Anatomical studies on the adventitious roots of the geophyte Urginea maritima (L.) Baker

Abstract

The anatomy and histochemistry of the adventitious roots of Urginea maritima (L.) Baker and the plant’s adaptive strategies to the Mediterranean climate were investigated. The adventitious roots of U. maritima are bounded by a multiple-layered velamen, responsible for rapid water uptake. Both the epidermis and endodermis of the root are uniseriate. The cortex is 741.3 Ìm thick and is composed of numerous large parenchyma cells with storing character. In the cortex, scattered idioblastic cells containing numerous raphides of calcium oxalate exist. The average length of the calcium oxalate needles is 72±22 Ìm. The presence in the cortex of cells containing in their vacuoles soluble polysaccharides is conspicuous after employing the Schiff’s staining technique. Also, numerous cortical cells are filled with lipids and become intensely stained brown to black when treated with sudan black B. Morphometric studies have shown that idioblastic cells occupy 19.83% of the cortex relative volume, cells containing lipids 14.38%, and cells containing polysaccharides 11.27%. The cortex storage cells occupy 34.11% of the total root volume. The average volume of the cortical cells is 73143 Ìm3. The vascular cylinder is usually 10-arched. The root xylem consists of vessels in short radial rows. The phloem consists of sieve elements located between the vessel rays. Urginea maritima possessing adventitious roots proves to be efficient in storing water during the long summer drought, less susceptible to climatic stress and well synchronized with the climatic fluctuations. Specialized features of U. maritima adventitious roots are, at least in part, responsible for the species’ occurrence and frequent dominance in a wide array of semiarid ecosystems of the Mediterranean region.