Satomi Ishizaki

Kin recognition affects plant communication and defence

The ability of many animals to recognize kin has allowed them to evolve diverse cooperative behaviours; such ability is less well studied for plants. Many plants, including Artemisia tridentata, have been found to respond to volatile cues emitted by experimentally wounded neighbours to increase levels of resistance to herbivory. We report that this communication was more effective among A. tridentata plants that were more closely related based on microsatellite markers. Plants in the field that received cues from experimentally clipped close relatives experienced less leaf herbivory over the growing season than those that received cues from clipped neighbours that were more distantly related. These results indicate that plants can respond differently to cues from kin, making it less likely that emitters will aid strangers and making it more likely that receivers will respond to cues from relatives. More effective defence adds to a growing list of favourable consequences of kin recognition for plants.

Deciphering the language of plant communication: volatile chemotypes of sagebrush

Volatile communication between sagebrush (Artemisia tridentata) individuals has been found previously to reduce herbivory and to be more effective between individuals that are genetically identical or related relative to between strangers. The chemical nature of the cues involved in volatile communication remains unknown for this and other systems. We collected headspace volatiles from sagebrush plants in the field and analyzed these using GC-MS. Volatile profiles were highly variable among individuals, but most individuals could be characterized as belonging to one of two chemotypes, dominated by either thujone or camphor. Analyses of parents and offspring revealed that chemotypes were highly heritable. The ecological significance of chemotypes and the genetic mechanisms that control them remain poorly understood. However, we found that individuals of the same chemotype communicated more effectively and experienced less herbivory than individuals of differing chemotypes. Plants may use chemotypes to distinguish relatives from strangers.

An Air Transfer Experiment Confirms the Role of Volatile Cues in Communication between Plants

Previous studies reported that sagebrush plants near experimentally clipped neighbors experienced less herbivory than did plants near unclipped neighbors. Blocking air flow with plastic bags made this effect undetectable. However, some scientists remained skeptical about the possibility of volatile communication between plants since the existence and identity of a cue that operates in nature have never been demonstrated. We conducted an air transfer experiment that collected air from the headspace of an experimentally clipped donor plant and delivered it to the headspace of an unclipped assay plant. We found that assay plants treated with air from clipped donors were less likely to be damaged by naturally occurring herbivores in a field experiment. This simple air transfer experiment fulfills the most critical of Koch’s postulates and provides more definitive evidence for volatile communication between plants. It also provides an inexpensive experimental protocol that can be used to screen plants for interplant communication in the field.

Plant communication – why should plants emit volatile cues?

Abstract There are now approximately 10 documented examples of volatile plant communication that affect resistance to herbivores. For several of these cases, plants have been found to experience fitness benefits by responding to information (cues) released by experimentally damaged neighbors. However, it remains puzzling why plants might emit these cues following herbivore attack. One possibility is that release of cues is not adaptive for the emitter but rather cues leak out as a consequence of damage. Hypothetical benefits of emitting cues include: repelling herbivores; attracting predators of herbivores; suppressing germination of competitors; communicating with other branches of the same plant; and communicating with genetic relatives. Progress will be made in this field if we can find a system that is more tractable, allowing the nature of the cue to be identified and manipulated or allowing us to examine genetic constraints and influences on communication.

Plant age, seasonality, and plant communication in sagebrush

Abstract Plants progress through a series of distinct stages during development and plant developmental phases link with changing seasons through a year. Recent work indicated that many plants activate systemic-induced resistance after herbivore attack, although the role of both plant ontogeny and seasonal variation in resistance against herbivores has not been a focus of this work. We previously reported that sagebrush become more resistant to its herbivores when neighboring sagebrush plants were experimentally clipped. In this study we asked how the age of sagebrush affected systemic-induced resistance and whether there was seasonal variation in systemic resistance. Young plants showed strong evidence of systemic-induced resistance only if airflow was permitted among branches. Moreover, volatile communication between individuals was stronger in young plants. We also found that plants with neighbors clipped in May accumulated less damage throughout the season relative to plants with neighbors that were clipped later in the summer.

Airborne signals of communication in sagebrush: a pharmacological approach

When plants receive volatiles from a damaged plant, the receivers become more resistant to herbivory. This phenomenon has been reported in many plant species and called plant-plant communication. Lab experiments have suggested that several compounds may be functioning as airborne signals. The objective of this study is to identify potential airborne signals used in communication between sagebrush (Artemisia tridentata) individuals in the field. We collected volatiles of one branch from each of 99 sagebrush individual plants. Eighteen different volatiles were detected by GC-MS analysis. Among these, 4 compounds; 1.8-cineol, β-caryophyllene, α-pinene and borneol, were investigated as signals of communication under natural conditions. The branches which received either 1,8-cineol or β-caryophyllene tended to get less damage than controls. These results suggested that 1,8-cineol and β-caryophyllene should be considered further as possible candidates for generalized airborne signals in sagebrush.

Effect of genetic relatedness on volatile communication of sagebrush (Artemisia tridentata)

Abstract Sagebrush (Artemisia tridentata) uses volatile cues to induce systemic resistance to herbivory within and between plants (so-called volatile communication). Previous study revealed that the volatile components varied among individuals and that sagebrush suffered less damage when it received volatiles from clonally potted genetically identical branches than when it received volatiles from genetically different potted branches. In this study, we investigated whether there are genetic relationships among individuals growing within 60 cm where volatile communication occurs under natural condition, and whether volatile components are influenced by genetic relationships. By using genetic analysis involving microsatellite markers, we found that genetically identical ramets which were thought to be clonally propagated and genetically closely related ramets were growing near to each other. In addition, volatile components were similar among genetically identical or closely related ramets. Our results imply that genetic relatedness and volatile similarities may influence the strength of induced resistance of ramets that received volatiles.