【正文】 contamination Fig. Limiting nutrient levels negatively affect growth ? Plant responses to limiting nutrients usually very visible: affects yield/growth! ? Again, chlorosis and necrosis of leaves is typical ? Sometimes straightforward relationship – ., in chlorosis, ? N: chlorophyll ponent ? Mg: cofactor in chlorophyll synthesis Fig. ? Sometimes NOT – Symptoms dependent on species and nutrient mobility Ctrl P Ca N Fe Let’s briefly discuss cellular roles and deficiency symptoms for the big 3 essential elements N: ? Abundant in atmosphere but metabolically unavailable to nonlegumes ? Usually absorbed as nitrate (NO3) and reduced to ammonia (NH4+) in the plant ? Agronomically, N is always limiting ? There is a direct relationship between N supplied and yield! ? Component of proteins, NAs (bases), PGRs, chlorophyll ? Symptoms of deficiency: slow growth, leaf chlorosis ? Mobilized from older leaves to sinks as soluble amines –NH3 and amides ? Therefore, older leaves show first signs ? Also accumulate anthocyanin pigments → because C skeletons can’t make chlorophyll, amino acids, etc…. (no N!) – This is a typical nutrient stress response! O C N CH3 CH3 Rost et al. “Plant biology”, 2nd edn Phosphorus is the most limiting element in natural environments P: ? Present in soil as phosphoric acid ( H3PO4 ) ? pH : H2PO4 → orthophosphate → most bioavailable form ? Deprotonated at higher pH → less available ? PO4 tends to precipitate and form unavailable plexes with – Metals – Organic molecules ? Present at 1 181。小麥胚芽中分離出的核糖體，合成蛋白質(zhì)達到最佳速率時，其所需 K+濃度為 130mM。作用方式為：同其他一價陽離子都是通過誘導(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。 ? (4) regulation of stomatal activity and water regime。 第六章 植物鉀營養(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。 ? (5) tolerance against biotic and abiotic stress factors, such as salt stress and drought stress. 1．鉀離子是植物細胞中含量最豐富的陽離子之一。在某些情況下 K+能增加酶對底物的親和力。 3 ． K+可能參與 tRNA與核糖體結(jié)合過程中的幾個步驟。M in most soils → it is the most limiting element for plant growth! ? Component of – HexoseP – Nucleotides (Pbackbone) – ATP! ? Symptoms of P deficiency include – Reduced yield, short stems – Intense green colour – Anthocyanin synthesis ? Mobilized from sources to sinks (young leaves) as for N Rost et al. “Plant biology”, 2nd edn Potassium is essential for controlling plant cell size K: ? Most abundant cation ? Supplied as potash: K2CO3 – High solubility, leaches from porous soils ? Biochemical functions: ? Enzyme cofactor activates enzymes of photosynthesis and respiration (pyruvate kinase in glycolysis) ? An osmoregulator in vivo → controls cell size – ., guard cell H2O uptake → controls stomata size – Balances charge of anions like Cl ? Mobile often leaves show deficiency first ? Symptoms chlorosis, necrosis, lodging of stems Rost et al. “Plant biology”, 2nd edn ?V? shape es forth along tip and margin of leaves. And brown spots appear on old leaves. 缺鉀癥狀 玉米缺鉀癥狀 K Deficiency Normal Small leaves of Tobacco Yellowing leaves of Cabbage when K defected Etiolation from margin of leaf, some brown spots and white dry tissue on rape when potassium defected. Small white spots appear on margin of old leaves Spinach K deficiency Leaves appear dark green, and tip and spots e forth on the margin leaves, which are brown and purple death tissue. Tender stem is thin and length. K deficiency K abundance Much flower when Comparison on Almond(杏 ) Leaves of Chestnut(栗子 ) ) Color of the flowers is light, and some irregular white spots on surfaces of leaves on carnation chrysanthemum Pink 一、轉(zhuǎn)運途徑 1 ．真核生物細胞膜上存在 Na+ K+ ATPase，高親和 K+吸收轉(zhuǎn)運體和組織特異性的 K+通道。它點燃了細胞和分子水平的生理學(xué)研究的熱火，其和基因克隆技術(shù)并駕齊驅(qū)，給生命科學(xué)研究帶來了巨大的前進動力。 1 ． 膜轉(zhuǎn)運蛋白：載體蛋白 (carrier protein，亦稱為載體或轉(zhuǎn)運體， transporter)和通道蛋白 (channel protein)。通道蛋白允許離子通過其所形成的水通道作被動運輸；而載體蛋白既可以與與離子相結(jié)合，順其電化學(xué)梯度進行被動運輸，也可以逆其電化學(xué)梯度進行主動運輸。 轉(zhuǎn)運體每次轉(zhuǎn)運循環(huán)只能轉(zhuǎn)運一個或幾個離子，轉(zhuǎn)運需要通過轉(zhuǎn)運蛋白的構(gòu)象改變而實現(xiàn)，轉(zhuǎn)運效率低，一般轉(zhuǎn)運速度為 1 x 103 /s, 三、植物對 K+的吸收機制 植物對 K+的被動吸收主要通過 K+通道完成。 Epstein和 Hagan把離子與載體的結(jié)合看成形式上相當于酶與其底物間的關(guān)系。即當載體有效位點滿負荷時的最高運輸速度，也稱為最大運輸速率，用Vmax表示。 Km值越低，即形成最大吸收速率一半時的離子濃度越低，意味著載體場位對離子的親和力越大。 高親和吸收服從簡單的 MichaelisMenten動力學(xué)方程，具有特異的選擇性。電化學(xué)勢梯度包括化學(xué)勢梯度和電勢梯度兩方面，離子的運輸方向取決于這兩種梯度的大小。 A．通過測量不同離子通過通道時的電導(dǎo)。利用這兩種方法得出的通道對離子的選擇性順序并不一定是一致的，在很多生理條件下，它們能得出不同的選擇順序。 （ 2）根據(jù)通道對刺激的反應(yīng)快慢及對配基的依賴性可分為：①延遲的 K＋ 通道（ delayed K＋ channel）；②早 K＋ 通道（ early K＋ channel）；③ Ca＋ +激活 K＋ 通道（ Ca+＋activated K＋ channel）；④ ATP激活的 K＋ 通道等。 4．植物內(nèi)向整流 K＋ 通道（ K＋ in）的特征 （ 1）位置：植物內(nèi)向整流 K＋ 通道（ K＋ in）主要是存在于細胞的質(zhì)膜上，具有特殊的電勢依賴性。 Cl及細胞中的蛋白質(zhì)分子（一般為靜