crossing cell membrane fastest route but never enter cell

8. 2005-2006 Long distance transport Bulk flow – movement of fluid driven by pressure flow in xylem tracheids & vessels – negative pressure – transpiration creates negative pressure pulling xylem sap upwards from roots flow in phloem sieve tubes – positive pressure – loading of sugar from photosynthetic leaf cells generates high positive pressure pushing phloem sap through tube

9. 2005-2006 Movement of water in plants cells are turgid cells are flaccid plant is wilting Water relations in plant cells is based on water potential – osmosis through aquaporins transport proteins – water flows from high potential to low potential

10. 2005-2006 Water & mineral uptake by roots Mineral uptake by root hairs – dilute solution in soil – active transport pumps this concentrates solutes (~100x) in root cells Water uptake by root hairs – flow from high H 2 O potential to low H 2 O potential – creates root pressure

11. 2005-2006 Controlling the route of water in root Endodermis – cell layer surrounding vascular cylinder of root – lined with impervious Casparian strip – forces fluid through selective cell membrane & into symplast filtered & forced into xylem vessels

12. Plant TISSUES Dermal – epidermis ( “ skin ” of plant) – single layer of tightly packed cells that covers & protects plant Ground – bulk of plant tissue – photosynthetic mesophyll, storage Vascular – transport system in shoots & roots – xylem & phloem

13. Plant CELL types in plant tissues Parenchyma –“ typical ” plant cells = least specialized – photosynthetic cells, storage cells – tissue of leaves, stem, fruit, storage roots Collenchyma – unevenly thickened primary walls – support Sclerenchyma – very thick, “ woody ” secondary walls – support – rigid cells that can ’ t elongate – dead at functional maturity

14. Parenchyma  Parenchyma cells are unspecialized, thin, flexible & carry out many metabolic functions  all other cell types in plants develop from parenchyma

15. Collenchyma  Collenchyma cells have thicker primary walls & provide support  help support without restraining growth  remain alive in maturity the strings in celery stalks are collenchyma

16. Sclerenchyma Thick, rigid cell wall – lignin (wood) – cannot elongate – mostly dead at maturity Cells for support – xylem vessels – xylem tracheids – fibers rope fibers – sclereids nutshells seed coats grittiness in pears

17. tracheids vessel elements Vascular tissue Aaaah … Structure – Function again! vessel element dead cells  Xylem  move water & minerals up from roots  dead cells at functional maturity  only cell walls remain  need empty pipes to efficiently move H 2 O  transpirational pull

18. Phloem: food-conducting cells  carry sugars & nutrients throughout plant sieve tube companion cell living cells plasmodesmata sieve plate

19. Phloem Living cells at functional maturity – cell membrane, cytoplasm control of diffusion – lose their nucleus, ribosomes & vacuole more room for specialized transport of liquid food (sucrose) Cells – sieve tubes sieve plates — end walls — have pores to facilitate flow of fluid between cells – companion cells nucleated cells connected to the sieve-tube help sieve tubes