Plant Response to Various Stresses

Flooding
Too much water could cause the plant to suffocate because the soil would lack air spaces that provides oxygen for the roots to perform cellular respiration.

Oxygen deprivation generally will stimulate the production of ethylene and cause many cells in the root cortex to die. Destruction of the root cortex would create new air bubbles that would function as "snorkels", providing oxygen to the submerged roots.

Salt
Excess amounts of salt can lower the water potential of the soil solution, causing water deficiency in plants. When the water potential of soil solution become more negative, the water potential gradient from soil to roots is lowered, reducing the plant's water intake. NaCl and other ionic salts are toxic to plants when there is high concentrations of them.

Plants typically respond by produce solutes that are well tolerated at high concentrations, mainly organic compounds that can keep water potential of cells more negative then that of the soil solution while not admitting toxic quantities of ionic salts.

Heat
Heat could be detrimental to a plant's survivability as it could denature many enzymes, killing the plants.

Transpiration helps to keep the leaves cool by evaporative cooling. Hot and dry weather tends to dehydrate plants, closing off the stomate would help to conserve water loss but it would compromise the plant's ability for evaporative cooling, Many plants have a backup response, especially when the temperature exceeds 40 degrees Celsius - plants would synthesize heat-shock proteins that would help protect other proteins from the extreme heat.