Lipochitooligosaccharide nodulation factors (NFs) secreted by endosymbiotic nitrogen-fixing rhizobia trigger Ca 2+ spiking in the cytoplasmic perinuclear region of host legume root hairs. To determine whether NFs also elicit Ca 2+ responses within the plant cell nucleus we have made use of a nucleoplasmin-tagged cameleon (NupYC2.1). Confocal microscopy using this nuclear-specific calcium reporter has revealed sustained and regular Ca 2+ spiking within the nuclear compartment of Medicago truncatula root hairs treated with Sinorhizobium meliloti NFs. Since the activation of Ca 2+ oscillations is blocked in M. truncatula nfp, dmi1, and dmi2 mutants, and unaltered in a dmi3 background, it is likely that intranuclear spiking lies on the established NF-dependent signal transduction pathway, leading to cytoplasmic calcium spiking. A semiautomated mathematical procedure has been developed to identify and analyze nuclear Ca 2+ spiking profiles, and has revealed high cell-to-cell variability in terms of both periodicity and spike duration. Time-lapse imaging of the cameleon Fö rster resonance energy transfer-based ratio has allowed us to visualize the nuclear spiking variability in situ and to demonstrate the absence of spiking synchrony between adjacent growing root hairs. Finally, spatio-temporal analysis of the asymmetric nuclear spike suggests that the initial rapid increase in Ca 2+ concentration occurs principally in the vicinity of the nuclear envelope. The discovery that rhizobial NF perception leads to the activation of cell-autonomous Ca 2+ oscillations on both sides of the nuclear envelope raises major questions about the respective roles of the cytoplasmic and nuclear compartments in transducing this key endosymbiotic signal.

Most solutions to the SLAM problem in robotics have utilized Range and Bearing sensors as the provided perception data is easy to incorporate, allowing immediate landmark initialization. This is not the case when using Bearing-Only information because the distance to the perceived landmarks is not directly provided. A whole estimate of a landmark position will only be possible via a set of measurements taken from different points of view. The vast majority of contributions to this problem utilize a parallel task to get this estimate, and hence the landmark initialization is delayed. We give a new insight to the problem and present a method to avoid this delay by initializing the whole ray that defines the direction of the landmark. We utilize a minimal and computationally efficient form to represent this ray and a new strategy for the subsequent updates. Simulations have been carried out to validate the proposed algorithms.