Centre for Plant Integrative Biology, University of Nottingham, Sutton Bonington LE12 5RD, United Kingdom.
Proc Natl Acad Sci U S A. 2012 Mar 20;109(12):4668-73. doi: 10.1073/pnas.1201498109. Epub 2012 Mar 5.
Gravity profoundly influences plant growth and development. Plants respond to changes in orientation by using gravitropic responses to modify their growth. Cholodny and Went hypothesized over 80 years ago that plants bend in response to a gravity stimulus by generating a lateral gradient of a growth regulator at an organ's apex, later found to be auxin. Auxin regulates root growth by targeting Aux/IAA repressor proteins for degradation. We used an Aux/IAA-based reporter, domain II (DII)-VENUS, in conjunction with a mathematical model to quantify auxin redistribution following a gravity stimulus. Our multidisciplinary approach revealed that auxin is rapidly redistributed to the lower side of the root within minutes of a 90° gravity stimulus. Unexpectedly, auxin asymmetry was rapidly lost as bending root tips reached an angle of 40° to the horizontal. We hypothesize roots use a "tipping point" mechanism that operates to reverse the asymmetric auxin flow at the midpoint of root bending. These mechanistic insights illustrate the scientific value of developing quantitative reporters such as DII-VENUS in conjunction with parameterized mathematical models to provide high-resolution kinetics of hormone redistribution.
重力对植物的生长和发育有深远的影响。植物通过向性反应来感知方向的变化，并以此来改变生长。80 多年前，Cholodny 和 Went 假设植物在对重力刺激做出反应时，通过在器官的顶端产生生长调节剂的侧向梯度来弯曲，后来发现这种调节剂是生长素。生长素通过靶向Aux/IAA 抑制蛋白的降解来调节根的生长。我们使用基于 Aux/IAA 的报告基因 DII-VENUS，并结合数学模型来定量分析重力刺激后生长素的重新分布。我们的多学科方法揭示了生长素在 90°重力刺激后几分钟内迅速分布到根的下侧。出乎意料的是，当弯曲的根尖达到与水平方向成 40°的角度时，生长素的不对称性迅速消失。我们假设根使用“临界点”机制来逆转根弯曲中点的不对称生长素流动。这些机制上的见解说明了开发定量报告基因（如 DII-VENUS）与参数化数学模型相结合以提供激素重新分布的高分辨率动力学的科学价值。
