Differentiation of germination characteristics in Scutellaria rubropunctata (Lamiaceae) associated with adaptation to rheophytic habitats in the subtropical Ryukyu Islands of Japan.

Seed germination characteristics of a facultative rheophyte Scutellaria rubropunctata, a perennial skullcap endemic to the subtropical Ryukyu Islands of Japan, were investigated at temperatures of 15 °C, 20 °C, 25 °C, and 30 °C. The rheophytic type of S. rubropunctata showed relatively simultaneous germination times and reached high germination rates under all temperatures tested. This characteristic may allow it to establish quickly without being influenced by temperature, giving a survival advantage in rheophytic habitats by avoiding seeds being washed away by the rising water. In contrast, the final germination rate of the terrestrial type of S. rubropunctata, as well as that of the congener S. indica var. parvifolia, was highest at 15 °C and declined drastically at 30 °C. Seeds of both of these plants that remained ungerminated at higher temperatures germinated soon after the temperature was changed to 15 °C, indicating that the germination suppression was a state of enforced dormancy that was released after transfer to the optimal temperature. These characteristics suggest an asynchronous germination which is thought to reduce the risk of disturbance in fluctuating environments. Our study may be the first to demonstrate the differentiation of seed germination characteristics in relation to adaptations to a rheophytic habitat. Because rheophytes occupy such a harsh environment under strong selective pressure, the adaptive differentiation of seed germination characteristics may occur in many other rheophytes.

[Oryzalin-induced chromosome doubling of Scutellaria barbata].

OBJECTIVE: To obtain polyploidy Scutellaria barbata. METHODS: Explants of stem segment of Scutellaria barbata were treated with oryzalin at various concentration and time duration in vitro. RESULTS: Comparing with the characteristics of diploid, mutant plants had significant changes in plant morphology inducing compact plant, darker leaf color, smaller leaf index, thicken stem, significantly larger stomata, guard cells and chloroplasts in stomata guard cells and significantly lower stomata density. Mutant plants were plant chimera of diploid and tetraploid assessed by chromosome counting and flow cytometry. CONCLUSION: The technique could be used for chromosome doubling in Scutellaria barbata.