Embryological features of Alhagi persarum (Fabaceae): Adapt to environmental constraints

Abstract

Reproductive organs, in flowering plants, are sensitive to stressful environments. Alhagi persarum Boiss. & Buhse copes with the stresses and produce reproductive organs under difficult climatic conditions. Embryological characters of this plant were investigated for the first time using different microscopy and staining techniques. The results of this study showed unique reproductive characters and strategies in A. persarum that we named reproductive adaptation. These characters have roles in protection and nutrition of reproductive organs, some of which were visible in ovule: accumulation of phenolic compounds, presence of ovular endothelium with its cuticle coat, hypostase, postament, endosperm haustorium, presence of operculum, curvature of the embryonic axis. The other characters in the seed are macrosclereid cells with cuticle coat, double palisade layer and lignified tracheids in hilar groove. Thickness increasing of endothecium and exine are the adaptive characters in anther. Unlike many of the stress-sensitive plants, all developmental stages of the embryo sac, anther, pollen and pollen tube are without any defects in these stress-tolerant plants. Seed germination rate is low in this species that is due to the hardness of seed coat which causes seed deep exogenous dormancy. This dormancy is also a developmental program for stress tolerance to keep seed viability for a long time in difficult conditions.