Phosphate Uptake Process

Phosphate Uptake Process Introduction Whilst soil moisture and nitrogen (N) are major limitations to agricultural production systems in the SAT, phosphorus (P) deficiency also limits crop growth on many soils. The cost and availability of phosphatic fertilizers to the majority of farmers in the region restrict their use. Attention has, therefore, turned to making more efficient use of the soil phosphate reserves by seeking crop genotypes and management systems that result in more effective uptake and utilization of soil-P. A number of promising strategies are being explored, many of which are presented in this Workshop. To be effectively developed, all of them require an under- standing of the mechanisms of phosphate uptake and utilization by crop plants. Use of molecular tools by nutritional physiologists in recent years has consider- ably enhanced the understanding of these mechanisms and provided new opportunities for manipulating nutrient uptake and utilization. Key genes involved in the process have been identified and information on their role and regulation is accumulating. This paper provides a summary of the phosphate uptake process and highlights some of the important molecular mechanisms involved. The external phosphate concentration Plant roots acquire their phosphate from the external soil solution where it is in equilibrium with phosphate sorbed onto soil minerals and colloids. These sorption reactions maintain low concentrations of phosphate in soil solution whilst buffering the amount of phosphate in solution. The movement of phosphate ions to the sites through which it is taken up into root cells occurs by diffusion. This is a relatively slow process and, in P-deficient soils, results in the concentration of phosphate in solution being depleted around plant roots. Thus, many of the strategies for improving phosphate uptake are aimed at reducing this depletion zone and increasing the solution phosphate concentration immediately adjacent to the sites of phosphate uptake in the roots. Extension of roots into undepleted regions of soil provides the root tip with external P concentrations similar to those in the bulk soil solution.   Further back along the root axis extension of root hairs from epidermal cells in many plant species considerably increases the volume of soil explored for phosphate. Still further back, the soil volume explored by some species growing in low phosphate soils may be enhanced by the presence of hyphae of mycorrhizal fungi which can extend several centimeters from the root surface. A cone of soil in which the concentration of phosphate in solution is depleted thus develops back from the root tip. Within this zone the equilibrium of the phosphate sorption will have shifted towards release of sorbed phosphate ions into solution. Distance to the uptake sites within the root and any barriers to phosphate diffusion determine whether the plant can access these ions. The root apoplasm The walls of root epidermal and cortical cells and the associated intercellular spaces make up the apoplasm. In young roots, these walls are composed of inter- laced fibres that form an open latticework (Peterson and Cholewa, 1998). Soil solution can therefore, move radially towards the central stellar region of the root through the pores in this latticework and the intercellular spaces. The suberised Casparian band around the tangential walls of endodermal cells prevents radial movement into the central stele of nutrients in the soil solution. The band also restricts nutrients within the stele from leaking out into the apoplasm. Older areas of some roots have another layer of suberised cells in the outer layers of cortical cells that form the exodermis. This layer further restricts apoplastic movement of external soil solution in these regions of the root. In slower growing roots, such as those on plants subjected to stress, the exodermis may be formed closer to the tip than in rapi dly growing roots (Perumalla and Peterson, 1986). Movement of solutes through the apoplasm also appears to be restricted near the meristematic region close to the root tip where the microfibrils of the cell walls appear densely packed (Peterson and Cholewa, 1998). The interlacing fibres of cell walls in the apoplasm serve to filter soil solution. They also increase the path length over which phosphate ions must diffuse to the underlying uptake sites on the plasmalemma. The presence of carboxyl groups associated with the pectic polysaccharides of the cell wall fibres results in an overall negative charge. Anions such as phos- phate are repelled by this charge and restricted to the larger pores within the apoplasm. Mucilages, ex- creted into cell walls and surrounding many roots, carry negatively charged hydroxyl groups which can further modify the flow of anions.   These, and other root excretions, provide substrates for rhizosphere micro-organisms that can influence nutrient concentrations close to the uptake sites. The net effect is that movement of phosphate may be impeded within the apoplast, further modifying the concentration of phosphate at the outer surface of the plasmalemma, particularly in cells in the inner cortex. Even in soils w ell supplied with phosphate this concentration is likely to be less than 2 micro molar. In the P-deficient soils of the SAT, the concentration will be much lower than this. Uptake of phosphate into the symplasm The plasmalemma of root epidermal and cortical cells provides the boundary between the apoplasm and the symplasm. Once inside the symplasm, nutrient ions in the cytoplasm can move radially through to the stele via plasmodesmata connections without encountering further membrane barriers (Clarkson, 1993). Trans- port of ions across the semipermeable plasmalemma is, therefore, a critical step that mediates and regulates the uptake of nutrients into the plant. The physiology and kinetics of transport of nutrients across the plas- malemma has been known for a long time. Epstein and colleagues (Epstein and Hagen, 1952; Epstein, 1953) conducted classical experiments over 40 years ago that showed that ion uptake by plant roots could be described by first order kinetics in a similar manner to many enzyme reactions. They also showed that, for the major nutrients studied, the process could be described by two phases a high-affinity system operating at low external nutrient concentrations and a low-affinity system operating at higher external concentrations. An implication arising from these experiments was that uptake through the plasmalemma was mediated by proteins embedded in this membrane. However, isolation and identification of the specific proteins involved proved to be very difficult until nutritional physiologists began to apply molecular techniques to the study of the mechanisms of ion transport in plants. With the aid of this new technology over the past 8 years, many of the specific proteins involved in transport of a number of nutrient ions in plants have been characterized, the genes encoding these proteins identified, and the complex regulatory systems involved have begun to be untangled. Genes encoding the phosphate transporter proteins responsible for influx of phosphate into the cells of roots and some other tissues have been isolated, and the roles of some of these have been defined. Uptake of phosphate into the root symplasm involves transport from concentrations less than 2 micro molar in the surrounding apoplasm across the membrane to the cytoplasm where phosphate concentrations are maintained in the mill molar range. This, together with the net negative charge on the inside of the plasmalemma, necessitates that strong electro- chemical gradients need to be overcome for successful transfer of phosphate anions into root cells. Trans- port of phosphate across the plasmalemma, therefore, requires a high-affinity, energy driven transport mechanism. The genes encoding such transporters have been isolated from a number of plant species during the past 4 years and the sequence and topology of the encoded transporter proteins inferred from the DNA sequences. Identification of plant phosphate transporters An Expressed Sequence Tag from an Arabidopsis clone containing similarities to the sequences of genes encoding phosphate transporters that had been isolated from yeast and fungi led to the isolation of the first reported genes encoding plant phosphate transporters (Muchhal et al., 1996: Smith et al., 1997a). These genes were isolated from Arabidopsis. They now form part of the rapidly growing Pht1 family of plant phosphate transporters which includes members isolated from tomato (Daram et al., 1998; Liu et al., 1998a), potato (Leggewie et al., 1997), Catharanthus (Kai et al., 1997), Medicago (Liu et al., 1998b), barley (Smith et al., 1999) and additional genes from Arabidopsis (Mitsukawa et al., 1997a). Eight different members of this family of phosphate transporters have been isolated from the barley genome to date (Smith et al., 1999). A member of a second family of phosphate transporters, Pht2, that has similarities to the quite different family of phosphate transporters represent ed by   some   mammalian   Na+/phosphate cotransporters has recently been isolated from Arabidopsis (Daram et al., 1999). This transporter, which functions as an H+/H2PO4− cotransporter in plants, is primarily expressed in Arabidopsis shoot tissues. It appears to be involved in the internal cycling of phosphorus within the plant.

The nature versus nurture debate Essay

The nature versus nurture debate was founded by Francis Galton in the 19th century. It basically states that all of your attributes are either hereditary or environmentally. There are many theories that have challenges the nature versus nurture theory. For example; some of the theories state that there are different kinds of attributes such as life experiences, how our parents raise us, what we are taught at school and our cultural backgrounds. It is obvious that we are born with some of our parents attributes, for example your parents may both have long legs that you inherited, but things like perhaps a love of poetry or your sexual preference weren’t inherited, and have influenced your personality from your surroundings. There are lots of identical twins separated at birth that reunite as adults to find they had been using the same brand of toothpaste or have named their dogs the same names. This proves the nature theory, proving that attributes are founded at birth. But other scientists are taking this further and into ethical questions such as â€Å"what if serial killers were born to commit their crimes?† The most current nature versus nurture debate is whether the â€Å"gay gene† exists or not. This would suggest that homosexuality is no more a choice than eye colour. There are also attributes that are a mixture of nature and nurture, such as: Personality: Nurture – often there are similarities and differences that come from your parents. Nature – Children develop personalities and lean towards certain behaviours such as shyness and anger. It sometimes cannot be explained because the parents sometimes don’t have these traits. Homosexuality: Nurture – It’s widely seen that it is a humans choice to be a homosexual, where as some people believe that it’s to do with someone’s upbringing. Nature – People believe that homosexuality is genetic, like your foot size or eye colour. The argument for this is the perspective that nature being responsible for the individual development in life. Intelligence: Nurture – This could be based on the childs educational background as well as how the individuals parents had raised them. Nature – Someones ability to achieve and someone who picks up on their parents level of intelligence and tries to match it. To conclude the nature versus nurture debate, It shows that the physical and mental aspects can be queried by an individual to show how a person can develop through their parents or nature. What’s most likely is that both nature and nurture play some role in how we all turn out. But no one really knows with certainty. The true answer as to which side tips the scale remains to be seen. How this affects Samora: Samora’s Early childhood- Physical – Samora would have inherited her average height and weight from her parents meaning that her parents must also be of average height and weight. This physical attribute is nature, and will affect Samora by making her less vulnerable to diseases like obesity and diet related issues. She had all the normal childhood diseases, meaning she was quite an average child. Mental – Samora’s development at this life stage would be brief. Her childhood is the most important part of her mental development as this is the time she would be nurtured to start moulding her personality. She is averagely intelligent, leaving school with a decent amount of A-C GCSE’s, and having good A level grades allowing her to go to university, This was nurtured in to her since she was a child as her parents must be clever as they both have quite well paid jobs, and her brother and sister do also. Emotional – At this age Samora would have become stubborn or angry when change occurred, as she doesn’t have full control over her emotions. As her early childhood progresses, she should have been nurtured to gain more control over her emotions and learn right from wrong. Social – At the beginning of Samora’s childhood she would have been the centre of attention, which her older siblings may not have liked. This could of affected her relationship with her siblings as the youngest child is always the most vulnerable to sibling jealousy. How nature/nurture affects early childhood – I believe that nature is obviously a very important part of a person’s early childhood, as  it is the attributes they are born with, and will live with for the rest of their lives. However, nurture plays an extremely important part in a person’s overall development. For example, if both of a person’s parents smoke, the person is more likely to smoke in the future, as they are nurtured in to believing that is the correct thing to do. Samora’s Adolescence- Physical – As Samora is of average height and weight, her physical attributes should develop averagely. For example, during adolescence Samora’s breast would start to develop, she would have started body hair, her weight should increase and she may develop acne. This is nature, as they are things that Samora can’t change. Samora started smoking at the age of 15, which is very young and could have shunted her full lung development. She also does dancing and netball, which would have helped her going through puberty, as she wouldn’t gain as much weight as she was active. Mental – This is where Samora decided her career. She is a qualified primary school teacher, which she would have had to of decided on when she started college. This could have been a stressful time for Samora as she had to decide the rest of her future at such a young age. She may have started smoking due to a false safety net, believing that bad things cant happen to her. For exampl e, she could have believed that she wouldn’t get addicted to cigarettes because she believed she was untouchable. Emotional – Adolescence is where you develop your identity, This could have been when Samora decided she was a lesbian. I believe that Samora wasn’t a troubled teenager as she isn’t addicted to drugs or alcohol, and she had good GCSE grades. This is due to the nurture of Samora. Social – It says that Samora is sociable meaning that she must have friends. During adolescence, teenagers may struggle making and maintaining friends as they will act out at anyone and everyone, This is nurture as you aren’t born with friends. How nature/nurture affects adolescence – Nature affects adolescence as they have to go through a lot of physical changes (puberty) which is a very important part of development. Nurture is also important as a person starts to develop their identity, and their surroundings could have an important influence on this.

Improved Management Decision Making Essay

Managers at all levels of a business are required to make decisions constantly. Whether it be at an often low risk operational level, or at high importance strategic level, precise analysis is essential, failure on doing so could end in disaster in business’s unforgiving world. Evidence of this can be seen in the strategic level of Dell management in 2004. A poor decision to enter the market with their DJ.Ditty MP3 player, Dell failed to address any strong marketing campaign along with failure to analyse stronger substitute products concluded in Dell discontinuing the product two years later in 2006. The decision made in the development of the product were likewise poor as rival companies such as Apple and Zen’s product features far overpowered Dells weak product. (Laubacher 2011). Simple research into Information Systems tells us they are able to display information that can lead us to answer questions we are often queried with. But often management decisions are not j ust simple rhetorical answers but strategic procedures that will aid the business in specific ways. In this essay I will assess the different methods of how IT based systems through the means of Information systems can aid management decisions or, if they do at all. (C.Lucas 1994)In his book information systems concepts for management, defines an IS as â€Å"a set of organised procedures, that when executed, provides information to support organisation. The information is a tangible or intangible entity that serves to reduce uncertainty about some state or event.† (Oz, Jones and Gowthorpe 2009) Back this definition up stating an â€Å"IS system is a computer based set of hardware, software and telecommunications components, supported by people and procedures to process data and turn it into useful information. The information system can then be divided up into different subsystems with varying goals that help gear towards the organisations main goal†. It is clear that ISs are significant in the day to day operation of a business. The fact that ISs can answer question is indisputable, but the process in which they answer them and the form of answers they give can be debated. Synergy defines the combined resource output exceeding the total output of the same resources if they were employed separately (Oz, Jones and Gowthorpe 2009). This theory can be stretched as far as the four stages of processing that an information system goes through. Input is the first stage of this process which is entered by the human. The next three stages include the processing of the IS system, these include changing and manipulating the data, extracting the information out of the information system and finally storing the information that the IS system has administered. This is a great example of synergy, the IS system calculates the data at a quicker and cheaper cost than if a human were to do it, but the IS system first needs input from an event or scenario from a human, this evidence of synergy. (C.Luckem 2002) Theory on complex event processing relates to this very well. He defines each business action (be this internal with staffing decisions or external with customers through sales) taking several stages of events to reach a final state and in today’s technological driven domain ISs play a very Important role in each of these states. He relates to the use of ISs gathering and storing of data, sharing of information and the ability of systems to automate and often control components playing a vital part of CEP. ISs that relate to CEP are systems such as Supply Chain Management, according to (B.Handfield and L.Nichols 1999) â€Å"Is a set of approaches utilized to efficiently integrate suppliers, manufacturers, warehouses, and stores, so that merchandise is produced (often by computer aided design) and distributed at the right quantities, to the right locations, and at the right time, in order to minimize system wide costs while satisfying service level requirements† It is easy to see how this can be related to management decision making, at each stage of a process with the use of SCM managers can stop the process and analyse production rates, therefore using IS systems to make a decision, which In the case of SCM means utilising every process so that wastage is at a minimum and costs remain low throughout production . Luckem further expresses that the use of IS systems in CEP does not function with remotely one source but needs both the Human and IS system to work collectively for any form of process to work accordingly. Although(Bider 2010) argues the reliability of information processed by ISs. He states that human error can often be the cause of incorrect data. This is not uncommon; often as information is filtered through the information map from department to department human error can cause faults. So an argument could be formed that managers can often put great analysis into ISs, but decisions can be made using the wrong output from the system. In relation to the four stages of processing, this output can then be stored incorrectly meaning any future decisions based on this first problem will not aid the answer process as the information will be incorrect. There are other types of systems that can significantly aid decision making DSSs or Decision Support Systems are systems that aid making decisions through the use of built in models. (Turban 1995) Defines it as â€Å"an interactive, flexible, and adaptable computer-based information system, especially developed for supporting the solution of a non-structured management problem for improved decision making. It utilizes data, provides an easy-to-use interface, and allows for the decision maker’s own insights.† DSSs are comprised of three modules data management, model management and dialog management or in profit terms (actual prior, possible sales, possible revenue, and possible profit). Using these modules DSSs helps find an ideal course of action, able to analyse and finally answer questions that are often asked upon humans, ‘What if’ or ‘How will this action impact revenue’ are example. DSSs are able to process raw data, and draw comparisons to generate information to aid a business decision. Although (Jensen, B.Lowry and Jeffery 2011) argue that the now more wide spread use of Decision Support Systems due to the increase in technology used in business today should not replace the decision making of a human. They argue that although â€Å"It is often difficult for people to assess credibility correctly in face-to-face interactions† but argue the use of DSSs cannot be used as an absolute decision making process â€Å"The capability of face-to-face interactions is critical to effective communication and decision making†. Their views can be seen as somewhat old fashioned when relating to decision making. Similar to DSSs are Strategic information systems. The root of this system is based upon Michael E. porter’s Concept of competitive advantage. This concept analyses the strategic steps a business undergoes to gain an advantage over its competitors. According to (E.Porter 1998), SIS works by enhancing opportunities through analysing competitors, recording seller patterns, identifying potential substitute products and finally retrieving information on keeping a healthy share in the business’s market. All of these should aid a business to create a competitive advantage through the means of SISs. The storing of data and analysis of this data is what managers will use to make decisions. In both the DSSs and SISs the analysis will often plan out a possible route in which the business may take to achieve its aims. It is then up to management to take these recommendations on board through adopting the ideas or not. IS used in the hierachary of a business are important to assess, at an operational level Systems used will be Transactional Process systems are Electronic point of sale, both of these systems allow managers to analyse structured data and draw conclusions for themselves, examples of this maybe the management of stock ordering to improve on wastage, or assessing what product sells at an appropriate time. These systems can then be assessed by the tactical level that may use the means of DSSs to assess new pricing strategies to adapt to the operational level through the help of DSSs but on the evidence of data outputted by TPSs or EPOS. The next and final stage will be the use of the systems at a strategic level. Strategic level will use DSSs and Executive information systems (similar to DSSs but often seen as more precise and concentrated form of system) along with unstructured data which occurs through the means of meetings, conversations and emails .Furthermore strategic level generally have access to IS of all subordinates ISs to help make decisions as well as ISs linked together with external commercial services, such as the latest stock prices and general business news are also common. It is clear that ISs aid management decisions, but in context of this it is important to assess the characteristics of the managers, as well of the management styles. For example managers that adopt an autocratic style of management will be less interested in staff well-being which may affect their reaction to support they receive through IS systems, meaning they may adopt any plans a DSS comes up with whether or not it has a negative effect on staff. Democratic style managers may rely heavily on the data produced from systems of their subordinate. When assessing the improvement of decision making through the means of ISs, I feel it is important to assess manager characteristics, it is clear that there are systems that aid the decision making process but as (Bider 2010) stated there can be human error caused through the input of a system which may lead to poor decision making. I feel steady analysis through each stage of the input process will allow data to be used correctly, therefore being pivotal in decision making process and consequently improving them. Bibliography B.HANDFIELD, Robert and L.NICHOLS, Ernest (1999). Introduction to Supply Chain Management. vol.1. 1st ed., Prentice Hall. Business Using IS , BIDER, IIia (2010). Enterprise, Business-Process and Information Systems Modeling. vol.50. 1st ed., Queensland, Springer. 364213050X. C.LUCAS, Henry (1994). Information systems concepts for management. 5 ed., indiana, Mitchell McGraw-Hill. 11. C.LUCKEM, David (2002). The Power of Events: An Introduction to Complex Event Processing in Distributed Enterprise Systems. 1 ed., Addison wesly. 1. E.PORTER, Michael (1998). Competitive advantage: creating and sustaining superior performance : with a new introduction. Havard, Simon and Schuster. JENSEN, Matthew, B.LOWRY, Paul and JEFFERY, Jenkins (2011). Effects of Automated and Participative Decision Support in Computer-Aided Credibility Assessment. Journal of management information syetems, 28 (1), 201-233. LAUBACHER, Robert (2011). Managing Corporate Reputation in the Blogosphere: The Case of Dell Com puter. Corporate Reputation Review, 14 (2), 133-144. OZ, JONES and GOWTHORPE (2009). Finacial and Management Informatoin. vol.2. London, Cengage Learning. TURBAN, Efriam (1995). Decision support, And what they do? In: Decision support and expert systems : management support systems. Englewood cliffs, Prentice Hall, p.576.

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