Huseyin Tombuloglu, Phd. GBE 304 Spring 2015 Chp4 Water Balance of Plants.
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Transcript of Huseyin Tombuloglu, Phd. GBE 304 Spring 2015 Chp4 Water Balance of Plants.
Huseyin Tombuloglu, Phd.GBE 304 Spring 2015
Chp4 Water Balance of Plants
Water uptake and movementin plants
Most water absorbed through root hairs Cellular solute potential greater than surrounding soil
Figure 4.3 Water uptake along roots; (A) Rate of water uptake along a pumpkin root
Figure 4.3 Water uptake along roots; (B, C) Diagram of water uptake
• Suberin is highly hydrophobic and a somewhat 'rubbery' material. Its main function is to prevent water from penetrating the tissue. In roots suberin is deposited in the radial and transverse cell walls of the endodermal cells. This structure is known as the Casparian strip or Casparian band.
Water entry into roots
• Water and ions must pass through plasma membranes and protoplasts of endodermal cells to reach the xylem.
• Follows one of three pathways to the vasculature• Transmembrane – crossing 2+ membranes• Symplastic – crossing only 1 membrane followed
by movement through plasmodesmata• Apoplastic – crossing no membranes (outside of
root cells)• Entry into vascular tissue constrained by Casparian
strip (suberin) at the endodermis
Guttation High humidity, Cool temperature, Low light exposure root pressure can push xylem fluids through leaf mesophyll and out some
larger pores in the leaves called hydathodes.
Tracheary elements in Xylem
(conifers)
The Xylem Consists of Two Types of Tracheary Elements
Vessel elements are found only in angiosperms, a small group of gymnosperms andperhaps some ferns.
Tracheids are present in both angiosperms and gymnosperms, as well as in ferns and other groups of vascular plants
Tracheids • elongated, spindle-shaped dead cells• Water flows between tracheids by means of the numerous
pits in their lateral walls
Vessel elements• shorter and wider than tracheids and have perforated end
walls that form a perforation plate at each end of the cell• Also dead cells
The Xylem Consists of Two Types of Tracheary Elements
Different types of pits and perforations
Evaporation from leaves produces a tension on entire water column extending down to the roots.
Gas in solution is released under negative tension
Bubbles in the xylem cause cavitations (or embolisms)Embolisms block xylem
Embolism or cavitation
Water detour around the embolized conduit by travelling through neighboring, water filling conduits.
Each year plants have secondary growth, means new xylem for each year
Plants repair - renew its water transport capacity; against xylem conduits loss due to embolism
Sieve Cells
Sieve Tube Members
The Phloem Consists of Two Types of Elongated Cells
• Transpirational pull•Translocation
• flow from greater to lower water concentration
• Cohesion & tension– cavitation breaks chain of water
molecules
Ascent of xylem sap
•Translocation
Regulation of transpiration Stomata open and close due to changes in turgor pressure of guard cells.
Turgor results from active uptake of potassium (K+) ions.Increase in K+ concentration creates a water potential that causes
water to enter osmotically, guard cells to become turgid, and stomata to open.
Stomatal Regulation
Conditions favouring closing Conditions favouring opening
Lack of water Abundant water Darkness Abundant Light High internal CO2 Low internal CO2
Presence of ABA High humidity(causes K+ to pass out of cells)
STOMATA
• HYPOSTOMATIC LEAF
• EPISTOMATIC LEAF
• AMPHYSTOMATIC LEAF
Nutrition of Plants1- Water
2- Mineral