Dormancy
During seed maturation , the embryo enters a quiescent phase in response to desiccation. Seed germination can be defined as the resumption of growth of the embryo of the mature seed; it depends on the same environmental conditions as vegetative growth does. Water and oxygen must be available, the temperature must be suitable, and there […]
Abscisic Acid
Unlike auxins, gibberellins, and cytokinins, the hormone abscisic acid(ABA) is represented by a single 15-carbon sesquiterpene. ABA also appears to have a more limited range of specific effects than auxins, gibberellins, and cytokinins. THE DISCOVERY OF ABSCISIC ACID As more investigators became interested in plant hormone research, it soon became evident that ether extracts of […]
Ethylene
During the 19th century, when coal gas was used for street illumination, it was observed that trees in the vicinity of streetlamps defoliated more extensively than other trees. Eventually it became apparent that coal gas and air pollutants affect plant growth and development, and ethylene was identified as the active component of coal gas. Dimitry […]
Cytokinins
The cytokinins were discovered in the search for factors that stimulate plant cells to divide (i.e., undergo cytokinesis). Since their discovery, cytokinins have been shown to have effects on many other physiological and developmental processes, including leaf senescence, nutrient mobilization, apical dominance, the formation and activity of shoot apical meristems, floral development, the breaking of […]
Gibberellins
Gibberellins are members of a large and varied family of plant constituents known as the terpenoids. Terpenes are normally recognized on the basis of their chemical structure, which may be dissected into one or more 5-carbon isoprene units. Gibberellins are thus biosynthetically related to the carotenoid pigments, sterols, latex, and other isoprene. Gibberellins are noted […]
Auxins
The first plant hormone we will consider is auxin. Auxin deserves pride of place in any discussion of plant hormones because it was the first growth hormone to be discovered in plants, and much of the early physiological work on the mechanism of plant cell expansion was carried out in relation to auxin action. Darwin’s […]
PLANTS CONTAIN SEVERAL ALTERNATIVE ELECTRON TRANSPORT PATHWAYS
The electron transport chain described above is shared in essentially the same form by virtually all organisms plants, animals and microorganisms. Plant mitochondria contain, in addition, several other redox enzymes, atleast two of which are unique to plants. These enzymes have been discovered largely by virtue of their insensitivity to certain classic inhibitors of electron […]
Electron Transport Chain
We noted earlier that one of the principal functions of the respiration is to retrieve, in useful form, some of the energy initially stored in assimilates. Our traditional measure of useful energy in most processes is the number of ATP molecules gained or consumed. By this measure alone, the yield from both glycolysis and the […]
Krebs cycle/ Citric Acid cycle
The second stage of respiration is the complete oxidation of pyruvate to CO2 and water through a series of reactions known as the citric acid cycle (CAC). The citric acid cycle is also known as the tricarboxylic acid (TCA) cycle or the Krebs cycle, in honor of Hans Krebs, whose research in the 1930s was […]
Glycolysis
The first stage of respiratory carbon metabolism is a group of reactions by which hexose sugars undergo a partial oxidation to the three-carbon acid pyruvic acid or pyruvate. Occurrence: These reactions, collectively known as glycolysis, are catalyzed by enzymes located in the cytosol of the cell. Parallel reactions occur independently in plastids, in particular amyloplasts […]