Support in Plants

Since plants have no skeletal system, they must have some other means to support. The stem supports the plant. The stem is a transport link between roots and the leaves. Stems are either herbaceous or woody. A plant with herbaceous stem is supported by the pressure of water that is hydrostatic pressure called turgor pressure in the cells of the stem. This pressure causes turgidity or stiffness. As a result the plant stands upright. If there is water shortage, then the stem loses turgidity and this causes the plant to wilt.

Plant cells, notably mature parenchyma cells have a large central vacuole surrounded by a membrane called tonoplast. The fluid they contain is called cellsap. It is a concentrated solution of mineral salts, sugars, organic acid, oxygen, carbon dioxide etc. Because of higher ionic concentration in vacuole than that of than that of extra-cellular fluid, water enters vacuole by osmosis and the cell becomes turgid. In this condition the cell provides turgidity i.e. mechanical support to the harbecous plants having soft tissue.

Collenchyma is a mechanical tissue providing support to those organs in which it is found e.g. cortex. Sclerenchyma cells are found in dicots. Their sole function is to assist in providing support and mechanical strength to the plant. The vascular bundles having xylem tissue are tough and inextensible, arranged in a ring within a stem. This arrangement provides very effective resistance to the wind stress, and weight bearing ability to the plant. The vascular bundles in some plants e.g. sunflower have sclerenchyma fibers, which form bundle cap, gives strength to the vascular bundles.