I. MINERAL NUTRIENT
A. Mycorrhizal Fungi and Their Association with Plant Roots
When plants live in challenging locations, they often develop mechanisms to
help them survive. These include morphological characteristics such as thickened,
small or narrow leaves to reduce water loss, slowing the plant's growth rate, or
developing a tolerance for high salts and low levels of nutrients. One important set of
survival mechanisms involves creating mutually beneficial (symbiotic) relationships
between plant roots and soil-borne organisms such as bacteria and fungi.
The good illustration for this is the Mycorrhizal fungi which is a type of fungi
that form mutualistic associations with the roots of most plants. The term
"mycorrhiza" comes from the Greek word 'mukès' means “fungus” and 'rhiza' means
“root”. The word mycorrhiza was coined by the German scientist Albert Bernhard
Frank in 1885. In this association, the mycorrhizal fungi colonize the roots of plants
and form a symbiotic relationship, where both the plant and the fungus benefit.
There are 95% of the world plant species form mycorrhizal relationship with
fungi. Present in 95% of plants are the dicots which consist of 83%, monocot which
has 79% and 100% of gymnosperm. There are two main types of mycorrhizal fungi:
endomycorrhizal and ectomycorrhizal fungi. Endomycorrhizal fungi form a
relationship with the roots of most plants, including agricultural crops and trees. They
penetrate the root cells of plants and form arbuscules, which are specialized structures
that allow for the exchange of nutrients between the fungus and the plant.
Ectomycorrhizal fungi form associations with the roots of trees and some
shrubs. Do not penetrate the root cells of plants, but rather form a sheath around the
root and extend hyphae (fungal filaments) into the soil to access nutrients.
Overall, the association between mycorrhizal fungi and plant roots is essential
for the growth and health of most plants. This symbiotic relationship allows plants to
access nutrients more efficiently, leading to better growth and increased resistance to
stressors such as drought and disease.
B. Essentially of elements; concepts, criteria and problems
Concepts:

Plants use inorganic minerals (E.g iron, calcium, sodium, potassium and
magnesium) for nutrition. Complex interactions involving weathering of rock
minerals, decaying organic matter, animals, and microbes take place to form
inorganic minerals in soil. Roots absorb mineral nutrients as ions in soil
water. Many factors influence nutrient uptake for plants.
Eg. Photosynthesis
Criteria:
The term essential mineral element (or mineral nutrient) was proposed by
Arnon and Stout (1939). They concluded three criteria must be met for an element to
be considered essential. These criteria are:
1. Which is required or essential for the normal growth reproduction of
plants.
2. They must be specific in requirement & their deficiency should not be
supplemented by other elements.
3. Directly involved in metabolism.
Problems:
1. Plants don't get enough mineral elements- Symptoms of nutrient
deficiency may include stunted growth, death of plant tissue, or yellowing of
the leaves caused by a reduced production of chlorophyll, a pigment needed
for photosynthesis. Nutrient deficiency can have a significant impact on
agriculture, resulting in reduced crop yield or reduced plant quality.
Nutrient deficiency- when a plant does not get enough minerals
2. Plants get too many mineral elements- Plants can't get rid of the excess
nutrients so the nutrients unfortunately cause root and leaf damage.
When there is leaf damage, or burn, it reduces the available surface
area for photosynthesis to occur. As a result, your plants will
produce less glucose that I s required for optimal growth.
C. Uptake and Assimilation of Mineral Elements
Mineral uptake is the natural process in which all the essential minerals enter
the plant's cellular material, typically following the same pathway as water. The
uptake of mineral nutrients occurs at both the roots and the leaves. Nutrient
assimilation is the process by which nutrients acquired by plants are incorporated into
the carbon constituents necessary for growth and development.
Assimilation of mineral elements is the process by which plants absorb and
incorporate essential mineral nutrients from the soil. These mineral nutrients include
macronutrients such as nitrogen, phosphorus, and potassium, as well as micronutrients
such as iron, zinc, and manganese. The assimilation of these minerals is crucial for
plant growth and development, as well as for the formation of important biomolecules
such as enzymes, nucleic acids, and chlorophyll.
Plants absorb mineral nutrients through their roots via two main processes:
passive uptake and active uptake. Passive uptake occurs when mineral ions move into
the root cells due to a concentration gradient. Active uptake, on the other hand,
involves the use of energy to move mineral ions against a concentration gradient. This
process is facilitated by proteins called transporters, which are embedded in the
membranes of root cells.
Once inside the root cells, the mineral ions are transported to the shoots
through the xylem vessels. In the shoots, the minerals are then incorporated into
various biomolecules and metabolic pathways. For example, nitrogen is assimilated
into amino acids, which are the building blocks of proteins. Phosphorus is
incorporated into nucleotides, which are the building blocks of nucleic acids such as
DNA and RNA. Potassium is involved in the regulation of stomatal opening and
closing, which is important for gas exchange and water balance in the plant.
The assimilation of mineral nutrients is regulated by a complex network of
signaling pathways that respond to both internal and external cues. For example,
plants can adjust their nutrient uptake in response to changes in soil pH, water
availability, and temperature. Additionally, nutrient availability can also affect gene
expression and protein synthesis, which can further modulate nutrient assimilation.
The process of uptake or transport of mineral nutrients is carried out by the
plant cells in two different ways:

Passive Absorption- It is the absorption of minerals without the direct
expenditure of metabolic energy.
 Active Absorption- It is the absorption of minerals with the direct
expenditure of metabolic energy. During the active absorption of minerals,
ions from the outer space of the cell move into the inner space and it
generally occurs against the concentration gradient. Hence it requires
metabolic energy and this energy is obtained from the cell’s metabolism
either directly or indirectly.
All the minerals cannot be transported passively in the roots as the
concentration is low in the soil and moreover they are present as a charged particle,
which cannot cross the cell membrane. These are actively transported in the roots
using energy stored as ATP. Minerals are transported by specific proteins present in
the membrane of the root hairs. Transport proteins are embedded in the plasma
membranes of endodermal cells and control the type and amount of solutes reaching
the xylem.
In conclusion, the assimilation of mineral elements is a complex process that
is critical for plant growth and development. By understanding the mechanisms
underlying this process, researchers can develop new strategies to improve crop
productivity and nutrient use efficiency, which is becoming increasingly important
given the growing global demand for food and the need to reduce the environmental
impact of agriculture.
D. Functions of Mineral Elements and Symptoms of Deficiencies
Mineral elements - They are inorganic elements that are essential for all life
processes. They are further divided into two, macrominerals and microminerals.
Some examples of macrominerals needed by plants are: phosphorous, carbon,
sodium, nitrogen, potassium, silicon, magnesium, hydrogen, calcium, oxygen,
selenium and suldur.
Some examples of microminerals that are vital for plants are: iron, boron,
nickel, manganese, copper, zinc, cobalt, chlorine, and molybdenum.
What are the functions of mineral elements?
•Needed in the formation of the
plant body
•Influence the permeability of
the cytoplasmic membrane
•Needed in the osmotic potential
of cells
•Catalytic and balancing effects
•Influence the pH of the plant
•Phloem
translocation
transport
or
Symptoms of Deficiencies of Mineral Elements on Plants:
•Yellow leaves
•Small or stunted leaves
•Yellow or brown leaf edges
•Yellow or brown spots on
leaves
•Holes in leaves
•Leaves look burnt or scorched
•Leaves have a purple or red tone
•Yellowing between leaf veins
•Twisted or misshaped leaves
•Stunted roots
•Yield differences
•Crop failure
II. SOLUTE TRANSPORT
A. Passive, Facilitated Diffusion, Active Transport in Plants

Passive- requires no energy, molecules are moved across the cell membrane and
are transported through the concentration gradient.
Example: Gases like carbon dioxide and oxygen diffuse into and out of a
plant cell via stomatal openings according to their respective concentration
gradients.

Facilitated Diffusion- A type of passive transport but it only allows certain
molecules to pass through. A transport protein or channel is present in this
diffusion.
Example: A facilitated diffusion example is the glucose transport. Since
glucose is a large polar molecule, it cannot pass through the lipid bilayer of
the membrane. Thus, it needs carriers called glucose transporters to pass
through.

Active Transport- It requires energy in the form of ATP. Movement happen by
pumping the molecules against the concentration gradient.
Example: Photosynthesis sugars move from leaves to the fruit. Ions
move from the soil to the roots of plants.
Importance of Transport Systems in Plants:
•Crucial for cell survival
•Ensure that biological functions run properly
•Movement of nutrients
A. Transport Across Biological Membranes
The plasma membrane or cell membrane is a lipid bilayer membrane in which
proteins are embedded that separates the cytoplasm of the cell from the extracellular
spaces. It is selectively permeable that regulates the transportation of molecules. The
transportation of molecules across the membrane can be active or passive.
1) Active transportation- is the movement of molecules (ions, glucose and amino
acids) across the membrane against the concentration gradient. It requires cellular
energy. The protein molecules embedded within the membrane act as channels
through which molecules can pass. These proteins are called carriers i.e, the molecule
attaches to the carrier protein which then transports that molecule into the cell.
2) Passive transportation- is the movement of molecular substances across cell
membranes along the concentration gradient without any energy.
Osmosis
Plant osmosis refers to the movement of water molecules from an area of high
water concentration to an area of low water concentration through a semi-permeable
membrane in plants. This occurs because plant cells have a higher solute
concentration inside than outside, which creates a concentration gradient that drives
the movement of water. As water moves into the plant cells, they become turgid,
which helps maintain the plant's structure and function. However, if too much water
enters the cells, they can become overly swollen and burst. Osmosis is a crucial
process for plants, as it helps them absorb water and nutrients from the soil, and
maintain their internal structure and function.
B. Phloem Translocation
In plants sugars are produced in sources, such as leaves, need to be delivered
to growing parts of the plant via the phloem in a process called translocation, or
movement of sugar. The points of sugar delivery, such as roots, young shoots, and
developing seeds, are called sinks. This is often a movement of sucrose from the
leaves to other areas of the plants. It is transferred through the phloem, which consists
of living sieve cells and the sucrose can flow both ways. Translocation occurs in the
phloem tissues, which consist of tube-like vessels called phloem vessels. These
phloem vessels run from the leaves into every other part of the plant and are
responsible for transporting dissolved organic solutes, such as sucrose and amino
acids, from the sources to the sinks.
Translocation depending on the season
In the summer, the source of sucrose is the mature leaves and stem of the
plant, as this is where the majority of photosynthesis takes place. The sink in the
summer is the roots, as the assimilates are stored there while excess sugars can be
made during the long daylight hours of the summer.
In the spring and winter, the daylight hours are still short, so there is not much
light available for photosynthesis. Therefore, the roots that have been storing sugars
become the source of translocation. Sucrose is transported from the source in the roots
to the sinks in the leaves so they can restart growth. As the movement of sucrose can
be in more than one direction, this movement is described as bidirectional.
C. Phloem Loading and Unloading Mechanism of Sieve Tube
Translocation
1. Loading sucrose into the phloem
2. Water flows into the phloem
3. The solution of sucrose and water moves towards the low pressure area
4. Unloading sucrose from the phloem
5. Water moves back into the xylem through osmosis