Occurrence of intracellular crystals in leaves of Thalassia testudinum

Abstract

Refractive, rhomboidal, intracellular crystals were identified in leaves of Thalassia testudinum Banks ex König (turtlegrass) from the Bahamas (Lee Stocking Island); Florida (Key Largo and Key West); and Texas (Laguna Madre). At all four collection sites, crystals were present in leaves of all ages and in most but not all epidermal cells. Crystals were not found in mesophyll cells. Epidermal cells generally contained a single, large crystal, but leaves collected from Key West frequently exhibited cells containing two or more conjoined crystals. Crystals dissolved in concentrated HCl and were partially soluble in concentrated NaOH. Transmission electron microscopy showed that crystals were contained within a vacuole. The size (as large as 12 μm × 6 μm), morphology, and distribution of crystals in turtlegrass leaves are similar to proteinaceous crystals described in marine red and brown macroalgae, but histology and spectroscopy results suggest a closer affinity to calcium oxalate crystals found in flowering plants. Although crystalline inclusions within plant cells have been linked to (inter alia) deterrence of herbivory and regulation of intracellular calcium ion concentrations, their function within leaves of turtlegrass remains to be determined.