Glycoproteins in Citrus Foliage and Callus Tissue as Affected by Cold-hardening Temperature and Abscisic Acid

Abstract

Soluble proteins were extracted from the foliage of several citrus genotypes that widely differed in cold hardiness after 4 weeks exposure to cold-hardening (16 °/5 °C) and noncold-hardening (30 °/21 °C) temperature regimes. The electrophoretic profiles of glycoproteins were analyzed after transfer to nitrocellulose filters by binding of wheat germ and soybean agglutinin as well as lectin from Lotus tetragonolobus. All three lectins detected a pattern of polypeptides that was highly conserved among citrus genotypes. Many of these polypeptides increased during cold-hardening; one exception was an M r 36,000 (Daltons) polypeptide which disappeared in Valencia orange grafted on rough lemon rootstock. Nearly the same glycoprotein profile was detected in callus lines derived from various tissues of Valencia orange. Polypeptides increased with the addition of abscisic acid ( 10 μm) in the medium and at low-temperature (10 °C). A concomitant reduction of freeze damage as assessed by electrolyte leakage was observed.