📚 Control and Coordination in Plants | 植物的控制与协调
Plants do not possess a nervous system, yet they continually detect and respond to light, gravity, touch, water availability and chemical signals. Control and coordination in plants rely on plant growth substances (plant hormones) which are produced in one region and transported to target cells, often at extremely low concentrations.
植物没有神经系统，但它们仍能持续感知并响应光照、重力、触碰、水分可用性和化学信号。植物的控制与协调依赖植物生长物质（植物激素），这些物质在某一部位产生并被运输到靶细胞，通常以极低浓度发挥作用。
1. Plant Responses and Signalling Systems | 植物响应与信号系统
Plants respond to directional stimuli by growth movements called tropisms. A tropism is a growth response in which the direction of growth is determined by the direction of the stimulus. Positive tropism is growth towards the stimulus; negative tropism is growth away from the stimulus.
植物通过称为向性的生长运动响应方向性刺激。向性是一种生长响应，其生长方向由刺激方向决定。正向性是朝向刺激生长；负向性是背离刺激生长。
Unlike rapid animal responses, plant coordination is usually slower because it involves changes in cell elongation or cell division. Signalling pathways include hormone perception by receptors, signal transduction, altered gene expression and transport of hormones such as auxin.
与动物的快速反应不同，植物的协调通常较慢，因为它涉及细胞伸长或细胞分裂的变化。信号通路包括激素被受体感知、信号转导、基因表达改变以及生长素等激素的运输。
2. Auxins: Discovery and Roles | 生长素：发现与作用
Auxins, especially indole-3-acetic acid (IAA), are produced in shoot and root apical meristems and young leaves. IAA moves mainly by active transport and by polar transport from cell to cell, allowing gradients to be established.
生长素，尤其是吲哚-3-乙酸（IAA），在茎尖和根尖分生组织及幼叶中产生。IAA主要通过主动运输和细胞间的极性运输移动，从而建立浓度梯度。
Auxin promotes cell elongation in shoots by increasing cell wall plasticity and water uptake. However, high auxin concentrations inhibit root cell elongation, which explains different responses in shoots and roots.
生长素通过增加细胞壁可塑性和水分吸收促进茎中的细胞伸长。但高浓度生长素抑制根细胞伸长，这解释了茎和根的不同响应。
3. Phototropism: Bending Towards Light | 向光性：向光弯曲
In shoots, unilateral light causes auxin to redistribute towards the shaded side. The higher auxin concentration on the shaded side stimulates faster cell elongation, so the shoot bends towards the light. This is positive phototropism.
在茎中，单侧光照使生长素重新分布到背光侧。背光侧较高的生长素浓度促进更快的细胞伸长，因此茎向光弯曲。这是正向向光性。
The photoreceptor phototropin detects blue light and triggers lateral auxin transport. Experiments by Darwin, Boysen-Jensen and Went showed that a mobile chemical signal from the coleoptile tip controls phototropic curvature.
光受体向光素检测蓝光并触发生长素的侧向运输。达尔文、博伊森-詹森和温特的实验表明，胚芽鞘尖端产生的一种可移动化学信号控制向光弯曲。
4. Gravitropism: Sensing Gravity | 向地性：感知重力
Roots show positive gravitropism (grow downwards) and shoots show negative gravitropism (grow upwards). In roots, statoliths (dense starch grains) in root cap cells settle under gravity and trigger redistribution of auxin to the lower side.
根表现为正向向地性（向下生长），茎表现为负向向地性（向上生长）。在根中，根冠细胞内的平衡石（致密淀粉粒）在重力作用下沉降，触发生长素重新分布到下侧。
In a horizontal root, the lower side accumulates more auxin. Because root cells are inhibited by relatively high auxin, lower-side cells elongate less than upper-side cells, so the root curves downward. In shoots, higher auxin on the lower side promotes elongation, so the shoot curves upward.
在水平放置的根中，下侧积累更多生长素。由于根细胞受相对较高浓度生长素抑制，下侧细胞伸长少于上侧细胞，因此根向下弯曲。在茎中，下侧较高生长素促进伸长，因此茎向上弯曲。
5. Apical Dominance | 顶端优势
Apical dominance is the inhibition of lateral bud growth by the growing shoot apex. Auxin produced by the apical bud moves downwards and suppresses the growth of lateral buds, maintaining a single main stem.
顶端优势是正在生长的茎尖对侧芽生长的抑制。顶芽产生的生长素向下移动并抑制侧芽生长，从而维持单一主茎。
Removing the apical bud removes the main auxin source, allowing lateral buds to grow. Cytokinins act antagonistically by promoting lateral bud outgrowth. The balance between auxin and cytokinin determines branching.
去除顶芽就移除了主要的生长素来源，使侧芽能够生长。细胞分裂素起拮抗作用，促进侧芽萌发。生长素与细胞分裂素的平衡决定分枝。
6. Gibberellins: Stem Elongation and Seed Germination | 赤霉素：茎伸长与种子萌发
Gibberellins (e.g. GA₃) are synthesised in young leaves, roots and seeds. They promote stem elongation by stimulating cell division and cell elongation, and they are responsible for stem elongation in dwarf varieties when applied externally.
赤霉素（如GA₃）在幼叶、根和种子中合成。它们通过刺激细胞分裂和细胞伸长促进茎伸长，外施赤霉素可使矮化品种恢复茎伸长。
During seed germination, gibberellins switch on genes for α-amylase synthesis in the aleurone layer of cereal grains. α-amylase hydrolyses starch into maltose and glucose for the growing embryo.
在种子萌发过程中，赤霉素启动谷物糊粉层中α-淀粉酶合成的基因。α-淀粉酶将淀粉水解为麦芽糖和葡萄糖，供生长中的胚使用。
7. Abscisic Acid and Stomatal Closure | 脱落酸与气孔关闭
Abscisic acid (ABA) is produced in response to water stress. When roots detect low water potential, ABA is transported to leaves, where it causes guard cells to lose potassium ions and water, closing stomata and reducing transpiration.
脱落酸（ABA）在水分胁迫下产生。当根检测到低水势时，ABA被运输到叶片，引起保卫细胞失去钾离子和水分，关闭气孔并减少蒸腾。
ABA also maintains seed dormancy and inhibits germination. High ABA levels block the action of gibberellins, whereas a fall in ABA or an increase in gibberellin breaks dormancy.
ABA还维持种子休眠并抑制萌发。高ABA水平阻断赤霉素的作用，而ABA下降或赤霉素增加则打破休眠。
8. Ethylene and Fruit Ripening | 乙烯与果实成熟
Ethylene is a gaseous plant hormone produced in ripening fruits, senescing tissues and stressed plant parts. It promotes fruit ripening, leaf abscission and flower wilting.
乙烯是一种气态植物激素，在成熟果实、衰老组织和受胁迫的植物部位产生。它促进果实成熟、叶片脱落和花朵凋萎。
Ethylene synthesis is stimulated by auxin and by positive feedback during climacteric ripening. It also induces the synthesis of enzymes such as cellulase and pectinase that soften cell walls.
乙烯的合成受生长素刺激，并在跃变型果实成熟过程中通过正反馈促进。它还诱导纤维素酶和果胶酶等酶的合成，使细胞壁软化。
9. Cytokinins and Cell Division | 细胞分裂素与细胞分裂
Cytokinins are produced in roots and transported upwards through xylem. They promote cell division, delay leaf senescence and stimulate lateral bud growth.
细胞分裂素在根中产生并通过木质部向上运输。它们促进细胞分裂、延缓叶片衰老并刺激侧芽生长。
In tissue culture, the ratio of auxin to cytokinin determines whether callus tissue forms roots or shoots: high auxin favours root formation, whereas high cytokinin favours shoot formation.
在组织培养中，生长素与细胞分裂素的比例决定愈伤组织形成根还是芽：高生长素有利于根形成，而高细胞分裂素有利于芽形成。
10. Commercial Uses of Plant Hormones | 植物激素的商业应用
Plant hormones are widely used in agriculture and horticulture. Synthetic auxins such as 2,4-D act as selective herbicides against broad-leaved weeds; auxins are also used in rooting powders to stimulate adventitious root formation in cuttings.
植物激素广泛用于农业和园艺。合成生长素如2,4-D作为选择性除草剂防除阔叶杂草；生长素也用于生根粉，刺激插条形成不定根。
Gibberellins are sprayed on grapes to increase fruit size and on barley to speed up malting. Ethylene or ethephon is used to ripen bananas and tomatoes during transport, while cytokinins extend the shelf life of cut flowers and leafy vegetables.
赤霉素喷洒在葡萄上可增大果实，喷洒在大麦上可加快麦芽制造。乙烯或乙烯利用于在运输中催熟香蕉和番茄，而细胞分裂素可延长切花和叶菜的货架期。
11. Investigating Plant Responses: Experiments | 植物响应实验研究
Classic experiments used oat coleoptiles. Darwin showed that the tip perceives light; Boysen-Jensen showed that a chemical signal diffuses across a permeable gelatin block but not an impermeable barrier; Went demonstrated that agar blocks containing auxin cause curvature in decapitated coleoptiles.
经典实验使用燕麦胚芽鞘。达尔文证明尖端感知光照；博伊森-詹森证明化学信号可通过透性明胶块扩散但不能通过不透性屏障；温特证明含有生长素的琼脂块能使去顶胚芽鞘弯曲。
Simple investigations can measure phototropic or gravitropic curvature, the effect of rooting powder on cuttings, or the effect of gibberellin on dwarf pea stem length. Control groups and standardised conditions are essential for valid comparisons.
简单的探究可以测量向光性或向地性弯曲程度、生根粉对插条的影响，或赤霉素对矮化豌豆茎长的影响。对照组和标准化条件是有效比较所必需的。
12. Summary and Exam Tips | 总结与考试技巧
Key hormones to learn are auxin, gibberellins, ABA, ethylene and cytokinins. For auxin, be precise about concentration-dependent effects: low concentrations promote shoot elongation, high concentrations inhibit root elongation.
需要掌握的关键激素是生长素、赤霉素、脱落酸、乙烯和细胞分裂素。对于生长素，要准确说明浓度依赖性效应：低浓度促进茎伸长，高浓度抑制根伸长。
Use the terms phototropism and gravitropism rather than ‘growing towards light’ or ‘growing away from gravity’. Explain mechanisms in terms of uneven auxin distribution, not simply ‘the hormone makes it bend’.
使用向光性和向地性等术语，而不是只说“向光生长”或“背离重力生长”。解释机制时要从生长素分布不均的角度说明，而不仅仅是“激素使它弯曲”。
In exam answers, link each hormone to its site of synthesis, transport route, target tissue and one named commercial application. Include control variables when describing experiments.
考试答题时，要把每种激素与其合成部位、运输途径、靶组织以及一个具体商业应用联系起来。描述实验时要包括控制变量。
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