The failure of the embryonic epidermis affects seed maturation and embryo growth in pea.

Abstract

AbstractPea plants were grown under a light/dark regime of 16/8 h at 16/19°C. Because the recessive E2748 seeds were lethal, the plants were maintained as heterozygotes. The endospermal vacuolar liquid volume was determined. The E2748 seed mutation affected embryo growth during maturation. Mutant embryos grew slowly and reached only ∼10% of the wild-type values. The endospermal vacuoles increased similarly up to ∼150 mg in both wild-type and mutant, then decreased continuously in the wild-type when their place was occupied by the fast-growing embryo. Within the mutant, endospermal vacuoles further increased until the seeds reached ∼250 mg. Endospermal vacuoles bearing mutant or wild-type embryos contained similar sugar concentrations. The hexose:sucrose ratio within the endospermal vacuole was unaltered in the mutant and was independent of normal embryo growth. Mutant embryos did not accumulate normal sucrose levels. Mutant cotyledonary epidermal cells de-differentiated at the beginning of seed maturation. A sucrose transporter-specific probe (VfSUT1) was used for in situ hybridizations on wild-type cotyledons of 60-mg seeds. SUT1-specific signals were present within the outermost layer, indicating gene expression within the epidermal cell layer. In wild-type cotyledons of 200-mg seeds, SUT1-specific signal was present within the outer layer with higher intensity in the abaxial region where transfer cells were formed. A steep gradient of label intensity was present, decreasing from the abaxial towards the interior, indicating lower expression in the parenchyma cells. In the mutant, the pattern was completely irregular. A stronger label occurred within the parenchyma, while it was much weaker in the outermost cell layer.