Feeling the force: how pollen tubes deal with obstacles

Abstract

these authors contributed equally to this work † Correspondence to: grossnik@botinst.uzh.ch, +41 44 634 82 40; bnelson@ethz.ch, +41 44 632 55 29 Number of figures: 5 (all in color) Word count: 3627 Number of supplementary videos: 2 2 Highlight 1Pollen tubes literally feel their way through their environment to avoid obstacles as they deliver male 2 gametes to the ovule. We measured their force sensitivity to understand this remarkable behavior. 3 Abstract 4 Physical forces are involved in the regulation of plant development and morphogenesis by translating 5 mechanical stress into the modification of physiological processes, which, in turn, can affect cellular 6

A role for diacylglycerol kinase 4 in signalling crosstalk during Arabidopsis pollen tube growth

“…Geitmann and co‐workers have reported that cellular stiffness is important for apical tip growth (Zerzour et al ., ) and that both the force exerted to penetrate the transmitting tissue and the responsiveness of the pollen tube to a tropic trigger involves the actin cytoskeleton (Gossot & Geitmann, ; Bou Daher & Geitmann, ). It has just been reported that pollen tubes have a perceptive force threshold, and when facing a barrier in their growth path they have a five‐stage response corresponding to contact, perception, adaptation, penetration and emergence (Burri et al ., ). Importantly, our AFM measurements support such findings.…”

Nano‐engineering pollination

“…How does the growing tip sense obstacles and navigate through the sporophyte tissue? Burri et al . begin to define techniques for developing a realistic interactive system for understanding cell navigation and penetration. The pollen tubes were grown through channels to an exit where the growing tip contacted a force sensing plate.…”

“…Burri et al . are mapping out new techniques to create a realistic growth system that provides direct quantitative details of the sensed forces and the growth response. With the advent of Lab‐on‐a‐Chip techniques coupled with force‐sensing, new avenues of research into cell growth and obstacle sensing become possible.…”

“…Scientists have not yet nano‐engineered pollination or tip growth – the driving force behind successful pollination in higher plants – but they are getting close. In this issue of New Phytologist , Burri et al . (pp. 187–195) describe a novel Lab‐on‐a‐Chip setup that is coupled with a capacitative force sensor with microNewton resolution to monitor the forces that growing pollen tips sense, and respond to, as they navigate obstacles.…”

Durotropic Growth of Pollen Tubes

“…The maximum (or stalling) force that a growing pollen tube can generate to overcome the mechanical resistance restricting its expansion within pistil tissues is determined by the product of the hydrostatic turgor pressure and the cross sectional area of the tube at its tip. Maximum forces generated by L. longiflorum tubes measured with capacitive force sensors (Burri et al, 2018) were found to be in the range of 9.6±1.6 µN, whereas forces generated by Camellia japonica pollen tubes measured with soft microcantilevers (Ghanbari et al, 2018) were found to be around 1.5 µN. However, direct force measurements using capacitive force sensors or micro-cantilevers are technically highly demanding (Agudelo et al, 2013;Ghanbari et al, 2014;Sanati Nezhad et al, 2014).…”