Fixed oils and fats are widely distributed in both vegetative and reproductive parts of the plant. They are more con- centrated in the seeds as reserved lipids. Fixed oils occur as small refractive oil globules, usually present in association with aleurone grains. Fixed oil and fat show certain common characteristics and respond to the following tests:
1. They are generally soluble in ether and alcohol with few exceptions.
2. 1% solution of osmic acid colours them brown or black.
3. Dilute tincture of alkanna stains them red on standing for about 30 minutes.
4. A mixture of equal parts of strong solution of ammonia and saturated solution of potash slowly saponifies fixed oil and fat.
Mucilage
Mucilages are polysaccharide complexes of sugar and uronic acids, usually formed from the cell wall. They are insoluble in alcohol but swell or dissolve in water. The following tests are useful for the detection of mucilage in cells.
1. Solution of ruthenium red stains the mucilage pink. Lead acetate solution is added to prevent undue swell- ing or solution of the substance being tested. 2. Solution of corallin soda and 25% sodium bicarbon-
ate solution (alkaline solution of corallin) stain the mucilage pink.
4.5. CELL DIVISION
From the smaller plants like algae to the large trees like eucalyptus, all starts their growth from a single cell called as egg cell. It is brought about by the development of new cells. Two important processes are continued which ultimately helps in the vegetative growth and also in the preservation of hereditary characteristics. It includes the division of nucleus termed as mitosis and the division of cell cytoplasm, referred to as cytokinesis.
Mitosis
Mitosis is a somatic cell division which is responsible for the development of vegetative body of the plants. A German Botanist Stransburger (1875) first studied it in detail. The process of mitotic cell division consists of four important stages, viz. prophase, metaphase, anaphase and telophase (Figure 4.15).
Prophase
This phase of chromosome fixation is the longest one in the mitotic cell division. Firstly, the indistinct chromosomes appear as the recognizable thread. Chromosomes are closely occurring double threads of which each longitudinal half becomes chromatid. Gradually chromosomes are thick- ened. Chromatid starts dividing longitudinally into two halves along with chromosomal substance matrix around it. Some gap start appearing in the chromosomes which is called as centromeres. At the end of prophase, nucleoli become smaller, matrix becomes clearer and the nucleus enters into metaphase.
Metaphase
During this phase nuclear membrane vanishes and the spindle formation takes place; Bipolar spindle is made up of delicate fibres. Later the nuclear membrane is removed; spindle appears into the nuclear region. Movement of chromosomes to the equatorial plane of spindle separates them from one another. Centromeres are along the equators while the arms of the chromosomes are directed towards the cytoplasm where they are most clearly revealed.
Protometaphase
Nucelear envelope fragments. Microtubes of spindle invade nuclear area and are able to interact with chromosomes. Chromosomes are more condensed. The two chromatids have kinetochore-protein structure. Microtubes attach to kinetochore and move the chromosomes back and forth. The kinetochore that do not attach interact with others from the opposite pole.
Anaphase
In anaphase, chromatid halves move away equatorially at two opposite poles with the tractile fibres. The chromatid separates completely from each other. The spindle under- goes maximum elongation to facilitate separation of diploid chromatids. It is a shortest phase of mitosis.
Telophase
In telophase, chromatids forms the close groups. The polar caps of the spindle disappear and the formation of nuclear membrane takes place around the groups of chromosomes. The matrix and spindle body disappears completely. Appear- ance of nucleoli and nuclear sap makes them recognizable as two distinct nuclei.
Once again nucleus formed grows in size and starts working as metabolic nuclei to enter again in the cycle of mitotic cell division. It mainly depends upon types of plants, plant part and temperature.
Cytokinesis
Cytokinesis is the partition of cytoplasmic material. It takes place either by formation of new cell walls or by cytoplasmic breakdown. New cells are formed by deposition of cellulosic
material in the equatorial zones, which forms the membrane and divide cytoplasm into newly formed cells.
Meiosis
Meiosis is a process of nuclear division in which the numbers of chromosomes are reduced to half (n) from the basic nucleus of 2n chromosomes. A German botanist Stransburger (1888) was the first researcher of this complex genetic process. Chromosomes are called as the carriers of hereditary characters, so the meiosis is the process of transmission of these genetic characteristics. All sexually reproducing plants and animals are gametes with haploid number of chromosomes. Fusion of the male and female gametes results into zygote whereby doubling of chromo- somes to 2n takes place to develop offspring.
Meiosis involves two successive divisions: the first process of division I is reduction division, while the second process of division II is similar to that of mitosis, (Figure 4.16).
Division I
In this process of meiosis mother nucleus undergoes com- plicated changes which can be subdivided into various phases as given below.
Fig. 4.15 Phases of mitotic cell division Nucleus Centrioles Nuclear envelope Nuclear envelop breaks down Nucleus Nucleolus Chromatin Daughter chromosomes Aster Prophase Telophase Anaphase Metaphase Prometaphase Chromatids of chromosome Centromere region Developing spindle
Centrioles Nucleus
Nucleolus
Prophase Metaphase
nterphase Telophase Anaphase
Prophase Metaohase Anaphase Germ cells
Fig. 4.16 Phases of meiosis