Electrical interactions between photoreceptors in the compound eye of Periplaneta americana

Visual Functional-Structural Plant Modeling Innovatively as a Compound Eye: Opening a New Way for Advancing the Scientific Cognition of Plant Vision

Plant vision is an interesting interdisciplinary branch of botany and vision science, and its emerging studies have composed an epic journey of discovery. However, there are few endeavors on modeling how a plant as an integrity sees. Inspired by the similarity between those discovered laws of plant vision and the visual performance of some insect species with compound eyes, the visual functional-structural plant modeling as a compound eye is innovatively proposed. Using this adapted basic-pattern-oriented modeling, we tried to validate its feasibility in terms of the structural support, visual pathway, and functional performance. First, for a diversity of woody plants, their crowns proved to show self-similar profiles, which render the omnidirectional surfaces for structurally supporting the proposed model. Second, for many plant species, their branching proved to abide by the Pareto front, which ensures the optimality of assuming the visual pathway along the branching network. Third, in canopies the varying, but existing horizontal and vertical modes of crown shyness are detected, which in functional performance accords with the panoramic visibility of the proposed model. Overall, the feasibility of compound eye modeling is validated preliminarily, with the implication of opening a way for advancing the scientific cognition of plant vision.

Opsin knockdown specifically slows phototransduction in broadband and UV-sensitive photoreceptors in Periplaneta americana

Photoreceptors with different spectral sensitivities serve different physiological and behavioral roles. We hypothesized that such functional evolutionary optimization could also include differences in phototransduction dynamics. We recorded elementary responses to light, quantum bumps (QBs), of broadband green-sensitive and ultraviolet (UV)-sensitive photoreceptors in the cockroach, Periplaneta americana, compound eyes using intracellular recordings. In addition to control photoreceptors, we used photoreceptors from cockroaches whose green opsin 1 (GO1) or UV opsin expression was suppressed by RNA interference. In the control broadband and UV-sensitive photoreceptors average input resistances were similar, but the membrane capacitance, a proxy for membrane area, was smaller in the broadband photoreceptors. QBs recorded in the broadband photoreceptors had comparatively short latencies, high amplitudes and short durations. Absolute sensitivities of both opsin knockdown photoreceptors were significantly lower than in wild type, and, unexpectedly, their latency was significantly longer while the amplitudes were not changed. Morphologic examination of GO1 knockdown photoreceptors did not find significant differences in rhabdom size compared to wild type. Our results differ from previous findings in Drosophila melanogaster rhodopsin mutants characterized by progressive rhabdomere degeneration, where QB amplitudes were larger but phototransduction latency was not changed compared to wild type.

Latency of phototransduction limits transfer of higher-frequency signals in cockroach photoreceptors

Visual transduction in rhabdomeric photoreceptors is compartmentalized and discretized. Signals of individual microvilli, the quantum bumps, are electrotonically summed, producing a graded response. Intrinsic dispersion of quantum bump latencies is thought to introduce noise and degrade signal transfer. Here, we found profound differences in the information rate and signaling bandwidth between in vitro patch-clamp and in vivo intracellular recordings of Periplaneta americana photoreceptors and traced them to the properties of quantum bumps and membrane resistance. Comparison of macroscopic and elementary light responses revealed differences in quantum bump summation and membrane resistance in vivo versus in vitro. Modeling of voltage bumps suggested that current bumps in vivo should be much bigger and faster than those actually recorded in vitro. Importantly, the group-average latency of dark-adapted photoreceptors was 30 ± 8 ms in intracellular (n = 34) versus 70 ± 19 ms in patch-clamp (n = 57) recordings. Duration of composite responses increased with mean latency because bump dispersion depended on mean latency. In vivo, latency dispersion broadened the composite response by 25% on average and slowed its onset. However, in the majority of photoreceptors, the characteristic durations of multiphoton impulse responses to 1-ms stimuli did not exceed the durations of mean voltage bumps. Consistently, we found strong associations between the latency and onset kinetics of the macroscopic response, on the one hand and the higher-frequency signal gain and information rate of the photoreceptor, on the other hand, indicating a direct connection between quantum bump latency and its dispersion and the signaling bandwidth.NEW & NOTEWORTHY When stimulated by light, microvilli of rhabdomeric photoreceptors produce discrete signals characterized by variable latencies. We show that this intrinsic latency dispersion restricts signaling bandwidth and information rate of photoreceptors in Periplaneta americana. Profound differences are found between the properties of photoreceptor responses in vivo and in vitro.