The laser microbeam trap as an optical tool for living cells.

Pulsed ultraviolet lasers coupled into a microscope can be used for micromanipulation of cells and subcellular structures. In addition, continuous infrared lasers can be used as ultrafine optical tweezers (or synonymously: optical trap). The pulsed UV lasers (for example excimer lasers or nitrogen lasers) can be used as optical scalpels for the preparation of protoplasts from plant root hairs. The precise microdissection of chromosomes with the laser microbeam provides access to chromosome segments where a specific gene is supported to be localized. From such segments, specific DNA libraries can be prepared for the search after such genes or markers in their environment. With the optical trap contact between effector cells of the immune system and their target cells can be established in a very simple and gentle way. The kinetics of the attack of a natural killer on an erythroleukemia cell can be studied from the first seconds after contact. Isolated plant cells as well as cells in a plant embryo tissue can be perforated and DNA or fluorescent molecules can be injected. From the temperature dependence of laser induced membrane lesions one can obtain predictions on laser induced cell fusion, which can be performed at slightly modified irradiation conditions under total microscopic control. Since focusing into the depth of a cell with an accuracy of better than a micrometer is possible, one can work on subcellular structures in the interior of a cell without opening it. For example, in rapeseed protoplasts subcellular structures such as mitochondria or chloroplasts can be perforated or moved out of their original position. Interestingly, such structures find their way back into the original position after the laser is switched off. From their speed one can obtain estimates on intracellular viscoelasticity.