Control and Coordination in Plants | 植物的调控与协调

📚 Control and Coordination in Plants | 植物的调控与协调

Plants lack a nervous system, yet they precisely sense and respond to their surroundings. Coordination is achieved through chemical signals – plant hormones – which regulate growth, development, and metabolic changes in response to light, gravity, water availability, and even touch. This article covers the major groups of plant hormones and examines the mechanisms behind tropisms, photoperiodism, and stress adaptations, linking molecular events to whole-plant responses.

植物没有神经系统，却能精确地感知并响应周围环境。它们的协调依赖化学信号——植物激素——来调控生长、发育以及代谢变化，以应对光照、重力、水分供应甚至触碰。本文介绍主要的植物激素类群，并剖析向性运动、光周期现象和胁迫适应的机制，将分子事件与整体植株反应联系起来。

1. The Need for Coordination in Plants | 植物协调的必要性

Unlike animals, plants are sessile organisms. They cannot move away from unfavourable conditions, so their survival depends on the ability to adjust growth and physiology in situ. This requires pathways that detect environmental cues, transmit signals, and bring about appropriate responses – a process that is fundamentally chemical and often results in differential cell elongation or division.

与动物不同，植物营固着生活。它们无法逃离不利环境，因此生存取决于其就地基质调控生长和生理状态的能力。这就需要能够探测环境线索、传递信号并引发恰当响应的通路——这一过程本质上是化学性的，往往导致细胞的不对称伸长或分裂。

2. Overview of Plant Hormones | 植物激素概述

Plant hormones, or phytohormones, are small organic compounds produced in one part of the plant and transported to another, where they trigger specific responses at very low concentrations. Unlike animal hormones, they are not produced in specialised glands, and their effects depend largely on the sensitivity of target cells. The table below summarises four key hormones examined in the Cambridge International A-Level syllabus.

植物激素（或称为植物生长调节物质）是在植物某一部分合成、经运输至其他部位并在极低浓度下引发特定响应的小分子有机化合物。与动物激素不同，它们并非由特化腺体分泌，其效应很大程度上取决于靶细胞的敏感性。下表总结了剑桥国际A-Level大纲中四类关键激素。

Hormone	Main Site of Synthesis	Key Roles
Auxins (primarily IAA)	Shoot apical meristem, young leaves	Cell elongation, phototropism, gravitropism, apical dominance
Gibberellins	Young shoots, developing seeds	Stem elongation, seed germination, fruit development
Abscisic acid (ABA)	Leaves and roots (under stress)	Stomatal closure, seed dormancy, drought tolerance
Ethene (ethylene)	Ripening fruits, senescing tissues	Fruit ripening, leaf abscission, triple response

All four hormones interact; for example, auxin and gibberellins often act synergistically to promote growth, while ABA frequently opposes their effects. The balance between these chemicals, rather than the absolute concentration of a single hormone, determines the physiological outcome.

这四类激素之间存在相互作用；例如生长素与赤霉素常协同促进生长，而脱落酸往往拮抗它们的效应。植物生理的最终结果往往取决于这些化学物质之间的平衡，而非单一激素的绝对浓度。

3. Auxins and Cell Elongation | 生长素与细胞伸长

Indole-3-acetic acid (IAA) is the most abundant natural auxin. It is synthesised mainly in the shoot apex and moves down the stem by polar transport. In shoots, IAA promotes cell elongation by increasing the plasticity of the cell wall, thereby allowing turgor-driven expansion. In roots, however, very low IAA concentrations may promote elongation while higher concentrations are inhibitory, which is a key concept in gravitropism.

吲哚-3-乙酸（IAA）是最丰富的天然生长素。它主要在茎尖合成并通过极性运输沿茎向下移动。在枝条中，IAA通过增加细胞壁的可塑性促进细胞伸长，从而借助膨压推动细胞扩大。然而在根中，极低浓度的IAA可能促进伸长，而较高浓度反而抑制生长，这是向地性中的一个关键概念。

Auxin’s effect is mediated by the activation of proton pumps (H⁺-ATPases) in the plasma membrane. The resulting acidification of the cell wall activates expansin proteins, which loosen the cellulose‑hemicellulose network. This mechanism is central to the acid growth hypothesis, which will be discussed in more detail shortly.

生长素的效应由质膜上质子泵（H⁺-ATP酶）的激活介导。细胞壁的酸化激活膨胀素蛋白，使纤维素‑半纤维素网络松弛。这一机制是酸生长假说的核心，稍后将详细讨论。

4. The Mechanism of Phototropism | 向光性机制

Phototropism is the directional growth of a plant shoot towards light. The classic experiments of Charles and Francis Darwin (1880) and later Frits Went (1928) established that a mobile signal – later identified as auxin – is produced in the tip of the coleoptile and diffuses downwards to the elongation zone.

向光性是植物茎朝光源方向弯曲生长的现象。Charles Darwin和Francis Darwin（1880年）以及后来的Frits Went（1928年）通过经典实验证实，一种可移动的信号——后来被鉴定为生长素——在胚芽鞘顶端产生，向下扩散至伸长区。

When unilateral light strikes the coleoptile tip, auxin is redistributed to the shaded side. The resulting higher auxin concentration on that side stimulates faster cell elongation, causing the shoot to bend towards the light. The lateral movement of auxin is driven by the redistribution of PIN efflux carrier proteins under the influence of phototropin photoreceptors.

当单侧光照射胚芽鞘顶端时，生长素被重新分配至背光一侧。该侧较高的生长素浓度刺激细胞更快伸长，导致茎向光弯曲。生长素的侧向运输是由向光素受体影响下PIN输出载体蛋白的重新分布所驱动的。

5. Gravitropism in Shoots and Roots | 茎和根的向地性

Gravitropism allows plants to orientate their growth relative to the gravity vector. In a horizontal root, statoliths (dense amyloplasts) sink to the lower side of root cap cells, triggering a redistribution of auxin. Here, the higher auxin concentration on the lower side inhibits cell elongation, so the upper side grows faster and the root bends downwards.

向地性使植物能够相对于重力矢量定向生长。在水平放置的根中，平衡石（致密的淀粉体）沉降至根冠细胞的下侧，触发生长素的重新分布。此处，下侧较高的生长素浓度抑制细胞伸长，因此上侧生长较快，根向下弯曲。

In shoots, the opposite occurs: accumulation of auxin on the lower side of a horizontal stem promotes elongation, causing the shoot to bend upwards. The differential sensitivity of shoot and root cells to auxin explains this inverse response – likely due to differences in the expression of auxin-responsive genes and downstream signalling components.

在茎中情况相反：水平放置的茎下侧积累的生长素促进伸长，导致茎向上弯曲。茎和根细胞对生长素的敏感性不同，解释了这种相反的反应——这可能与生长素响应基因及下游信号组分的表达差异有关。

6. The Acid Growth Hypothesis | 酸生长假说

The acid growth hypothesis provides a molecular explanation for auxin-induced cell expansion. According to this model, auxin stimulates the activity of plasma membrane H⁺-ATPases, pumping protons into the cell wall space. The drop in apoplastic pH (to around 5.0) activates expansins, which break hydrogen bonds between cellulose microfibrils and hemicellulose, allowing the wall to yield to turgor pressure.

酸生长假说从分子层面解释了生长素诱导的细胞扩张。根据该假说，生长素刺激质膜H⁺-ATP酶的活性，将质子泵入细胞壁空间。质外体pH降至约5.0，激活膨胀素，后者打破纤维素微纤丝与半纤维素之间的氢键，使细胞壁在膨压作用下伸展。

Auxin → H⁺-ATPase activation → cell wall acidification → expansin activity → wall loosening → cell elongation

生长素 → H⁺-ATP酶激活 → 细胞壁酸化 → 膨胀素活化 → 壁松弛 → 细胞伸长

This rapid mechanism does not involve new wall synthesis, explaining how plants can bend within minutes. Over longer periods, auxin also up-regulates the expression of genes involved in wall building and cell division, sustaining growth.

这种快速机制不涉及新的细胞壁合成，这可以解释植物如何在数分钟内弯曲。较长时间尺度上，生长素还会上调参与细胞壁构建和细胞分裂的基因表达，从而维持生长。

7. Gibberellins and Growth | 赤霉素与生长

Gibberellins (GAs) are a large family of diterpenoid compounds that promote stem elongation, especially in dwarf varieties. They exert their effects by triggering the degradation of DELLA repressor proteins. DELLAs normally restrain growth by inhibiting the transcription of genes necessary for cell elongation and division; when GA binds its receptor, DELLAs are tagged with ubiquitin and degraded via the 26S proteasome.

赤霉素（GAs）是一大类二萜化合物，可促进茎的伸长，尤其在矮生品种中效果显著。它们通过引发DELLA抑制蛋白的降解来发挥作用。DELLA蛋白通常通过抑制细胞伸长和分裂所需基因的转录来限制生长；当GA与其受体结合，DELLA就被标记上泛素并经26S蛋白酶体降解。

In seed germination, gibberellins synthesised in the embryo diffuse to the aleurone layer, where they initiate the transcription of α‑amylase. This enzyme hydrolyses starch stored in the endosperm into sugars, fuelling the growing embryo. The classic barley seed half-seed experiment elegantly demonstrated this GA‑dependent amylase induction.

在种子萌发中，胚合成的赤霉素扩散至糊粉层，在那里启动α‑淀粉酶的转录。该酶将胚乳中储存的淀粉水解为糖，为生长中的胚提供能量。经典的大麦半粒种子实验巧妙证明了这种依赖于GA的淀粉酶诱导作用。

8. Abscisic Acid and Stress Responses | 脱落酸与胁迫响应

Abscisic acid (ABA) is often called the ‘stress hormone’ because its concentration rises dramatically under drought, salinity, and cold. Its best‑characterised role is the regulation of stomatal aperture. When soil water becomes limited, roots produce ABA that is transported to the guard cells.

脱落酸（ABA）常被称为“胁迫激素”，因为其在干旱、高盐和寒冷条件下浓度会急剧升高。其被研究得最透彻的功能是调控气孔开度。当土壤水分不足时，根部合成ABA并运至保卫细胞。

ABA binds to receptors on the guard cell plasma membrane, triggering a signalling cascade that leads to the efflux of K⁺ and anions, followed by the osmotic loss of water. The guard cells lose turgor and the stomata close, reducing transpiration. This response can occur within minutes and is essential for plant survival under water deficit.

ABA与保卫细胞质膜上的受体结合，触发信号级联，导致K⁺和阴离子外流，继而水分子渗透性散失。保卫细胞丧失膨压，气孔关闭，蒸腾作用减弱。这一反应可在数分钟内发生，对于植物在缺水条件下的生存至关重要。

ABA also maintains seed dormancy by inhibiting the expression of gibberellin‑induced hydrolytic enzymes, thereby preventing premature germination until conditions become favourable. The ABA/GA ratio is a critical checkpoint for the germination decision.

ABA还通过抑制赤霉素诱导的水解酶表达来维持种子休眠，从而阻止在条件适宜之前过早萌发。ABA/GA比值是决定是否萌发的关键检查点。

9. Ethene and Fruit Ripening | 乙烯与果实成熟

Ethene (C₂H₄) is a gaseous hormone that plays a central role in fruit ripening, leaf abscission, and the triple response of etiolated seedlings. It promotes the conversion of starch to sugars, the breakdown of chlorophyll, and the softening of cell walls by activating enzymes such as pectinase and cellulase.

乙烯（C₂H₄）是一种气体激素，在果实成熟、叶片脱落以及黄化幼苗的三重反应中起核心作用。它通过激活果胶酶和纤维素酶等酶，促进淀粉转化为糖、叶绿素降解以及细胞壁的软化。

Ripening is autocatalytic: a small amount of ethene produced by a mature fruit stimulates further ethene production, leading to a burst of ripening. This is why a single ripe banana can accelerate the ripening of other fruit stored in a confined space. Ethene is widely used commercially to synchronise fruit ripening, for instance in the banana and citrus industries.

果实成熟是自催化的：成熟果实产生的少量乙烯会刺激更多乙烯的合成，导致成熟进程迅速爆发。这就是为什么一只成熟的香蕉能加速密封空间内其他水果的成熟。乙烯在商业上被广泛用于同步催熟，例如香蕉和柑橘产业。

10. Phytochrome and Light Responses | 光敏色素与光反应

Phytochrome is a photoreceptor that enables plants to perceive red and far‑red light. It exists in two photoconvertible forms: Pr (absorbs red light, λ = 660 nm) and Pfr (absorbs far‑red light, λ = 730 nm). Pr is the inactive form synthesised in the dark; upon exposure to red light, Pr is converted to the active Pfr form. Far‑red light reverts Pfr back to Pr, and in darkness Pfr slowly decays back to Pr.

光敏色素是一种使植物能够感知红光和远红光的光受体。它以两种可相互转换的形式存在：Pr（吸收红光，λ = 660 nm）和Pfr（吸收远红光，λ = 730 nm）。Pr是在黑暗中合成的无活性形式；暴露于红光时，Pr转变为活性形式Pfr。远红光使Pfr回复为Pr，而在黑暗中Pfr也会缓慢衰变回Pr。

The ratio of Pfr to total phytochrome tells the plant whether it is in the light or dark and can provide information about canopy shade (low R:FR ratio). Pfr acts as a molecular switch, moving into the nucleus and regulating the transcription of hundreds of genes involved in de‑etiolation, shade avoidance, and flowering.

Pfr占总光敏色素的比例使植物能够知晓自己是处于光下还是黑暗中，并能够提供关于冠层遮阴（低R:FR比值）的信息。Pfr起着分子开关的作用，进入细胞核，调控数百个与去黄化、避阴和开花有关的基因转录。

11. Photoperiodism and Flowering | 光周期与开花

Photoperiodism is the ability to measure day length, allowing plants to flower at the appropriate season. Three main categories are recognised: short‑day plants (SDPs) flower when the night length exceeds a critical duration; long‑day plants (LDPs) flower when nights are short; and day‑neutral plants flower independently of day length.

光周期现象是植物测量日照长度的能力，使其能够在合适的季节开花。主要可分三类：短日植物（SDPs）在夜长超过临界时长时开花；长日植物（LDPs）在夜短时开花；日中性植物开花则不受日照长度影响。

Experiments with interrupted night treatments demonstrated that it is the uninterrupted length of darkness, rather than the length of the light period, that determines the flowering response. A night break with red light prevents flowering in SDPs and promotes flowering in LDPs, and the effect is reversible by far‑red light, confirming phytochrome involvement.

中断暗期的实验表明，决定开花反应的是连续的暗期长度，而非光期长度。红光暗期间断可阻止短日植物开花而促进长日植物开花，且该效应可被远红光逆转，这证实了光敏色素的参与。

In LDPs, Pfr promotes the expression of the FLOWERING LOCUS T (FT) gene in leaves; the FT protein (florigen) is then transported via the phloem to the shoot apical meristem, where it triggers the transition from vegetative to reproductive growth.

在长日植物中，Pfr促进叶片中FLOWERING LOCUS T（FT）基因的表达；FT蛋白（成花素）随后通过韧皮部运输至茎顶端分生组织，在那里启动从营养生长向生殖生长的转换。

12. Commercial Applications of Plant Hormones | 植物激素的商业用途

Understanding plant coordination has led to numerous agricultural and horticultural applications. Synthetic auxins such as 2,4‑D and NAA are widely used as selective herbicides and rooting powders. Gibberellins are applied to delay senescence in citrus fruits and to induce seedless fruit development (parthenocarpy) in grapes. ABA analogues are being explored to reduce water loss in drought‑prone crops.

对植物协调机制的理解催生了众多农业与园艺应用。2,4‑D和NAA等合成生长素被广泛用作选择性除草剂和生根粉。赤霉素被用来延迟柑橘类果实的衰老并诱导葡萄产生无籽果实（单性结实）。脱落酸类似物正被探索用于减少干旱易发区作物的水分损失。

Ethene generators or inhibitors (e.g. 1‑MCP) are used to manage fruit ripening in supply chains. Knowledge of photoperiodism enables precise control of flowering in ornamental plants such as chrysanthemums and poinsettias, ensuring they reach the market exactly when demanded. These examples highlight how basic plant biology translates directly into practical innovation.

乙烯发生剂或抑制剂（如1‑MCP）被用于管理供应链中果实的成熟。对光周期现象的了解使人们能够精确控制菊花和一品红等观赏植物的开花时间，确保其正好在市场需求时上市。这些例子突出了基础植物生物学如何直接转化为实践创新。

Published by TutorHao | Biology Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Control and Coordination in Plants | 植物的调控与协调