Inductive Flood Tolerance in Swamp Tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.)

Under flooding or anoxia the newly initiated roots of swamptupelo produce et hanol and lactio acid and oxidize their rhizosphere.Unflooded roots produce less ethanol than flood roots and donot oxidize their rhizosphere. Oxygen enters the stem via thelenticels and appears to be diffused or transported via thecortex or phloem. Flood roots have less suberization in theepidermis in the terminal 2-cm section and casparian stripswere less evident than in the same sections in unflooded roots.Swamp tupelo roots tolerated 10 per cent CO₂ without adverseeffects but 31 per cent CO₂ reduced the initiation of new roots,rate of O₂ uptake, and transpiration rate. Tolerance to highCO₂ around the root seemed to be related to the oxidation ofthe rhizosphere by new roots. The combined adaptations of acceleratedanaerobic respiration in the absence of O₂, oxidation of therhizosphere, and CO₂ tolerance of new roots appear to be sufficientconditions to account for flood tolerance in this species.     

Ion and Osmoregulation in Prenatal Elasmobranchs: Evolutionary Implications

The elasmobranchs represent a fascinating series of experimentsin the evolution of maternal support for developing embryos.In oviparous species, eggs are enclosed in a tough, fibrouscapsule. The capsule is very permeable and the embryonic tissuesare bathed in a solution ionically similar to sea water withinhours of oviposition. In the primitively viviparous speciesSqualus acanthias, early embryos in egg capsules are retainedin utero and are bathed in a solution similar to maternal plasma.Several months into the 22 month gestation period the embryosare capable of independent iono- and osmoregulation in a uterinesolution that resembles sea water. Embryos of more advancedviviparous species develop in a solution that is similar tomaternal plasma. Iono- and osmoregulation by these embryos wouldappear to beminimal. It is clear that in the oviparous elasmobranchs,the ability of the egg/embryo to maintain salts and urea atappropriate levels is present at the earliest stage of development.The ability of prenatal elasmobranch embryos to iono- and osmoregulatewould allow the evolution ofa diverse array of reproductivestrategies in the elasmobranchs.