Mechanosensing and anesthesia of single internodal cells of .

The giant (2-3 × 10 m long) internodal cells of the aquatic plant, , exhibit a rapid (>100 × 10 m s) cyclic cytoplasmic streaming which stops in response to mechanical stimuli. Since the streaming - and the stopping of streaming upon stimulation - is easily visible with a stereomicroscope, these single cells are ideal tools to investigate mechanosensing in plant cells, as well as the potential for these cells to be anesthetized. We found that dropping a steel ball (0.

Model scientists.

There is an increasing trend for the focus of biology to be determined more by administrators who have short-term pecuniary interests in science rather than by individuals who are "doing science" to further the fundamental human desire to understand ourselves, the natural environment, and our place in the world, though questioning. We feel that this ceding of the scope of science from the questioners to the administrators is at variance with the traditions of science, which heretofore have resulted in the remarkable advancements made in the field of biology. In contrast to the plethora of day-to-day conversations on how to fit into the administrators' directives, this essay provides a historical context, particularly though its extensive bibliography, to encourage today's biologists to question authority and question nature.

Cytochalasin D does not inhibit gravitropism in roots.

It is generally thought that sedimenting plastids are responsible for gravity sensing in higher plants. We directly tested the model generated by the current statolith hypothesis that the gravity sensing that leads to gravitropism results from an interaction between the plastids and actin microfilaments. We find that the primary roots of rice, corn, and cress undergo normal gravitropism and growth even when exposed to cytochalasin D, a disruptor of actin microfilaments.

The effect of the external medium on the gravitropic curvature of rice (Oryza sativa, Poaceae) roots.

The roots of rice seedlings, growing in artificial pond water, exhibit robust gravitropic curvature when placed perpendicular to the vector of gravity. To determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best accounts for gravity sensing in rice roots, we changed the physical properties of the external medium with impermeant solutes and examined the effect on gravitropism. As the density of the external medium is increased, the rate of gravitropic curvature decreases.

The effect of the external medium on the gravity-induced polarity of cytoplasmic streaming in Chara corallina (Characeae).

Gravity induces a polarity of cytoplasmic streaming in vertical internodal cells of Chara such that the downwardly directed stream moves faster than the upwardly directed stream. In order to determine whether the statolith theory (in which intracellular sedimenting particles are responsible for gravity sensing) or the gravitational pressure theory (in which the entire protoplast acts as the gravity sensor) best explain the gravity response in Chara internodal cells, we controlled the physical properties of the external medium, including density and osmolarity, with impermeant solutes and examined the effect on the polarity of cytoplasmic streaming. As the density of the external medium is increased, the polarity of cytoplasmic streaming decreases and finally disappears when the density of the external medium is equal to that of the cell (1015 kg/m3).