Flower vs Vegetative Branch (Difference between Flower and Reproductive Shoot)
The flower is the reproductive structure formed in the plant group Angiosperms or Magnoliophyta, commonly called as the ‘Flowering Plants’. The flower is a ‘modified branch’ or axis developed from a ‘determinate’ apical meristem. The term ‘determinate’ indicates the absence of further growth of the apical meristem after the production of flowers. Even though the flower is a modified shoot, the morphological and anatomical features of a flower and a vegetative branch show many differences. The present post discusses the Difference between a Flower and a Vegetative Branch with a Comparison Table.
Heterospory and Seed Habitat (Origin of Seeds and Seed Habitat in Vascular Plants from Heterospory)
Heterospory is the production of two or more types of spores
Heterospory is a condition of the production of more than one type (usually two) of spores in a single plant. These two types of spore differ in their formation, structure and most importantly its functions and sexuality. In Pteridophytes, these two spores are called as Microspores and Megaspores.
Microspores are small sized spores produced in large numbers inside the microsporangium. They are male spores which on germination produce male gametophyte.
Megaspores are comparatively large spores produced in limited numbers (1 to 4) inside the megasporangium. They are female spores which on germination produce the female gametophyte.
Learn more: Difference between Microspores and Megaspores
The production of two types of spores with different sexuality was first evolved in Pteridophytes. Even though, the condition of heterospory is now represented only by eight living species of Pteridophytes, they are Selaginella, Isoetus, Marsilea, Salvinia, Azolla, Pilularia, Regnellidium and Platyzoma.
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.
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.
Xerophytic Adaptations of Plants (Ecological Adaptations of Desert Plants)
What are xerophytes?
Ø Xerophytes (xerophytic plants) are plants growing in dry habitats (xeric conditions) where the availability of water is very less.
ØXeric habitat: places where water is NOT present in adequate quantity.
Ø Xerophytes are the characteristic plants of deserts or semi-deserts areas.
Ø Xerophytes can also grow in mesophytic conditions.
Ø Xerophytes can tolerate:
$. Extreme dry condition
$. Low humidity
$. High temperature
$. High wind-flow
Ø Three types of xeric habitats occurs on the earth:
(1). Physically dry habitat: the water retaining capacity of the soil very low and climate is dry (Example: a desert).
(2). Physiologically dry: water is present in excess, but not in the absorbable conditions or the plants cannot absorb it (Example: high salt water, high acidic water and high cold water, water as snow).
(3). Physically and physiologically dry: water present as mist, plants cannot absorb water from the atmosphere directly. (Example: mountain slopes)