Plant Responses to Brief Touching: A Mechanism for Early Neighbour Detection?

Abstract

In natural habitats plants can be exposed to brief and light contact with neighbouring plants. This mechanical stimulus may represent a cue that induces responses to nearby plants. However, little is known about the effect of touching on plant growth and interaction with insect herbivores. To simulate contact between plants, a soft brush was used to apply light and brief mechanical stimuli to terminal leaves of potato Solanum tuberosum L. The number of non-glandular trichomes on the leaf surface was counted on images made by light microscope while glandular trichomes and pavement cells were counted on images made under scanning electronic microscope. Volatile compounds were identified and quantified using coupled gas chromatography–mass spectrometry (GC-MS). Treated plants changed their pattern of biomass distribution; they had lower stem mass fraction and higher branch and leaf mass fraction than untouched plants. Size, weight and number of tubers were not significantly affected. Touching did not cause trichome damage nor change their total number on touched terminal leaves. However, on primary leaves the number of glandular trichomes and pavement cells was significantly increased. Touching altered the volatile emission of treated plants; they released higher quantities of the sesquiterpenes (E)-β-caryophyllene, germacrene D-4-ol and (E)-nerolidol, and lower quantities of the terpenes (E)-ocimene and linalool, indicating a systemic effect of the treatment. The odour of touched plants was significantly less preferred by the aphids Macrosiphum euphorbiae and Myzus persicae compared to odour of untouched plants. The results suggest that light contact may have a potential role in the detection of neighbouring plants and may affect plant-insect interactions.

Aboveground mechanical stimuli affect belowground plant-plant communication

“…Touch is one of the most common mechanical stimuli in higher plants and is known to induce strong morphogenetic changes over time. A recent study has demonstrated that brief touching among neighbouring plants can be used as a cue in the detection of potential competitors [ 22 ]. As plants grow in communities closely associated with other plants, they constantly monitor specific cues that may occur above- or belowground.…”

“…It is believed that canopies of trees stop expanding when they touch canopies of neighbouring trees [ 20 ]. Recent studies have shown that modest touching of leaves can cause changes in the biomass allocation strategy and alter the chemical composition of the emitted compounds [ 21 , 22 ]. Still, it is unknown whether and how aboveground plant-plant communication through mechano-stimuli ( e .…”

The genetics underlying natural variation of plant–plant interactions, a beloved but forgotten member of the family of biotic interactions

“…For example, VOCs produced by damaged sagebrush plants protect neighboring Nicotiana attenuata plants from herbivores (Karban et al, 2014). Soft mechanical stimulation also triggers VOC emission protecting plants from herbivores (Markovic et al, 2016). VOCs emitted by undamaged neighboring plant can also trigger changes in biomass allocation between shoots and roots in focal plants (Ninkovic, 2003).…”

Who is my neighbor? Volatile cues in plant interactions

“…The wide range of interactions between plants in these communities determine species' coexistence and performance, as well as community organization. 1,2 Plants perceive their neighbors through different kinds of cues that indicate their proximity, such as light quality, 3,4 root chemicals, 5,6 acoustic cues, 7 mechanical stimuli 8 , and airborne volatile organic compounds (VOCs). 9 The constantly present chemical cues that plants sense force them to distinguish between essential one predicting competitive neighbors from cues that are not crucial for their own fitness.…”