Role of peroxidase in the development of water-impermeable seed coats in Sida spinosa L.

Abstract

The seed coats of S. spinosa (prickly sida, Malvaceae) become impermeable to water during seed development on the mother plant. After the seeds have dehydrated during the final maturation stages, piercing of seed coats is necessary to induce imbibition of water and germination. Onset of impermeability occurs during seed coat browning, well in advance of seed dehydration. I. Marbach and A.M. Mayer (1975, Plant Physiol. 56, 93-96) implicated polyphenol oxidase (PO; EC 1.10.3.1) as catechol oxidase in the formation of insoluble polymers during development of coat impermeability in a wild strain of pea (Pisum elatius) seeds. We found, however, that peroxidase (EC 1.11.1.7), not PO, is instrumental in the development of water-impermeable seed coats in prickly sida. We isolated coats and embryos from seeds harvested at several stages of development. Highest peroxidase activity of coat extracts correlated well with the developmental stages of maximum conversion of soluble phenolics to insoluble lignin polymers. Although seed extracts oxidized dihydroxyphenylalanine, this activity was eliminated by catalase, indicating that the oxidation of phenolics in the coat is catalyzed by peroxidase rather than PO. Histochemical localization of peroxidase was strongest in the palisade layer; both the level and time of appearance of activity was proportional to the spectrophotometric assays of seed-coat extracts. The presence of peroxidase and the absence of PO in the seed coat were also confirmed with immunocytochemistry. Our results support the view that peroxidase is involved in the polymerization of soluble phenolics to insoluble lignin polymers during development of prickly sida seed coats, causing the formation of a water-impermeable barrier prior to seed dehydration. As dehydration proceeds, the chalazal area finally becomes impermeable resulting in the hard mature seeds of prickly sida.

Toxic action of aqueous wheat straw extract on horse e purslane

“…The consumption of H 2 O 2 was observed at 240 nm and one unit of CAT was defined as the amount of enzyme required to oxidize 1 µM H 2 O 2 min -1 . Peroxidase (POX) activity was recorded as described by Egley et al (1983). The increase in absorbance due to guaiacol oxidation was measured at 470 nm.…”

The seed coat as a modulator of seed-environment relationships in Fabaceae

“…The biochemical mechanism of the hardening process may vary among plant families (Egley et al 1983) and the specific site of impermeability within species varies according to genotype. In soybean, seed coat impermeability has also been associated with the waxy cuticle (Arechavaleta-Medina & Snider 1981), high calcium and low phosphorus seed coat concentrations (Saio 1976), high xylose concentration (Mullin & Xu 2000), to a phenolic layer, lack of pores, a prominent light line and cutin in the hilum region (Harris 1987), to embedded waxy substances between the palisade cells and to high lignification of the palisade cell base and the hypodermal cell tops (BaciuMiclaus 1970) and to the presence, number and shape of pores (Yaklich et al 1986).…”

“…It is involved with lignification in different plant organs of several species as well as with the polymerization of soluble phenolics to insoluble polymers, such as lignin. It is particularly active during seed coat development in Sida spinosa (Malvaceae) and, possibly, wild pea (Egley et al 1983) and soybean (Mullin & Xu 2000), promoting impermeabilization. Studies carried out by Werker et al (1979) with several Pisum species indicated that testa impermeability depends on the presence of quinones in the palisade or osteosclereids layer as a continuous layer.…”

Wheat Herbage Amendments Alter Emergence Dynamics, Seedling Growth of Lambsquarter and Soil Properties

“…The consumption of H 2 O 2 was observed at 240 nm and one unit of CAT was defined as the amount of enzyme required to oxidize 1μ M H 2 O 2 min -1 . The peroxidase (POX) activity was recorded as described by Egley et al (1983). Increase in absorbance due to guaiacol oxidation was measured at 470 nm.…”