Plant Water Relations and Transpiration

Wilting of the plant occurs when there is scarcity of water in the plant. Xylem is responsible for the movement of water throughout the plant. Hence, when the xylem is blocked, it causes wilting of the plant.

Loss of turgor from the cells causes drooping of leaves during day, but they recover from it during night. It is referred to as temporary wilting.

Gaseous exchange in submerged hydrophytes takes place through general epidermis.

Increase in carbon dioxide concentration around the leaf results in complete closure of stomata.

Increase in temperature and velocity of wind cause an increase in transpiration initially but later it slows down because of closure of stomata.

Some of the growth regulators affect stomatal opening. Closure of stomata is brought about by abscisic acid.

The action spectrum of transpiration is blue and far red.

A well-watered herbaceous plant exhibits a decrease in rate of transpiration in intense light due to partial closure of stomata.

The spraying of phenyl mercuric acetate on leaves reduces transpiration.

Guttation occurs only in mesophytic herbs. A mesophytic herb is a plant needing only a moderate amount of water.

In lotus plant, the metabolism might be hindered if the leaves are coated with wax on their upper surface. The reason is that the exchange of gases takes place through the leaf surface, present on the upper surface. Since the upper surface of the leaf is above water, hence high frequency of stomata is present on the upper surface only. So, when the upper surface is coated, the gas exchange and other activities will eventually stop.

Succulents are plants having some parts that are more than normally thickened and fleshy, usually to retain water in arid climates or soil conditions. Stomata open at night and close during day time in succulents.

Root pressure is the maximum when transpiration is very low and absorption is high.

The actual water vapour content in the air is called absolute humidity.

A potometer is a device used for measuring the rate of water uptake of a leafy shoot. The causes of water uptake are photosynthesis and transpiration. Potometer method uses cut twig for measuring transpiration.