دانلود رایگان ترجمه مقاله پاسخ گیاه به کمبود پتاسیم – Academic 2005

مقاله انگلیسی رایگان

ترجمه فارسی رایگان 

بخشی از ترجمه فارسی مقاله:

چکیده :
میزان دسترسی گیاه به پتاسیم ، به واسطه ی دگرگونی های پیچیده خاک ، که به شدت تحت تأثیر واکنش های « ریشه خاک » می باشد ، بسیار متنوع است .
سطح پایین پتاسیم درگیاه موجب بروز انتقال گرهای K+ با تمایل بالا می شود . برخی کانال ها K+ را تنظیم و باعث افزایش آن می شوند . ملکولهایی که سطح پایین K+ را علامت می دهند شامل گونه های فعال اکسیژن و هورمون های گیاهی از جمله اكسین ، اتیلن و اسید ژاسمونیک می باشند . محرومیت از پتاسیم ، جدای افزایش دادن پروتئین های انتقال گر و تنظیم فرآیندهای متابولیک ، واکنش های رشدی درریشه ها را نیز بر می انگیزاند .
تمامی این عملکردهای سازگار سازی ، گیاهان را قادر به ادامه ی بقا و رقابت جهت کسب مواد مغذی در محیطی متغیر و پویا با میزان دسترسی متغیر به پتاسیم می سازد .
در دسترس بودن پتاسیم و دینامیک مواد مغذی در ریزوسفر
پتاسیم یکی از مواد مغذی اصلی است که برای تکامل و رشد گیاه ضروری است . اگرچه میزان تراکم K+ درخاک تنها در دامنه ی بین µm 6- 1/0 است گیاهان مقادیربالایی از این عنصر را که حدود 2 تا 10 درصد وزن خالصشان را تشکیل می دهد دارند . مقادیر تراکم K+ درسیتوزول در دامنه ای محدود ، حدود Mm 100 است که برای کارکرد آنزیم های سیتوزولی بهینه است حفظ می شوند . ظرفیت یا میزان واکوئلی پتاسیم بسته به میزان قابلیت دسترسی به پتاسیم و نوع بافت متغیر تر بوده و عموما در دامنه ای حدود Mm 200 – 20 مشاهده می شود . پتاسیم چهارمین ماده ی غنی معدنی است که حدود 5/2 درصد لیتوسفر را شکل می دهد . پتاسیم خاک طبق میزان دسترسی گیاه به آن به 4 گروه متفاوت نسبت داده می شود .
• محلول خاک
• K قابل تبادل
• K ثابت
• K شبکه

از آنجا که گیاهان می توانند K+ را تنها از محلول به دست آورند قابلیت دسترسی به آن بستگی به دگرگونی های مواد مغذی و نیز میزان ( ظرفیت ) کل k دارد .
تبادل پتاسیم بین گروه های مختلف درخاک به شدت بستگی به تراکم دیگر درشت مواد مغذی در خاک برای مثال نیترات دارد .

بخشی از مقاله انگلیسی:

Abstract

The availability of potassium to the plant is highly variable, due to complex soil dynamics, which are strongly influenced by root–soil interactions. A low plant potassium status triggers expression of high affinity K1 transporters, up-regulates some K1 channels, and activates signalling cascades, some of which are similar to those involved in wounding and other stress responses. The molecules that signal low K1 status in plants include reactive oxygen species and phytohormones, such as auxin, ethylene and jasmonic acid. Apart from up-regulation of transport proteins and adjustment of metabolic processes, potassium deprivation triggers developmental responses in roots. All these acclimation strategies enable plants to survive and compete for nutrients in a dynamic environment with a variable availability of potassium.

Potassium availability and nutrient dynamics in the rhizosphere

Potassium is one of the major nutrients, essential for plant growth and development. Although concentrations of K+ in soil solution ([K+ ]o) are in the range of only 0.1–6 mM (Adams, 1971), plants accumulate large quantities of this element, which constitutes between 2% and 10% of plant dry weight (Leigh and Wyn Jones, 1984; Tisdale et al., 1993). Concentrations of K+ in the cytosol are maintained in a narrow range, around 100 mM, which is optimal for the function of cytosolic enzymes. Vacuolar content is more variable, depending on potassium availability and tissue type, and is commonly found to be in the range of 20–200 mM (Leigh and Wyn Jones, 1984; Walker et al., 1996). Potassium is the fourth most abundant mineral, constituting about 2.5% of the lithosphere. However, actual soil concentrations of this mineral vary widely, ranging from 0.04 to 3% (Sparks and Huang, 1985). In accordance with its availability to plants, soil potassium is ascribed to four different pools: (i) soil solution, (ii) exchangeable K, (iii) fixed K, and (iv) lattice K (Syers, 1998). As plants can only acquire K+ from solution, its availability is dependent upon the nutrient dynamics as well as on total K content. The exchange of potassium between different pools in soil is strongly dependent upon the concentration of other macronutrients in the soil solution, for example, nitrate (Yanai et al., 1996). The release of exchangeable K is often slower than the rate of K+ acquisition by plants (Sparks and Huang, 1985) and, consequently, K+ content in some soils is very low (Pretty and Stangel, 1985; Johnston, 2005). Plant potassium status may further deteriorate in the presence of high levels of other monovalent cations such as Na+ and NH4 + that interfere with potassium uptake (Spalding et al., 1999; Qi and Spalding, 2004; Rus et al., 2004). Apart from long-term deprivation, plant roots can experience transient shortages of potassium because of spatial heterogeneity and temporal variations in the availability of this nutrient. The main sources of soil heterogeneity are often plant roots themselves, the K+ transport activity of which creates zones with elevated or reduced nutrient content. Contact between a root and nutrient may occur because of (i) root growth into the area where a nutrient is located, and (ii) transport of a nutrient to the root surface through the soil (Jungk and Claassen, 1997). The first process, termed ‘root interception’, constitutes less than 1–2% of total K+ uptake because of rapid removal of K+ at the root surface (Barber, 1985; Rosolem et al., 2003). The second process, K+ translocation through the soil to the root surface, is facilitated by diffusion and mass flow (Barber, 1962). Diffusion is the dominant mechanism of K+ delivery to the root surface (Seiffert et al., 1995) and constitutes up to 96% of total soil K+ transport (Oliveira et al., 2004). Therefore, K+ depletion around the root is the most frequently observed phenomenon associated with plant-evoked soil potassium perturbations. If nutrient delivery by diffusion is always associated with the reduction of K+ content in the areas adjacent to the root surface, mass flow may, conversely, result in K+ accumulation around the root if transpiration is high (Vetterlein and Jahn, 2004). Experimentally, development of a depletion profile around individual maize root segments has been demonstrated using 86Rb as a potassium tracer (Jungk and Claassen, 1997). These data are consistent with results obtained by Yamaguchi and Tanaka (1990), who demonstrated that roots compete for potassium if half the distance between them is less than 4 mm. Similar results were obtained with flat mats of maize (Zea mays L.), rape (Brassica napus L.), and rice (Oryza sativa L.) roots (Jungk and Claassen, 1997; Hylander et al., 1999; Vetterlein and Jahn, 2004). Variations in soil density may also affect potassium availability. Soil compaction is associated with higher volumetric water content and therefore tends to facilitate K+ transport to the root surface (Kuchenbuch et al., 1986). However, the dense soil may also cause a reduction in the root length and so the higher bulk density does not necessarily result in increased K+ accumulation (Seiffert et al., 1995). The spatial heterogeneities in K+ distribution encountered by a root are often superimposed with temporal variations in K+ availability, caused by continuously changing soil moisture content. In dry soils, bulk K+ content is normally higher, but mass flow and diffusion are restricted (Seiffert et al., 1995; Vetterlein and Jahn, 2004; Kuchenbuch et al., 1986). The negative effects of drought on K+ transport in soil are likely to be more significant than increases in [K+ ]o and therefore these environmental conditions lead to reduced availability of the nutrient (Kuchenbuch et al., 1986; Seiffert et al., 1995; Liebersbach et al., 2004).