The embryo of the maize grain (Zea mays L.) is separated from the starchy endosperm by a fibrous structure, which is called the fibrous layer (FL). Using histochemical staining, it was determined that the FL is composed of collapsed cellular layers that contain phenols, neutral lipids, and 1,3-β-glucan. Due to its composition, the FL prevents free diffusion and separates the embryo from the endosperm during germination. Twenty-four hours after imbibition, the scutellum epidermis initiated a series of asynchronous spatial modifications, including cell growth, the perforation of cell walls, increased peroxidase activity in the apoplastic space, and elevated levels of superoxide, phenols, and other components that interact with the fibrous layer, enabling its transformation in addition to the free flow between compartments. During storage at high relative humidity levels, which leads to fast or slow deterioration depending on the temperature, the activity of phenol peroxidase in the scutellum was associated with a loss of vigor and reduced germination capacity when compared with low temperature and low relative humidity conditions. Such deterioration is associated with alterations in autofluorescent emissions from endogenous compounds in the scutellum, indicating changes in the microenvironment or in the differential proportions of epidermal and FL components.

Maize is one of the most important cereal crop species due to its uses for human and cattle nourishment, as well as its industrial use as a raw material. The yield and grain quality of maize depend on plant establishment, which starts with germination. Germination is dependent on embryo vigor and the stored reserves in the scutellum and endosperm. During germination, the scutellum epidermis changes and secretes enzymes and hormones into the endosperm. As a result, the hydrolysis products of the reserves and the different soluble nutrients are translocated to the scutellum through epithelial cells. Then, the reserves are directed to the embryo axis to sustain its growth. Therefore, the microenvironment surrounding the scutellum modulates its function. Zinc (Zn) is a micronutrient stored in the maize scutellum and endosperm; during imbibition, Zn from the endosperm is solubilized and mobilized towards the scutellum. During this process, Zn first becomes concentrated and interacts with cell wall charges, after which excess Zn is internalized in the vacuole. Currently, the effect of high Zn concentrations on the scutellum function and germinative processes are not known. In this paper, we show that, as a function of the concentration and time of exposure, Zn causes decreases in the radicle and plumule lengths and promotes the accumulation of reactive oxygen species (ROS) and flavonoids as well as changes in the activity of the cell wall Class III peroxidase (POD), which was quantified with guaiacol or catechin in the presence of H₂O₂. The relationship between the activity index or proportion of POD activity in the scutellum and the changes in the flavonoid concentration is proposed as a marker of stress and the state of vigor of the embryo.

Maize is among the world’s three most important cereals because it is used for human consumption and agricultural feed. The embryo in monocotyledons contains a cotyledon that is the scutellum, which in Chalqueño maize constitutes approximately 80% of the embryo’s mass. The activation of metabolism during germination is accompanied by the production of reactive oxygen species, which must be maintained at a low level to avoid damage. Little is known about the oxidative state of the scutellum, but it is important to understand the control of oxidative stress during the final phase of germination and the embryo–seedling transition. Among the enzymes involved are class III peroxidase (POX), catalase (CAT), and superoxide dismutase (SOD), which were observed in the scutella of isolated imbibed embryos between 0 and 36 h. The activity of SOD fluctuated over a baseline value. The activity of class III POX was greater than that of CAT, showing differences between them in germination and postgermination. The activities of CAT and POX increased during germination (0 to 18 h), stabilized towards the final phase of germination (18 to 24 h), and then increased again in postgermination (24 to 36 h). The POX activity is a biochemical marker of the scutellum metabolism and marks the transition from germination to the embryo–seedling transition.