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Plant Project cont.
Transcript of Plant Project cont.
endothermic heating in floral tissues Plants, invertebrates and vertebrates have multiple, nonspecific immune responses. Bacteria, fungi, & viruses can’t infect the plant, but through evolution some bacteria are able to break through the cell wall of the plant and cause a disease. Some plants have resistance genes and are able to develop a genetic mechanism of allowing them to fight off these pathogens. If a plant produces salicyclic acid, they are able to fight off the first pathogen that affects them as well as others. Plant defenses against pathogens include molecular recognition systems with systemic responses; infection triggers chemical responses that destroy infected and adjacent cells, thus localizing the effects Plants that produce salicyclic acid can float off to other plants & influence other plants to become more resistant. Plants can recognize molecules and pathogens and activate defense. When pathogens enter the plant, the plant cell will recognize this and fight for its life. Endothermy requires the absorption of heat. It is not known why endothermy occurs in flowers but it is starting to be understood. It may be to increase rates of pollination through the release of its attracting chemicals, or heat for pollinating insects, or just a protection of low temperatures in plants. Thermoregulation is sensing temperature on the outside & being able to regulate heat production to maintain tissue temperature. Researchers have studied these two plants in detail for thermoregulation, Nelumbo nucifera (a eudicot), and Symplocarpus renifolius (a monocot). They find in fascinating how thermoregulation can occur in plants because they don’t have the same items needed to undergo thermoregulation like animals do. Thermoregulation High temperature plants are those that grow best at 70° to 80° F. During the day and 65° to 70° F at night. Usually in C4 plants, they can tolerate higher temperatures. Elevated floral temperatures are usually higher in tropical plants rather than normal plants. On urban islands, or tropical islands, these plants are able to carry out photosynthesis but not photorespiration. Elevated floral temperatures in some plant species Communication involves transduction of stimulatory or inhibitory signals from other cells, organisms or the environment. Plants & animals undergo cytokinesis, but in plants it is way different. Plants have a cell wall where a contractile ring forms in the middle of the cell. The Golgi apparatus releases vesicles that have contain cell wall items forming the cell plate. Eventually the cell divides into two. Cells communicate over short distances by using local regulators that target cells in the vicinity of the emitting cell. Cells can communicate by physical contact through cell junctions. This occurs in the plasmodesmota in plants and allows molecules to move through the cells. Local regulators (synaptic signaling) is when a nerve cell secretes neurotransmitter molecules that are soon sensed by nearby target cells. Plant immune response Every plant cell has a cell wall, and so do the neighboring plant cells that form a extracellular domain known as the “apoplast”. Since the cell walls are permeable to proteins & other solutes, the plasmodesmota in plants allows cell to cell communication. Signal Transduction Pathways -Stimulation of the receptor initiates a specific signal transduction pathway-For stimulus to elicit a response, certain cells must have an appropriate receptor-There are three stages: reception, transduction, and response Reception It is the internal and external signals are detected by receptors, proteins that changes in response to specific stimuli. Transduction The second messengers transfer and amplify signals from receptors to proteins that cause responses. The receptors can be sensitive to very weak environmental or chemical signals. Response Signal transduction pathway leads to regulation of one or more cellular activities. In most cases, these responses to stimulation involve increased activity of enzymes. This can occur by transcriptional regulation or post-translational modification. Hormones Any response resulting in curvature of organs toward or away from a stimulus is called tropism (often caused by hormones). In late 1800s, Charles Darwin and his son Francis conducted experiments on phototropism, plant’s response to light. In general, hormones control plant growth and development by affecting the division, elongation, and differentiation of cells. Plant hormones are produced in very low concentration, but a minute amount can greatly affect growth and development of a plant organ. Different types of hormones are auxin, cytokinins, gibberellins, brassinosteriods, abscidic acid (ABA), ethylene. Interactions between hormones and signal transduction pathways make it hard to predict how genetic manipulation will affect a plant. Hormones are chemical signals that coordinate different parts of an organism. They originated from the studies of animals and was adopted by plant physiologists in the early 1900s. Multiple hormones can influence a single process. A single process can regulate an amazingly diverse array of cellular and developmental processes. Photoperiodism Photoperiod, relative lengths of night and day, is the environment stimulus plants use most often to detect time of year. Photoperiodism is a physiological response to photoperiod. Some processes require a certain photoperiod, including flowering in many species. Plants that flower when light period is shorter than critical length are called short-day plants. Plants that flower when light period is longer than certain number of house are called long-day plants. Flowering in day-neutral plants is controlled by plant maturity, not photoperiod. -Researchers discovered that flowering and other responses to photoperiod are actually controlled by night length, not day length-Short-day plants are governed by whether the critical night length sets a minimum number of hours of darkness-Long-day plants are governed by whether the critical night length sets a maximum number of hours of darkness-Red light can interrupt the nighttime portion of the photoperiod-Some plants flower after only single exposure to required photoperiod-Many plants need several successive days of the required photoperiod-Others need an environment stimulus in addition to required photoperiod Critical Night Length Apoptosis -It is the onset of programmed cell death
-Is very busy time in cell’s life, requiring new gene expression
-Newly formed enzymes break down many chemical components, including chlorophyll, DNA, RNA, proteins, and membrane lipids
-Burst of ethylene is almost always associated with the programmed destruction of cells, organs, or the whole plant -If there is more resources like energy, sunlight, nutrients, etc. the plants can store more, grow more, and use more energy.-If there is less resources like sunlight, the plants will be at loss of mass and eventually die. Acquired free energy vs. required free energy Positive vs. Negative Feedback Mechanism Negative Feedback is when there is accumulation of an end product of a process slows that process. Example would be the cell’s breakdown of sugar generates chemical energy in the form of a substance called ATP. When a cell makes more ATP than it can use, the excess ATP feeds back and inhibits an enzyme near the beginning of the pathway. Positive Feedback is when an end product speeds up its production. Example would be clotting of your blood in response to injury. When blood vessel is damaged platelets begin to aggregate at the site. It occurs as chemicals released by the platelets attract more platelets. Defenses Against Herbivores Herbivory, animals eating plants, is a stress that plants face in any ecosystem
Plants counter excessive herbivory with physical defenses such as thorns and chemical defenses such as distasteful or toxic compoundsSome plants even “recruit” predatory animals that help defend against specific herbivoresPlants damaged by insects can release volatile chemicals to warn other plants of the same speciesMethyljasmonic acid can activate the expression of genes involved in plant defenses Sources http://en.wikipedia.org/wiki/Apoptosis