拟南芥花萼尖端褶皱现象的测量和分析

The measurement and analysis and of the surface wrinkling of the calyx tip in Arabidopsis thaliana

宏观褶皱现象在自然界普遍存在,但是在生物微观世界却鲜有报道。本文对不同生长阶段的拟南芥花萼进行观测,在其外表皮尖端细胞层面发现了微观褶皱现象;利用原子力显微镜和扫描电镜对该区域褶皱的几何形貌和力学性能进行测量,得到花萼尖端区域细胞的杨氏模量为131.1kPa,原生质体细胞的弹性模量为37.53kPa,褶皱的特征长度为572.4nm,细胞壁壁厚为85.03nm。上述实验结果与硬膜-软基底的褶皱方程相吻合。我们猜测是由于花萼外表皮细胞生长较快,造成面内细胞彼此挤压,所以产生了压应力。当压应力达到一定阈值时,细胞为释放应力而产生面外位移,形成了褶皱。通过理论计算得出花萼尖端细胞发生褶皱的临界应力为32.54~39.48kPa,而其下方未发生褶皱区域的临界应力为43.27~52.51kPa,因此,我们推测花萼面内应力为40kPa。

Surface wrinkling is a common phenomenon in the macrocosm of organisms.However,it is rarely reported in the microcosms.We identified the subcellular wrinkling on the surface of the sepal cells of Arabidopsis thaliana.We characterized the morphology and mechanical properties of the wrinkles at different growth stages.The Young′s modulus of the tip of the flower bud was 131.1 kPa.The elastic modulus of the protoplast cells was 37.53 kPa.The cell wall thickness was 85.03 nm.The wrinkle wavelength was 572.4 nm.These quantities are consistent with the buckling equation for hard film on soft matrix.We determined that the critical stress of surface wrinkling of calyx tip was between 32.54 kPa and 39.48 kPa whereas that in the region under the calyx tip was between 43.27 kPa and 52.51 kPa.Therefore,the in-plane stress of the smooth region under the calyx tip was about 40 kPa,below the critical stress.As for the underlying mechanism of the formation of the wrinkles,we hypothesized the relatively fast growth of the outer epidermal cells of the calyx might lead to a compression in the epidermis and consequently generates periodic wrinkles.The strain energy could be released once the wrinkles formed,which helps to maintain the structural integrity of the calyx and avoid catastrophic structural failure.This energy release has remarkable significance for plant growth.