This covers the leaf anatomy, Abiotic stress on plants. very helpful for easy explanation.

1. Leaf Anatomy
and
Drought
By
Arslan Ahmad
Roll no. 05

2. Leaf Anatomy
• Leaves are complex structures mainly consisting of two
dissimilar layers of photosynthesizing cells, with different
packing and cell orientation, interspersed by vascular tissues,
all between two epidermis, which are perforated by stomatal
pores.
• During photosynthesis, the CO2 entering the leaves through
stomata has to diffuse from internal cavities to the sites of
carboxylation inside the stroma through the leaf mesophyll.

5. • It is generally assumed that the overall leaf internal diffusion
conductance in the photosynthetic pathway can be divided in at
least two main components:
• Gas intercellular air spaces (Gaseous phase conductance)
• CO2 diffusion from the cell walls to the chloroplasts. (Liquid phase
conductance).

6. • Taking into consideration that both components can be significantly
affected by the as well as that abiotic
stress considerably affects leaf anatomy.
• So, it is obvious that abiotic stresses can influence photosynthetic
performance through alterations in leaf structure.

7. The Gias Component
• First anatomical feature that influences gias
is the stomatal distribution between leaf
surfaces.
• If Stomata can occur on either both surfaces
then called as amphi-stomatous.
• If only on one surface usually lower only
called as hypo-stomatous, but also upper
only, then it is called as hyper-stomatous.

8. • The real path length for CO2 diffusing in the leaf depends on leaf
anatomy and mesophyll organization.
• In species with succulent leaves, mesophyll cells are large and tightly
packed and reduced air spaces fraction.
• Shaded leaves obtained from the four forest species tended to have
high porosities (34– 48%) compared to those fully exposed to sun.
• Grasses have comparatively more porosity then the succulent leaves.

9. • Due to abiotic stresses, a plant could also result in alterations in leaf
anatomy characteristics impairing CO2 diffusion.
• For example, growth under saline conditions reduced Air spaces
fraction in Spinacia oleracea from 32 to 24%.
• In addition, comparative studies of paradermal leaf sections of two
olive varieties subjected to different irrigation regimes indicate a
significant reduction in intercellular air spaces in drought stressed
compared to well irrigated plants.

10. Liquid Phase
Conductance
• Liquid phase component of mesophyll
conductance is quite complex
depending on many leaf anatomical
traits.
• As chloroplasts are usually tightly
coupled to cell membranes facing
intercellular air spaces, it was
assumed that CO2 would not have to
cross the cytosol, entering the
chloroplasts directly after crossing the
cell wall and plasma and chloroplast
membranes.
• That’s why, mesophyll conductance is
lower in liquid component as
compared to gaseous one.

11. Eco-physiological Significance of Mesophyll
Conductance
• Mesophyll Conductance is not only based on species and cultivars, its also
depends on the environmental variables.
• Mesophyll conductance decrease in response to water stress, low nitrogen
availability, salinity, high altitude, water logging, leaf temperature, and leaf
aging.
• Mesophyll conductance also respond to Environmental variables.
• For example, leaf desiccation, rapid changes in leaf temperature, changes
in CO2 concentration, and changes in light intensity all result in significant
changes in Mesophyll conductance.
• In particular, cutting the leaf petiole resulted in immediate reduction of
both stomatal conductance and mc of about 30% after only 10 min.

12. • Under drought conditions, photosynthesis is reduced due to
consequent increase in transpiration plant water losses.
• An increase in photosynthetic performance by means of increasing
mc may result in increasing photosynthesis without additional water
losses, thus increasing plants water use efficiency.
• Castanea sativa (Sweet Chestnut), from low rainfall areas had a higher
WUE.

13. Conclusion and Future Perspective
• Plants have evolved a large variety of distinct anatomical alterations
operating in both organs and organism level in order to adjust to
unfavorable environmental conditions.
• At organs level significant changes in certain anatomical
characteristics in plants exposed to abiotic stresses have been
observed.
• In two directions researches are being conducting,
The first one refers to a system-based approach relating changes in
environmental parameters and molecular signals to anatomical changes.
The second focus on the detailed analysis of certain anatomical changes
induced in different organs by abiotic stress.