Ch3- Water and Plant Cell Dr. Huseyin Tombuloglu GBE310 Spring, 2015

Why do we start with water? Water is critical for plants functionally and structurally Water relations are fundamental to plant growth and function

What roles does water play in plants? 1.The universal solvent 2.The largest constituent of all cells, and plant cells in particular 80 to 90% water by weight 3.Acts as medium for macromolecular structure, 4.Participates in biochemical reactions 5.Medium for transport 6.Evaporative cooling, moderates the rate of temperature changes 7.Hydrostatic support, helps provide structure for plants 8.Driving force for movement 9.Driving force for growth 10.And more...

“(there is) no doubt that water has the largest collection of anomalous properties of any common substance” Kramer and Boyer (1995): Water Relations of Plants and Soils

How water molecules goes up to the higgest parts of a plant?

Water Properties 1. Partial polarity

Water Properties 2. Hydrogen bonding FIGURE 3.4 (A) Hydrogen bonding between water molecules results in local aggregations of water molecules. (B) Because of the continuous thermal agitation of the water molecules, these aggregations are very short-lived; they break up rapidly to form much more random configurations.

Water Properties 3. Highly stable High specific heat & latent heat of vaporization Resistant to compression and tension (>-30 MPa)

Latent heat of vaporization is the energy needed to separate molecules from the liquid phase and move them into the gas phase at constant temperature—a process that occurs during transpiration. For water at 25°C, the heat of vaporization is 44 kJ mol –1 —the highest value known for any liquid. Most of this energy is used to break hydrogen bonds between water molecules LiquidLatent heat of vaporization cal/g Water540 Ethanol204 Acetone125 Chloroform59

Water Properties 4. Displays adhesion Attraction to surfaces 5. Displays cohesion Attraction to other water molecules Capillary action = adhesion + cohesion + surface tension

Contact angle (A) and capillarity (B) of water Low surface tension High surface tension

Unit I Opener Light micrograph of a soybean root stele

Water movement ALWAYS PASSIVE! There are only two ways water can move 1- Diffusion 2- Bulk flow

Water movement 1- Diffusion Movement down a concentration gradient Driven solely by a concentration gradient A slow process

Water movement 2- Bulk (or mass) flow – Driven solely by a pressure gradient – A faster process Examples: Water movement through aquaporins

Cellular examples of water transport Diffusion through membranes Bulk flow through aquaporins

Nutrition of Plants 1- Water 2- Mineral