• Choose a category
• All
• Classic-Fiction

By Root 441 0

choice by dodder: âWhether the potentially adaptive ability to choose resources is accessible to all plants or is dictated by the cloning ability or para sitism of dodder is unknown. However, the increased efficiency of resource acquisition that modular âchoiceâ could provide would be beneficial to any plant, parasitic, clonal, or otherwiseâ¦The results presented here also necessarily show active choice on the part of a parasitic plant and outline a means by which choice might be tested for other parasitic angiospermsâ (p. 12196). Gilroy and Trewavas (2001) write: âDecisions about exploitation of basic nutrient resources can be made by plants before any nutritional benefit is derived. Dodder, a parasitic plant, can sense the level of circulating nutrients when it first touches a putative host. Within one hour, it âdecidesâ whether it is worth initiating a developmental program, which involves shoot-coiling around the host and the formation of haustoria several days later. Rejection of the putative host is frequent. Once haustoria penetrate the host vascular system, nutrients are gained and used for growth. Remarkably, the number of coils of the parasite around the host stem reflects with some accuracy the nutrients in the host and the likely subsequent return in growth resources. What is required of plant-cell signal-transduction studies, then, is to account for the capacity for âintelligentâ decision-making; computation of the right choice between close alternativesâ (p. 308).

Â

P. 89: CALCIUM AND LEARNING IN PLANTS AND NEURONS

Trewavas (1999b) writes: âIn an unstimulated plant, information flow from a signal through Ca2+ (calcium ion)-dependent pathways will be slow; in a stimulated plant, information flow from the self-same signal will be enormously faster. However these data are viewed, they represent a form of cellular learningâ¦Signal-transduction networks share properties with neural networks, and the learning parallels can be drawn easily. Neural networks learn by increasing the numbers of connections (and the strength of the connections) between the neurons representing the chosen path to connect signal and response. The result of learning (reinforcement) is to accelerate the information flux rates between the signal and the response. Elevating calcium ion transduction constituents is analogous to increasing the numbers of connections in a neural network. The increased information flow that results represents a kind of cellular learning. This cellular learning, coupled with the memory built into signal-transduction systems, suggests an unexpected form of cellular intelligenceâ (p. 4218). See Gilroy, Read and Trewavas (1990) for the initial research on calciumâs role in plant cells. Toni et al. (1999) write: âStructural remodeling of synapses and formation of new synaptic contacts has been postulated as a possible mechanism underlying the late phase of long-term potentiation (LTP), a form of plasticity which is involved in learning and memory. Here we use electron microscopy to analyze the morphology of synapses activated by high-frequency stimulation and identified by accumulated calcium in dendritic spines. LTP induction resulted in a sequence of morphological changes consisting of a transient remodeling of the postsynaptic membrane followed by a marked increase in the proportion of axon terminals contacting two or more dendritic spines. Three-dimensional reconstruction revealed that these spines arose from the same dendrite. As pharmacological blockade of LTP prevented these morphological changes, we conclude that LTP is associated with the formation of new, mature and probably functional synapses contacting the same presynaptic terminal and thereby duplicating activated synapsesâ (p. 421). Ottersen and Helm (1999) comment that neuronal spines âare tiny protrusions from long, slender extensions (dendrites) of nerve cells, and they constitute the receiving parts of synapsesâthe contacts that mediate neuron-to-neuron signaling. Spines are believed to be the most basic functional units in the brain, and their