Ultrastructural aspects of the embryo and different endosperm compartments, in Eruca sativa Hill cv. Nemat (Brassicaceae) during Heart and Torpedo stages

Abstract

These observations are the first on the ultrastructure of the embryo and the endosperm of Eruca sativa Hill. We investigated the cv. Nemat, which is characterized by a particularly high amount of lipids and glucosinolates. Our observations suggested that the thick and abundant micropylar endosperm, completely surrounding the suspensor, may be the main active source of nutrients for the embryo. This endosperm, like the central chamber endosperm, is particularly rich in functional chloroplasts and cellularizes later with respect to the other previ- ously investigated Brassicaceae. The last (distal with respect to the embryo) suspensor cell exhibits important features related to the passage of nutrients, such as wall ingrowths. In fact these ingrowths appear as highly convoluted labyrinthine wall projections. Such ultrastructural features are typical of transfer cells. The accumu- lation stage in E. sativa cv. Nemat appears to occur early (Heart stage of embryo development, as Brassica na pus). The endosperm compartment called Chalazal Endosperm Cyst (CEC), contributes actively to the embryo trophism during the Heart and Torpedo stages. This function is evident because of the high number of chloro- plasts in the cyst and for the observed continuity between the CEC and the other endosperm compartments (CC endosperm and micropylar endosperm) in cv. Nemat. The morphology of the CEC appeared to be more similar to the pyriform shape sensu Brown et al., but with a more flattened base with respect to the proposed examples, and without labyrinthine wall. The Chalazal Chamber appeared to be more similar to the Brown’s type B in E. sativa. The presence of chloroplasts with a well developed thylakoid system indicates an active photosynthetic activity by the majority of the seed tissues. E. sativa leaves are normally harvested for food, while the seeds of cv. Nemat appear to be particularly rich in oil. The premature independence of seeds and fruits from the necessity of absorbing nutrients from the rest of the plant, could indicate the possibility of harvesting both leaves (earlier) and seeds (later) in this plant without compromising a full seed maturation.

Keywords:

• Biofuels
• Endosperm
• Eruca sativa
• Lipids
• Seed development