Huseyin Tombuloglu, Phd. GBE 304 Spring 2015 Chp4 Water Balance of Plants

Water uptake and movement in 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 and perhaps 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 CO 2 Low internal CO 2 Presence of ABA High humidity (causes K+ to pass out of cells)

STOMATA HYPOSTOMATIC LEAF EPISTOMATIC LEAF AMPHYSTOMATIC LEAF

Nutrition of Plants 1- Water 2- Mineral