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小麦花药发育的形态学观察及发育时期判定
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明确和准确判断小麦花药发育的不同时期对研究小麦花药或花粉发育至关重要。今天和大家一块分享一篇刚发表在Frontiers in Plant Science上的文章：Anther Morphological Development and Stage Determination in Triticum aestivum (doi: 10.3389/fpls.2018.00228) 该文章将小麦花药发育的整个过程分为15个时期，并且研究了叶环距、穗长、小花长度、花药长度和宽度与花药发育不同时期的相关性。研究发现叶环距和和穗长可以作为不同花药发育时期的快速鉴定指标，而花药长度可进一步对不同的发育时期进行精准鉴定。另外，小麦花药发育到四分体末期和小孢子产生的早期（第8-9期），绒毡层开始出现PCD（programmed cell death），并一致持续到第11期（ vacuolate pollen stage）。小麦绒毡层细胞的PCD与水稻相比开始稍晚，但比拟南芥要早两个时期。
小麦花药发育15个不同时期的界定及形态徐特点可以参见下表（左划可看全文）：
| Stage | Stage name | Description |
| 1 | Stamen primordia stage | Anther is round or oval, with epidermis clear. Inner tissue comprised of primordial cells with little or no differentiation. |
| 2 | Archesporial stage | Anther becomes oval in shape. Archesporial tissue begins to form the connective tissue to separate the theca of the anther. |
| 3 | Sporogenous tissue stage | Four independent lobes begin to form, with parietal and sporogenous tissue present at corners of anther. Vascular region begins to form. |
| 4 | Lobe formation stage | Four lobes are separate and clearly defined, each containing an endothecium and middle layer. Sporogenous tissue is still present. Vascular tissue is more highly developed. |
| 5 | Pre-callose stage | Tapetal layer is present around the locules. Upper and lower locules separate at the stomium region and maintain distinct epidermal layers. |
| 6 | Central callose stage | Tapetal cells grow larger as tapetum becomes complete and uniform. Microspore Mother Cells form from sporogenous tissue. Callose is visible in the center of the locules, encasing the MMCs. |
| 7 | Meiotic stage | MMCs begin to undergo meiosis as the tapetum continues to grow and vacuolate. Anther size increases and meiotic microspores move to wall of tapetum, leaving a hollow region in the center of the locules. Meiotic cells exhibit globular shape as they move toward tapetal wall. |
| 8 | Tetrad stage | Meiotic cells break apart to form tetrads. Middle layer begins to be crushed between tapetum and outer layers. |
| 9 | Young microspore stage | Callose wall surrounding tetrads degrades and tetrads are released as young microspores. Middle layer is barely present and tapetum is at its largest and most swollen size. Young microspores are loose within the locules. |
| 10 | Vacuolate microspore stage | Microspores become vacuolate and press into tapetal wall. An exine layer begins to develop on the now vacuolate microspores. Orbicules are visible between tapetum and microspores at high magnification. Tapetum begins to reduce in size as anther grows larger. |
| 11 | Vacuolate pollen stage | Microspores grow larger and more spherical, becoming multi-nucleate. Two nuclei are visible in microspores. Tapetal layer is thinner and uneven as tapetal degeneration is at its peak. |
| 12 | 3-nucleate pollen stage | Pollen grains become round and starch filled. Gametes develop within pollen grains. Tapetum is very minimal or completely gone. The anther is at its largest point. |
| 13 | Bilocular stage | Pollen grains dehydrate and contract. The septal region separating the upper and lower locules degrades, causing the anther to become bilocular. |
| 14 | Dehiscence | Epidermal cells at stomium region degrade, causing locules to open and the now mature pollen grains to be released. |
| 15 | Senescence | Pollen continues to be released as the anther becomes brittle and degrades. Eventually the senescing anther will release from the filament and fall from the flower. |
作者同时研究了叶环距（auricle distance）、穗长（spike length）、小花长度（spikelet length）、花药长度（anther length）和宽度（anther width）五个指标与花药发育时期之间的相关性。每个指标的定义可参见下图：
简单概括一下（具体细节可以参见原文）：
叶环距：由于不同材料之间的株高差异较大，相应地叶环距（旗叶叶耳到倒二叶叶耳的距离）的变化也就较大，在同一材料中叶环距的大小与花药发育时期的线性关系较好，可用于同一品种内花药发育时期的鉴定，但其绝对长度并不适合株高差异明显的不同材料之间的判断。
花药长度：在花药发育的第4-10期，花药长度可以作为一个相对准确的参数来确定不同品种的发育时期，但在花药发育的后期准确性下降。
花药宽度：在花药发育的第8-10期，花药宽度变化并不明显（停止变宽），因此并不适合作为花药发育时期的判断指标。
穗长和小花长度：除了花药发育的第8和第9期之外，穗长和小花长度在第4-12期基本是线性增加的，但在不同品种中又存在差异，因此可以作为同一品种内部花药发育时期判定的指标。
这篇文章应该是首次对小麦花药发育的不同时期进行了全面而详细的定义和介绍，并给我们提供了一个相对准确地判断花药发育时期的方法：我们可以通过花药的长度对某个材料的发育阶段进行判断，不同材料之间花药绝对长度的变化不明显；叶环距和穗长在同一材料内部还是与花药发育阶段有较好的相关性，是一个简单有效地判断指标，但在评价之前需要提前建立一个标准。
https://blog.sciencenet.cn/blog-1094241-1101740.html
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