How To Grow Tobacco At Home
The development of roots and shoots in both tissue culture and in girdled stems is also regulated by a combination of auxins and cytokinins. Experiments with living pith cells of tobacco plants have shown that such cells will enlarge when supplied with auxin and nutrients, but they will not divide unless small
Viral Gene Knockdown RNAi can be used to protect host genome against virus infections by suppressing viral expression. An shRNAwas constructed to silence the niaprotease (Pro) gene of potato virus Y (PVY) in tobacco plants 63 . siRNAs were used successfully to silence the respiratory syncytial virus (RSV), an RNA virus that is responsible for severe respiratory disease in neonates and infants 8 . siRNAs targeting the M-BCR ABL fusion site were introduced into human K562 cell and specifically silenced leukemic cells 71 . To silence viral genes effectively, we want to
In the late 1970's Lang, Chailakhyan, and I. A. Frolova, working with tobacco plants, discovered that there was also a floral inhibitor they called antiflorigen. Later, several genes controlling the production of an inhibitor in pea cotyledons and leaves were identified in other laboratories. In addition to leaf-derived inhibitors, root-derived inhibitors have been shown to regulate flowering in black currant and tobacco plants. Aside from the clear role of gibberellin in flowering, none of the other promoters and inhibitors has been identified. Nutrient levels and allocation throughout the plant may also control the time of flowering.
Although it is reasonable to assume that these antimicrobial compounds play a role in the nonhost resistance of plants to microbial pathogens, unequivocal proof is rare. Evidence suggesting that secondary metabolites contribute to plant defense include the enhanced disease susceptibility of maize mutants defective in the ability to synthesize 2,4-dihydroxy-1,4-benzoxazin-3-one (28) and of tobacco plants with reduced accumulations of phenypropanoids (10). Perhaps the best example of a clear role of preformed toxic metabolites in nonhost resistance comes from the study of saponin-deficient mutants in oats. These mutants are susceptible to a fungal pathogen that is normally a pathogen of wheat roots (12). Significantly, saponin deficiency does not increase susceptibility to a leaf-infecting nonpathogen of oat, illustrating the need for experimental evidence to reveal which of a plant's battery of defensive features are effective in a given example of nonhost resistance.
Allard of the U.S. Department of Agriculture studied the behavior of a newly discovered mutant tobacco plant. The mutant, named 'Maryland Mammoth,' had large leaves and exceptional height. When the other plants in the field flowered, 'Maryland Mammoth' plants continued to grow. Garner and Allard took cuttings of 'Maryland Mammoth' into their greenhouse, and the plants that grew from those cuttings finally flowered in December.
Figure 11.11 A root cap of a tobacco plant. The force of gravity is at the bottom of the picture. Note that the amyloplasts (more or less spherical dark objects) are toward the bottom of each cell. There is conflicting evidence as to whether or not the amylo-plasts play a role in the perception of gravity by roots, x 2,000. (Light micrograph courtesy John Z. Kiss) Figure 11.11 A root cap of a tobacco plant. The force of gravity is at the bottom of the picture. Note that the amyloplasts (more or less spherical dark objects) are toward the bottom of each cell. There is conflicting evidence as to whether or not the amylo-plasts play a role in the perception of gravity by roots, x 2,000. (Light micrograph courtesy John Z. Kiss)
Several well-known spices, including sassafras, sarsa-parilla, licorice, and angelica, are obtained from roots. Sweet potatoes are used in the production of alcohol in Japan. Some important red to brownish dyes are obtained from roots of members of the Madder Family (Rubiaceae), to which coffee plants belong. Drugs obtained from roots include aconite, ipecac, gentian, and reserpine, a tranquilizer. A valuable insecticide, rotenone, is obtained from the barbasco plant, which has been cultivated for centuries as a fish poison by primitive South American tribes. When thrown into a dammed stream, the roots containing rotenone cause the fish to float but in no way poison them for human consumption. In tobacco plants, nicotine produced in the roots is transported to the leaves. Other uses of roots are discussed in Chapter 24.
Many substances move from cell to cell within the symplast by way of plasmodesmata (see Figure 35.7). Among their other roles, plasmodesmata participate in the loading and unloading of sieve tube elements. The mechanisms vary among plant species, but the story in tobacco plants is a common one. In tobacco, sugars and other solutes in source tissues enter companion cells by active transport from the apoplast and move on to the sieve tube elements through plasmodesmata. In sink tissues, plasmodesmata connect sieve tube elements, companion cells, and the cells that will receive and use the transported compounds.
The development of the first transgenic tobacco plant expressing the firefly luciferase (luc) gene 45 demonstrated the feasibility of using bioluminescent reporter genes to monitor gene expression in vivo. Bioluminescence refers to the generation of (visible) light by living organisms, commonly due to an enzymatic reaction 46,47 . Reporter genes are used to study the expression of a gene of interest. This is achieved by inserting into the host cell genome a gene cassette containing the reporter gene construct under the control of the target gene. Bioluminescent reporters yield exquisite sensitivity as there is no endogenous background signal in mammalian cells, resulting in high signal-to-background ratios. Using sensitive detection devices, such as photomultiplier tubes or cooled charge-coupled devices (CCD), sensitivity is sufficient to count only a few emitted photons.
Allard found an unusually large tobacco plant growing in a field. The plant stood out because it failed to flower they named it the Maryland Mammoth. Maryland Mammoth cuttings flowered in a greenhouse that December, and subsequent experimentation demonstrated that flowering would occur only when days were short and nights long. The Maryland Mammoth is an example of a short-day plant. Short-day plants generally flower in the spring or fall, when day lengths are shorter. Other examples of short-day plants are poinsettias, cockleburs, Japanese morning glories, and chrysanthemums. Plants such as spinach, lettuce, and henbane will flower only if a critical day length is exceeded they are categorized as long-day plants and generally flower during long summer days.
One of the earliest host responses to pathogen attack is the production of ROS (13). Production of ROS, referred to as the oxidative burst, is triggered within just minutes after infection and involves a series of signaling events that involve guanosine Triphos-phate (GTP)-binding proteins, changes in protein phosphorylation, Ca2+ flux, and H+ K+ ion exchange, resulting in intracellular acidification. The production of ROS, such as H2O2, and superoxide (-O2-) radicals results in cellular damage to both the plant and the invading microbe. H2O2 probably also contributes to cell wall reinforcement. For example, H2O2 has been demonstrated to be essential to lignification of cell walls (14). Cell wall strengthening around the site of pathogen ingress might serve to limit microbial spread to uninfected plant tissues. ROS have also been suggested to be critical components of defense signaling. Indeed, ROS were shown to induce a variety of defense-related genes (7,15,16). Exogenous...
Grafts between different species of the same genus can usually be done, as can grafts between different genera of the same family. Tissue compatibility is necessary. Lilacs can be grafted to privet almonds can be grafted to peach stock peaches can be grafted to cherry stock and pecans and English walnuts can be grafted to black walnut. Potatoes and tomatoes are related and can thus be grafted. They are in the same family, Solanaceae. If a tomato scion is grafted to a tobacco rootstock, the leaves of the tomato will have nicotine, demonstrating that the nicotine in tobacco leaves is produced in the roots of the tobacco plant.
In the early 1900s, two American plant physiologists, Wightman W. Garner and Henry A. Allard, became curious about a tobacco plant growing at a research center in Beltsville, Maryland. The plant grew 3 to 4 meters (10 to 13 feet) tall during the summer but failed to flower in August when the normal-sized tobacco plants flowered. They brought the giant plant into a greenhouse for protection during the winter and were surprised when it flowered in December. Garner and Allard decided to conduct some experiments with the tobacco plants. If the plants were started in pots in the fall in a greenhouse, they grew only about a meter (3 feet) tall before flowering. They wondered what would happen if they kept the tobacco plants, as well as some soybean seedlings that would not bloom in Beltsville before September, in complete darkness from 4 P.M. until 9 A.M., thereby allowing them only 7 hours of daylight.
Nicotine, the best known agonist, is extracted from the leaves of the tobacco plant Nicotiana tabacum. Other agonists include carbachol and succinylcholine (suxamethonium). The latter dissociates only slowly from the nAChR and consequently induces a long-lasting epp that triggers a brief train of muscle action potentials and muscle twitches. This is followed by a depolarizing neuromuscular block that results from the inactivation of voltage-gated Na+ channels. Probably the best known antagonist of nAChRs is curare, which was used by South American Indians as an arrow poison. Its active ingredient is d-tubocurarine. a-Bungarotoxin, isolated from the venom of banded krait, is another classical antagonist. Its affinity for the nAChR is so high that it was used for biochemical isolation of the receptor (Changeux et al, 1970) and for determining the number, distribution and lifetime of nAChRs at the neuromuscular junction. The tran-quiliser chlorpromazine...
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