Sensitive, real-time monitoring of UV-induced stress in a single, live plant cell using an optical trap

An optical trap is used to monitor bio-deleterious effects induced by ultra-violet (UV) radiation in a single, live cell. When placed in a laser optical trap, Chlamydomonas reinhardtii cells undergo rotation because of the interplay of flagellar-based forces and optical forces generated by the laser light. Such rotation is sustained by the trapped cell's flagellar action, thereby unveiling a robust and quantitative cellular assay for flagellar function. UV induces flagellar damage, leading to dose-dependent attenuation of cellular rotation. At UV doses larger than ∼9 J m−2 rotational motion ceases. The ability of the cell to rotate in an optical trap is, therefore, a measure of the damage response of the cell. By monitoring cell rotation, we can quantify UV damage with high sensitivity, at threshold doses as low as 2 J m−2. Apart from the capability of UV-damage detection, our rotation assay is also sensitive to the cellular protective responses against such damage. To illustrate this additional facet, we quantify the efficacy of ascorbic acid in combating the UV-damage response of individual cells. Upon addition of this antioxidant, there is no cessation of rotations for doses as high as 25 J m−2. This represents the first single-cell sensor that robustly quantifies a complex pleiotropic cellular response.