Chapter 2   Nutrient Uptake

[目的与要求]

1．掌握植物养分的吸收机理；

2．熟悉主动吸收与被动吸收的过程；

3．了解影响养分吸收的因素；

[重点]

植物必需养分有那些？

植物如何吸收养分？

养分的来源？吸收途径? 吸收器官？吸收机理？影响因素？

[难点]

1．离子的吸收机理

2．主动吸收

[课堂组织]

讲述、讨论和多媒体教具结合

[教学内容]

2.1 Nutrition component of plant(植物的养分组成)

2.1.1 Plant Composition

2.1.2 Concept of Essential nutrition element

An essential element to be considered essential , three criteria must be met (Arnon and Stout 1939): 

1. A given plant must be unable to replaceable its life cycle in the absence of the mineral element（必不可少）

2.The function of the element must not be replaceable by another mineral element (不可替代)

3.The element must be directly involved in plant metabolism (直接性)

Table 2—1   Macroelements (9)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Element          Discovery of Essentiality         Year

───────────────────────────────

C                De Saussure                 1804

  H                De Saussure                 1804

  O                De Saussure                 1804

  N                De Saussure                 1804

  P                Ville                       1860

S                von Sachs, Knop              1860’s

Ca                von Sachs, Knop              1860’s

Mg               von Sachs, Knop              1860’s

K                   Lucanus                   1865

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

Table 2—2   Microelement (7 nor 8)

Element            Discovery of Essentiality       Year

───────────────────────────────

   Fe                 J Sachs                    1860

   Mn                J S Mchargue               1922

   B                 K Warington                1923

   Zn                Sommer and Lipman          1926

   Cu                Lipman and MacKinney       1931

   Mo               Arnon and Stout              1939

   Cl                T C Broyer et al              1954

Co              P H Brown et al               1987

Depending on content in RW of Plant:

Macroelements:  >0.1% in Dry matter (9)

Microelements:  <0.1% in Dry matter (7)

Table 2—3   Essentiality of Mineral Elements

───────────────────────

Classification                          Element

───────────────────────

Macroelement                      N, P, K, Ca, Mg, S

   Microelement                   Fe, Mn, Cu, Zn, B, Mo, Cl

Beneficial element                  Na, Si, Co, I, V

───────────────────────

2.1.3 2.1.3  General Function of Essential Elements

2.1.3.1  Constituents of plant organic structure

2.1.3.2  Regulation of enzyme activities

2.1.3.3  Osmoregulation

2.2 Ion Uptake Mechanisms(离子吸收机理)

2.2.1 Characteristics of plant to absorb nutrients

A. Selectivity  

B. Accumulation

C. Genotype

2.2.2 Influx into the Apparent Free Space

2.2.2.1 Root Morphology

单子叶植物的根属须根系主根不够发达,在茎基和茎节等处长出许多不定根,并大量形成粗细差不多的各级侧根。所以,须根系是粗细比较均匀的体系,根长与表面积也都比较大。相反,双子叶植物的根属直根系，其主要支、干根都可进行次生生长，并形成粗细悬殊较大的不均匀结构体系，在根长与总吸收表面积上都比须根系小。

2.2.2.2 Location of Absorption Zone

The principal zone for nutrition absorption is the root tip or root hair 0.1 to 1mm in length for each root hair and  as many as 103 root hairs per cm of root

2.2.3          the Apparent Free Space

2.2.4 

Free Space (自由空间)：The volume of root tissue available for passive solute movement (10%)

Apoplast (质外体)：植物体内共质体以外的所有空间,包括细胞壁、细胞间隙和木质部空腔等。

Apparent Free Space (AFS) = WFS + DFS

Water Free Space （WFS）is freely accessible to ion

Donnan Free Space（DFS） where cation exchange and anion repulsion take place

CEC in root:  Dicotyledonous >Monocotyledonous

Plasma Membrane (cytoplasm, 质膜)：

※  Main site of nutrient uptake;

※  The principal site of active transport in either direction

※  Effective barrier against the diffusion of solutes for both  influx and efflux

※  The other main barrier to diffusion for ion

※  The main compartment for ion accumulation

※  Comprise more than 90% of the cell volume

2.2.3.1  Structure and Composition of Membranes

The fluid-membrane model (Branton 1969, Singer 1972)

The unit-membrane model (Danielli and Davson 1935)

Two phospholipid layers Protein ---extrinsic proteins

                           ---intrinsic proteins

图 2—1   细胞膜上的离子运输方式

被动运输是离子顺电化学势梯度进行的扩散运动，不需要能量，也没有选择性；

主动运输是在消耗能量的条件下，离子逆电化学势梯度进行的运转，不仅需要能量，而且具有明显的选择性；

2.2.3.2 离子的被动吸收

主要通过扩散作用—不需能量（非代谢吸收）

2.2.3.2.1 简单扩散

图 2—1   离子跨膜的主动（“上坡”）和被动（“下坡”）运输示意图

前提:细胞内外浓度差

Passway: Lipid, Carriers and Aqueous pores

2.2.3.2.2 杜南扩散

[Nai+] × [Cli-]= [Nao+] × [Clo-]

2.2.3.3 Active absorption of Ion(离子的主动吸收)

定义：指溶质分子或离子有选择地逆浓度梯度或电化学势梯度进入细胞的过程。

特点：

1.需要消耗代谢能

2.吸收的离子具有选择性

3.根系逆浓度梯度吸收养分

主动吸收的机理：

理论：

1.载体假说

2.载离子体假说

3.离子泵学说：能量来源于ATP

2.2.3.3.1Carrier theory

载体：是生物膜上能携带离子穿过膜的蛋白质或其它物质。

学说要点：

1.质膜上的载体是大分子；

2.载体具有专一性、饱和性和竞争性；

3.运载是逆着电化学势梯度运动的，且要消耗能量。

载体的专一性：某一载体只能运输某种或某几种化学性质近似的离子。

能较好地解释下面三个问题：

1.离子的选择性吸收；

2.离子通过质膜以及在质膜上的转移；

3.离子吸收与代谢作用的密切关系。

离子泵是存在于细胞膜上的一种蛋白质，它在有能量供应下可使离子在细胞膜上逆电化学势梯度主动地吸收。

K+/Na+泵

Electogenic Pumps(H+--ATPase

Strength of interact between membrane constituents and ion:

Unchanged molecules < Cat+, An-< Cat 2 +, An 2 -< Cat 3 +, An 3 -

Conversely, the uptake rate often decrease in this order.

2.3 Factors Affecting Ion Uptake(影响离子吸收的因素)

1.介质中养分的浓度

2.温度

3.光照

4.水分

5.通气状况

6.土壤反应(pH值)

7.离子理化性状和根的代谢作用

8.离子间的相互作用

9.苗龄和生育阶段

2.4 Nutrient Uptake by Leave and Other Aerial Plant Parts(叶片和其它器官对养分的吸收)

植物通过叶片（或茎）吸收养分的营养方式叫植物的根外营养

2.4.1 Structure and Composition of Plant Leaves

植物叶片是进行光合作用的主要场所它是由表皮组织、叶肉组织及疏导组织所组成，而叶片上的表皮组织含有大量的表皮细胞，气孔就是表皮细胞分化出来的组织，并按一定的距离分布于叶表面上。

2.4.2 Uptake of Gasses through Stomata

要提高叶片营养的有效性，就必须使营养物质从叶表面能进入表皮细胞（或保卫细胞）的细胞质。

2.4.3 Uptake of Solutes

2.4.4 Foliar Application of Mineral Nutrients

2.4.4.1 Practical importance

2.4.4.1.1  Low Nutrient Availability in Soil

Fe, Mn in calcareous or high pH soils;

Mo in acid soil

2.4.4.1.2  Dry Topsoil

2.4.4.1.3 Decrease in Root Activity during the Reproductive Stage

As a result of sink competition for carbohydrates, root activity and nutrient uptake by the root decline with the onset of reproductive stage

2.4.4.1.4 Increase in protein Content of Cereal Seeds

2.4.5叶部营养特点

1.防止养分在土壤中的固定

2.叶部营养能及时满足植物对养分的需要

3.叶部营养能直接促进植物内的代谢作用

4.叶部营养只能作为根部营养的补充，不以能完全取代根部

2.4.6影响叶部吸收养分的因素

1.溶液的组成

2.溶液的浓度及反应

3.溶液湿润叶片的时间

4.叶片的类型

2.5 Beneficial Elements(有益元素)

2.5.1 Definition

Mineral elements which either stimulate growth but are not essential or which are essential only for certain plant species, or under given condition, are usually defined as Beneficial elements

2.5.2 Silicon  (硅)

2.5.2.1 Content, distribution and form of Si

Depending on SiO2 content(% DW), they can be divided three main groups:

A: Wetland Gramineae(禾本科), such as rice10-20%;

B: Dryland Gramineae, such as sugarcane and most of the cereal species, 2-4%;

2.5.2.2 Nutrition function of silicon

Composition of cell wall

Plant growth

Interaction with other nutrients (Si---N、Si-Mn)

2.5.3 Sodium(钠)

2.5.3.1 Content of Sodium

~2.8% in the earth’s crust, 2.6% for potassium

In general,  0.1% of dry weight which is about 1/10 of potassium in plant.

Plant species are characterized as natrophilic(喜钠 ) or natrophobic(厌钠) depending on their growth response.

2.5.3.2 Nutrition function of sodium

A.刺激生长

B.调节渗透压

C.影响植物水分平衡与细胞伸展

D.Substitution of potassium by sodium

In general, four groups according to the difference in their growth response to Na：

In group A  not only can a high proportion of K be replaced by Na without an effect on growth;additional growth stimulation occures which cannot be achieved by increasing the K content of plant

In group B specific growth response to Na are observed, but they are much less distinct,Also a much smaller proportion of K can be replaced without a decline in growth

In group C only minor substitution is possible and Na has not specific effect on growth.

In group D no substitution of K is possible.

2.5.4 Cobalt(钴)

2.5.4.1 Content

About 0.02~0.5 mg/kg of DW in plant;

Legumes: 0.24~0.52 mg/kg;

Cereals: 0.08~0.26 mg/kg.

2.5.4.2 Nutrition function of cobalt

N2 fixation

Growth stimulation

Stabilization Chlorophyll

2.5.5 Nickel(镍)

2.5.5.1 Content and Distribution

Normally range from about 0.1 to 1.0 mg/kg WT

Critical toxicity levels for sensitive, moderately tolerant crop species are >10 and 50 mg, respectively.

2.5.5.2 Nutrition Function of Nickel

Stimulation of germination growth of various crop species

Urease activity

Defense against some disease

2.5.6 Selenium(硒)

2.5.6.1 Content

The average Se content of crop varies between 0.01 and 1.0 mg/kg DW.

The toxic levels of Se are above 5 mg/kg DW

Plants were divided into three groups depending their content

A: Accumulator plant

B: Subaccumulator plant

2.5.6.2 Nutrition function of Selenium

Growth Stimulation

Cleanup Active Oxygen

2.5.7 Aluminum(铝)

2.5.7.1 General

Al concentration in plans vary between 20 and 200 mg/kg ;

In the tea plant, the most Al-tolerant crop, as high as 27 mg/kg.

2.5.7.2 Nutrition Function of Aluminum

Growth Stimulation

Affecting Color of plant 

Enzyme activity

[思考题]

1.名词解释：矿质营养学说、养分归还学说、最小养分律、生物路线的农业化学学派、主动吸收、被动吸收、拮抗作用、大量营养元素、

2.植物必需营养元素有哪些？其判断标准？

3.什么是有益元素？试举几例。

4.植物根系吸收矿质养分的形态和部位？

5.主动吸收与被动吸收的区别？各有何特点？机理？

6.叶部营养与根部营养的异同点？

7.简述外界因素对根系吸收养分的影响。

8.如何理解叶部营养的作用

9.有哪些有益元素？其主要的营养功能和必需的作物？