ABSTRACT
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.
ABSTRACT
Resumen Mimosa aculeaticarpa var. aculeaticarpa y M. luisana son endémicas de México y consideradas plantas multipropósito, ya que ofrecen diversos servicios a los ecosistemas y pobladores en donde se establecen. Además, son valoradas por su potencial como restauradoras de ambientes tropicales, por lo que el objetivo de este estudio fue modelar su distribución conocida y potencial. En el año 2014, se obtuvieron registros de dos bases de datos (CONABIO y MEXU); cada resgistro fue validado taxonómica, geográfica y estadísticamente, una vez validados, se obtuvo la distribución conocida y potencial para M. aculeaticarpa var. aculeaticarpa (basada en 99 registros) y M. luisana (basada en 50 registros), utilizando el algoritmo MAXENT. La distribución conocida de ambos taxa se sobreposicionó en las capas de: elevación, clima, suelo, provincias biogeográficas y cuencas hidrológicas. Mimosa aculeaticarpa var. aculeaticarpa presenta amplia distribución en México (16 estados); mientras que M. luisana se encuentra restringida a los estados de Puebla y Oaxaca. M. aculeaticarpa var. aculeaticarpa se establece entre 1 900 y 2 700 msnm y M. luisana entre 500 y 1 760 msnm. Ambas se encuentran en climas áridos y semiáridos; sin embargo, M. aculeaticarpa var. aculeaticarpa también se puede encontrar en climas templados y mésicos. Asimismo, ambos taxa se distribuyen en suelos de tipo regosol calcárico; aunque, M. aculeaticarpa var. aculeaticarpatambién está en regosol éutrico, vertisol crómico y feozem háplico. La distribución de M. aculeaticarpa var. aculeaticarpa abarca ocho provincias biogeográficas y tres cuencas hidrológicas; mientras que M. luisana se localiza en tres provincias y dos cuencas; ambas coinciden en las provincias del Eje Volcánico y la Sierra Madre del Sur. Los modelos de distribución potencial se consideran excelentes, ya que poseen un AUC de 0.91 y 0.97, respectivamente. Los modelos indican que las condiciones de temperatura y precipitación son propicias para que ambos taxa pudieran ampliar su distribución. Igualmente, los modelos generados pueden considerarse como una aproximación al conocimiento de la distribución potencial de las mimosas mexicanas. Aunque, es importante considerar que los modelos son estáticos y no consideran a las interacciones bióticas, por lo que su relación con la realidad puede variar; por lo que se recomienda analizar los modelos mediante diferentes escenarios de cambio climático y de uso de suelo.
Abstract Mimosa aculeaticarpa var. aculeaticarpa and M. luisana are endemic to Mexico, and are considered as multipurpose plants, due to the diverse services they offer to ecosystems and to local people. Additionally, they are appreciated for their potential to restore tropical environments; hence, the objective of this study was to model the present and potential distribution of these taxa. In 2014, species registers were obtained from two databases (CONABIO and MEXU); each register was taxonomically, geographically and statistically validated. Once validated, the present and potential distribution of M. aculeaticarpa var. aculeaticarpa (based on 99 registers) and M. luisana (based on 50 registers) were obtained using the MAXENT algorithm. For both taxa, the present distribution was overlapped using the layers of: elevation, climate, soil, biogeographic provinces, and hydrologic basins. Mimosa aculeaticarpa var. aculeaticarpa showed a wide distribution in Mexico (16 states); whilst M. luisana was restricted to the states of Puebla and Oaxaca. M. aculeaticarpa var. aculeaticarpa establishes between 1 900 and 2 700 masl, and M. luisana between 500 and 1 760 masl. Both species were established in arid and semiarid climates; however, M. aculeaticarpa var. aculeaticarpa can also be found in temperate and mesic climates. Moreover, both taxa are distributed in calcareous regosol soils; although, M. aculeaticarpa var. aculeaticarpa is also found in eutric regosol, chromic vertisol and haplic phaeozem. The distribution of M. aculeaticarpa var. aculeaticarpa includes eight biogeographic provinces and three hydrologic basins; whilst M. luisana was only located in three provinces and two hydrologic basins; both are present in the Eje Volcánico and Sierra Madre del Sur provinces. The potential distribution models are considered as excellent ones due to an AUC of 0.91 and 0.97, respectively; these models indicated that the temperature and precipitation conditions would be suitable for the enlargement of their distribution. Likewise, these models can be considered an approach to the potential distribution knowlegment of the Mexican mimosas. Nevertheless, it is important to note that the models are static and do not take into account any biotic interaction; therefore, their relationship with reality can vary. Thus, it is recommended to analyze the models through different climate change and land use scenarios. Rev. Biol. Trop. 66(1): 321-335. Epub 2018 March 01.
ABSTRACT
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-ß-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.
ABSTRACT
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.
