5. Discus about Pathways of Water Movements in Roots. (With Diagram).
Ans.
The torrowing
points highlight the two types of routes of water passage from rootl hair
toxvlem inside the root. The types are:. Apoplast Pathway2.
Symplast Pathway.
Type # 1. Apoplast Pathway:
Here water
passes from root hair toxylem through the walls of intervening cells without
crossing any membrane oreytoplasm. The pathway provides the least
resistance to movement of water. However, it is interrupted by the
presence of impermeable lignosuberin casparian strips in the walls of
endodermal cells.
Type! 2 . Symplast Pathway:
Water passes
from cell to cell through their protoplasm. It does not enter cell
vacuoles. The cytoplasm of the adjacent cells are connected through bridges
called plasmodesmata. For entering into symplast, water has to pass
through plasma lemma (cell membrane) at least at one place. It is also
called trans membrane pathway. Symplastic movement is aided by
cytoplasmic streaming of individual cells. It is. However, slower
than apoplastic movements.
Figure
Both the
routes are involved in the movement across the root. Water flows via
apoplas in the cortex. Itenters the symplast pathway in the endodermis
where walls are impervious to flov of water due to the presence of casparian
strips.
Here, only
plasmodesmata are helpful to allow passage of water into pericycle from wher it
enters the xylem. Mineral nutrients also have the same pathway as that of
water. However, then absorption and passage into symplast mostly occurs
through active absorption. Once inside th xylem, the movement is purely
along the pressure gradient.
Mycorrhizal Water Absorption:
In mycorrhiza
a large number of fungal hyphae are associated with the young roots. Th
fungal hyphae extend to sufficient distance into the soil. They have a
large surface area. Th hyphae are specialized to absorb both water and
minerals.
The two are
handed over to the root which provides the fungus with both sugars and N
containing compounds. Mycorrhizal association between fungus and root is
often obligate. Pinu and orchid seeds donot germinate and establish
themselves intoplants withoutmycorrhizal association
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