Age Effects on Hypocotyl Mechanics.

Friederike Saxe,Michaela Eder,Jan Lisec,Antje Reinecke,Susann Weichold,Lutz Neumetzler,Anett Döring,Ingo Burgert,Sara Amancio

doi:10.1371/journal.pone.0167808

Abstract

Numerous studies deal with composition and molecular processes involved in primary cell wall formation and alteration in Arabidopsis. However, it still remains difficult to assess the relation between physiological properties and mechanical function at the cell wall level. The thin and fragile structure of primary cell walls and their large biological variability, partly related to structural changes during growth, make mechanical experiments challenging. Since, to the best of our knowledge, there is no reliable data in the literature about how the properties of the fully elongated zone of hypocotyls change with age. We studied in a series of experiments on two different seed batches the tensile properties the region below the growth zone of 4 to 7 day old etiolated Arabidopsis hypocotyls. Additionally, we analysed geometrical parameters, hypocotyl density and cellulose content as individual traits and their relation to tissue mechanics. No significant differences of the mechanical parameters of the non-growing region between 5–7 day old plants could be found whereas in 4 day old plants both tensile stiffness and ultimate tensile stress were significantly lower than in the older plants. Furthermore hypocotyl diameters and densities remain almost the same for 5, 6 and 7 day old seedlings. Naturally, hypocotyl lengths increase with age. The evaluation whether the choice–age or length—influences the mechanical properties showed that both are equally applicable sampling parameters. Additionally, our detailed study allows for the estimation of biological variability, connections between mechanics and hypocotyl age could be established and complement the knowledge on biochemistry and genetics affecting primary plant cell wall growth. The application of two different micromechanical devices for testing living Arabidopsis hypocotyls allows for emphasizing and discussing experimental limitations and for presenting a wide range of possibilities to address current and future questions related to plant cell wall mechanics, synthesis and growth in combination with molecular biology methodologies.

Highlights

The plant cell wall directs and determines plant cell and organ shape and provides mechanical stability despite other functions like the defence against pathogens, protection against dehydration and cell-cell-interactions
We studied the mechanical behaviour during tension of the lower part of 4, 5, 6 and 7 day old etiolated Arabidopsis hypocotyls with two different experimental setups
To exclude the possibility that deviations in cross-section occurred due to variations in growth conditions, 4 day old plants were grown in the following alterations of the growth conditions compared to the standard conditions: a) less medium, b) addition of 10 ml of water to the standard medium on each plate, c) an increase in growth temperature from 22 ̊C to 26 ̊C and d) a combination of an increase in temperature and additional water (Fig 3)

Summary

Introduction

The plant cell wall directs and determines plant cell and organ shape and provides mechanical stability despite other functions like the defence against pathogens, protection against dehydration and cell-cell-interactions. If grown in the dark, the seedlings become etiolated and have the shape of long and slender cylinders without significant cell division or differentiation during growth [5] Due to this geometry, the hypocotyls are experimentally well accessible for structural and mechanical investigations. The highly active and dynamic field of molecular biology creates numerous Arabidopsis thaliana mutants with various changes in cell wall composition and structure [6]. These mutants are of high value for further studies to explore the impact of alterations on structure, which directly affect mechanical properties [2, 7,8,9,10]

Results

Discussion

Conclusion