Changes in anatomy and chlorophyll synthesis in orchids propagated in vitro in the presence of urea

Abstract

The environmental and nutritional conditions during plant growth can influence cell differentiation, resulting in anatomical and physiological adaptations. The objective of this study was to investigate the anatomical characteristics and chlorophyll content of L. purpurata during in vitro propagation when different concentrations of urea were applied. After 120 days of culture in a greenhouse, the growth characteristics, chlorophyll content, leaf anatomy and root features were assessed. Plants cultivated in a medium containing 75% urea exhibited modifications in their growth, increase in the number of leaves and roots, changes in the leaf and root dry matter content. There was an increase in the contents of “a” and “b” chlorophyll in plants treated with 50, 75 and 100% urea. An increase in the ratio of chlorophyll a to chlorophyll b (“a/b”) was observed in plants treated with 25% urea compared with the controls. In plants treated with 75% urea, increases in the thicknesses of the mesophyll and the leaf blade were observed, and reductions in the number of layers of root cells, the velamen thickness, the exodermis and the vascular cylinder were observed. These results indicate that this species has a tolerance to urea and exhibits higher growth in vitro.