Applied Plant Anatomy:

1. Applied Plant Anatomy: Part 1: The origin of cells, tissues and systems in plants

2. outline Where do cells come from? What controls their formation? What controls their organization?

3. meristems mother cells procambium Go! stop tissue origins Go! stop protophloem Go! stop fundamental dermal vascular protoxylem Go! stop Go! stop metaphloem protoderm Go! stop metaxylem epidermis parenchyma collenchyma sclerenchyma

4. The shoot & root apex The dermal tissue system arises in the shoot and root apical meristems The protoderm produces epidermal cells similar layers are formed in roots

5. differentiation differentiation starts in meristematic cells, and new cells which are formed in specialized layers, such as the procambium shown at left. Here, you can see a strand of protophloem differentiating. These cells are not functional yet. Question: Why does the protophloem differentiate before the protoxylem? Question: Why do cells enlarge, what is the optimum size for cells Do all cells have the same optima?

6. systems cell and tissue systems protective epidermis, periderm parenchyma, collenchyma, sclerenchyma filling collenchyma, sclerenchyma support phloem, xylem conductive meristematic procambium, cambium. periderm storage, synthesis transport reproductive functional

7. the dermal system the epidermis may become replaced by a new protective layer, called the periderm. This layer is also responsible for gas exchange, through structures called lenticels

8. Specialized cells Plants are composed of many different cell types – all have specific functions and size, shape, wall structure and function, will be determined by position in the root, stem or leaf. Specialization does not equate to complexity. For example, parenchyma cells in the cortex of roots and shoots, may well have a storage function. OR even bigger:- Remember;.. gas exchange requires the presence of stomata in leaves, gas exchange is facilitated if intercellular spaces are present, as in these aerenchyma cells in the Canna leaf.

9. specialized cells Gymnosperms contain modified cells which form ducts that contain resins and terpenoids all leaves contain parenchyma cells which are specialized for photosynthesis, called mesophyll cells

10. supporting tissue 1 supporting tissue takes on many forms and can be simple or complex.

11. supporting tissue 1 3 2 waterlilly petiole pea root Xylem in 1-4 provides support to roots, stems & leaves 1 pea stem 4 5 young Pelargonium stem New Zealand flax extensive fibre capssupport vascular tissue & leaf

12. supporting tissue 2 -- collenchyma in stems, angular lamellar distribution varies (a) at corners in angular stems OR:- the shape in cross section varies - usually angular or lamellar it forms an ring, under the epidermis [outer cortex]; or it occurs mixed between other tissues, or as an inner cortical band

13. collenchyma - facts

14. supporting tissue 4 supports vascular bundles in leaves distribution varies (a) at corners in angular stems (see collenchyma). it forms an ring, under the epidermis [outer cortex]; or it occurs mixed between other tissues, or as an inner cortical band

15. sclerenchyma - facts

16. transport systems 1 Vascular tissue is always arranged into vascular bundles in stems and leaves. bicollateral In stems, xylem is normally inside of (endarch to) the phloem is described as being outside of (exarch to) the xylem. In a minority of families, phloem occurs on both sides of the xylem. These are bicollateral vascular bundles. phloem phloem xylem collateral xylem

17. transport systems 2 in roots and an equivalent number of phloem poles or strands monocotyledonous roots contain many (more than 6-7 xylem strands.

18. The xylem – cell organization protoxylem Protoxylem forms in regions where rapid cell elongation is still ongoing. As such, secondary thickening is limited, to accommodate stretching.

19. xylem development – juvenile to mature xylem differentiation involves a number of critical steps – during each degradation of content occurs simultaneously with formation and synthesis of new, secondary cell walls. In the he final stages, the cytoplasmic content (nuclei, organelles etc.) are broken down, and flushed out to be recycled. The end product is a series of cells fit for rapid transport of water and water-soluble products. from Esau: Anatomy of seed plants

20. the xylem – structural changes in development Diagrams and micrographs from Esau: Plant Anatomy,

21. the xylem - an overview although most of the cells of the xylem are dead at maturity (vessels, tracheids, fire-tracheids and fibers), xylem parenchyma cells are alive and contain cytoplasm a nuclei and organelles Diagrams and micrographs from Esau: Plant Anatomy,

22. the xylem 3 cells and tissue Xylem in dicots and monocots contain vessel members (V); tracheids (T); fibres (F) and xylem parenchyma elements F X T In gymnosperms, vessels are absent Diagrams and micrographs from Esau: Plant Anatomy,

23. The xylem – transporting water moving water longitudinally as well as laterally, requires apertures within cell walls. The xylem contain=s a variety of apertures called pits, which facilitate water movement, and minimize potential damage caused by embolisms (cavitation of the water column under high negative water potential). Diagrams and micrographs from Esau: Plant Anatomy,

24. the xylem 4 – safer transport Perforation plates in vessels are important structures, that will retard, or trap air bubbles which are formed during embolisms. Embolisms will, unless trapped, cause complete loss of functionality of the file of xylem vessels in which the bubbles occur. unsafe

25. sieve plate evolution of sieve tubes from Esau Anatomy of Seed Plants phloem transfusion tissue transport systems - the phloem 1 CC ST phloem in melon petiole phloem tissue in angiosperms contains sieve tube members, joined end to end to form sieve tubes; as well as companion cells and phloem parenchyma cells. in gymnosperms, the phloem comprises sieve cells, albuminous cells and parenchyma cells. It is also associated with transfusion tissue. This is a more primitive system than the angiosperm one. vascular tissue in a pine needle

26. transport systems -the phloem in detail in the monocotyledon leaf, the phloem is made up of parenchyma cells, sieve tubes (ST) and companion cells (CC). Two types of sieve tubes occur - thick- (TWST) and thin-walled (ST) ones. TWST are not associated with CC. light microscopy is only a starting point to understanding the structure of cells and tissues. The image to the right is a Transmission electron micrograph, which demonstrates the level of detail and power of TEM!

27. transport systems - the phloem electron microscopy in leaves, the sieve tubes are always narrower in diameter that associated parenchymatous elements, including the companion cells. This is because most phloem loading is an active process, either mediated by osmotic potential alone, or in combination with sucrose transporters, which are involved in loading the companion cell sieve tube complex.

28. moving carbohydrates -- the phloem phloem is a complex tissue. Moving metabolites requires very specialized cells, called sieve tubes (in angiosperms) which, at maturity, do not have a vacuole, and do nto have a nucleus! Their end walls are perforate and the cells, joined end to end by these walls, form sieve tubes, through which assimilates move from a source (of the assimilate) to the sink (where they are used). Diagrams and micrographs from Esau: Plant Anatomy,

29. sieve plates sieve plates maintain cell integrity. Keep structures an proteins within cells, in place. The also have an important regulatory function

30. moving metabolites sieve areas The phloem is protected from damage (sudden pressure change) through the formation of callose on sieve plates and sieve areas sieve plate phloem is the principal carbohydrate transport channel – this channel is controlled

31. electron microscopy sieve tubes contain plastids. These sieve type plastids have prominent protein bodies in them, with unknown function. Sieve tubes are relatively uncluttered with a clear lumen. Companion cells are associated nucleate cells

32. All differentiation is under gene control. A great deal of work has been done using Arabidopsis For example: Origins: Control and regulation through genes 1. Genes affecting early stages of vascular patterning,prior to provascular network formation, may promote differentiation along wide pathways ratherthan narrow canals, because of failures to establishefficient canals of auxin flow. 2. It is known that Knotted1-like homeobox1 (knox) genes are expressed in very specific patterns within shoot meristems and these genes play an important role in meristem maintenance. In plants, MADS box genes are most well known. 3. Misexpression of the knox genes, KNAT1 or KNAT2, in Arabidopsis produces a variety of phenotypes, including lobed leaves and ectopic stipules and meristems in the sinus, the region between lobes. ---------------------- 1A DNA sequence within genes involved in the regulation of development, about 180 base pairs long. It encodes protein (the homeodomain, which binds DNA http://en.wikipedia.org/wiki/Homeobox#Plants

33. In the Arabidopsis root meristem, initial cells undergoasymmetric divisions to generate the cell lineages ofthe root. Thescarecrowmutation results in roots thatare missing one cell layer owing to the disruption ofan asymmetric division that normally generates cortexand endodermis. Cell 86: 432-433 Laurenzio et al. 1996 More examples When differentiating cells leave the meristem field, they actively maintain a pool of uncommitted cells in the SAM. This suggests the maintenance of the meristem cells in an undifferentiated state - this is likely to be shared by other plant species Shoot apical meristems (SAMs) do not share their set of regulatory factors with root apical meristems (RAMs), yet both adjust their cell populations according to the same basic mechanisms, such as intercellular signaling. In both SAMs and RAMs, these mechanisms involve interactions between two groups of cell populations, the pluripotent undifferentiated cells –in the organizing center of the SAM and in the quiescent center (QC) in the RAM – and the differentiating cells that will be incorporated into the plant body1. 1Nakajima and P. Benfey, Signalling in and out: control of cell division and differentiation in the shoot and root. Plant Cell 14 Suppl. (2002), pp. S265–S276.

34. Complex issues PIN genes: Encode components of auxin efflux carriers. Two promoters

35. it has been suggested that class III homeodomain leucine-zipper1 proteins (HD-Zip III) are involved invascular development. However, little is known about the mechanisms of spatial andtemporal organization in each vascular cell. More…zippers Arabidopsis inflorescence stems develop extraxylary fibers at specific sites in interfascicular regions. The spatial specification of interfascicular fiber differentiation is regulated by the INTERFASCICULAR FIBERLESS1 (IFL1) gene because mutation of that gene abolishes the formation of normal interfascicular fibers in Arabidopsis stems. A protein structural motif involved in protein-protein interactions in many eukaryotic regulatory proteins (C/EBP prototype). Contain a repeat structure: Leu residues in every seventh position, causes a large amount of DNA to loop out. http://www.fhsu.edu/chemistry/twiese/glossary/biochemglossary.htm

36. Zipping vascular evolution Arabidopsis class III homeodomain-leucine zipper (HD-Zip III) proteins play overlapping, distinct, and antagonistic roles in key aspects of development that have evolved during land plant evolution. • See http://www.nature.com/nrm/journal/v5/n5/full/nrm1364.html • Plant signals Figure 1   Model of how CLASS III HD-ZIP1 and KANADI activities pattern lateral organs and vasculature. A centrally derived signal (red) activates CLASS III HD-ZIP genes, whose activity is antagonistic with that of KANADI activity. Both KANADI and MIR165/166 negatively regulate CLASS III HD-ZIP genes, (relationship between the two is not presently known). In lateral organs, CLASS III HD-ZIPactivity promotes adaxial fates and KANADIactivity promotes abaxial fates. In the vascular bundles, interactions between the two gene classes pattern the arrangement of xylem and phloem tissues. The vascular bundle shown is already differentiated, but the initial patterning events likely occur just below the apical meristem where provascular cells are being specified. –––––––––––––––-– 1Class III homeodomain-leucine zipper proteins

37. Which comes first? • The provision of nutrient and water becomes priority problems within the developing shoot or root axis. As the axis elongates and the diameter increases, so transport becomes more problematic • Short-distance transport may be accommodated by:- • diffusion, provided there are adequate cell to cell connections • or by transmembrane transport, either through cells or along the cell wall free space interface

38. Size and shape; long is better for transport Fig. 1. Changes in surface-to-volume ratios during cell expansion. When a cell (shown here as a cube), doubles its dimensions via (a) isotropic expansion its volume increases 8-fold whereas its surface increases only 4-fold and its surface-to-volume ratio is reduced from 6 to 3. (b) Anisotropic expansion of the same volume, producing long thin cells, increases the surface area to a greater extent and improves the surface-to-volume ratio. (c) The original ratio of surface-to-volume can be maintained when cell expansion is followed by cell division. From: Kondorosi et al, Current Opinion in Plant BiologyVolume 3, Issue 6, 1 December 2000, Pages 488-492

39. Applied plant anatomy Next: Part 2: the root-stem-leaf continuum Intro Anatomy 1