Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
9/14/2014 Bi 151 Plant Morpho-anatomy Lecture 5 Meristems, Growth and Differentiation Jan Lorie M. Robil, M.Sc. Meristems Meristems • ‘merismos’ - division • embryonic tissue regions that are primarily concerned formation of new cells. • restricted to certain parts of the plant • Initials – result of evolutionary specialization – a.k.a. initiating cells or meristematic initials – cells that maintains the meristems as continuing source of new cells • Derivatives – products of initials – divides to give rise to somatic or body cells Initials Classification of Meristems • analogous to stem cells • totipotency • Based on their position to plant body – able to produce entire spectrum of cells – develop into complete plant – Apical meristems – Lateral meristems – Intercalary meristems • plasticity – evolutionary response to sessile form of life – adjust to environmental conditions 1 9/14/2014 Classification of Meristems • Based on the nature of cells that give rise to their initial cells – Primary • protoderm → epidermal tissues • procambium → primary vascular tissues • ground meristem → fundamental/ground tissue – Secondary • cork cambium (phellogen) → periderm • vascular cambium → secondary vascular tissues How will you categorize fascicular and interfascicular cambia? Growth Patterns of Meristems • Periclinal division Periclinal Division – parallel to the axis – increase in thickness of the organ • Anticlinal division Radial Anticlinal Division – surface growth of the organ – perpendicular to the axis • Radial anticlinal – parallel with the radius • Transverse anticlinal – perpendicular to the long axis Transverse Anticlinal Division 2 9/14/2014 Differentiation Differentiation • succession of changes in form, structure, and function of progenies of meristematic derivatives, and their organization into tissues and organs. • Histogenesis – tissues e.g. xylem, phloem • Organogenesis – organs • Morphogenesis – specific form • Senescence - Programmed Cell Death • histological diversity results from changes in individual cells. • controlled by a number of genetic, physiological and even physical factors – environmental cues (biotic and abiotic) – hormones Apical Meristems • refers to a group of meristems at the apex of shoot or root • lay the foundation of the primary plant body • First organized when the plant is still an embryo in the seed Equisetum Polypodium 3 9/14/2014 What is the evolutionary selective advantage to having an apical cell? • It divides less rapidly than its derivatives, thus helping prevent the multiplication of abnormalities. Tunica-Corpus Organization Tunica-Corpus Organization Initial region of apical meristem consists: • Tunica – one or more peripheral layers of cells – divides in planes perpendicular to the surface • Corpus – a mass of cells several layers deep – divides in various planes Features Of The Tunica-corpus • Separate tiers of apical initials occur at the distal position at the apex = stratified meristems • tunica is one or more layers thick and it divides anticlinally. • Corpus provides the bulk, tunica the mantle or covering of the shoot. 4 9/14/2014 Cyto-histological Zonation • differentiation of regions with distinctive cytological characteristics • prominent in most Gymnosperms and Angiosperms • Central Zone • Rib Zone • Peripheral Zone Stem LS showing shoot apex with a core and mantle organization, apical cell, central mother cell zone, peripheral zone, pith meristem; Prepared slide Shoot Apex • can produce both vegetative or reproductive (i.e. foliar and floral structures) • produces lateral organs (e.g. branches, twigs) • contains the primary meristems • starts with an apical cell that gives rise to all cells Root Apex • Consider the longitudinal zones of root • Calyptrogen. Meristem that creates and resupplies parenchyma to the root cap. • This meristem is adjacent to a dermatogen that produces the epidermis • Thus, the root cap and epidermal cells have independent origins – only in Monocot Solenostemon (Coleus) the tunica is two-layered 5 9/14/2014 6