Effect of low-level monochromatic radiations on some morphological and physiological parameters of plants

Studying the behavior of living organisms under the action of some physical or chemical factors (corpuscular or electromagnetic radiation, magnetic or electric field, sound waves, salinity, stimulants etc.) is enjoying major interest nowadays.(1,2)) The main goal is to understand the mechanisms of action of these factors on biological tissues, and use this knowledge for applications in biology and medicine. A special place in modern medicine is occupied by the therapeutic applications of laser radiation.

In the current study we are attempting to determine whether the therapeutic lasers used in medicine have the potential to produce changes of some morphological and physiological parameters of plants. If these changes actually occur, the next task is to determine whether they are due to laser action on water used for watering by changing its properties, or by the direct action of laser radiation on the plants cells. Matcrials and Mcthods: We used as samples two groups of wheat seeds, planted in cotton. In the first group we only irradiated irrigation water, while in the second group only plants. We used as sources of radiation lasers and LEDs, with wavelengths between 455 nm and 850 nm. Power density was P = 50 mW/cm(2) for all samples, the exposure time ranged between 1s and 80s, and energy density (or fluence) between 0 and 4J/cm(2). We measured modifications of some morphological and physiological parameters (the biomass quantity, germination rate of seeds, number and height of the seedlings etc.) as a function of fluence.

When only irrigation water was irradiated, we have found for all wavelength used a strong inhibitory effect on germination (between 30% and 50% for samples grown in the ground and between 13% and 40% for those grown in cotton). Regarding the other parameters determined, a stimulating effect, but less pronounced than if the plant was only irradiated, was noticed. When only plant was irradiated, the effects are altered depending on the wavelength and fluence.

Although apparently different, plant and animal cells have some similar characteristics, the differences between them not being essential, involving mainly the quantitative aspect. In these circumstances the study of the monochromatic radiation effects on plants is useful to characterize the action of those radiations on the animal and human tissues. Studies on plants exhibit a series of advantages: they are cheap, easily reproduced and suitable for producing good statistics etc. It can also be verified as to which extent the laws of classic photobiology show modifications when low level lasers are utilized.