Post lab lecture on root anatomy

1. ROOT ANATOMY Post lab discussion

2. shoot apical meristem terminal bud leaf axillary bud blade vascular tissue petiole node Shoot system internode vascular tissue vascular tissue Root system Lateral roots dermal tissue root apical meristem ground tissue root cap root tip vascular tissue

3. protoderm ground meristem procambium Root Elongation region tip Meristematic region Actively dividing cells in various stages of mitosis Root cap Produces mucigel for protection, lubrication, water and nutrient absorption

4. Maturation region Maturation region - characterized by the presence of root hairs - is made up of primary tissues that develop from transitional meristems of the elongation region epidermis Protoderm cortex Ground meristem pericycle phloem Procambium vascular cambium xylem

5. ROOT HAIRS -Increase the surface area for the absorption of water - trichoblast

6. ROOTS vs STEM STEM Endarch with appendages With stomata Branches arise from apical merisetm and EXOGENOUSLY ROOT Exarch No appendages comparable to leaves Devoid of stomata Braches arise from mature tissue and ENDOGENOUSLY

7. ROOT vs Stem Root wider cortex Roots have no or lesser supporting tissues. WHY? Roots protosteleic; stem siphonostelic

8. Roots vs STEM Roots– x and p arranged alternately Stem– in bundles

9. Internal structure Root cap Epidermis Cortex– parenchymatous (dicot and gymno); + sclerenchym (monocot) EXODERMIS/ Hypodermis- suberized/ protective ENDODERMIS- prevents inward flow of water and nutrients via apoplast - uniseriate - shed together with cortex during 2 growth Vascular cylinder – surrounded by pericycle---

10. lateral root arising from pericycle Anatomy of a young dicot root xylem phloem endodermis with casparian strip cortical parenchyma uncutinized epidermis with root hair

13. cortical parenchyma endodermis xylem of vascular cylinder Casparian strip H20 Endodermis (surface and side views)

14. primary root xylem lateral root Lateral roots develop from the pericycle

15. Pericycle >uniseriate in most angio >several layers in monocot and gymno >Gives rise to Lateral roots Phellogen Portion of vascular cambium >procambiumor ground meristemorigin

16. epidermis cortex vascular cylinder Young dicot root actinostele tetrarch exarch

17. Differentiating metaxylem at the centre of the root The Dicotyledonous root Young dicot roots usually have two, three four or morePOLES of XYLEM which are interspersed with STRANDS OF PHLOEM MX

18. metaxylem vessel protoxylem vessel Monocot root actinostele polyarch exarch exarch

19. Parenchymatous central pith Large number of xylem strands PX exarch, MX endarch. thick‑walled endodermal cells Cortex: Wide and parenchymatous hypodermis the outer walls of which are not thickened epidermis Zea mays root

20. PASSAGE CELLS allow transport of water Phloem occurs as STRANDS. Alternates with protoxylem Central core contains tracheids endodermis MX Protoxylem is exarch Metaxylem is endarch

22. Secondary growth in roots Monocots do not exhibit secondary thickening

23. Roots which have undergone Secondary growth are shown below Primary xylem The structure of the root in Secondary growth is similar With the structure of stem in secondary except for the absence of pith in roots. Secondary xylem Primary xylem

24. This is a cross section of the Stem with secondary growth. Take note of the presence of pith

25. Older roots– for conduction, storage, anchorage Feeder roots– of primary state– for absorption ROOTS vs STEM (secondary growth) Roots have: 1. higher bark to wood ratio 2. less fibers in the bark and wood 3. larger and uniform vessels 4. less distinct growth increment 5. large volume of ray tissue 6. wider and longer tracheids (gymno) 7. large volume of living cells