The maize weevil (MW), Sitophilus zeamais (Motsch.), is a storage pest that causes serious losses in maize (Zea mays L.) in developing countries. This study was conducted to investigate the role of pericarp cell wall components as factors that contribute to MW resistance in nine genotypes of tropical maize. Six susceptibility parameters to MW were measured and related to cell wall components such as simple phenolic acids, diferulic acids (DiFAs), hydroxyproline‐rich glycoproteins (HRGPs), and nutritional and physical traits. Weevil susceptibility was negatively correlated (P < 0.001) with total DiFAs (r = −0.77), HRGPs (r = −0.82), grain hardness (r = −0.87), pericarp/whole kernel (P/K) ratio (r = −0.68), and pericarp thickness (r = −0.86). A detailed analysis of phenolics indicated the presence of trans‐ferulic acid (FA), p‐coumaric acid (CA), and four isomers of DiFA. The most prominent were 5,5′‐DiFA, 8‐O‐4‐DiFA, and 8,5′‐DiFA benzofuran form (DiFAb). On the basis of regression models, 5,5′‐DiFA, 8‐O‐4‐DiFA, trans‐FA, and p‐CA were the most important phenolic components of resistance. Grain hardness was correlated (P < 0.001) with cell wall bound HRGPs (r = 0.61) and DiFAs (r = 0.75). Cell wall cross‐linking components could contribute to MW resistance by fortification of the pericarp cell wall as well as increase grain hardness. This structurally based mechanism should be considered in the development of hybrids and varieties where storage pests are prevalent.

Plant peroxidases (PODs) are involved in resistance to pathogens and insects. This study investigated the role of POD in maize (Zea mays L.) resistance to the maize weevil, Sitophilus zeamais (Motsch.). Insect bioassays were performed under controlled conditions to assess maize weevil resistance. Peroxidase activity was measured in the major grain tissues using guaiacol and peroxide. Significant variation (P > 0.001) among genotypes was observed in both the insect bioassay traits and POD activity. Peroxidase was detected in the embryo, endosperm, and pedicel, but it was not detected in the pericarp. Significant correlations were found between endosperm POD activity and maize weevil resistance (r = 0.89, P < 0.001). Histological staining confirmed POD activity in the vascular cylinder of the embryo, while activity in the endosperm was restricted to the aleurone layer. This study shows that POD activity is correlated with maize weevil resistance and may be used as a potential biochemical marker.

Considerable amounts of information is available on the complex carbohydrates that are mobilized and utilized by the seed to support early seedling development. These events occur after radicle has protruded from the seed. However, scarce information is available on the role of the endogenous soluble carbohydrates from the embryo in the first hours of germination. The present work analysed how the soluble carbohydrate reserves in isolated maize embryos are mobilized during 6–24 h of water imbibition, an interval that exclusively embraces the first two phases of the germination process. It was found that sucrose constitutes a very significant reserve in the scutellum and that it is efficiently consumed during the time in which the adjacent embryo axis is engaged in an active metabolism. Sucrose transporter was immunolocalized in the scutellum and in vascular elements. In parallel, a cell-wall invertase activity, which hydrolyses sucrose, developed in the embryo axis, which favoured higher glucose uptake. Sucrose and hexose transporters were active in the embryo tissues, together with the plasma membrane H+-ATPase, which was localized in all embryo regions involved in both nutrient transport and active cell elongation to support radicle extension. It is proposed that, during the initial maize germination phases, a net flow of sucrose takes place from the scutellum towards the embryo axis and regions that undergo elongation. During radicle extension, sucrose and hexose transporters, as well as H+-ATPase, become the fundamental proteins that orchestrate the transport of nutrients required for successful germination.

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The purpose of this study was to identify visible and microscopic symptoms as well as certain biochemical changes associated with chilling injury (CI) in "Atlixco" cactus stems. Cladodes were harvested, disinfected, minimally processed and stored at 4, 12 and 26C for 14-21 days. Results indicated that cactus stems were sensitive to CI at 4 and 12C and exhibited pitting and bronzing as visible symptoms of this disorder. Confocal microscopy showed that mitochondrial integrity was maintained at 4C whereas a deterioration of these organelles occurred at 12 and 26C. Electrolyte leakage, together with an increase in the levels of Adenosine triphosphate (ATP), glutathione and the reduced form of ascorbic acid were associated with CI. In spite of the presence of CI at 4C, cactus stems were still able to preserve their taste quality and no adverse effects were observed on either firmness or color for 21 days. PRACTICAL APPLICATIONSMinimally processed products should be refrigerated at ≤4C in order to maintain their quality and prevent the growth of harmful microorganisms. However, the refrigeration of cactus stems at suboptimal temperatures causes the appearance of chilling injury (CI). Previous studies have mentioned the general symptoms of this physiological disorder in cactus stems, but no one has described the symptomatology in detail and there is yet to be reported histological and biochemical characterization that might serve to confirm or diagnose its presence. This study describes the symptoms of CI and provides histological and biochemical indicators for its early identification during storage. It also constitutes the preliminary stage to the future application of postharvest technologies that induce tolerance to CI, preventing browning and preserving the quality of minimally processed cactus stems in order to expand their domestic and international markets.