Komarov Botanical Institute of Russian Academy of Sciences, Popov St. 2, St. Petersburg, 197376, Russia.
Planta. 2017 Sep;246(3):471-493. doi: 10.1007/s00425-017-2702-z. Epub 2017 May 5.
Our findings suggest a new approach to pollen ontogenetic investigations, entailing consideration of physical factors, which enable a better understanding of exine developmental processes. The sporopollenin-containing part of the pollen wall-the exine-is one of the most complex cell walls in plants. By tracing each stage of microspore development in Larix decidua with TEM, we aimed to understand the underlying mechanisms of its exine establishment. Our hypothesis is that self-assembly interferes with exine development. Our specific aim is to generate experimental simulations of the exine developmental pattern. The sequence of events leading to exine development includes the appearance of spherical units in the periplasmic space, their rearrangement into radial columns, and the appearance of white-lined endexine lamellae. The final accumulation of sporopollenin proceeds in the post-tetrad period. The sequence of self-assembling micellar mesophases corresponds with that of the developmental events: spherical micelles; columns of spherical micelles; and laminate micelles separated by strata of water and visible as white-lined lamellae in TEM. Several patterns, simulating structures at different stages of exine development in Larix, were obtained from in vitro experiments. Purely physicochemical processes of self-assembly, which are not under direct genetic control, play an important role in exine development and share control with the genome. These findings suggest that a new approach to ontogenetic investigations, entailing consideration of physical factors (e.g., cell tensegrity), is required for a better understanding of developmental processes.
我们的研究结果表明，需要考虑物理因素来研究花粉个体发生，这将有助于更好地理解外壁发育过程。花粉壁中含有孢粉素的部分——外壁，是植物中最复杂的细胞壁之一。通过在 TEM 下追踪落叶松花粉小孢子发育的各个阶段，我们旨在了解其外壁建立的潜在机制。我们的假设是，自组装会干扰外壁的发育。我们的具体目标是生成外壁发育模式的实验模拟。导致外壁发育的事件序列包括质膜空间中出现球形单元、它们在径向柱中的重新排列，以及出现白线内外壁薄片。最后，在四分体后时期进行孢粉素的积累。自组装胶束中间相的顺序与发育事件的顺序相对应：球形胶束；球形胶束柱；以及由水层和 TEM 中可见的白线状层隔开的层状胶束。从体外实验中获得了几种模拟落叶松外壁发育不同阶段结构的模式。纯粹的物理化学自组装过程，不受直接遗传控制，在外壁发育中起着重要作用，并与基因组共享控制。这些发现表明，需要考虑物理因素（例如，细胞整体性）的新个体发生研究方法，对于更好地理解发育过程是必要的。
