Transition To Land-GroundTissue

Parenchyma tissues perform most of the synthetic functions in plants.

The development of Specialized Photosynthetic Tissues has been of great adaptive significance.

Ancestral plants had a uniform, isodiametric Chlorenchyma with small air spaces.

More Advanced plants have a Palisade/Spongy organization or Kranz Anatomy.

Aerenchyma Link

Aerenchyma Link

Storage Parenchyma is also important. Common storage products are Starch, Oils (Coffee) and crystals. The latter deter herbivory.

Waste products may also be confined in Parenchyma Cells.

The Endodermis provides physiological control of water & solute movements in All Roots, Many Stems & a Few Leaves.

This is one of the most important vegetative adaptations of land plants.

It provides a structural & physiological mechanism to bring water and solute movement under biological control.

Endodermal cells can lead to solute exclusion OR concentration. The latter is used to produce "Root Pressure" which is the first step in the transport of water from the root into the shoot. Transpiration provides the tension to finish this process.

Secondary Growth

The Cork Cambium originates in Parenchyma cells.

Interfascicular Parenchyma cells are recruited into the Vascular Cambium.

Sclerenchyma provides support for aerial organs. Its thick walls are highly organized and impregnated with Lignin which makes them very strong and waterproof. They are often found in bundles of highly elongated cells which have overlapping (inter-digitating) end walls. The latter adds to their strength.

Sclerenchyma cells are frequently present in the Vascular Tissues (Xylem & Phloem) and they account for some of their strengthening properties.

Lycopodium Leaf with uniformly shaped, round Chlorenchyma

Columnar Chlorenchyma in Ohi'a lehua (dicot)

Kranz-type Chlorenchyma in Amophyla (monocot)

Starch is the most common storage product!

The Oil in Coffee is responsible for its aroma!

Crystals which inflame animal epithelial cells are commonly found in leaves & stems.

An Endodermis is present in all roots, and the stems of many ancestral plants.

Each Endodermal Cell has a thickened band of Suberized Cell Wall that encircles it like a belt. This is the Casparian Strip! The Plasmalemma is strongly attached the the CS which blocks apoplastic transport. Water and solutes must pass through the Plasmalemma twice before entering or leaving the Stele.

Model of a solitary Endodermal Cell: Suberin is also deposited in the primary cell walls near the Casparian Strip. This forms a continuous barrier across the Cell Walls of contiguous Endodermal cells (above & below).

Nothing can pass through the Apoplast of Endodermal Cells, not even water!

Sclerenchyma Fibers are long, tapered cells with extremely thick, highly organized and lignified Cell Walls. They are very strong!!!!

In extreme cases there is little room left for the cell's protoplast!

Bundle of Fibers isolated from Oak wood.

Fibers are present in the Secondary Phloem of Podocarpus and other plants like Tilia (below).