【正文】 第六章 植物鉀營(yíng)養(yǎng)分子生理 Zichao Mao Why potassium is important ? Potassium (K) play key roles in physiological and biochemical processes, which greatly influence the growth and development of plants. Particular physiological processes affected substantially by inadequate supply of K ? (1) partitioning of carbohydrates between roots and shoots。 ? (2) photosynthetic carbon metabolism。 ? (3) formation of reactive O2 species and related photooxidation。 ? (4) regulation of stomatal activity and water regime。 ? (5) tolerance against biotic and abiotic stress factors, such as salt stress and drought stress. 1．鉀離子是植物細(xì)胞中含量最豐富的陽(yáng)離子之一。它的功能： K+能促進(jìn)細(xì)胞內(nèi)酶的活性。細(xì)胞內(nèi)有 50多種酶或完全依賴于 K+ ，或受 K+的激活，如丙酮酸激酶、谷胱合成酶、 6磷酸果糖激酶等能被 K+激活。作用方式為：同其他一價(jià)陽(yáng)離子都是通過(guò)誘導(dǎo)酶構(gòu)象的改變，使酶得到活化，從而提高催化反應(yīng)的速率。在某些情況下 K+能增加酶對(duì)底物的親和力。 K+對(duì)膜結(jié)合 ATP酶也有激活作用。 +與蛋白質(zhì)的合成有關(guān)。小麥胚芽中分離出的核糖體，合成蛋白質(zhì)達(dá)到最佳速率時(shí)，其所需 K+濃度為 130mM。 3 ． K+可能參與 tRNA與核糖體結(jié)合過(guò)程中的幾個(gè)步驟。 Mineral nutrition of plants P K N S Ca Fe Mg Plants need elements other than C to grow and develop ? Must integrate carbon with other inanic minerals taken up by roots from environment ? Together, these elements are the building blocks of plex molecules (proteins, nucleic acids, etc.) ? Mineral (inanic) nutrition dependent on C metabolism and viceversa – Need for understanding how plants gain nutrition from environment – People no longer grew their own food! – Need to optimize growth conditions to feed more people – central role of NPK fertilizer to boost yield Hydroponic growth facilitated the discovery of essential mineral nutrients ? Further definition of “essential”: Sachs (mid19th century) used hydroponic culture – now used for vegetable production – roots are cultured in solution, not in soil ? More modern growth media – Hoagland?s solution → now slightly MODIFIED – Murashige and Skoog (M + S) ? Solutions have high nutrient levels relative to soil – Required because the supply is often not replenished frequently ? Hydroponic culture can be as simple as a plant supported in an aerated pot – If roots waterlogged, what happens to yield? Ca N K S Mg P Fe B Mn Zn Cu Mo ? Main disadvantage of simple solution culture → as plant grows, it selectively depletes certain minerals – When one bees limiting, growth will slow significantly – Can grow in vermiculite/perlite (inert, nonnutritive) and refertilize daily ? Commercially, it is often cheaper and easier to continuously bathe roots in a nutrient solution (nutrient film technique) – Aerates – Standard nutrient level maintained – Continuous process monitoring ? To define “essential”, researchers need inert materials contributing low levels of nutrients (NO METAL PARTS!) Fig. Fig. Hydroponic culture techniques e in different flavors There are 17 essential elements required for plant growth What defines an “essential” element? 1. In its absence the plant cannot plete a normal life cycle 2. The element is part of an essential molecule (macromolecule, metabolite) inside the plant ? Most elements fall into both categories above (., structural vs. enzyme cofactor) ? These 17 elements are classified as – 9 macronutrients (present at 10 mmol / kg dry wt.) – 8 micronutrients ( 10 mmol / kg dry wt.) ? Environmental (silicon [dust]) and/or cultural (from equipment, water, impure salts) contamination make assigning “essentiality” difficult ? Essentiality of micronutrients (→1 ug/L!) especially difficult to establish – Difficult to detect low concentrations → push detection limit of mon analytical techniques (., flame spectrometry) The availability of some minerals to the plant for growth is dependent on environmental conditions ? There may be high levels of nutrient present in soil but it is not in a metabolically useful form – ., Fe ? Need to supply a lot ? Dependent on pH (precipitates out of solution) ? Fe2+ more bioavailable (soluble) ? Many plant “diseases” are actually mineral deficiencies (mon: Mn, B, Cl) ? Some inessential elements are still beneficial to plant health → required at sub micronutrient concentrations – Na (in C4 plants involved in transporting C between bundle sheath and mesophyll cells) – Si (in cell walls。 prevents lodging) – Co (by Nfixing bacteria) The absence of essential elements causes deficiency symptoms ? Essential because of their metabolic functions ? Characteristic deficiency symptoms shown because of these roles ? Typical deficiency responses are – Chlorosis: yellowing。 precursor to – Necrosis: tissue death ? Expressed when a supply of an essential metabolite bees limiting in the environment ? Element concentrations are limiting for growth when they are below the critical concentraion – This is the concentration of nutrient in the tissue just below the level giving maximum growth Concept of critical concentration illustrated ? Above critical concentration, there is no