Meristems and plant structure The plant body Tissue systems Meristems Stems Roots Secondary thickening

The plant body A tomato plant young leaf flower node leaf seeds shoot tip (terminal bud) young leaf lateral (axillary) bud flower node internode EPIDERMIS Dermal tissue leaf VASCULAR TISSUES The plant body seeds (inside fruit) GROUND TISSUES withered cotyledon SHOOT SYSTEM ROOT SYSTEM A tomato plant primary root root hairs lateral root root tip root cap

Tissues A tissue is a cooperative unit of many similar cells performing a specific function within a multicellular organism Tissues usually have cells that are specialized for particular functions The vascular tissue system conducts water and nutrients from roots to leaves through specialized cells and conducts the products of photosynthesis, sugars, from leaves in different but equally specialized cells.

There is continuity of tissue systems through the plant Cells conduct water and nutrients and products of photosynthesis Cells protect the plant The body of the plant. Tissues with different functions: ee.g., storage, support

Function of apical meristems Shoot apical meristem activity at meristems Actively dividing cells near the dome-shaped tip new cells elongate and start to differentiate into primary tissues The apical meristems descendants divide, grow and differentiate to form: Protoderm Ground meristem Procambium new cells elongate and start to differentiate into primary tissues activity at meristems Root apical meristem Function of apical meristems Root cap Fig. 29.4 p501

Meristems-> Tissues Immature leaf shoot apical meristem procambrium protoderm procambrium ground meristem Fig. 29.11, p. 504 Meristems-> Tissues Meristems Tissues primary xylem cortex procambrium primary pholem pith

What does a meristem look like? Coleus Apical meristem Transverse section through the apical meristem and newly forming leaves Longitudinal section through the apical meristem

Scanning electron microscope picture of Myriophyllum apical meristem The apical dome is usually convex or flat, as in this example, and its surface is smooth. Scanning electron microscope picture Developing leaves cover the apex   Most recently budded leaves Water-milfoil

Coleus Axilliary bud meristem The axilliary meristem may develop into a foliated branch.

Do roots grow differently to shoots? What is their problem? What may it affect? Is anything easier for roots rather than shoots?

Root meristem and structure Roots must ‘force’ their way through the soil Protection of the apical mersitem Delayed initiation of the lateral meristems (not shown in diagram) Different requirements for support and water collection and distribution

Zea mays root apex Zea mays root apex showing the junction between root apex and the root cap

Lateral root development in Zea mays A meristem develops from parenchyma and the lateral root grows out through the cortex

Which is the most important function of a tree trunk: support of branches and foliage, conducting water, nutrients and sugars? How might you find out?

Stem thickening Lateral meristems Two lateral meristems in older stems and roots of woody plants produce secondary growth that results in an increase in diameter (whereas apical meristems result in an increase in length). Vascular cambium secondary vascular tissues, xylem phloem Cork cambium periderm (replaces the epidermis), bark tissue vascular cambrium secondary xylem Bark secondary phloem cork cambrium thickening

Secondary growth

Cell divisions of the cambium Cambium cells in yellow outer surface of stem or root Phloem production division division Xylem production direction of radial growth Fig. 29.22, p. 511

Cells of vascular tissue Fig. 29.8, p. 502 Cells of vascular tissue cytoplasm absent (cells dead at maturity TRACHEIDS pit in cell wall one vessel member VESSEL sieve plate sieve-tube member companion cell (living) Sugar transport Water conduction PHLOEM SIEVE TUBE

Transverse section of Quercus rubra wood vessel EARLY WOOD LATE WOOD toward stem surface Fig. 29.25, p. 513

Taking sections through a stem Transverse Section Radial Longitudinal Section Tangential Longitudinal Section Fig. 29.3, p. 501