Speed and force of spore ejection in Selaginella martensii

Abstract

Schneller J., Gerber H. and Zuppiger A. 2008. Speed and force of spore ejection in Selaginella martensii. Bot. Helv. 118: 13 -20.Spores of the genus Selaginella are discharged through an ejection mechanism caused by the anatomical differentiation of the sporangium. To understand the evolution of these specialised dispersal mechanisms, it is important to know how effective they are, i.e. what distance is reached by the spores, how rapidly they are ejected, and what forces must be developed by the plants to achieve this speed. Here we present a method to determine these important variables. We observed the spore discharge process for Selaginella martensii using a high-speed camera, which allowed us to resolve the movement to 1/1000 s. The mico-and megasporangia opened slowly, separating into two ovoid valves, which subsequently dried and closed in a sudden, quick movement, ejecting the spores. The distances of spore dispersal were determined by placing single shoots of Selaginella on paper in the laboratory. Microspores reached up to 5 -6 cm from the spore source, while megaspores reached up to 65 cm from the source, with a mean flight distance of 21.3 cm. Based on the flight trajectories observed on the photographs and the mean weight of a megaspore (1.4 mg), we calculated the speed and forces responsible for the ejection mechanism. The speed of the spores at ejection time was 0.6 m/s for microspores, and 4.5 m/s for megaspores. The initial impulse of one megaspore was estimated as 6.3 pNs. A force greater than 7 mN is necessary to accelerate the megaspore in less than 1 ms to this speed. Our new method to determine the impulse and initial speed of Selaginella spores makes possible more detailed studies about the role and function of biological structures responsible for spore ejection.

Shooting Mechanisms in Nature: A Systematic Review

“…A similar pollen dispersal mechanism as those in common ferns is observed in representatives of the genus Selaginella (phylum: Tracheophyta (Lycopodiophyta), class: Lycopodiopsida, order: Selaginellales, family: Selaginellaceae), such as in Selaginella martensii , a spikemoss that is native to Mexico and Central America and in which both microspores and megaspores are actively dispersed [ 96 ]. S .…”

“… a Stored elastic energy: 8.87 J (efficiency of 0.5%) [ 69 ] b Average angular velocity: 69,800 rad/s and peak angular acceleration: 5·10 6 rad/s 2 [ 74 ] c Mean estimated stored energy: 0.482 ± 0.219 J (21.3 ± 10.3% efficiency) [ 75 ] d Initial angular velocity: 200 ± 100 rad/s [ 82 ] e Estimated released elastic energy: 2.72·10 −3 J [ 82 ] f Energy stored in the compressed air: 0.27 mJ [ 1 ] g Indicated values for microspore discharge. Macrospore (mass 0.0014 mg) discharge via drying squeeze catapult with a mean launch velocity of 4.5 m/s and a mean launch distance of 0.21 m (peak 0.65 m) [ 96 ]. The estimated impulse of one macrospore is 6.3 pN·s [ 96 ].…”

“… g Indicated values for microspore discharge. Macrospore (mass 0.0014 mg) discharge via drying squeeze catapult with a mean launch velocity of 4.5 m/s and a mean launch distance of 0.21 m (peak 0.65 m) [ 96 ]. The estimated impulse of one macrospore is 6.3 pN·s [ 96 ].…”

Fern and lycopod spores rain in a cloud forest of Hidalgo, Mexico

“…It is known that leptosporangiate ferns have a specialized spore release mechanism (catapult) that only launches spores under low relative humidity (\60 %) at 10 ms -1 Noblin et al 2012;Poppinga et al 2015;Schneller 1995). In similar way, the sporangium of the genus Selaginella releases spores by a dehydration process (Filipini-De Giorgi et al 1997;Webster 1995;Schneller et al 2008). Thus, the peak of sporulation shown in Table 2 and the dry season preferred sporulation period in Table 3 reflect the spore release mechanism of the sporangium.…”

Ontogenia de los esporangios, formación y citoquímica de esporas en licopodios (Lycopodiaceae) colombianos

“…Las observaciones de esta investigación indican que independientemente de su grado de desarrollo, los engrosamientos de lignina están siempre presentes en las células epidérmicas que forman la pared madura de los esporangios de todos los taxones analizados. Se ha señalado que en helechos leptosporangiados y algunos licófitos heterosporados, estos engrosamientos diferenciales de lignina facilitan la liberación de las esporas actuando a manera de "catapulta", dispersándolas a cierta distancia de la planta madre (Moran, 2004;Noblin et al, 2012;Webster, 1995;Schneller, Gerber & Zuppiger, 2008). En Lycopodiaceae la liberación de las esporas ocurre por la separación de las dos valvas que forman el esporangio y podría estar relacionado con algún tipo de mecanismo fisiológico de colapso celular controlado.…”