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1、第六章 植物钾营养分子生理,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 carbohyd
2、rates 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钾离子是植物细胞中含量最丰富的
3、阳离子之一。它的功能： K+能促进细胞内酶的活性。细胞内有50多种酶或完全依赖于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。作用方式为：同其他一价阳离子都是通过诱导酶构象的改变，使酶得到活化，从而提高催化反应的速率。在某些情况下K+能增加酶对底物的亲和力。K+对膜结合ATP酶也有激活作用。,2.K+与蛋白质的合成有关。小麦胚芽中分离出的核糖体，合成蛋白质达到最佳速率时，其所需K+浓度为130mM。 3 K+可能参与tRNA与核糖体结合过程中的几个步骤。,Mineral nutrition of plants,-P,-K,-N,-S,-Ca,-Fe,-Mg,
4、Plants need elements other than C to grow and develop,Must integrate carbon with other inorganic minerals taken up by roots from environment Together, these elements are the building blocks of complex molecules (proteins, nucleic acids, etc.) Mineral (inorganic) nutrition dependent on C metabolism a
5、nd vice-versa 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,Furthe
6、r definition of “essential”: Sachs (mid-19th century) used hydroponic culture now used for vegetable production roots are cultured in solution, not in soil More modern growth media Hoaglands solution now slightly MODIFIED Murashige and Skoog (M + S) Solutions have high nutrient levels relative to so
7、il 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 deplet
8、es certain minerals When one becomes limiting, growth will slow significantly Can grow in vermiculite/perlite (inert, non-nutritive) and refertilize daily Commercially, it is often cheaper and easier to continuously bathe roots in a nutrient solution (nutrient film technique) Aerates Standard nutrie
9、nt level maintained Continuous process monitoringTo define “essential”, researchers need inert materials contributing low levels of nutrients (NO METAL PARTS!),Fig. 12.1,Fig. 12.2,Hydroponic culture techniques come in different flavors,There are 17 essential elements required for plant growth,What d
10、efines an “essential” element? In its absence the plant cannot complete a normal life cycle The element is part of an essential molecule (macromolecule, metabolite) inside the plant Most elements fall into both categories above (e.g., structural vs. enzyme cofactor) These 17 elements are classified
11、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 (0.11 ug/L!) especially difficult to
12、establish Difficult to detect low concentrations push detection limit of common analytical techniques (e.g., 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
13、metabolically useful form e.g., Fe Need to supply a lot Dependent on pH (precipitates out of solution) Fe2+ more bioavailable (soluble) Many plant “diseases” are actually mineral deficiencies (common: Mn, B, Cl) Some inessential elements are still beneficial to plant health required at sub-micronutr
14、ient concentrations Na (in C4 plants involved in transporting C between bundle sheath and mesophyll cells) Si (in cell walls; prevents lodging) Co (by N-fixing bacteria),The absence of essential elements causes deficiency symptoms,Essential because of their metabolic functions Characteristic deficie
15、ncy 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 becomes limiting in the environment Element concentrations are limiting for growth when they are below the critical
16、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 net benefit (e.g., yield increase) if more nutrient is supplied Below critical concentration, nutrient level limits growth! Not shown on diagram: all elements eventually become toxic at very high concentrations This is more common for micronutrients in polluted environments,
