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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Botany lecture notes

Mutation Breeding Technique for the Improvement of Crop Plants (with PPT)


what is mutation breeding

Mutation Breeding
(Induced Mutations for Crop Improvement)

What is mutation?

Mutation is the “Sudden heritable change in an organism”. Mutation may be the change in gene, chromosome or plasmagene (genetic material inside mitochondria and chloroplasts. The mutation produced by change in the base sequence of gene is called point mutation or gene mutation. The gene mutation may be further classified as transition, transversion, deletion, duplication or inversion. Chromosomal mutations are the change in chromosome structure. The change in the structure of chromosome can occur as a result of large deletion, inversion, duplication, translocation and change in chromosome number. Most of the mutations are lethal to the organism. A very small number of mutations are beneficial to the organism. Additionally, by the use of mutation inducing agents, a breeder can induce desirable changes in the genetic constitution of plants and thereby he can improve the performance of a cultivated variety.

Mutation Breeding

Definition: “The utilization of induced mutations in crop improvement is called mutation breeding”

The term mutation breeding was first coined by Freisleben and Lein in 1944 to refer to the deliberate induction and development of mutant lines for crop improvement.

Spontaneous and Induced mutations:

(1). Spontaneous mutation:

Mutation occurs in nature are called spontaneous mutation. Spontaneous mutation occurs in the organism without any treatment at low rate in the nature. The frequency of spontaneous mutation is 10-6 (one in 10 lakhs). Different genes in and organism show different mutation rate.

(2). Induced mutation:

Mutations induced in an organism by treatment with physical or chemical mutagen are called induced mutations. The agents which are used to induce mutation are called mutagens. Certain genes in an organism promote the mutation of other genes nearby in the chromosomes. For example, the gene Dt in Chromosome number 9 of maize increases mutation rate of other genes.

Characteristics of Mutation:

Ø  Mutations are generally recessive; Dominant mutations do occur in nature.

Ø  Mutations are generally harmful to organism; small percentage of mutation is beneficial.

Ø  Mutation occurs at random in the chromosome, may occur in any gene.

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Botany lecture notes

Host Selective and Non-Host Selective Toxins in Host Parasite Interactions and Pathogenesis


toxins in plant pathogen interactions

Toxins in Plant Pathogenesis
Toxins in Plant Pathogen Interaction

The process of pathogenesis (the onset of diseased condition) in plants is facilitated by many factors such as virulence of the pathogen, susceptibility of the host, presence of suitable environmental conditions and various enzymes and metabolites of pathogens. Previously we have discussed the importance of different enzymes involved in plant pathogen interactions. These enzymes facilitate the entry of the pathogen into the host and help to colonize inside the host cell. The production of different hydrolytic enzymes may not always result in the establishment of pathogen inside the host tissue. Certain plant pathogen may successfully invade the host tissue area but fail to induce the onset of disease. These findings highlighted the involvement of certain toxins, microbial toxins or aggressins, in the establishment of diseased conditions in plants. The present post describes the Toxins involved in plant pathogen interaction and pathogenesis with examples.

What is meant by ‘toxin’ in Plant Pathology?

Ø  Definition: Any substances produced by a pathogen which is injurious to host and it directly and immediately play a crucial role in pathogenesis.

Ø  Toxins involved in plant parasite interactions are also called as aggressin.

Ø  According to Koch’s postulates, a substance to be called as a ‘toxin’ should follow the following criterions:

@.   The compound must be isolated from the diseased plant

@.   It should NOT be present in the healthy plant

@.   Compound must be chemically characterized

@.   When isolated toxin is reintroduced to a healthy host, it should produce the original symptoms.

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