Komarov Botanical Institute, St Petersburg, Russia.
Ann Bot. 2019 Jul 8;123(7):1205-1218. doi: 10.1093/aob/mcz027.
Decades of research have attempted to elucidate the underlying developmental mechanisms that give rise to the enormous diversity of pollen and spore exines. The organization of the exine starts with the establishment of an elaborate glycocalyx within which the subsequent accumulation of sporopollenin occurs. Ontogenetic studies using transmission electron microscopy of over 30 species from many different groups have shown that the sequence of structures observed during development of the exine corresponds to the sequence of self-assembling micellar mesophases (including liquid crystals) observed at increasing concentrations of surfactants. This suggested that self-assembly plays an important part in exine pattern determination. Some patterns resembling separate layers of spore and pollen grain walls have been obtained experimentally, in vitro, by self-assembly. However, to firmly establish this idea, columellate and granulate exines, the most widespread forms, needed to be simulated experimentally.
We used our original method, preparing mixtures of substances analogous to those known to occur in the periplasmic space of developing microspores, then leaving the mixtures undisturbed for specific periods of time to allow the process of self-assembly to occur. We developed our method further by using new substances analogous to those present in the periplasmic space and performing the experiments in a thin layer, more closely resembling the dimensions of the periplasmic space.
The artificial microstructures obtained from our in vitro self-assembly experiments closely resembled the main types of exines, including tectate-columellate, granulate, alveolate and structureless, and permitted comparison with both developing and mature microspore walls. Compared with the previous attempts, we managed to simulate columellate and granulate exines, including lamellate endexine.
Our results show that simple physico-chemical interactions are able to generate patterns resembling those found in exines, supporting the idea that exine development in nature involves an interplay between the genome and self-assembly.
几十年来的研究试图阐明导致花粉和孢子外壁巨大多样性的潜在发育机制。外壁的组织始于在其中发生随后的孢子外壁物质积累的精细糖萼的建立。使用来自许多不同组的超过 30 种物种的透射电子显微镜的个体发生研究表明，在发育过程中观察到的结构序列对应于在表面活性剂浓度增加时观察到的自组装胶束中间相（包括液晶）的序列。这表明自组装在外壁图案确定中起着重要作用。一些类似孢子和花粉粒壁的单独层的图案已经通过自组装在实验中、体外获得。然而，为了牢固地确立这个想法，需要在实验中模拟柱状和粒状外壁，这是最广泛的形式。
我们使用我们的原始方法，制备类似于已知在发育小孢子质周腔中存在的物质的混合物，然后让混合物在特定时间段内不受干扰，以允许自组装过程发生。我们通过使用类似于质周腔中存在的物质的新物质进一步发展了我们的方法，并在更接近质周腔尺寸的薄层中进行实验。
从我们的体外自组装实验中获得的人工微结构与主要的外壁类型非常相似，包括有层纹的柱状外壁、粒状外壁、泡状外壁和无结构外壁，并允许与正在发育和成熟的小孢子壁进行比较。与以前的尝试相比，我们设法模拟了柱状和粒状外壁，包括板层状的内外壁。
我们的结果表明，简单的物理化学相互作用能够产生类似于外壁中发现的图案，支持这样的观点，即自然界中外壁的发育涉及基因组和自组装之间的相互作用。
