076N.HTML????????..? Kranz Anatomy

 

Grass leaf with Kranz anatomy: Grama-grass

Two bundle sheaths

Outer one is parenchymatous; inner is a mestome sheath

Grama-grass (Bouteloua breviseta), another C4 plant. Characteristic of this xerophyte is very compact arrangement of cells, two layers of Kranz mesophyll cells and the presence of the second, inner bundle sheath, a so-called mestome sheath. The mestome sheath cells have thickened walls (stained red here) and contain only a few organelles including small little-differentiated plastids. The outer parenchyma sheath contains well-differentiated centripetally displaced chloroplasts.

The adaxial grooves between the veins are lined with enlarged epidermal cells, which are continuous with similarly enlarged colorless mesophyll cells, the hinge cells. During water deficit, hinge cells become flaccid and enable the leaf to fold or to roll in order to reduce water loss. Note the thick cuticle characteristic of a xerophyte.

Identify xylem with metaxylem vessels, phloem, mestome and parenchyma bundle sheaths, two-layered Kranz mesophyll, sclerenchyma caps and hinge cells.

 
   
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