Plant Tissues: Meristematic Tissues PDF

Plant Tissues: Meristematic Tissues Chapter Objectives: – To define the function of meristem – To be familiar with the characteristics and classifications of meristem.  Meristematic – Dividing, Undifferentiated cells/tissue – Meristematic tissues are clumps of small cells with d...

Plant Tissues: Meristematic Tissues Chapter Objectives: – To define the function of meristem – To be familiar with the characteristics and classifications of meristem.  Meristematic – Dividing, Undifferentiated cells/tissue – Meristematic tissues are clumps of small cells with dense cytoplasm and proportionately large nuclei.  Classification of Meristems 1) According to origin 2) According to position 3) According to angle of the cell division plane  According to Origin Promeristems – dividing cells of the shoot tip and the root tip. – Function: to produce the cells of the primary meristems. – Composition: – Initials - continuous division; direct embryonic origin; is restricted to the plumule and the radicle – Quiescent centre - Surrounded by the initials; preserve the genetic material within the promeristem; totipotent According to Origin Primary meristems/ Histogens – Cells of the primary meristems have determined faith. 3 Types of primary meristems in the SHOOT TIP: – dermatogen (protoderm) producing the epidermis – ground meristem giving rise to the ground tissue system – procambium that cuts off the vascular tissues. Shoot Apical Meristem  According to Origin Primary meristems/ Histogens 4 Types of primary meristems in the ROOT TIP: – Dermatogen producing the rhizodermis – Periblem forming the primary cortex – Plerome giving rise to the stele and the – calyptrogen that produces the calyptra  According to Origin Secondary meristems – Arise by the differentiation of primary tissue cells. Vascular cambium -> secondary thickening of the plant organs Cork cambium (phellogen) -> periderm (secondary dermal tissue). According to Position Type of Meristem According to Position TYPE LOCATION FUNCTION APICAL MERISTEM Shoot and the root Growth; increase tips length at tips INTERCALARY Between the tip and Elongation of certain MERISTEM base of stem and organs being leaves ( between positioned in their differentiated tissues) basal region (Ex. Extension of leaf petioles or the internodes.) LATERAL MERISTEM Sides of stems and Growth; Increase in roots diameter.  Apical Meristems – located at the apices or tips - directly involved in their elongation – Plant tissues that result from primary growth are called primary tissues – make up primary plant body – Root apical meristem protected by root cap Apical Meristems They create derivatives which form primary growth. – Protoderm which forms the outer dermal layer of tissues, – Procambium which forms the vascular tissue and – Ground meristem which forms the cortical cells  Lateral Meristem – responsible for horizontal expansion. A. Vascular meristem-internal growth in girth which involves secondary tissues (xylem and phloem). B. Cork cambium- external girth growth beyond the phloem area. They form the characteristic corky layer as well as an internal layer.  Lateral Meristem 1-2-3-year old stems MC Whole root large MC Basswood – root in cross section Basswood – stem in cross section; 1, 2, 3 year old stems  Intercalary Meristem – Occurs between mature tissues sections in the vicinity of the nodes or leaf attachment; – * common in grasses (occur at bases of nodes); – * helps regenerate parts removed (by lawnmowers, herbivores, etc.) Intercalary Meristem  According to the cell Division Plane Apical zone of the shoot – Promeristem and certain cells of the primary meristems divided into the regions of the tunica and the corpus. TUNICA - outer cell layers – the cells of which divide anticlinal (perpendicular to the surface). – a single cell layer, yet it may be composed of several (up to 8) cell rows. On the average, it consists of 1-3 layers. CORPUS - region covered by the tunica – cells divide both anticlinally and periclinally.  Lateral Meristems – secondary growth in woody plants This stem has two lateral meristems. They are the vascular cambium and the cork cambium. (This is 1 year) Lateral Meristem- 2 years – This is the 2nd year and you can see there are two layers of xylem for each year. The pith is also referred to as the “Heartwood”