Plant structure, growth & development; Resource acquisition and transport Chapter 35

What you should know: YOU MUST KNOW Plants grow only at meristems How leaf anatomy relates to photosynthesis The role of root hairs and mycorrhizae in resource acquisition Roots, stems, and leaves interact in essential plant life functions YOU MUST KNOW How passive transport, active transport, and cotransport function to move materials across plant cell membranes The role of water potential in predicting movement of water in plants How the transpiration cohesion-tension mechanism explains water movement in plants How bulk flow affects movement of solutes in plants Mechanisms by which plant cells communicate with other distant cells

I. Plant organization Root system – multicellular organ beneath the ground to anchor plant, absorb water and minerals, and store sugars and starches 1. Root hairs – at the tips, extensions of root cells that increase surface area for absorption 2. Mycorrhizae – fungi in a symbiotic relationship with roots that help with absorption

Shoot System – multicellular organ above the ground consisting of stems and leaves 1. Stems – display the leaves 2. Leaves – main photosynthetic organs of the plants

Tissue types – compose roots and shoots 1. Dermal tissue – single layer of closely packed cells that cover the entire plant to protect and prevent water loss and prevent pathogen invasion a. Cuticle – particularly waxy dermal tissue around leaves

Vascular tissue – transports materials between the roots and shoots a. Xylem – transport water and minerals up from the roots, dead at maturity b. Phloem – transports sugars and other organic compounds from the leaves to other parts of the plant

A. Meristems – where cell division occurs for plant growth 1. Apical meristems –primary growth (elongating roots and shoots), located at the tips of roots and buds of shoots Height of bicycle will not change – growth only occurs at the meristems

2. Lateral meristems – secondary growth (adding thickness) a 2. Lateral meristems – secondary growth (adding thickness) a. Vascular cambium tissue – located between xylem and phloem, produces secondary xylem (wood) b. Cork cambium tissue – produces tough covering that replaces epidermis early in secondary growth

c. Bark – all tissues outside vascular cambium, includes living phloem from vascular cambium 1. The wood (xylem) of large trees is dead when its functional 2. The living part of the tree is almost entirely bark (injuries to bark may kill tree if it interferes with movement of materials through phloem) Plant version of cell differentiation and specialization

Organization of leaves

Organization of leaves Xylem – transports water from roots Phloem – transports sugars to rest of plant Large number of chloroplasts Lightly packed for gas exchange Stomata – pores for gas exchange (CO2 enters, O2 and water vapor exit) Guard cells – open and close stomata

IV. Transport Electrochemical gradients – combined effects of concentration gradient and voltage differential across membrane Cotransport – using a steep concentration gradient of one solute to transport another solute along with it 1. Drop in potential energy of the first pays for the transport of the second

Water potential – combined effects of solute concentration and physical pressure *Remember -water potential of pure water in an open container = 0 -solute potential is always negative (-) -turgor pressure – contents of cell press against the cell wall

Sample Problem: Calculate the solute potential of the potato cores in the figure below if the temperature is 21 degrees C. Express your answer in bars, round to the nearest one-hundredth.

= -(1)(0.35M)(0.0831 liter bar/mole K) (273 +21) = -8.55 bars Calculate the solute potential of the potato cores in the figure below if the temperature is 21 degrees C. Express your answer in bars, round to the nearest one-hundredth = -(1)(0.35M)(0.0831 liter bar/mole K) (273 +21) = -8.55 bars

Aquaporins – transport protein channels for the passage of water Bulk flow – long-distance transport, movement of liquid in response to a pressure gradient 1. From regions of high pressure to low pressure

V. Transpiration Water and minerals from the soil enter through the root epidermis, cross the body of the root, and flow up the xylem (xylem sap) through the shoot and exit the plant through the leaves Transpiration is the loss of water vapor from the plant

C. Transpiration Cohesion-Tension Theory 1. Water moves down concentration gradient (out of plant) Creates negative pressure *Remember the importance of hydrogen bonds!

C. Transpiration Cohesion-Tension Theory 2. Water lost by transpiration is replaced by water from xylem 1. Water moves down concentration gradient (out of plant) Creates negative pressure *Remember the importance of hydrogen bonds!

C. Transpiration Cohesion-Tension Theory 2. Water lost by transpiration is replaced by water from xylem 1. Water moves down concentration gradient (out of plant) Creates negative pressure 3. Vessel water column is maintained by cohesion/adhesion *Remember the importance of hydrogen bonds!

C. Transpiration Cohesion-Tension Theory 2. Water lost by transpiration is replaced by water from xylem 1. Water moves down concentration gradient (out of plant) Creates negative pressure 3. Vessel water column is maintained by cohesion/adhesion *Remember the importance of hydrogen bonds! 4. Water is pulled from root cortex into xylem cells

C. Transpiration Cohesion-Tension Theory 2. Water lost by transpiration is replaced by water from xylem 1. Water moves down concentration gradient (out of plant) Creates negative pressure 3. Vessel water column is maintained by cohesion/adhesion *Remember the importance of hydrogen bonds! 4. Water is pulled from root cortex into xylem cells 5. Water is pulled from the soil into the roots

Rate of transpiration 1. Regulated by stomata 2. Large leaf surface area increases rate of photosynthesis AND water loss by transpiration 3. Guard cells – open and close stomata (reducing water loss also reduces amount of CO2 uptake) 4. Inverse relationship between K+ concentration and water potential

Guard cells – stimulated to open by light, loss of CO2, circadian rhythms. Triggers K+ pumps. When guard cells take in K+ causes decrease in water potential causing water to enter the guard cell, cells bulge and open stomata When guard cells lose K+, also lose water, pore closes

VI. Sugar Transport Translocation – movement of sugar from photosynthesis from leaves to rest of plant through phloem using pressure flow Sugar source = net producer of sugars (leaves) Sugar sink = net consumer or storer of sugar (fruit, roots)

1. Loading of sugar at source – reduces water potential, causing uptake of water by osmosis

1. Loading of sugar at source – reduces water potential, causing uptake of water by osmosis 2. Uptake of water creates positive pressure, forcing sap to flow

1. Loading of sugar at source – reduces water potential, causing uptake of water by osmosis 2. Uptake of water creates positive pressure, forcing sap to flow 3. Pressure is relieved by unloading of sugars (and water) to sink

1. Loading of sugar at source – reduces water potential, causing uptake of water by osmosis 2. Uptake of water creates positive pressure, forcing sap to flow 3. Pressure is relieved by unloading of sugars (and water) to sink 4. Xylem recycles water from sink to source

VII. Symplast Network of living phloem cells that connects all parts of a plant Plasmodesmata – allow for movement of informational molecules (RNA, proteins) that coordinate development between cells 1. Respond to changes in turgor pressure, pH, ion levels C. Long-distance electrical signaling – can regulate transcription, respiration, photosynthesis, etc. in distant locations in the plant