The Microstructure Organization and Functional Peculiarities of Euphorbia paralias L. and Polygonum maritimum L. – Halophytic Plants from Dunes of Pomorie Lake (Bulgaria)

The aim of this research was to investigate the leaf surface microstructure, pigments spectrum, hormones status and lipids composition of halophytes Polygonum maritimum L. and Euphorbia paralias L. that grow under natural conditions on the dunes of Pomorie Lake, (Bulgaria). It was shown that the existence in saline and dry soils provided among others adaptive mechanisms by specific microstructure of leaf. The adaxial and abaxial surfaces of P. maritimum leaves are covered with a dense layer of cuticle wax, stomata are located on the leaf both sides below the cuticle level. In E. paralias the cuticle is also well developed on the adaxial surface of leaf laminas. The epidermis of the leaf lower side is covered with a less dense cuticle layer formed by large wax crystals. This plant has stoma pores only on the abaxial side of small leaves below the cuticle level and they are surrounded with hump-shaped cuticle constructions. A high amount of carotenoids (as compared with that of chlorophylls) in P. maritimum leaves indicates that these pigments have a light-collecting function and could transfer an additional energy to chlorophylls. The high performance liquid chromatography method has been used to provide a qualitative and quantitative analysis of hormones. It was shown that in leaves of E. paralias and P. maritimum free abscisic (ABA) and conjugated indole-3-acetic (IAA) acids prevailed. A high level of active ABA is correlated with the salt tolerance and ability to survive and grow in stress conditions. A high level of conjugated form of IAA demonstrated that activity of this hormone is limited. The cytokinins qualitative and quantitative analyses demonstrated that in E. paralias leaves zeatin forms dominated, and the level of inactive cytokinins (cis-zeatin and zeatin-O-glucoside) was much higher than that of active ones (trans-zeatin and zeatin riboside). P. maritinum leaves contained a significant quantity of isopentenyl forms – isopentenyladenine and isopentenyladenosine, and among zeatin forms, zeatin-O-glucoside prevailed. Studies on the fatty acids content showed that in halophytes the salt resistance mechanism is based on the regulation of plasmatic membrane transport function that involves non-saturated fatty acids. The presence of a large amount of saturated fatty acids provides a decrease of membrane permeability and better resistance against soil salinity.