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From Wikipedia

Guard cell

Guard cells are specialized cells located in the leaf epidermis of plants. Pairs of guard cells surround tiny stomatal airway pores (Figure 1). These tiny holes in the surface of leaves are necessary for gas exchange into and out of the plant; carbon dioxide (CO2) enters the plant allowing the carbon fixation reactions of photosynthesis to occur. Oxygen (O2) exits the plant as a byproduct of photosynthesis. The opening and closing of the stomatal gas exchange holes is regulated by swelling and shrinking of the two surrounding guard cells (Figure 1). Due to the presence of the stomatal pores on plant leaf surfaces, water evaporates through the stomatal openings causing plants to lose water. Over 95% of water loss from plants can occur by evaporation (transpiration) through the stomatal pores. Therefore, it is important for plants to be able to balance the amount of CO2 being brought into the plant with the amount of water escaping as a result of the open stomatal pores. Hence, the guard cells are the gate keepers of the plants ability to take in CO2 from the atmosphere for photosynthesis – while regulating how much water plants lose to the atmosphere. Opening and closure of the stomatal pore (Figure 1) is mediated by changes in the turgor pressure of the two guard cells. The turgor pressure of guard cells is controlled by movements of large quantities of ions and sugars into and out of the guard cells. When guard cells take up these solutes, the water potential (Ψ) inside the cells decreases, causing osmotic water flow into the guard cells. This leads to a turgor pressure increase causing swelling of the guard cells and the stomatal pores open (Figure 2). The ions that are taken up by guard cells are mainly potassium (K+) ions and chloride (Cl-) ions. In addition guard cells take up sugars that also contribute to opening of the stomatal pores.

Engineering Plant Water Loss And Water Use Efficiency Of Plants

Water stress (drought and salt stress) is one of the major environmental problems causing severe losses in agriculture and in nature. Drought tolerance of plants is mediated by several mechanisms that work together, including stabilizing and protecting the plant from damage caused by desiccation and also controlling how much water plants loose through the stomatal pores during drought. A plant hormone, abscisic acid (ABA), is produced in response to drought. A major type of ABA receptor has been identified. Future research is needed to test if these receptors can be used to engineer drought tolerance in plants. The plant hormone ABA causes the stomatal pores to close in response to drought, which reduces plant water loss via transpiration to the atmosphere and allows plants to avoid or slow down water loss during droughts. The use of drought tolerant crop plants would lead to a reduction in crop losses during droughts. Since guard cells control water loss of plants, the investigation on how stomatal opening and closure are regulated could lead to the development of plants with improved avoidance or slowing of desiccation and better water use efficiency.

Ion Channels And Transport Proteins Mediate Ion Uptake And Release In Guard Cells

Ion uptake into guard cells causes stomatal opening: The opening of gas exchange pores requires the uptake of potassium ions into guard cells. Potassium channels and pumps have been identified and shown to function in the uptake of ions and opening of stomatal apertures (Figure 2). Ion release from guard cells causes stomatal pore closing: Other ion channels have been identified that mediate release of ions from guard cells, which results in osmotic water efflux from guard cells due to osmosis, shrinking of the guard cells, and closing of stomatal pores (Figures 1 and 2). Specialized potassium efflux channels participate in mediating release of potassium from guard cells. Anion channels were identified as important controllers of stomatal closing. Anion channels have several major functions in controlling stomatal closing: (a) They allow release of anions, such as chloride and malate from guard cells, which is needed for stomatal closing. (b) Anion channels are activated by signals that cause stomatal closing, for example by intracellular calcium and ABA. The resulting release of negatively charged anions from guard cells results in an electrical shift of the membrane to more positive voltages (depolarization) at the intracellular surface of the guard cell plasma membrane. This electrical depolarization of guard cells leads to activation of the outward potassium channels and the release of potassium through these channels (Figure 2). At least two major types of anion channels have been characterized in the plasma membrane: S-type anion channels and R-type anion channels.

Vacuolar Ion Transport For Stomatal Movements

Vacuoles are large intracellular storage organelles in plants cells. In addition to the ion channels in the plasma membrane, vacuolar ion channels have important functions in regulation of stomatal opening and closure because vacuoles can occupy up to 90% of guard cell’s volume. Therefore, a majority of ions are released from vacuoles when stomata are closed. Vacuolar K+ (VK) channels and fast vacuolar channels can mediate K+ release from vacuoles. Vacuolar K+ (VK) channels are activated by elevation in the intracellular calcium concentration. Another type of calcium-activated channel, is the slow vacuolar (SV) channel. SV channels have been shown to function as cation channels that are permeable to Ca2+ ions, but their exact functions are not yet known in plants.

Guard Cell Signal Transduction

Guard cells perceive and process environmental and endogenous stimuli such as light, humidity, CO2, temperature, drought, and plant hormones to trigger cellular responses resulting in stomatal opening or closure. These signal transduction pathways determine for example how quickly a plant will loose water during a drought period. Guard cells have become a model for single cell signaling. Using A

Guard (grappling)

The guard is a ground grappling position where one combatant has their back to the ground, while holding the other combatant using the legs. In pure grapplingcombat sports, the guard is considered an advantageous position, since the bottom combatant can attack with various joint locks and chokeholds, while the top combatant's priority is to transition into a more dominant position, a process known as passing the guard. In mixed martial arts competition or hand-to-hand combat in general, it is possible to effectively strike from the top in the guard, even though the bottom combatant exerts some control. There are various types of guard, with their own advantages and disadvantages.

The guard is utilized in judo but has no formal name in it, though is sometimes referred to as "d�-osae" in Japanese, meaning "trunk hold",. The guard is called the "front body scissor" in catch wrestling.

Pulling guard

Transitioning directly from standing to the guard position is known as pulling guard. Tsunetane Oda, a judo groundwork specialist who died in 1955, demonstrated the technique on video.

Closed guard

Sometimes referred to as full guard. The closed guard is the typical guard position. The legs are hooked behind the back of the opponent, preventing them from standing up or moving away. The opponent needs to open the legs up to be able to improve positioning. The bottom combatant might transition between the open and closed guard, as the open guard allows for better movement, but also increased risk in the opponent passing the guard.

Open guard

The open guard is typically used to perform various joint locks and chokeholds. The legs can be used to move the opponent, and to create leverage. The legs open allows the opponent to stand up or try to pass the guard, so this position is often used temporarily to set up sweeps or other techniques. Open guard is also a general term that encompasses a large number of guard positions where the legs are used to push, wrap or hook the opponent without locking the ankles together around them.

Butterfly guard

The butterfly guard involves both of the legs being hooked with the ankles in between the opponents legs, against the inside of the opponents thighs. The opponent is controlled using both legs and arms. The butterfly guard is often short-lived since the opponent might be able to move quite freely. The leverage in the butterfly guard allows for powerful sweeps. The butterfly guard also allows one to elevate or set the opponent off balance, because of this it is particularly useful in avoiding damage from ground and pound and for many transitions. This guard very effective in mixed martial arts, with B.J. Penn as an advocate of it in an MMA setting.

X-guard

The x-guard is an open guard where one of the combatants is standing up and the other is on their back. The bottom combatant uses the legs to entangle one of the opponent's legs, which creates opportunities for powerful sweeps. The x-guard is often used in combination with butterfly and half guard. In a grappling match, this is an advantageous position for the bottom combatant, but in general hand-to-hand combat, the top combatant can attack with stomps or soccer kicks. This having been said, skilled use of the X guard can prevent the opponent from attempting a kick, or throw them off balance should they raise a leg. The X-guard was popularised by Marcelo Garcia.

Spider guard

The spider guard comprises a number of positions all of which involve controlling the opponents arms while using the soles of the feet to control the opponent at the biceps, hips, thighs or a combination of them. It is most effective when the sleeves of the opponent can be grabbed, for instance if the opponent is wearing a gi. The spider guard can be used for sweeps and to set up joint locks or chokeholds.

De la Riva guard

The De la Riva guard (also called the De la Riva hook and jello guard) is an open guard that was popularized in Brazilian Jiu-Jitsu by black belt Ricardo de la Riva Goded, who was successful with it in competition. In it, one of the legs is wrapped behind the opponent's leg from the outside, the ankle held with one hand, and the other hand grips one of their sleeves. The De la Riva guard offers many sweeps, transitions and submissions, and is often used in combination with spider guard.

Rubber guard

This is a position that keeps the opponent down in your guard. First used by Nino Schembri but popularized and made as a system by Eddie Bravo, many techniques have been developed from this position including sweeps, submissions, and striking defense. By being flexible and using a leg to hold the opponent down, one arm is free to work on submissions sweeps or to strike the opponent's trapped head.

50-50 Guard

The 50-50 (Fifty-fifty) guard is a position popularized by Roberto “Gordo� Correa and extensively used by the Mendes Brothers, Rafael and Guilherme Mendes, Bruno Frazzato, and


From Yahoo Answers

Question:A. are under high pressure (turgor) when the stomata are open b. are under low pressure (turgor) when the stomata are open c. keep the stomata open during the night d. do not have a nucleus e.do not have chloroplast

Answers:i think its A in plants, a minute opening boarderd by guard cells.

Question:I will look up guard cell and stuff about the stomata pops up, pleas help

Answers:Each stomata is surrounded by two guard cells which control the opening and closing of the stomata. When the guard cells are turgid and full of water the stomata are open. When the guard cells are flaccid the stomata close.

Question:For a biology lab, we had to make stomata open and close using salt water and fresh water. Now we are being asked how we account for the difference involving some information about what type of solutions (isotonic, hypotonic, hypertonic) the stomata were placed in. I'm just not sure which water is which solution. I would greatly appreciate some help.

Answers:Stomata's opening and closing is regulated by calcium and sodium ions.See when you use hypotonic solution it means that solution is less conc.than stoamats so what happens is proton pumps H+ in guard cells,this results in influx of potassium ions and now because conc. of ions in stomatas are more than hypotonic medium, turgar pressure increase ,water comes in and u get open stomatas.In case of hypertonic solution abscissic acid is produced in cells which results in influx of calcium ions and loss of potassium ions and u get closed stomatas.So remamber when stomatas are open,that means condition is hypotonic and there is influx of potassium ions ,when stomatas are closed ,conditions is hypertonic/water deficient ,calcium ions goes in,potassium ions goes out.abscissic acid which was produced under hypertonic conditions is named because it means surrounding environment outside the cell is water deficient.

Question:2nd question : What is the function of selerenchyma in the vascular bundles of herbaceous plants 3rd: discuss the theories of a. food translocation in the phloem b. water conduction in the xylem c. water and mineral uptake by plant root\ --thanx so much

Answers:when there is more photosynthesis, the cells produce more water. This more or less 'inflates' the guard cells and the open for better gas exchange. When their is less photosynthetic action, the guard cells lose water, shrivel, and close the stomata opening. The other question s i cant be bothered aswering soz