Botany lecture notes

Root Stem Transitions in Plants with PPT

Root Stem Transitions in Plants

Root Stem Transition in Plants (with PPT)
(Theories of Anatomical Transition from Root to Stem In Angiosperms)

Root and stem form a continuous structure in plants called the axis. The vascular tissue in root is radial (xylem and phloem arranged separately in different radii) whereas in the stem is conjoint (xylem and phloem are arranged together in same radii as vascular bundles). Thus, there should be a region in the axis where the vascular structures of the root and the stem meet and merge together. This peculiar region is called the Root-Stem Transition Zone. The current post describes the various types of root-stem transitions found in Angiosperms.

Ø  The epidermis, cortex, endodermis, pericycle and the secondary vascular tissue are continuous from root to stem.

Ø  Only the primary vascular tissue in the axis undergoes a change in their position and orientation.

Ø  The exarch arrangement of xylem in root changes to endarch position in the stem.

Ø  In the transition zone, the vascular tissue undergoes many changes such as Forking, Multiplication, Rotation and Fusion.

Ø  The vascular tissue also increases their diameter.

Ø  The exact position of the transition zone is different in different plants.

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Botany lecture notes

Dicot Leaf (Dorsiventral Leaf) Structure with PPT

Anatomy of Dicot Leaf PPT

Dicot Leaf Cross Section (Dorsiventral Leaf)
(Anatomical Structure of a Dicot Leaf- Ixora, Mangifera, Hibiscus)

Ø  Leaves are structurally well adapted to perform the photosynthesis, transpiration and gaseous exchange.

Ø  A leaf composed of:

(1). Leaf blade: also called leaf lamina is the flattened expanded part of the leaf chiefly composed of mesophyll tissue and vascular bundles.

(2). Petiole: the stack of leaf

Ø  Based on the differentiation of mesophyll, two categories of leaves are present among Angiosperms

(1). Dorsiventral Leaf

(2). Isobilateral Leaf

(1). Dorsiventral Leaf:

Ø  Also called bifacial leaf.

Ø  They have anatomically different dorsal and ventral sides.

Ø  The mesophyll tissue is differentiated into upper palisade and lower spongy tissues.

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Botany lecture notes

Anatomy of Monocot Root Cross Section Key Points with PPT

Monocot Root Cross Section

Anatomy of Monocot Root
(Monocot Root Cross Section Under Microscope with Diagram)

Ø  The anatomical features of a monocot root can be studied through a cross section (CS) through the root.

Ø  Anatomically, the monocot root has been differentiated into the following parts:

(1).    Epidermis

(2).    Cortex

(3).    Endodermis

(4).    Pericycle

(5).    Vascular Tissue

(6).    Conjunctive Tissue

(7).     Pith

(1). Epidermis

Ø  Epidermis in the root is also known as epiblema, piliferous layer and rhizodermis.

Ø  It is the outermost layer in the root, composed of closely packed parenchymatous cells.

Ø  Usually, the epidermis is single layered with thin walled cells.

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Molecular Biology Tutorials

Different Forms of DNA (A-DNA, B-DNA and Z-DNA) A Comparison Table with PPT


Different Types of DNA Conformations
(A-DNA, B-DNA and Z-DNA: A Comparison Table)

DNA, the genetic information carrier molecule of the cell, is a long polymer of nucleotides and can adopt different types of structural conformations. The various types of conformations that the DNA can adopt depend on different factors such as:

1.      Hydration level
2.      Salt concentration
3.      DNA sequence
4.      Quantity and direction of super-coiling
5.      Presence of chemically modified bases
6.      Different types of metal ions and its concentrations
7.      Presence of polyamines in solution.

The most common types of structural conformations of DNA are named as:

(1).  A-DNA

(2).  B-DNA

(3).  Z-DNA

Among these three types, the most abundant type of DNA is B-DNA, commonly known as Watson-Crick Model of DNA double helix. The present post describes the structural features of A, B and Z forms of DNA in a comparative manner. We will also discuss the similarities and differences between A-DNA, B-DNA and Z-DNA.

(1). A-DNA

A-DNA is a rare type of structural conformation that a DNA can adopt under dehydrating conditions. A-DNA is a double stranded helical structure almost similar to B-DNA but with a shorter and more compact structural organization. A-DNA was discovered by Rosalind Franklin and the credit for the naming of A-DNA and B-DNA was also accounted to her. Important structural features of A-DNA are given below:

Ø  A-DNA is formed from B-DNA under dehydrating condition.

Ø  A-DNA is much wider and flatter than B-DNA.

Ø  Similar to B-DNA, the A-DNA is also a right handed helix.

Ø  The helix diameter of A-DNA is 26 Å.

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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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