Download Fruits

Fruits
Fruit Types
• A fruit may be defined as a matured ovary
• There are two basic fruit types – dry or fleshy.
These types arise from the development of the
pericarp
• The pericarp may become dry and these form
dry fruits
• The pericarp may also become soft, thick and
fleshy – and these form fleshy fruits
Apples and Pears
Violet
flower
types
Plant Transport Mechanisms
Guttation
Brown algae – Macrocystis and Laminaria - California
Giant
Sequoia
Plant Transport
Plant transport occurs at three levels:
1. The uptake and loss of water and solutes by
individual cells, such as absorption of water and
minerals from the soil by root cells.
2. Short-distance transport of substances from cell to
cell at the level of tissues and organs, such as moving
sugar from photosynthetic cells of leaf to the phloem
sieve tubes
3. Long distance transport of sap within xylem and
phloem at the level of the entire plant.
Transport at the Cellular Level
• Substances will tend to diffuse across the cells plasma
membrane from areas of high concentration to areas of low
concentration – this is down a concentration gradient and is
done by passive transport.
• We can also get movement of substances across plasma
membranes against their concentration gradient – this is
movement uphill and requires the expenditure of energy. It is
known as active transport. This almost always uses ATP for
energy.
• Cotransport is a process where a transport protein couples the
downhill movement of one substance (such as H+) to the
uphill passage of another. It can be used by root cells to take
in NO3 nitrate or uptake of sugars like sucrose.
Water Potential
• The movement of water in and out of plant cells is
driven by water potential. The net uptake or loss of
water by a cell occurs by osmosis, the passive
transport of water across a membrane. Water usually
moves from hypotonic (low solute concentration) to
hypertonic (high solute concentration) – this is what
happens in animal cells. But plants have a rigid cell
wall that provides physical pressure. So in plants the
movement of water depends upon a combination of
solute concentration and physical pressure known as
water potential symbolized by the Greek letter psi Ψ
Plant cells have three basic compartments
1. Outside the cell is a thick cell wall that helps
maintain the plant cells shape. It does not regulate
the movement of material in and out of the cell – that
is done by the plasma membrane.
2. The plasma membrane serves as the barrier between
the cell wall and the cytosol – the cytoplasm inside
the cell but outside of the organelles
3. Most mature plant cells have a large vacuole that
contains cell sap. It may occupy 90% of the cell
volume. It is surrounded by the tonoplast and
regulates traffic between the cytosol and the cell sap.
Symplast and Apoplast
• Most plant cells have openings in the cell
walls called plasmodesmata. The
plasmodesmata connect the cytosol
compartments of neighboring cells allowing
easy movement of substances between cells.
The connected cytoplasms of many cells is
known as the symplast.
• The cell walls for a continuum of spaces
between cells. This is known as the apoplast.
Lateral transport can happen in three ways:
1. Substances can move out of one cell and into another
making repeated crossings of the plasma membranes.
This is fairly slow and not that common.
2. Substances can move via the symplast – crossing a
plasma membrane once and then traveling through
many cells.
3. Substances can move via the apoplast, traveling
between cell walls without ever entering into a cell.
Root with mycorrhizae
Transport in Xylem
• Once water and minerals reach the xylem via lateral
transport they move up the xylem vessels via bulk
flow the movement of a fluid driven by pressure.
• Xylem sap flows upward to the veins of leaves due to
the pressure of transpiration – the loss of water
vapor from the leaves and other aerial parts of the
plant.
• An early botanical question was whether xylem sap
was pushed up or pulled up the plant.
Water – pushed or pulled?
• Pushing of the xylem sap occurs via root pressure –
root cells expend energy to pump mineral into the
xylem. Minerals accumulate in the xylem sap
lowering water potential there. Thus water flows into
the xylem, generating a positive pressure that pushes
fluid up the xylem.
• But root pressure can only push sap up a few meters
and many plants generate no root pressure at all.
How does water reach leaves of 100 m tall trees?
• Xylem sap is pulled up the plant via transpirational
pull. Leaves actually generate the negative pressure
necessary to bring water to them.
Guttation – from root pressure
Transpiration
Translocation
• The transport of food throughout a plant is known as
translocation.
• Sugar from mesophyll cells in the leaves and other
sources must be loaded before it can be moved. In
some species, sugar moves all the way from
mesophyll cells to sieve tube members via the
symplast. In other species, sugars moves by a
combination of symplast and apoplast.
• Often sieve tube members accumulate very high
sucrose concentrations – 2 to 3 times higher than
concentrations in the mesophyll – so phloem requires
active transport using proton pumps
Translocation
• At the sink end of a sieve tube, the phloem unloads its
sugar. Phloem unloading is a highly variable process;
its mechanism depends upon the plant species and the
type of organ. In any case, the concentration of sugar
in the sink cells is lower than in the phloem because
the sugar is either consumed or converted into
insoluble polymers like starch.
• Phloem moves at up to 1 m/hour – too fast to be by
diffusion. So phloem also moves via bulk flow –
pressure drives it.