Effects of silver nitrate (AgNO3) on growth and anatomical structure of vegetative organs of liquorice (Glycyrrhiza glabra L.) under in vitro condition

Abstract

Liquorice (Glycyrrhiza glabra L.) has been used worldwide as a medicine for a long time. In this research, the effect of silver nitrate (AgNO3) as a growth regulator and anti-ethylene in in vitro culture was investigated on growth and anatomical structure of vegetative organs (root, hypocotyl, shoot, leaf) as well as the number of stomata and trichomes in the leaves of liquorice under in vitro culture condition. The seeds were cultured in MS culture media containing different concentrations of AgNO3 (0, 2, 4, 8, and 10 mg L-1). Investigations on 20-day seedlings after three replications showed a significant increase in length and growth of roots, hypocotyls and shoots, and decreased number of stomata and trichomes in the samples treated with AgNO3 (P≤0.05). The effects of AgNO3 on anatomical structures of the organs included the increased cell division in root and shoot tips, reduced vascular tissues and sclerenchyma-fiber (with lignified cell walls), increased thickness of Casparian strip and cell walls of endodermis, reduced thickness of epidermis and increased intercellular spaces in mesophyll. The leaf area was measured in the 4-month plantlets, showing a significant increase in the samples treated with AgNO3. Furthermore, there was significant difference in increased leaf area applying 10 mg L-1 treatment and other concentrations as well as between the concentrations of 2 and 8 mg L-1. It seems that these results are due to the inhibitory effects of AgNO3 on the production and function of ethylene and the plant strategy to increase the tolerance against silver metal.