Food for Thought: Stem cells in plants are localized in “meristems” Shoot apical meristem Root apical meristem Lateral or axial meristems Floral meristem
Cell fate in root is determined by position Meristem renewal Differentiation Cells leave meristem and enter files (colors) and differentiate into specific fates (stele, endodermis, cortex etc.) endodermis cortex stele Very similar to animal tissues
Cells of adult plants remain totipotent: cloning a carrot Parallels to animals? 1 mm 3 fragments (“explants”) from adult root… Culture explants in liquid culture medium… Cells “dedifferentiate” and begin to divide, forming “callus” tissue… Induce with hormones to initiate shoot and root formation… Culture “embroid” in liquid culture, then agar… Move to soil… Regenerated adult plant…
A life story… A life story… Human development starts with just 1 cell – the fertilized egg. This cell divides to produce 2 ‘daughter cells’. These daughters divide, and their daughters divide again, and so on. There are a great many steps needed to form an adult body, or even a baby. Along the way, lots of different types of cells must be made.
GAMETES 2N 1N 1N 1N 1N 1N 1N 2N 1N 1N 1N 1N 1N 1N 4 HAPLOID SPERM 4 HAPLOID EGGS
FERTILIZATION Image courtesy of L. De Vos- U.L.B.- Biodic
EMBRYOGENESIS ; Image courtesy of NIH resource for stem cell research Image courtesy of Brad Smith, University of Michigan
What is a stem cell? Note: The next slide provides an alternative version of this diagram that some younger audiences may find easier to understand. It aims to avoid the misconception that a stem cell always makes one copy of itself and one specialized cell when it divides (see below). The concept of a stem cell is very well explained in the short film, “A Stem Cell Story” at What the diagram shows Stem cells are different from other cells of the body because stem cells can both: 1)Self-renew: Make copies of themselves AND 2) Differentiate: Make other types of cells – specialized cells of the body. ‘Specialized’ or ‘differentiated’ cells play particular roles in the body, e.g. blood cells, nerve cells, muscle cells. Specialized cells cannot divide to make copies of themselves. This makes stem cells very important. The body needs stem cells to replace specialized cells that die, are damaged or get used up.
Cell division - possible questions 1) 16+ year old students may remember learning about 2 kinds of cell division – mitosis and meiosis. They may have learnt that mitosis happens in wound healing or to replace short-lived cells, but probably won’t have discussed stem cells in this context. You might therefore need to explain that most specialized cells cannot undergo mitosis. There are a few exceptions (e.g.
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- Spring '14