Morpho-anatomical responses to in vitro germination and glutamine supplementation in the rare orchid Eltroplectris paranaënsis (Orchidaceae: Spiranthinae)

Abstract As few studies have been conducted on the growth and development of Neotropical terrestrial orchids, little is known about their germination patterns, anatomy, and nutrition requirements. Eltroplectris paranaënsis is a rare orchid from the Brazilian Cloud Forest, considered Critically Endangered due to its reduced population size and threatened habitat. To aid in the conservation of the species, in vitro germination was performed in two culture media compositions, WPM and MS/2 basal salts. Then, the seedlings were grown in vitro with glutamine supplementation at the concentrations of 6.8 or 13.6 mM, and a control without glutamine. Protocorm and seedling development were assessed concerning their morphology, anatomy and pigment accumulation. The highest germination was achieved on WPM medium, reaching 50.8%, while MS/2 had higher protocorm mortality. Starch accumulation begins in the protocorm tissue at Stage II. Cyclocytic stomata were seen for the first time in the Cranichideae tribe. Glutamine enhanced leaf length and shoot meristem height at both concentrations tested. Chlorophyll a and carotenoids were also higher for glutamine treatments. In the roots, more protoxylem arches and starch were seen as response to the presence of the amino acid. Thus, it is recommended that 6.8 mM glutamine is used for seedling elongation and tissue development. Studies of the growth pattern of the plants enable better understanding of their relationship with the habitat, which in turn leads to more efficient conservation strategies and a wider comprehension of the group’s evolution.