Water-1 
Importance of Water
1] Water constitutes the large Central Vacuole in most plant cells. This accounts for approximately 90% of the Protoplast. Cytoplasm accounts for the remaining 10% and it also contains water.
Succulent organs have the highest water content (95%).
Woody structures have a lower water content (50%).
Seeds have the lowest water content (10%).
2] It is the most abundant and best Solvent in nature. It is the medium for major transport processes in plants.
It affects the structure of proteins, carbohydrates, & nucleic acids.
3] Water is the medium in which biochemical reactions occur in plants.
4] Water participates directly in some important biochemical reactions.
The Oxygen we breathe comes from the splitting of water in Photosynthesis.
Water is continuously absorbed and lost by plants.
A leaf may loose 100% of its water content in one hour under dry, hot conditions.
A plant may loose its entire fresh weight 100 times during its lifetime.
5] Water evaporation is important for regulating Leaf Temperatures.
Transpiration is the process by which leaves regulate water loss.
Evaporation cools leaves and prevents them from overheating.
This may dissipate 50% of the heat from solar irradiation.
6] Essential Minerals like Phosphate & Potassium are transported throughout the plant in aqueous solutions. (Aqueous = water)
Water is the most limiting factor for agriculture.
It is also limiting for many natural ecosystems. The latter can be due to its absence (more typical) or its over abundance.
