Rumor Has It…: Relay Communication of Stress Cues in Plants

Recent evidence demonstrates that plants are able not only to perceive and adaptively respond to external information but also to anticipate forthcoming hazards and stresses. Here, we tested the hypothesis that unstressed plants are able to respond to stress cues emitted from their abiotically-stressed neighbors and in turn induce stress responses in additional unstressed plants located further away from the stressed plants. Pisum sativum plants were subjected to drought while neighboring rows of five unstressed plants on both sides, with which they could exchange different cue combinations. On one side, the stressed plant and its unstressed neighbors did not share their rooting volumes (UNSHARED) and thus were limited to shoot communication. On its other side, the stressed plant shared one of its rooting volumes with its nearest unstressed neighbor and all plants shared their rooting volumes with their immediate neighbors (SHARED), allowing both root and shoot communication. Fifteen minutes following drought induction, significant stomatal closure was observed in both the stressed plants and their nearest unstressed SHARED neighbors, and within one hour, all SHARED neighbors closed their stomata. Stomatal closure was not observed in the UNSHARED neighbors. The results demonstrate that unstressed plants are able to perceive and respond to stress cues emitted by the roots of their drought-stressed neighbors and, via ‘relay cuing’, elicit stress responses in further unstressed plants. Further work is underway to study the underlying mechanisms of this new mode of plant communication and its possible adaptive implications for the anticipation of forthcoming abiotic stresses by plants

Is ABA the exogenous vector of interplant drought cuing?

We have recently demonstrated that root cuing from drought-stressed plants increased the survival time of neighboring plants under drought, which came at performance costs under benign conditions. The involvement of abscisic acid (ABA) was implicated from additional experiments in which interplant drought cuing was greatly diminished in ABA-deficient plants. Here, we tested the hypothesis that ABA is the exogenous vector of interplant drought cuing. Pisum sativum plants were grown in rows of three split-root plants. One of the roots of the first plant was subjected to either drought of benign conditions in one rooting vial, while its other root shared its rooting vial with one of the roots of an unstressed neighbor, which in turn shared its other rooting vial with an additional unstressed neighbor. One hour after subjecting one of the roots of the first plant to drought, ABA concentrations were 106% and 145% higher around its other root and the roots of its unstressed neighbor, compared to their respective unstressed controls; however, the absolute concentrations of ABA found in the rooting media were substantially low. The results may indicate that despite its involvement in interplant drought and the commonly observed exchange of ABA between drought-stressed plants and their rhizospheres, ABA is not directly involved in exogenous interplant drought cuing. However, previous studies have shown that even minute concentrations of ABA in the rhizosphere can prevent ABA leakage from roots and thus to significantly increase endogenous ABA levels. In addition, under drought conditions, plants tend to accumulate ABA, which could markedly increase internal ABA concentrations over time and ABA concentrations in close proximity to the root surface might be significantly greater than estimated from entire rooting volumes. Finally, phaseic acid, an ABA degradation product, is known to activate various ABA receptors, which could enhance plant drought tolerance. It is thus feasible that while the role of ABA is limited, its more stable degradation products could play a significant role in interplant drought cuing. Our preliminary findings call for an extensive investigation into the identity and modes of operation of the exogenous vectors of interplant drought cuing

The Effects of Nutrient Dynamics on Root Patch Choice

Plants have been recognized to be capable of allocating more roots to rich patches in the soil. We tested the hypothesis that in addition to their sensitivity to absolute differences in nutrient availability, plants are also responsive to temporal changes in nutrient availability. Different roots of the same Pisum sativum plants were subjected to variable homogeneous and heterogeneous temporally – dynamic and static nutrient regimes. When given a choice, plants not only developed greater root biomasses in richer patches; they discriminately allocated more resources to roots that developed in patches with increasing nutrient levels, even when their other roots developed in richer patches. These results suggest that plants are able to perceive and respond to dynamic environmental changes. This ability might enable plants to increase their performance by responding to both current and anticipated resource availabilities in their immediate proximity

Pupation success

Each row represents a clutch of eggs laid at the same day by a group of females fed on the same host individua

Effects of water pulsing on individual performance and competitive hierarchies in plants

In a glass house experiment, we investigated the effect of both the frequency of water pulses and the total amount of water supplied on individual performance in the absence and presence of neighbors. We used monocultures and all combinations of pairs of seedlings of three species of perennial grasses, characteristic of different points along a soil moisture gradient within a semi-arid grassland in New Mexico, USA. In the absence of neighbors, higher total water or more frequent (but smaller) pulses significantly increased growth of all three species. The species with the fastest intrinsic growth rate, and from the most productive habitat, exhibited the largest increase in absolute and relative growth in response to higher total water quantity. Competitive effects were highly significant overall and there were significant hierarchies of competitive ability. Under frequent pulses, the fast-growing species from the most productive environment was the best competitor in terms of both ability to suppress other plants and ability to tolerate the presence of neighbors. However, under infrequent pulses, the slowest growing species from the least productive environment became a much stronger competitor, again in terms of both suppression and tolerance of neighbors. While differences in total water availability had greater effects than differences in pulsing regime on individual plant performance in the absence of competition, pulsing regime had much stronger effects on relative competitive abilities and thus may be more likely to influence field distribution patterns.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74078/1/3236604.pd

Data from: Use it or lose it: reproductive implications of ecological specialization in a haematophagous ectoparasite

Using experimentally induced disruptive selection, we tested two hypotheses regarding the evolution of specialization in parasites. The ‘trade-off’ hypothesis suggests that adaptation to a specific host may come at the expense of a reduced performance when exploiting another host. The alternative ‘relaxed selection’ hypothesis suggests that the ability to exploit a given host would deteriorate when becoming obsolete. Three replicate populations of a flea Xenopsylla ramesis were maintained on each of two rodent hosts, Meriones crassus and Dipodillus dasyurus, for nine generations. Fleas maintained on a specific host species for a few generations substantially decreased their reproductive performance when transferred to an alternative host species, whereas they generally did not increase their performance on their maintenance host. The results support the ‘relaxed selection’ hypothesis of the evolution of ecological specialization in haematophagous ectoparasites, while suggesting that trade-offs are unlikely drivers of specialization. Further work is needed to study the extent by which the observed specializations are based on epigenetic or genetic modifications

Egg production

Each row represents eggs laid by a group of fleas fed simultaneously on the same host