Difference between Mesophyll and Bundle Sheath Cells and Chloroplasts in C4 Plants


chloroplast variation of C4 plants

Differences between Mesophyll and Bundle Sheath Cells and Chloroplasts in C4 Plants
(
Mesophyll vs Bundle Sheath Chloroplasts: A Comparison Table)

The C4 cycle or Hatch and Slack pathway of dark reaction of photosynthesis are characterized by two structurally and functionally different chloroplasts in their leaves. The leaves of C4 plants such as maize possess the classical Kranz anatomy. In Kranz anatomy, each vascular bundle is surrounded by a ring of bundle sheath cells, followed by one or more concentric layers of mesophyll cells. Bundle sheath cells have thick cell walls and contain centrifugally arranged chloroplasts with large starch granules and unstacked thylakoid membranes, whereas the mesophyll cells contain randomly arranged chloroplasts with stacked thylakoids and little or no starch grains.

The mesophyll chloroplasts in C4 plants are highly specialized to do the light dependent reactions of photosynthesis whereas the bundle sheath cells are specialized to perform the light independent reactions. In C4 cycle, the atmospheric CO2 is first accepted by PEP in the cytoplasm of the mesophyll cells and converted to OAA with the help of the enzyme PEP carboxylase. OAA is then transported from the mesophyll cells to the bundle sheath cells. In the bundle sheath cells, OAA releases molecular CO2 and which is accepted by the regular RuBP to run the Calvin cycle or C3 cycle for the synthesis of carbohydrate precursors. 

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Difference between C3 and C4 Cycles of Photosynthesis in Plants


C3 vs C4 Cycles of Photosynthesis

Similarities and Differences between C3 and C4 Cycles: A Comparison Table
(Calvin Cycles Vs Hatch and Slack Cycle)

Photosynthesis is one of the vital events in the earth in which the green plants fix the energy from the sunlight and synthesis nutrients with carbon dioxide and water. Almost all living things on earth, either directly or indirectly, depend on photosynthesis for energy. The process of photosynthesis in plants is completed in two major pathways, a light dependent ‘Light Reaction’ and a light independent ‘Dark Reaction’. In the light reaction, the chlorophyll molecules in the plants absorb energy from sunlight and synthesize energy rich chemical molecules such as ATP and reduced coenzymes (NADPHH+). In the dark reaction, this energy rich molecules are used up for the synthesis of carbohydrates from carbon dioxide. The first describe dark reaction pathway, better known as Calvin cycle (Melvin Calvin who discovered this pathway), is called C3 cycle. For a considerable period of time, the Calvin cycle (C3 cycle) was thought to be the only dark reaction pathway in plants. Later, a new pathway of dark reaction called Hatch and Slack pathway or C4 cycle was described in some plants. Both these cycles (C3 and C4 cycles) show many similarities and differences. The present post describes the similarities and differences between C3 cycle and C4 cycle of the dark reaction of photosynthesis.

Similarities between C3 cycle and C4 cycle

Ø  Both C3 and C4 cycles are pathways of dark reaction of photosynthesis.

Ø  Both are light independent reactions.

Ø  Both C3 and C4 cycle requires energy from ATP or reduced coenzymes.

Ø  Both C3 and C4 plants accept carbon dioxide to perform dark reaction.

Ø  End products of C3 and C4 cycle are similar.

Ø  Both C3 and C4 cycle requires RuBP and RUBISCO to complete the pathway.

Difference between C3 cycle and C4 cycle:

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Botany lecture notes

Types of Stelar Systems and its Evolution in Pteridophytes and Higher Plants with PPT


types of steles in pteridophytes

Stelar Evolution in Vascular Plants
(Origin and Evolution of Stele in Pteridophytes and Higher Plants)

What is stele? What are the components of stele?

Ø  Stele is the central cylinder or core of vascular tissue in higher plants.

Ø  The stele consists of xylem, phloem, pericycle and medullary rays and pith if present.

Ø  The term ‘stele’ was for the first time used by Van Tieghem and Douliot in 1886 in their ‘Stelar Theory’.

What is ‘stellar theory’?

Ø  Proposed by Van Tieghem and Douliot in 1886.

Ø  Major highlights in stellar theory are:

$.  The stele is a real entity and present universally in all axis of higher plants.

$.  The primary components of stele are xylem and phloem.

$.  Tissues like pericycle, medullary rays and pith are also the components of stele.

$.  ‘Stelar theory’ also says that the cortex and the stele are the two fundamental parts of a shoot system.

$.  Both these components (stele and cortex) are separated by the endodermis.

$.  In higher vascular plants (Pteridophytes, Gymnosperms and Angiosperms), the leaf traces are large, and it appears that they play an important role in the vascular system of the axis.

$.  The whole set-up of leaf traces appears as a composite structure in these plants.

$.  Such composite structures do not remain within the limits of stellar theory of Van Tieghem and Douliot.

What are the different types of steles in plants (Pteridophytes and higher plants)?

Ø  On the basis of ontogeny and phylogeney, there are THREE broad categories of steles in vascular plants.

Ø  They are:

(1).  Protostele

(2).  Siphonostele

(3).  Solenostele

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Botany lecture notes

Receptacular vs Appendicular Theory of Inferior Ovary Development in Flowers


Origin and Evolution of Inferior ovary

Receptacular vs Appendicular Theory
(A Comparative Approach)

Based on the position of ovary there are three types of flowers- (1) Hypogynous, (2) Perigynous, and (3) Epigynous.

(1). Hypogynous Flower: The most primitive type with convex shaped Thalamus (torus). The ovary is superior and all other floral parts (calyx, corolla and androecium) arise from the base of the ovary.

(2). Perigynous Flower: An intermediate or transient type between Hypogynous and Epigynous flowers. The thalamus is more or less cup shaped and the ovary is half inferior, located at the centre of the thalamus cup. All other floral parts arise from the rim of the thalamus cup. Sometimes the thalamus cup forms a long tube like structure called hypanthium.

(3). Epigynous Flower: The most advanced type of flower. The ovary is inferior and all other floral parts arise from the above portion of the ovary.

Ovary Position Classification

(image source: cc wikipedia)

Ø  The origin and evolution of inferior ovary is a well debated question in the phylogenetics of Angiosperms.

Ø  Comparative morphological, anatomical and paleo-botanical studies suggest that the inferior ovary has evolved many times among different groups of Angiosperms in different ways and in different times in the remote past.

Ø  In order to explain the formation of inferior ovary, two theories have developed by the evolutionary biologists.

Ø  The two theories are:

(1). Appendicular Theory

(2). Receptacular (axial) Theory

Ø  Both these theories are proposed on close attention to the organization of the course of vascular bundles supply to the ovules in the flower.

Ø  The two theories also considered that the hypogynous flower is the most primitive one. Moreover, the epigynous condition evolved from a hypogynous condition through the transient perigynous state.

(1). Appendicular Theory

Ø  Proposed by Eames in 1961.

Ø  According to this theory, extensive fusion (both connation and adnation) of the outer lower portion floral whorls to one another and to the ovary wall has occurred. This result in the formation of an inferior ovary (epigynous condition).

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Botany lecture notes

Gamma Gardens for Mutation Breeding and Crop Improvement (Advantages and Disadvantages)


atomic garden

Satellite Map of a Gamma Garden at Institute of Radiation Breeding, Hitachiohmiya, Japan

Gamma Gardens (Atomic Gardens)

What are Gamma Gardens or Atomic Gardens?

Gamma garden or Atomic garden is a concept popularized after the Word War 2 for the peaceful use of atomic energy (atoms for peace) for the crop improvement. Gamma gardens or atomic gardens are a type of induced mutation breeding where radioactive sources particularly gamma rays from cobalt -60 or Caesium-137 are used to induce desirable mutations in crop plants. 

Salient features of Gamma Garden

Ø  Gamma gardens are “area subjected to gamma irradiation of crop plants”.

Ø  They are giant structures, enclosed by thick high wall to protect the plants and animals outside.

Ø  The purpose of a gamma garden is to irradiate the whole plants during different stages of development and of varying duration.

Ø  The source of radiation used is Cobalt-60.

Ø  Rarely Caesium-137 is also used as the source of radiation.

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