Ortega Joseph E, Lesh-Laurie Georgia E, Espinosa Mark A, Ortega Elena L, Manos Steve M, Cunning Melissa D, Olson Jessica C
Department of Mechanical Engineering, Bioengineering Laboratory, Campus Box 112, University of Colorado at Denver, Denver, CO 80217-3364, USA.
Planta. 2003 Feb;216(4):716-22. doi: 10.1007/s00425-002-0946-7. Epub 2002 Nov 22.
An understanding of the relationship between the two components of helical growth (rotation rate and elongation rate) is fundamental to understanding the biophysical and molecular mechanism(s) of cell wall extension in algal cells, fungal cells, and plant stems and roots. Helical growth occurs throughout development of the sporangiophores of Phycomyces blakesleeanus. Previous studies within the growth zone of stage-IVb sporangiophores have reported conflicting conclusions. An implicit assumption in the previous studies [E.S. Castle (1937) J Cell Comp Physiol 9:477-489; R. Cohen and M. Delbruck (1958) J Cell Comp Physiol 52:361-388; J.K.E. Ortega et al. (1974) Plant Physiol 53:485-490] was that the relationship between rotation rate and elongation rate was independent of the magnitude of the elongation rate. In the present study, for stage-IVb sporangiophores growing at a steady rate, it is shown that the ratio of rotation rate and elongation rate decreases as the elongation rate increases. Previously proposed biophysical and molecular mechanisms cannot account for the observed behavior. The previously postulated fibril-reorientation mechanism [J.K.E. Ortega and R.I. Gamow (1974) J Theor Biol 47:317-332; J.K.E. Ortega et al. (1974) Plant Physiol 53:485-490] is modified to accommodate this new finding. Other experiments were conducted to determine how the ratio of rotation rate and elongation rate behaves during a pressure response (a transient decrease in elongation rate produced by a large step-up in turgor pressure using the pressure probe). Results of these experiments indicate that this ratio increases during the pressure response.
了解螺旋生长的两个组成部分（旋转速率和伸长速率）之间的关系，对于理解藻类细胞、真菌细胞以及植物茎和根中细胞壁伸展的生物物理和分子机制至关重要。螺旋生长发生在布氏毛霉孢子囊柄的整个发育过程中。此前在IVb期孢子囊柄生长区的研究得出了相互矛盾的结论。此前研究[E.S. 卡斯尔（1937年）《细胞与比较生理学杂志》9:477 - 489；R. 科恩和M. 德尔布吕克（1958年）《细胞与比较生理学杂志》52:361 - 388；J.K.E. 奥尔特加等人（1974年）《植物生理学》53:485 - 490]中一个隐含的假设是，旋转速率和伸长速率之间的关系与伸长速率的大小无关。在本研究中，对于以稳定速率生长的IVb期孢子囊柄，结果表明旋转速率与伸长速率的比值随着伸长速率的增加而降低。先前提出的生物物理和分子机制无法解释观察到的行为。对先前假定的原纤维重新定向机制[J.K.E. 奥尔特加和R.I. 加莫夫（1974年）《理论生物学杂志》47:317 - 332；J.K.E. 奥尔特加等人（1974年）《植物生理学》53:485 - 490]进行了修改以适应这一新发现。还进行了其他实验来确定在压力响应期间（使用压力探针通过大幅提高膨压产生的伸长速率的瞬时降低）旋转速率与伸长速率的比值如何变化。这些实验结果表明，该比值在压力响应期间会增加。
