Tropisms in Phycomyces: sine law for gravitropism, exponential law for photogravitropic equilibrium

• Published in: Planta Vol. 214; no. 6; pp. 931 - 938
• Main Authors: Galland, P., Wallacher, Y., Finger, H., Hannappel, M., Tröster, S., Bold, E., Grolig, F.
• Format: Journal Article
• Language: English
• Published: Berlin Springer-Verlag 01-04-2002; Springer
• Subjects: Action of physical and chemical agents; Albinism; Bending; Biological and medical sciences; Earth gravitation; Fluence; Fundamental and applied biological sciences. Psychology; Gravitropism; Gravitropism - physiology; Gravity Sensing - physiology; Gravity Sensing - radiation effects; Irradiation; Law of sines; Light; Microbiology; Models, Biological; Movements; Mycology; Phototropism; Phototropism - physiology; Phycomyces; Phycomyces - physiology; Phycomyces - radiation effects; Plant physiology and development; Plant Structures - physiology; Plant Structures - radiation effects; Signal Transduction - radiation effects; Sine function; Space life sciences; Tropism; Light effect; Phycomycetes; Phototropism; Phycomyces blakesleeanus; Sporangiophore; Equilibrium; Exponential function; Fungi; Tilt angle; Light; Trigonometric function; Gravitropism; Statolith; Thallophyta
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-001-0705-1

Sporangiophores of Phycomyces blakesleeanus that are gravitropically stimulated by inclining them relative to the earth's gravitational vector obey the sine law for inclination angles between 0° and 150°. The quantitative relation between gravitropism and phototropism was analyzed for sporangiophores that were kept in balance between opposing gravitational and phototropic stimuli. The gravitropism of inclined sporangiophores was compensated with unilateral light impinging at right angles relative to the axis of the sporangiophore. The fluence rate of unilateral blue light (466 nm) that was required to counteract the negative gravitropism increased exponentially with the sine of the inclination angle of the sporangiophore. The establishment of photogravitropic equilibrium during continuous unilateral irradiation is thus determined by two different laws: the well-known sine law for gravitropism and a novel exponential law of phototropism described in this work. Furthermore, the specific form of the exponential relationship depends on the presence of statoliths (vacuolar protein crystals) and on wavelength.