EPICUTICULAR WAXES AND SILICON DEPOSITS IN Festuca pallescens (St. Yves) Parodii LEAVES.

FIORETTI, M.N.; BAIONI, S.S.; BREVEDAN, R.E.

Tandil, Argentina

Congreso; X Congreso Argentino de Ciencias Morfológicas; 2006

Festuca pallescens is a forage resource of the semiarid Patagonia. Epicuticular waxes and silicon content of the leaves affect the regulation of the water status of the plants through a reduction in transpiration and a greater leaf reflectivity to incoming solar radiation. The objective was to study the silicon content and distribution, and the quantity and morphology of the epicuticular waxes placed over the leaves of ecotypes of Festuca pallescens (Pampa del Castillo (PC), Media Luna (ML), Triana (T)) that are arranged along an increasing moisture deficit gradient. Plants were grown in a greenhouse. Treatments were: Control (soil kept at field capacity) and Stress (irrigation suspended until -3.5 MPa, and then irrigated to field capacity, three times). Epicuticular waxes were quantified gravimetrically after dilution with Cl4C and the leaf surfaces were observed with a scanning electron microscope. Leaf silicon content was measured in liquid extracts with a plasma espectrophotometer. The depositional pattern of silicon in leaf tissues was observed by SEM and silicon dot maps were done with energy-dispersive X-ray analysis. The ecotype PC accumulated 2.7 times more wax in stressed plants. A uniform wax layer was observed in all ecotypes, but in PC wax tubes juxtapose into tufts on the surface. In PC and T silicon content was 30% higher in stress. Silicon accumulation pattern was different for adaxial and abaxial surfaces. Adaxial epidermis showed silicon in trichomes while in abaxial surfaces silicon occurs in specialized cells.