Idioblasts and Raphides

From: Ted.Held at hstna.com on 2001.08.14 at 23:24:49(7238) You all may remember my query a while back on how to find raphides. One of the responses included mailing me a copy of an old article from Aroidiana, originally published in Carolina Tips in 1982, by Father Eugene Middendorf. This article had a description of a technique of tissue mastication (mashing and grinding), adding a little extra water, filtering out the big chunks, and collection raphides and idioblasts that settle to the bottom of a container (like a test tube). There were also several pictures of idioblasts and raphides collected by this means. For those many who have not seen the article, the idioblast looks like a transparent cucumber with two rounded protrusions at either end. Because of the transparency, raphides can be seen as a collection of extremely thin, needle-like bodies within the center part of the cucumber. They look like a fist full of pick-up-sticks, if people remember what those look like. Another picture shows an apparently depleted idioblast with two messier stacks of raphides at either end, the idioblast looking depleted. The caption on this picture indicates that this idioblasts has discharged its load of raphides from both directions. The basic shape of the spent idioblast looks to be the same as the loaded one (i.e., emptied of raphides, but not deflated or smaller). +More To me the article raised several questions. Since my correspondent was at a loss to answer my questions, it was suggested to put them out for the list. Maybe people have some ideas? The questions: 1. What do you suppose is the launching mechanism for discharge of raphides from an intact idioblast? From the picture in the article, the idioblast looks like a simple bladder filled with fluid. Even at astonishingly high pressures, the launching power of a liquid is basically nil from a fixed-volume enclosure. Either we need a gas, which can rapidly expand, or a flexible bag that can deflate, assuming, of course, that raphides are not self-propelled. 2. How can an idioblast possibly discharge from both ends? If one tip is breached, the propellant power will be dissipated out that opening, leaving no more power to launch from the opposite side. If, by impossible luck, both ends are stimulated simultaneously, two open ends should preclude any discharge at all. Maybe there is an unseen membrane parallel to the raphide package that divides the idioblast into two separate chambers, one discharging one way, the other in the other direction? The physics don't make sense. 3. Why is mastication a good way to find idioblasts? Wouldn't I discharge every idioblast when I masticate? That is why I tried the simple sectioning at first. I think mastication and settling separation is probably a good way to gather a large number of raphides. But not intact idioblasts. 4. I wonder how idioblasts are oriented in Diffenbachia tissue. My guess is that they would be perpendicular to the leaf surface and near it, ready to fire away. Maybe they are inside regular cells? Maybe they are between them? Perhaps there are some adepts on this list that would know the answers to these questions. Thanks for any help. ted.held@hstna.com

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