Chapter 20GA in GerminationChapter 21Chapter 22Chapter 23Chapter 25Chapter 20Outline the key enzymatic control points in the GA biosynthetic pathway (slide 6) that determines height growth in plants; include an explanation of the negative feedback pathway in GA synthesis and explain why plants would place limits on their height growth.GA in Germination1. H2O uptake by embryo2. embryo creates GA and sends it to aleurone3. GA causes increased alpha-amylase4. protease from aleurone activates beta-amylase in endosperm5. alpha-amylase and beta-amylase breakdown starch to glucose6. glucose fuels growth of embryo through respiration-more germination with more after-ripening time (after-ripening time can be replaced by GA to increase germinationConservation of energy, producing too much gibberellin could stretch the plants resources too far killing, or damaging the plants fitness. It shold also be noted that GA’s can be regulated by IAA, removal of IAA reduces the amount of GA that is produced. Auxin regulates concentration of GA’s. Ethylene decreases GA.GA20ox and GA3ox are key regulatory enzymes which catalyze the formation of bioactive GA9 and GA4Negative feedback regulation of bioactive GA: GA2ox synthesizes GA34 which inhibits GA20ox & GA30x activity. Auxin stimulates GA3ox and inhibits GA2oxHow did manipulating traits for height related to GA regulation lead to the Green Revolution?A chronic food shortage was feared during the rapid climb in world population in the 1960s. This wasaverted with the development of a high-yielding variety of rice. This variety of semi-dwarf rice is called IR8, and it has a short height because of a mutation in the sd1 gene.[46] Sd1 encodes GA20ox, so a mutant sd1 is expected to exhibit a short height that is consistent with GA deficiency.Explain at the molecular and cellular levels how GA increases stem growth.GA induces stem growth by stimulating cell division, GA activates auxin that moves a pathway to acidify the cell wall that allows expansins to stretch the cell wall and stem growth occurs via cell elongation. Explain at the molecular and cellular levels how GA stimulates seed germination.Bioactive GAs and abcisic acid levels have an inverse relationship and regulate seed development and germination.Levels of FUS3, an Arabidopsis transcription factor, are upregulated by ABA and downregulated by GA, which suggests that there is a regulation loop that establishes the balance of GA and ABA.GA is believed to break down the starch that surrounds seeds and makes it bioavailable to the plants. Thus starting germination can break down seed coat. Chapter 21While working at a plant biotechnology company you are given the task to bioengineer plants that are more drought tolerant. Using your understanding of plant transformations, tissue culture, and cytokinins biological role and its biosynthetic pathway explain in detail your strategy and rationale for designing a more drought tolerant plant.To design a plant that is more drought tolerant an increased sensitivity to ABA could be helpful as it will close stomata aperature under drought conditions. Drought conditions also inhibits the synthesis of cytokinins, reduction in cytokinin production will promote root growth and decrease apical meristem and shoot growth. This is good for drought tolerant plantsExplain at the cellular level how cytokinins influence plant growthreduction in cytokinin activity reduces apical meristems, producing smaller shoots, more roots.Cytokinins inhibit root growthIf you added NO3 to a plant, or moved it from low to high light how would that influence cytokinin production and what would be the corresponding plant growth responses?Cytokinin produduction would increase thus the plant growth response would increase (especially in the lateral direction) What would be three expected phenotypic differences between a wild-type plant and one that overexpresses IPT?It would be expected that cytokinin would be synthesized which would promote lateral growth in the plant, delayed senescence, and increased cell differentiationChapter 22Outline how ethylene mediates lateral growth and apical hook formation in young seedlings. Explain why these two characteristics are important in early seedling development.Apical hook protects the apical meristem as the plant pushes it’s stem out of the ground and into the open air (this is done from ethylene promotion of auxin mediated asymmetrical growth). Lateral growth is promoted by ethylene’s orientation of the micro fibrils in a vertical direction this helps the plant be more stable and structurally sound as it pushes out of the ground.What are three developmental processes that are promoted by ethylene toward the end of the growing season? Explain how each of these processes occurs and explain how they benefit the plant?Ethylene promotes the senescence in leaves (following the removal of nutrients) this benefits the plant by getting them ready for winter/ when water becomes less available. Fruit ripening, ethylene promotesthe ripening of fruit which helps get it’s seeds ready to be transported around and placed in the ground. Seedling development and flower senescence are other developments that are helped along by ethylene. What morphological changes are mediated by ethylene that helps plants cope with drought and flooding stress? Explain how these two stresses increase ethylene concentrations.Flooding: Submerging induces rapid internode or petiole elongation, growth is stimulated because ethylene builds up in the tissue b/c gas diffuses slowly through water thus ethylene is increases plant sensitivity to GA by antagonizing ABA. Can also produce aerenchyma in roots via cell death, this can create a conduit for oxygen transport.Outline ethylene’s signaling pathway and explain how its regulation is unique from the other four major plant hormones. If you overexpressed CTR1 what would be the expected phenotype of a seedling in early development?It’s regulation is unique because it is a gaseous hormone, this makes catabolism/conjugation play less of a role. The plant mainly controls ethylene at the synthesis level. Also the plant has an increased sensitivity that it controls with a greater number of receptors. It is negatively regulated as wellThere are multiple receptors encoded by genes for each of the major hormones in Arabidopsis. Give two reasons why plants have evolved multiple receptors for the same hormone.Multiple receptors