📚 IB AQA Biology: Plant Hormones – Key Points | 植物激素考点精讲
Plant hormones (phytohormones) are chemical messengers that coordinate growth, development, and responses to environmental stimuli in plants. Unlike animal hormones, they are often produced in one region and can act nearby or be transported to distant target cells, and they function at very low concentrations. Understanding their roles and interactions is essential for the IB and AQA biology specifications, as they illustrate fundamental principles of signal transduction and control in living systems.
植物激素（植物生长物质）是化学信使，负责协调植物的生长、发育以及对环境刺激的反应。与动物激素不同，它们通常在某一部位产生，可在附近起作用或被运输到远处的靶细胞，并且在极低浓度下就能发挥作用。理解它们的角色和相互作用是 IB 和 AQA 生物考试的重要内容，它们展示了生命体中信号转导和控制的基本原理。
1. Introduction to Plant Hormones | 植物激素概述
Plants rely on hormones to regulate processes such as germination, stem elongation, flowering, fruit ripening, and leaf fall. The five major groups covered in the syllabus are auxins, gibberellins, cytokinins, abscisic acid, and ethylene. Each hormone has multiple effects, and often it is the balance between two or more hormones that determines the final outcome.
植物依靠激素来调控发芽、茎的伸长、开花、果实成熟和落叶等过程。大纲涵盖的五大类激素是生长素、赤霉素、细胞分裂素、脱落酸和乙烯。每种激素都有多重效应，而且通常是由两种或多种激素之间的平衡来决定最终的结果。
Hormonal action involves binding to specific receptor proteins, setting off a signal transduction cascade that alters gene expression or activates existing enzymes. For example, auxin binds to the TIR1 receptor, leading to the degradation of repressor proteins and switching on auxin-responsive genes. This molecular mechanism underpins many of the visible physiological responses.
激素作用包括与特异性受体蛋白结合，启动信号转导级联反应，从而改变基因表达或激活已有的酶。例如，生长素与 TIR1 受体结合，导致抑制蛋白降解，开启生长素响应基因。这一分子机制是许多可见生理反应的基础。
2. Auxins: Discovery and Chemical Nature | 生长素的发现与化学本质
Auxins were the first plant hormones discovered, primarily through studies of phototropism in grass coleoptiles. Charles and Francis Darwin demonstrated that the tip of the coleoptile perceives light and sends a signal downward. Later, Peter Boysen-Jensen showed that the signal diffused through agar, and Frits Went isolated a growth-promoting chemical he named auxin (from Greek ‘to grow’).
生长素是最早被发现的植物激素，主要通过对禾本科胚芽鞘向光性的研究而确认。查尔斯·达尔文和弗朗西斯·达尔文证明了胚芽鞘的尖端感知光线并向下传递信号。后来，彼得·博伊森-詹森证明该信号能通过琼脂扩散，弗里茨·温特分离出一种促进生长的化学物质，并将其命名为生长素（源自希腊语“生长”）。
The most abundant natural auxin is indole-3-acetic acid (IAA), synthesised mainly in shoot apical meristems, young leaves, and developing seeds. In laboratory and agricultural settings, synthetic auxins such as NAA (naphthalene acetic acid) and 2,4-D are widely used because they are more stable and can be applied as herbicides or rooting powders.
最丰富的天然生长素是吲哚-3-乙酸 (IAA)，主要在茎顶端分生组织、幼叶和发育中的种子中合成。在实验室和农业环境中，合成的生长素如萘乙酸 (NAA) 和 2,4-D 被广泛使用，因为它们更稳定，可用作除草剂或生根粉。
3. Auxins: Phototropism and Polar Transport | 生长素：向光性与极性运输
Phototropism is the directional growth of a plant towards (positive) or away from (negative) light. In shoots, unilateral light causes a redistribution of auxin towards the shaded side. This is mediated by PIN efflux carrier proteins, which move auxin in a polar fashion. Higher auxin concentration on the shaded side stimulates cell elongation, causing the shoot to bend towards the light.
向光性是指植物朝着（正向）或背着（负向）光源方向生长。在枝条中，单侧光引起生长素向背光面重新分布。这一过程由 PIN 外排载体蛋白介导，它们能使生长素以极性方式运输。背光侧较高的生长素浓度刺激细胞伸长，导致枝条向光弯曲。
Polar auxin transport (PAT) is an energy-requiring process specific to auxins, driven by the asymmetric location of influx carriers (AUX1) and efflux carriers (PIN proteins) on cell membranes. It allows auxin to move from the shoot tip downwards towards the roots, establishing concentration gradients that guide development. This basipetal movement is crucial for maintaining apical dominance and vascular tissue differentiation.
极性生长素运输 (PAT) 是生长素特有的需能过程，由输入载体 (AUX1) 和输出载体 (PIN 蛋白) 在细胞膜上的不对称分布所驱动。它使生长素能够从茎尖向下部运输至根部，建立起指导发育的浓度梯度。这种向基性运输对于维持顶端优势和维管组织分化至关重要。
4. Auxins: Apical Dominance, Root Growth, and Fruit Development | 生长素：顶端优势、根系生长和果实发育
Apical dominance is the phenomenon where the main shoot tip suppresses the growth of lateral buds. The shoot apex produces auxin, which is transported downwards and inhibits the outgrowth of axillary buds. If the apical bud is removed (decapitation), auxin levels drop, and cytokinins from the roots become more influential, promoting lateral bud growth and bushier plants.
顶端优势是主茎顶芽抑制侧芽生长的现象。茎尖产生生长素，向下运输并抑制腋芽的萌发。如果切除顶芽（打顶），生长素水平下降，来自根部的细胞分裂素作用相对增强，促进侧芽生长，从而使植株更加茂盛。
Auxin also plays a concentration-dependent role in root initiation. Low concentrations of auxin stimulate adventitious root formation, a property exploited in commercial rooting hormone powders. In contrast, high auxin concentrations inhibit root elongation but can be utilised in selective herbicides, where synthetic auxins cause uncontrolled growth and death in broad-leaved weeds.
生长素在根的发生中起着浓度依赖性的作用。低浓度生长素刺激不定根的形成，这一特性被商业生根激素粉所利用。相反，高浓度生长素抑制根伸长，但可被用于选择性除草剂，其中合成生长素导致阔叶杂草的不受控生长和死亡。
In developing seeds, auxin stimulates the growth of the fruit ovary wall, resulting in fruit formation. This ability to trigger fruit development without fertilisation, known as parthenocarpy, can be commercially applied using auxin sprays to produce seedless fruits like tomatoes and cucumbers.
在发育中的种子里，生长素刺激子房壁的生长，导致果实形成。这种无需受精即触发果实发育的能力称为单性结实，可商业性地使用生长素喷雾来生产无籽果实，如番茄和黄瓜。
5. Gibberellins: Stem Elongation and Bolting | 赤霉素：茎的伸长与抽薹
Gibberellins (GAs) are a large family of diterpenoid acids; the most common bioactive form is gibberellic acid (GA₃). They are synthesised in young shoots, developing seeds, and roots. The primary effect of gibberellins is the promotion of stem elongation by stimulating both cell division and cell elongation, particularly in internodes.
赤霉素 (GAs) 是一个庞大的二萜酸家族；最常见的活性形式是赤霉酸 (GA₃)。它们在幼枝、发育中的种子和根中合成。赤霉素的主要作用是促进茎的伸长，通过刺激细胞分裂和细胞伸长，特别是在节间部分。
In rosette plants such as cabbage, rapid stem elongation (bolting) is triggered either by long-day photoperiods or by cold treatment (vernalisation), both of which increase endogenous gibberellin levels. Application of exogenous gibberellin can induce bolting even in the absence of these environmental cues, demonstrating the central role of GAs in this developmental switch.
在如卷心菜等莲座植物中，快速的茎伸长（抽薹）由长日照光周期或冷处理（春化作用）触发，这两种情况都会提高内源赤霉素水平。即使在缺乏这些环境信号的情况下，外源赤霉素的施用也能诱导抽薹，证明了 GAs 在这一发育转换中的核心作用。
6. Gibberellins: Seed Germination and Enzyme Mobilisation | 赤霉素：种子萌发与酶动员
Gibberellins play a crucial role in breaking seed dormancy and promoting germination. In cereal grains, water uptake by the embryo triggers gibberellin production, which diffuses to the aleurone layer. There, GA induces the synthesis of hydrolytic enzymes such as α-amylase, protease, and nucleases.
赤霉素在打破种子休眠和促进萌发中起着关键作用。在谷类种子中，胚吸收水分后触发赤霉素的产生，赤霉素扩散至糊粉层。在那里，GA 诱导水解酶如 α-淀粉酶、蛋白酶和核酸酶的合成。
These enzymes break down stored starch, protein, and nucleic acids in the endosperm into soluble sugars, amino acids, and nucleotides, which are then transported to the growing embryo. This classic system demonstrates a clear hormone signal transduction pathway and is a common examination model for gene activation by a hormone.
这些酶将胚乳中储存的淀粉、蛋白质和核酸分解为可溶性糖、氨基酸和核苷酸，然后被运输到生长中的胚。这一经典系统展示了清晰的激素信号转导途径，是考试中常见的激素激活基因的模式模型。
7. Cytokinins: Cell Division, Differentiation, and Senescence Delay | 细胞分裂素：细胞分裂、分化与延缓衰老
Cytokinins are a group of hormones that promote cytokinesis (cell division) in plant roots and shoots. They are mainly synthesised in root tips and transported upwards via the xylem. Naturally occurring cytokinins include zeatin and isopentenyl adenine. Their effects are often synergistic or antagonistic with auxins.
细胞分裂素是一类促进植物根和茎中胞质分裂（细胞分裂）的激素。它们主要在根尖合成，通过木质部向上运输。天然的细胞分裂素包括玉米素和异戊烯基腺嘌呤。它们的作用常与生长素协同或拮抗。
The ratio of auxin to cytokinin determines the pattern of differentiation in tissue culture. A high auxin : cytokinin ratio promotes root formation, a balanced ratio leads to undifferentiated callus growth, and a high cytokinin : auxin ratio stimulates shoot formation. This principle is widely exploited in micropropagation and plant biotechnology.
生长素与细胞分裂素的比例决定了组织培养中的分化模式。高生长素/细胞分裂素比促进根的形成，平衡比例导致未分化的愈伤组织生长，高细胞分裂素/生长素比刺激芽的形成。这一原理被广泛应用于微繁殖和植物生物技术中。
Cytokinins also delay leaf senescence by reducing the breakdown of chlorophyll and proteins, maintaining the leaf as a sink for nutrients. This anti-senescence effect is commercially used to extend the shelf-life of cut flowers and leafy vegetables.
细胞分裂素还能通过减少叶绿素和蛋白质的降解来延缓叶片衰老，使叶片持续作为养分的库。这种抗衰老效应在商业上用于延长切花和叶菜类蔬菜的货架期。
8. Abscisic Acid: Stress Responses, Stomatal Closure, and Dormancy | 脱落酸：胁迫响应、气孔关闭与休眠
Abscisic acid (ABA) is often called the ‘stress hormone’ because its levels rise sharply under adverse conditions such as drought, salinity, and cold. Contrary to its historical name, ABA is not the primary trigger for abscission but rather plays a key role in inhibiting growth and closing stomata during water deficit.
脱落酸 (ABA) 常被称为“胁迫激素”，因为在干旱、盐碱和寒冷等逆境条件下其水平会急剧升高。与其历史名称相反，ABA 并不是器官脱落的主要触发因子，而是在水分亏缺时抑制生长和关闭气孔的关键角色。
When roots sense low soil water potential, ABA is synthesised and transported to guard cells via the transpiration stream. There, ABA binds to receptors, opening Ca²⁺ channels and allowing K⁺ and anions to exit, which reduces turgor and closes the stomatal pore. This mechanism reduces transpirational water loss and is a fundamental adaptation of land plants.
当根系感知到低土壤水势时，ABA 被合成并通过蒸腾流运输到保卫细胞。在那里，ABA 与受体结合，打开 Ca²⁺ 通道，允许 K⁺ 和阴离子外流，从而降低膨压并关闭气孔。这一机制减少了蒸腾失水，是陆生植物的一项基础适应策略。
ABA also maintains seed dormancy, preventing premature germination (vivipary) while the seed is still on the parent plant. Its ratio to gibberellins usually determines whether a seed remains dormant or germinates. In temperate regions, cold stratification lowers ABA levels, allowing GA to act and trigger spring germination.
ABA 还能维持种子休眠，防止种子还在母体植株上时过早萌发（胎萌）。它和赤霉素的比例通常决定了种子是保持休眠还是萌发。在温带地区，冷层积处理降低了 ABA 水平，使 GA 得以行使作用，触发春季萌发。
9. Ethylene: Fruit Ripening, Senescence, and Abscission | 乙烯：果实成熟、衰老与脱落
Ethylene (C₂H₄) is a gaseous hormone unique in its ability to diffuse freely through tissues and even influence neighbouring plants. It is produced from the amino acid methionine via the Yang cycle and promotes a wide range of responses including fruit ripening, leaf and flower senescence, and organ abscission.
乙烯 (C₂H₄) 是一种气态激素，其独特之处在于可以自由扩散通过组织，甚至影响邻近植物。它由氨基酸甲硫氨酸通过杨氏循环合成，促进果实成熟、叶片和花的衰老以及器官脱落等一系列反应。
In climacteric fruits such as bananas, apples, and tomatoes, a burst of ethylene production at the start of ripening acts autocatalytically, stimulating the synthesis of more ethylene. This leads to coordinated changes: starch to sugar conversion, chlorophyll breakdown, cell wall softening, and production of aroma compounds. The phrase ‘one bad apple spoils the barrel’ has a biochemical basis in ethylene diffusion.
在如香蕉、苹果和番茄等更年型果实中，成熟启动时乙烯产生的爆发起到自催化作用，刺激合成更多的乙烯。这导致协调的变化：淀粉转化为糖、叶绿素降解、细胞壁软化以及香气化合物的产生。“一颗老鼠屎坏了一锅粥”这句谚语在乙烯扩散上找到了生化依据。
Ethylene also promotes abscission by stimulating the production of cellulase and pectinase enzymes in the abscission zone, weakening cell walls and causing leaves or fruits to drop. In agriculture, ethylene blockers such as 1-MCP (1-methylcyclopropene) are used to delay ripening and extend storage life, while synthetic ethylene-releasing compounds such as ethephon are used to synchronise ripening.
乙烯还通过刺激离层区纤维素酶和果胶酶的产生来促进脱落，削弱细胞壁，导致叶片或果实脱落。在农业上，乙烯阻断剂如 1-MCP (1-甲基环丙烯) 用于延迟成熟和延长贮藏期，而合成乙烯释放化合物如乙烯利则用于同步催熟。
10. Commercial and Agricultural Applications of Plant Hormones | 植物激素的商业与农业应用
Understanding plant hormones has led to numerous practical applications. Synthetic auxins like 2,4-D are used as selective weed killers because broad-leaved dicots are more sensitive than narrow-leaved monocots (such as cereals). Rooting powders containing NAA or IBA promote adventitious root formation on cuttings, aiding clonal propagation.
对植物激素的理解带来了许多实际应用。合成生长素如 2,4-D 被用作选择性除草剂，因为阔叶双子叶植物比窄叶单子叶植物（如谷物）更为敏感。含有 NAA 或 IBA 的生根粉促进插条上不定根的形成，有助于克隆繁殖。
Gibberellins are sprayed on seedless grapes to elongate the fruit stalks and increase berry size, and on sugarcane to boost internode length and sugar yield. Cytokinins are incorporated into tissue culture media and used to prolong the green of leafy vegetables. Ethylene-releasing agents or inhibitors are carefully managed to control ripening schedules during transport and marketing.
赤霉素喷洒在无籽葡萄上以伸长果柄并增大浆果，在甘蔗上用以增加节间长度和糖产量。细胞分裂素被掺入组织培养基，并用于延长叶菜类蔬菜的绿色期。乙烯释放剂或抑制剂经过精心管理，以控制在运输和销售过程中的成熟时间表。
Knowledge of hormonal cross-talk allows more precise agricultural interventions. For instance, maintaining a high cytokinin-to-auxin ratio keeps cut flowers fresh, while managing ABA levels through controlled irrigation can improve water-use efficiency. These applications are testable exam content that illustrates the link between fundamental biology and real-world technology.
对激素交叉作用的理解使得更精确的农业干预成为可能。例如，维持高细胞分裂素与生长素的比例可保持切花新鲜，而通过控制灌溉管理 ABA 水平可提高水分利用效率。这些应用是可考查的考试内容，展示了基础生物学与现实世界技术之间的联系。
11. Experimental Approaches and Key Investigations | 实验方法与关键研究
Examinations often require the ability to interpret experimental data related to plant hormones. Classic investigations such as the Darwin–Went coleoptile experiments, decapitation and agar block replacement studies, and the use of GA-deficient mutants (e.g., dwarf peas) are essential knowledge. Students should be prepared to describe controls, analyse hormone concentration gradients, and predict outcomes when hormone applications are altered.
考试常要求能够解释与植物激素相关的实验数据。经典的调查研究如达尔文–温特胚芽鞘实验、去顶及琼脂块置换研究，以及利用赤霉素缺陷突变体（如矮生豌豆）都是必要知识。学生应准备好描述对照组、分析激素浓度梯度，并预测激素处理改变后的结果。
Bioassays such as the α-amylase production assay in barley half-seeds, or the rice seedling elongation test, allow quantitative measurement of hormone activity. Modern molecular techniques include reporter gene constructs and transcriptomics, but the underlying principles of dose–response and receptor specificity remain central to the curriculum.
生物测定法如大麦半粒种子的 α-淀粉酶产生分析，或水稻幼苗伸长试验，可以定量测量激素活性。现代分子技术包括报告基因构建和转录组学，但剂量–反应和受体特异性的基本原理仍然是课程的核心。
12. Summary of Plant Hormone Functions | 植物激素功能总结
The following table summarises the major hormones, their primary sites of synthesis, main actions, and typical applications. This synoptic table aids last-minute revision and highlights the interactions that often appear in extended-response questions.
下表总结了主要激素、它们的初级合成部位、主要作用和典型应用。这个总结表有助于考前快速复习，并突出常在扩展回答题目中出现的相互作用。
| Hormone | Synthesis Site | Key Actions | Commercial Use |
|---|---|---|---|
| Auxin (IAA) | Shoot apex, young leaves | Cell elongation, apical dominance, rooting, fruit development | Rooting powder, herbicides (2,4-D), parthenocarpy |
| Gibberellin (GA₃) | Young shoots, seeds | Stem elongation, seed germination, enzyme mobilisation | Grape elongation, malting, sugarcane yield |
| Cytokinin | Root tips | Cell division, shoot formation, senescence delay | Tissue culture, shelf-life extension |
| Abscisic acid (ABA) | Roots, mature leaves | Stomatal closure, seed dormancy, stress response | Water-use efficiency management |
| Ethylene (C₂H₄) | Ripening fruits, nodes | Fruit ripening, abscission, senescence | Ripening control, 1-MCP storage, ethephon |
Recognising that hormones rarely work in isolation is fundamental. In exam scenarios, always consider the balance of multiple hormones when analysing a physiological response, such as stem elongation (auxin + GA), stomatal closure (ABA), or bud outgrowth (auxin-to-cytokinin ratio).
认识到激素很少孤立工作是基础。在考试情境中，分析生理反应时始终考虑多种激素的平衡，例如茎伸长（生长素 + 赤霉素）、气孔关闭（脱落酸）或芽的萌发（生长素与细胞分裂素的比例）。
Published by TutorHao | Biology Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导