Properties of action potentials in Drosera tentacles

Action potentials of Drosera tentacles resemble those of vertebrate peripheral nerves in that they appear to be comprised of relatively uniform spikes, variable shoulders or negative after-potentials, and variable positive after-potentials. The peaking of the spike corresponds to a period of great refractoriness, while action potentials of low amplitude may be fired readily during the negative after-potential. The action potentials fired during the negative after-potential appear to be unlike those of peripheral nerves in that they are of abnormally brief duration. Also apparently different from the case in peripheral nerves is the dependence of the duration of an action potential on the interval separating it from the preceding action potential.Action potentials propagate from the neck of the stalk to its base at about 5 mm s(-1) at room temperature. Propagation may be reversed artificially, consistent with the possibility that the neuroid cells are electrically coupled.

Canavanine distribution in jackbean fruit during fruit growth

Canavanine is an arginine analogue found in the seeds of many common legumes and is known to inhibit protein synthesis and growth in a number of organisms. Yet canavanine may comprise as much as 4% of the seed dry weight of the jackbean (Canavalia ensiformis).Canavanine is accumulated during earlier development in the pod, but disappears upon ripening. A corresponding increase in seed canavanine of about the same magnitude as the loss in the pod takes place during this latter time, but there is a subsequent significant increase of canavanine content of the seed after all detectable canavanine has disappeared from the pod. The first of these changes suggests synthesis of canavanine in the pod and transport into the seeds while the second one indicates a synthesis of canavanine in the seeds themselves, or possibly in the leaf or pod with rapid translocation to the seed.Canavanine was found to be at its highest concentration in the seed coats and pods when they were growing most rapidly and to gradually decline afterwards; however, the canavanine concentration of the seeds was found to be constant throughout fruit development.The pattern of canavanine mobilization in jackbean fruits was quite similar to the known pattern of total nitrogen mobilization typical of other leguminous fruits. This is consistent with a role as a nitrogen transport and storage compound.

Luminescence in KI:Tl

Freshly cleaved single crystals of KI:TI containing various concentrations of Tl have been irradiated in a vacuum monochromator in the 2800-1100 A region at temper. atures between -140 and 45 �0. The relative luminescence efficiencies in the Tl absorption bands and the host crystal fundamental absorption show that energy is transferred from host crystal to impurity centre to produce luminescence at room temperatures. To the high energy side of a threshold, which appears to depend on activator concentration, the luminescence efficiency is superlinear above about 15 �0 for KI:Tl (0�0005%).