The algae Micrasterias with its star-shaped cell pattern is a perfect unicellular model system to study morphogenesis. How the indentations are formed in the primary cell wall at exactly defined areas puzzled scientists for decades, and they searched for chemical differences in the primary wall of the extending tips compared to the resting indents. We now tackled the question by Raman imaging and scanned in situ Micrasterias cells at different stages of development. Thousands of Raman spectra were acquired from the mother cell and the developing semicell to calculate chemical images based on an algorithm finding the most different Raman spectra. Each of those spectra had characteristic Raman bands, which were assigned to molecular vibrations of BaSO₄, proteins, lipids, starch, and plant cell wall carbohydrates. Visualizing the cell wall carbohydrates revealed a cell wall thickening at the indentations of the primary cell wall of the growing semicell and uniplanar orientation of the cellulose microfibrils to the cell surface in the secondary cell wall. Crystalline cellulose dominated in the secondary cell wall spectra, while in the primary cell wall spectra, also xyloglucan and pectin were reflected. Spectral differences between the indent and tip region of the primary cell wall were scarce, but a spectral mixing approach pointed to more cellulose fibrils deposited in the indent region. Therefore, we suggest that cell wall thickening together with a denser network of cellulose microfibrils stiffens the cell wall at the indent and induces different cell wall extensibility to shape the lobes.

具有星形细胞模式的藻类Micrasterias是研究形态发生的完美单细胞模型系统。几十年来，科学家们一直困惑着在精确定义的区域的初级细胞壁上如何形成凹痕，他们寻找延伸尖端的初级壁与静止凹痕相比的化学差异。我们现在通过拉曼成像解决了这个问题，并 在不同发育阶段原位扫描了 Micasterias细胞。从母细胞和发育中的半细胞中获取数千张拉曼光谱，以根据一种算法计算化学图像，找到最不同的拉曼光谱。这些光谱中的每一个都具有特征拉曼谱带，这些谱带被分配给 BaSO _{4的分子振动}、蛋白质、脂质、淀粉和植物细胞壁碳水化合物。可视化细胞壁碳水化合物揭示了在生长的半细胞的初级细胞壁的凹痕处细胞壁增厚和纤维素微纤维单平面取向到次级细胞壁中的细胞表面。结晶纤维素在次生细胞壁光谱中占主导地位，而在初级细胞壁光谱中，木葡聚糖和果胶也被反射。初级细胞壁的凹痕和尖端区域之间的光谱差异很少，但光谱混合方法表明更多的纤维素原纤维沉积在凹痕区域。因此，我们建议细胞壁增厚与更密集的纤维素微纤维网络一起使凹处的细胞壁变硬，并诱导不同的细胞壁延展性形成裂片。