L4: Meristems II, Secondary growth and vascular system Flashcards
What is meant by the root:shoot ratio?
Balance needs to be maintained between total SA available for food manufacturing and SA available for water & mineral absorption.
What happens to the root:shoot ratio as plants age?
Decreases gradually.
What trend do roots follow as they grow through soil?
Follow the path of least resistance.
What is the rootcap?
Mass of living parenchyma cells that protects apical meristem and aids in penetration of the soil.
What is produced by cells in the root cap? What does it do?
Mucilage; lubricates root during passage through soil.
What are the mucilage-producing cells called?
Border cells
What are some additional roles of border cells and their exudates?
Protect meristem from infection
Maintaining root-soil contact
Mobilization of elements taken up by roots
Short-term desiccation prevention
Specific bacteria attraction or repulsion
Why is the rootcap called the multifunctional molecular relay station?
Because in addition to protection, it senses, processes, and transmits signals to meristem and elongation region of the root.
What is the columella of the root cap?
Central column of cells.
What is the lateral rootcap?
Lateral portion of cells on the rootcap that surrounds columella.
What part of the rootcap senses gravity and water potential gradients?
Columella.
What is the difference between open type and closed type meristems?
Closed type: rootcap, vascular cylinder, and cortex are their own individual layers and have their own initials.
Open type: all regions arise from one group of initials.
What is the quiescent center of the rootcap?
The relatively inactive region of the meristem (i.e., does not divide as often).
What is the region of cell division?
Region where cells divide actively.
What causes the majority of root length increase?
Elongation of cells in the area of elongation.
Where does root growth occur in the root?
Near the root tip
What is the region of maturation?
Where most cells of primary tissues mature and where root hairs are produced.
Why are root hairs developed in the region of maturation and not the region of elongation?
If produced in region of elongation, they would be sheared off by the roots pushing through the soil.
Are there strict boundaries between the regions of cell division, elongation, and maturation?
No, there are gradual transitions between each region. Sometimes they overlap.
What are the three tissue systems of the root in the primary stage of growth?
epidermis, cortex and vascular tissues.
What shape do vascular tissues typically form in the root?
Cylinder
What facilitates the uptake and water of minerals in the roots?
The root hairs
Why are root hairs ideal for taking in water and minerals?
Greatly increase the absorptive surface area of the root.
Where are root hairs mainly confined?
Region of maturation.
What are mycorrhizae?
Symbiotic associations between fungi and roots
Why are micorrhizae beneficial?
Enables plant to obtain water and nutrients from much larger volume of soil than made possible by root hairs.
What tissue takes up the majority of the primary body of roots?
The cortex
Why does cortical tissue have an abundance of intracellular spaceS?
Essential for aeration of roots.
What are aerenchyma?
Parenchyma cells with large and abundant intercellular spaces.
How are cortical cells attached to each other?
Plasmodesmata attach protoplasts to each other.
What pathways can substances moving across the cortex take?
Symplastic - protoplast to protoplast
Apoplastic - via cell walls
Both
How does the endodermis differ from the cortex?
Tightly packed, lacks air spaces.
What do the Casparian strips in the endodermis do?
Prevent movement of water and ions
What is the exodermis?
Compact layers of cells with Casparian strips in most angiosperm roots.
What does the exodermis do?
Prevent water loss and protect against microorganism attacks.
What makes up the vascular cylinder?
Primary vascular tissue and the pericycle.
Why is the pericycle considered part of the vascular cylinder?
It originates from procambium like vascular tissues.
What does secondary growth consist of?
- Formation of secondary vascular tissue
- Formation of periderm
Does the shoot apical meristem have its own version of a rootcap?
No. But it is usually covered by young leaves, which offer some protection.
Differentiate between the ways in which tunica and corpus cells divide. What do these divisions result in in terms of plant growth?
Tunica divide anticlinally, contributing to surface growth.
Corpus divides periclinally, adding bulk to the developing shoot.
Outline the layers of eudicot apices.
L1 and L2 = tunica
L3 = initial corpus
