Munoz Cindy M, Ortega Joseph K E
Department of Mechanical Engineering University of Colorado Denver Denver Colorado.
Plant Direct. 2019 Dec 27;3(12):e00195. doi: 10.1002/pld3.195. eCollection 2019 Dec.
The sporangiophores of are large cylindrical aerial cells that elongate vertically at rates between 10 μm/min and 60 μm/min. Wild-type sporangiophores grow toward light, opposed to gravitational acceleration and away from solid barriers (tropic responses). Sporangiophores of stiff mutants C149 and C216 exhibit diminished tropic (bending) responses. Originally, it was thought that the altered genes affect the "stiffness" (elastic wall deformation) of the cell wall. Subsequent investigations employing the pressure probe demonstrated that the irreversible (plastic) wall deformation was smaller for the stiff mutants compared to wild type and could account for the diminished tropic responses. However, it was not shown whether the elastic wall deformation was altered in these stiff mutants. Recent theoretical studies have identified dimensionless numbers that can be used to quantitate the magnitudes of biophysical processes involved in expansive growth of walled cells. In this study, dimensionless numbers are used to determine the magnitudes of elastic deformation rate, plastic deformation rate, and stress relaxation rate of the cell wall during expansive growth of the stiff mutant sporangiophores. It is found that the altered genes reduce stress relaxation rates and plastic deformation rates of the wall, but do not significantly alter the magnitude of the elastic deformation rates of the wall. These results indicate that the mutant genes reduce wall loosening chemistry in these sporangiophores and the genetic mutation is not expressed in a change in "wall stiffness," but in "wall viscosity" or "wall extensibility."
的孢子囊梗是大型圆柱形气生细胞，以10μm/分钟至60μm/分钟的速率垂直伸长。野生型孢子囊梗向光生长，与重力加速度方向相反且远离固体障碍物（向性反应）。刚性突变体C149和C216的孢子囊梗表现出减弱的向性（弯曲）反应。最初，人们认为基因改变影响了细胞壁的“刚性”（弹性壁变形）。随后使用压力探针进行的研究表明，与野生型相比，刚性突变体的不可逆（塑性）壁变形较小，这可以解释向性反应减弱的原因。然而，并未表明这些刚性突变体的弹性壁变形是否发生了改变。最近的理论研究确定了无量纲数，可用于量化有壁细胞膨胀生长过程中涉及的生物物理过程的大小。在本研究中，无量纲数用于确定刚性突变体孢子囊梗膨胀生长过程中细胞壁的弹性变形率、塑性变形率和应力松弛率的大小。研究发现，改变的基因降低了细胞壁的应力松弛率和塑性变形率，但并未显著改变细胞壁弹性变形率的大小。这些结果表明，突变基因降低了这些孢子囊梗中细胞壁的松弛化学作用，并且基因突变并非表现在“壁刚性”的变化上，而是表现在“壁粘度”或“壁伸展性”的变化上。
