Callitriche as a potential model system for evolutionary studies on the dorsiventral distribution of stomata.

Controlling the distribution of stomata is crucial for the adaptation of plants to new, or changing environments. While many plant species produce stomata predominantly on the abaxial leaf surface (hypostomy), some produce stomata on both surfaces (amphistomy), and the remaining few produce them only on the adaxial surface (hyperstomy). Various selective pressures have driven the evolution of these three modes of stomatal distribution. Despite recent advances in our understanding of stomatal development and dorsiventral leaf polarity, the genetic basis for the evolution of different stomatal distributions is still unclear. Here, we propose the genus Callitriche as a new model system to investigate patterns in the evolution of stomatal distribution. Callitriche comprises species with diverse lifestyles, including terrestrial, amphibious, and obligately aquatic plants. We found that species in this genus cover all three modes of dorsiventral stomatal distribution, making it a desirable model for comparative and evolutionary analyses on distribution modes. We further characterized the genetic basis of the different distribution modes, focusing on the stomatal key transcription factor SPEECHLESS. Future research using the promising model system Callitriche would open a new direction for evolutionary developmental biology studies on stomata.

Micromorphological and histochemical attributes of flowers and floral reward in Linaria vulgaris (Plantaginaceae).

The self-incompatible flowers of Linaria vulgaris have developed a range of mechanisms for attraction of insect visitors/pollinators and deterrence of ineffective pollinators and herbivores. These adaptive traits include the flower size and symmetry, the presence of a spur as a "secondary nectar presenter," olfactory (secondary metabolites) and sensual (scent, flower color, nectar guide-contrasting palate) signals, and floral rewards, i.e. pollen and nectar. Histochemical tests revealed that the floral glandular trichomes produced essential oils and flavonoids, and pollen grains contained flavonoids, terpenoids, and steroids, which play a role of olfactory attractants/repellents. The nectary gland is disc-shaped and located at the base of the ovary. Nectar is secreted through numerous modified stomata. Nectar secretion began in the bud stage and lasted to the end of anthesis. The amount of produced nectar depended on the flower age and ranged from 0.21 to 3.95 mg/flower (mean = 1.51 mg). The concentration of sugars in the nectar reached up to 57.0%. Both the nectar amount and sugar concentration demonstrated a significant year and population effect. Pollen production was variable between the years of the study. On average, a single flower of L. vulgaris produced 0.31 mg of pollen. The spectrum of insect visitors in the flowers of L. vulgaris differed significantly between populations. In the urban site, Bombus terrestris and Apis mellifera were the most common visitors, while a considerable number of visits of wasps and syrphid flies were noted in the rural site.