Acclimation kinetics of physiological and molecular responses of plants to multiple mechanical loadings

Abstract

During their development, plants are subjected to repeated and fluctuating wind loads, an environmental factor predicted to increase in importance by scenarios of global climatic change. Notwithstanding the importance of wind stress on plant growth and development, little is known about plant acclimation to the bending stresses imposed by repeated winds. The time-course of acclimation of young poplars (Populus tremula L.xP. alba L.) to multiple stem bendings is studied here by following diameter growth and the expression of four genes PtaZFP2, PtaTCH2, PtaTCH4, and PtaACS6, previously described to be involved in the mechanical signalling transduction pathway. Young trees were submitted either to one transient bending per day for several days or to two bendings, 1-14 days apart. A diminution of molecular responses to subsequent bending was observed as soon as a second bending was applied. The minimum rest periods between two successive loadings necessary to recover a response similar to that observed after a single bending, were 7 days and 5 days for growth and molecular responses, respectively. Taken together, our results show a desensitization period of a few days after a single transitory bending, indicating a day-scale acclimation of sensitivity to the type of wind conditions plants experience in their specific environment. This work establishes the basic kinetics of acclimation to low bending frequency and these kinetic analyses will serve as the basis of ongoing work to investigate the molecular mechanisms involved. Future research will also concern plant acclimation to higher wind frequencies.

Forest trees filter chronic wind‐signals to acclimate to high winds

“…For all of the artificial bending treatments, trees were bent once per day, on Monday, Tuesday and Wednesday during the 6 wk from 16 June 2014 to 24 July 2014 (as this sequence was shown to lead to maximal sensitivity of trees to bending by reducing accommodative desensitization, Martin et al, 2010). The trees were previously attached at the crown base with a rope that was pulled manually or with a winch.…”

“…Very few reports are available on the filtering of recurrent bending deformations, all involving simplified artificial loads. It is striking, however, that Martin et al (2010), in a controlled study in poplars, observed that their young plants also filtered out a daily mechanical stimulus (after an initial 'training period').…”

To respond or not to respond, the recurring question in plant mechanosensitivity

“…As soon as 1 h after the first stimulation, a second touch was less effective in inducing ACS6 expression, a gene encoding 1-aminocyclopropane-1-carboxylic acid (ACC) synthase enzyme ( Figure 1A ). In the conditions described above after the second bending of the poplar stem, about seven days without any bending stimulus were necessary to recover the full capacity for induction of gene expression ( Figure 1A , Martin et al, 2010), suggesting that this state of desensitization to mechanical loads lasts for several days. Such desenzitisation was also observed in case of the typical defensive leaf-folding reflex of Mimosa plants (Gagliano et al, 2014).…”

“…In poplar, controlled stem flexing at a sub-saturation level was coupled with kinetics analyses of the responses to each successive bending. The result was a rapid reduction in responsiveness of both radial growth and gene expression (Martin et al, 2010). In particular, these experiments showed that the second bending, 24 h after the first, was markedly weaker in inducing four early mechanoresponsive genes encoding, respectively, two calmodulins, a C2H2 transcription factor ( Figure 1A ) and a xyloglucan endotransglycosylase.…”

Responses to environmental stresses in woody plants: key to survive and longevity

“…Overexpression of the PeSCL7 gene in transgenic Arabidopsis plants showed improved tolerance to drought and salt stresses (Ma et al 2010). Martin et al (2010) analyzed the mechanical stress with repeated via wind loads, and identified the zinc-finger type transcription factor ZFP2 as the bending signal inducible factor. They found increased diameter growth after the repeated bending stress.…”