Specific tropism caused by ultraviolet C radiation in Phycomyces

Area of Science:

• Plant science
• Photobiology
• Mycology

Background:

• Phycomyces blakesleeanus sporangiophores display phototropism, orienting towards blue light and away from ultraviolet C (UV-C) radiation.
• Previous studies indicate complex responses to light stimuli, but the specific mechanisms for UV-C avoidance are not fully elucidated.

Purpose of the Study:

• To investigate the sensory mechanisms underlying ultraviolet (UV) phototropism in Phycomyces blakesleeanus.
• To determine if UV-C avoidance is a modification of blue light phototropism or mediated by a distinct sensory pathway.

Main Methods:

• Isolation and characterization of fifteen ultraviolet-insensitive (uvi) mutants of Phycomyces blakesleeanus.
• Comparative analysis of phototropic responses to blue and UV-C light in wild-type and mutant strains using a computer-aided device.
• Assessment of UV-C absorption properties of sporangiophores.

Main Results:

• Mutants exhibited normal blue light phototropism but impaired UV-C avoidance, indicating a defect in UV sensing.
• Wild-type sporangiophores showed differential turning responses to blue and UV-C light, even with similar energy distributions.
• Mutants displayed reduced or absent responses to weak UV-C stimuli compared to wild-type.

Conclusions:

• Phycomyces blakesleeanus possesses a separate sensory system for ultraviolet radiation detection, distinct from its blue light photoreceptor system.
• UV-C avoidance is not merely a consequence of high UV absorption by sporangiophores but involves specific UV sensory pathways.