Alma Orozco-Segovia

Ecological significance of light controlled seed germination in two contrasting tropical habitats.

SummaryThe effects of temperature, photoperiod, phytochrome photoreversion and the response to a R/FR ratio gradient were investigated in seeds of four species from two contrasting tropical habitats; two species from a rain forest (Cecropia obtusifolia and Piper umbellatum) and two from a high altitude lava field covered by low vegetation (Buddleja cordata and Chenopodium ambrosioides). In the rain forest seed species the photoblastic response seems to be adapted to light quality changes due to canopy destruction, on the other hand, the lava field seed species seem to be adapted to instantaneous light stimulus such as would be produced by the sudden exposure of a buried seed to the soil surface light environment.

Seed response to temperature of Mexican cacti species from two life forms: an ecophysiological interpretation

The effect of seven different constant temperatures and five ranges of alternating temperatures on seed germination of seven species of cacti from Puebla, México was analyzed. Six cacti species germinated in a wide range of temperature. Columnar cacti were more tolerant to low temperatures and germinated in a wider range of temperature than barrel cacti. One of the barrel cacti studied (Ferocactus recurvus) only reached full germination at 25 °C . Temperature fluctuations did not produce significant effects on germination compared to the results obtained at constant temperatures. This may reveal differing ecophysiological adaptations with respect to temperature requirements during the establishment conditions for each life form. Columnar cacti may become established mainly under the shade of desert shrubs, whereas barrel cacti maybe can also become established in open areas, beneath the shade of small rocks or soil irregularities. In both cases, temperature fluctuations are attenuated by the shade, but mean temperatures may be higher in the second condition than beneath the shade of plants.

Germination of the hard seed coated Opuntia tomentosa S.D., a cacti from the México valley

Abstract Germination of Opuntia tomentosa seeds collected during 1998 was evaluated using treatments of scarification (H2SO4), gibberellic acid (GA3), dry heat, soaking, light, after-ripening and stratification at constant and alternating temperatures. Seeds were positive photoblastic, germinated best at constant temperatures, and showed a combined dormancy (physiological and physical). Acid scarification, GA3, and heating induced germination, soaking and stratification did not. After 15 and 18 months, GA3 inhibited germination. Dormancy of seeds collected during 2000 was overcome with a short scarification. Differences between baths could be due to 1998 was very dry due to “El Nino”. It is important to identify maternal effects.

Natural priming of Wigandia urens seeds during burial: effects on germination, growth and protein expression

To determine whether seeds of the weedy shrub Wigandia urens, from the Valley of Mexico, undergo natural priming when buried in soil, comparative experiments were performed with seeds: (1) harvested directly from the plants; (2) buried in three natural habitat conditions; and (3) laboratory primed with polyethylene glycol. Seeds were sown in a growth chamber and in a shade house. Final germination percentages, emergence, germination and emergence rates, survival and initial growth were determined. Burial and priming enhanced the germination and emergence parameters evaluated in the laboratory and in the shade house. Effects of treatments on survival were not significantly different. Nevertheless, burial improved emergence and mean survival, and induced differences in specific leaf area of seedlings that could have ecological significance. Heat-stable proteins were extracted and electrophoresed. Proteins formed in W. urens seeds during burial had molecular weights (14‐21 kDa) similar to those reported for late embryogenesis abundant (LEA) proteins induced by priming in other species. Nevertheless, the presence and abundance of proteins expressed (14‐23, 36 and more than 45 kDa) differed among control, primed and buried seeds. During soil burial, molecular and physiological responses were induced that were similar to the effects of priming.

LIGHT EFFECT ON SEED GERMINATION OF FOUR MAMMILLARIA SPECIES FROM THE TEHUACÁN-CUICATLÁN VALLEY, CENTRAL MEXICO

Abstract Seed germination of 4 species of Mammillaria (Cactaceae) from the Tehuacán-Cui-catlán Valley in central México were compared at 4 light treatments (red, far-red, white light, and darkness) at 25°C and at 2 light treatments (white light and darkness) at 2 alternating temperatures (15/30°C and 20/35°C). Seeds were positive photoblastic, but germinated at far-red light. For all species, best germination results were obtained at 25°C with white and red light, and there were no significant differences among treatments. Higher germination percentages were obtained at 25°C than at alternating temperatures. None of the species exhibited any morphophysiological mechanisms of dormancy.

Seed reserve composition in 19 tree species of a tropical deciduous forest in Mexico and its relationship to seed germination and seedling growth

BACKGROUND AND AIMS The size and composition of seed reserves may reflect the ecological strategy and evolutionary history of a species and also temporal variation in resource availability. The seed mass and composition of seed reserves of 19 co-existing tree species were studied, and we examined how they varied among species in relation to germination and seedling growth rates, as well as between two years with contrasting precipitation (652 and 384 mm). METHODS Seeds were collected from a tropical deciduous forest in the northwest of Mexico (Chamela Biological Station). The seed dry mass, with and without the seed coat, and the concentrations of lipids, nitrogen and non-structural carbohydrates for the seed minus seed coat were determined. The anatomical localization of these reserves was examined using histochemical analysis. The germination capacity, rate and lag time were determined. The correlations among these variables, and their relationship to previously reported seedling relative growth rates, were evaluated with and without phylogenetic consideration. KEY RESULTS There were interannual differences in seed mass and reserve composition. Seed was significantly heavier after the drier year in five species. Nitrogen concentration was positively correlated with seed coat fraction, and was significantly higher after the drier year in 12 species. The rate and lag time of germination were negatively correlated with each other. These trait correlations were also supported for phylogenetic independent contrasts. Principal component analysis supported these correlations, and indicated a negative association of seedling relative growth rate with seed size, and a positive association of germination rate with nitrogen and lipid concentrations. CONCLUSIONS Nitrogen concentration tended to be higher after the drier year and, while interannual variations in seed size and reserve composition were not sufficient to affect interspecific correlations among seed and seedling traits, some of the reserves were related to germination variables and seedling relative growth rate.

Analysis of fern spore banks from the soil of three vegetation types in the central region of Mexico.

The vertical structure of fern spore banks was studied in a xerophilous shrubland, montane rain forest, and pine-oak forest in Hidalgo, Mexico, using the emergence method. Soil samples were collected in April 1999 at depths of 0-10, 10-20, and 20-30 cm. Viable spores decreased significantly with depth in all vegetation types, and the highest number of prothallia and sporophytes was found in the uppermost layer. The montane rain forest and the xerophilous shrubland had the largest and the richest banks, respectively. Twenty-three fern taxa were registered in the aboveground vegetation, 12 in the soil banks, and 43.5% were in both. Aboveground and in the soil bank, the xerophilous shrubland, the montane rain forest, and the pine-oak forest had, 17 and 7, 1 and 6, and 7 and 3 taxa, respectively. These were distributed differentially in relation to depth. The Sørensen index indicated a similarity of 61.5% between the xerophilous shrubland and the montane rain forest, and the Czeckanovsky index indicated 19.75%. The presence of viable spores in the soil of all vegetation types confirmed the existence of natural spore banks. Long-distance dispersal was an important factor determining the specific composition of the xerophilous shrubland and the pine-oak forest.

Effect of heat shock on germination of 23 plant species in pine–oak and montane cloud forests in western Mexico

We determined the effect of heat shock on seed germination of 23 species growing in fire-prone areas covered by pine–oak and montane cloud forests. Seeds of each species were exposed to 60, 80, 100 or 120°C for 5 or 60 min in dry and moist sand. Seeds of nine species were incubated for 15 h in moist sand and exposed to the temperature that best promoted germination. Eighteen species required heat shock for germination, and five tolerated it. Dry heat shock for 5 min promoted germination of these species; heat shock in moist sand at 100°C induced germination of 10 species. Exposure for 60 min to heat shock in dry and moist sand improved germination of 14 and 5 species respectively. Logistic models indicate that germination probabilities of most species are increased by temperatures of 70–120°C. Depending on substrate and seed hydration, heat shock increased or left unchanged the germination of most pine–oak and montane cloud forest species. Thus, montane cloud forest seeds can survive low-intensity surface fires. Most species with seeds hydrated before heat shock showed little or no germination. Prescribed burns at the end of the rainy season may therefore be harmful to pine–oak and montane cloud forest species.

Effects of seed burial on germination, protein mobilisation and seedling survival in Dodonaea viscosa.

Ecological restoration of disturbed areas requires substantial knowledge of the germination of native plants and the creation of novel methods to increase seedling establishment in the field. We studied the effects of soil matrix priming on the germination of Dodonaea viscosa seeds, which exhibit physical dormancy. To this end, we buried both pre-scarified (in H2SO4, 3 min) and non-pre-scarified seeds in the Parque Ecológico de la Ciudad de México. After seeds were unearthed, they were post-scarified for 0, 2, 6 and 10 min and their germination percentages compared to the germination of a control batch of laboratory-stored seeds. For both control and unearthed seeds, the protein pattern was determined in the enriched storage protein fraction in SDS-PAGE gels stained with Coomassie blue. Percentage germination increased as the scarification time increased. Pre-scarification significantly increased percentage germination of post-scarified seeds in relation to the control and non-pre-scarified seeds. In seeds unearthed from the forest site, the buried pre-scarified seeds had relatively high percentage germination, even in the absence of post-scarification treatment. A 48-kDa protein was not found in unearthed, pre-scarified seeds nor in the control germinated seeds, indicating that mobilisation of this protein occurred during soil priming. Burying seeds for a short period, including the beginning of the rainy season, promoted natural priming, which increased protein mobilisation. Functionally, priming effects were reflected in high percentage seedling survival in both the shade house and the field. Seed burial also reduced the requirement for acidic post-scarification.

BIIDXI, the At4g32460 DUF642 gene, is involved in pectin methyl esterase regulation during Arabidopsis thaliana seed germination and plant development

BackgroundDUF642 proteins constitute a highly conserved family of proteins that are associated with the cell wall and are specific to spermatophytes. Transcriptome studies have suggested that members of this family are involved in seed development and germination processes. Previous in vitro studies have revealed that At4g32460- and At5g11420-encoded proteins interact with the catalytic domain of pectin methyl esterase 3 (AtPME3, which is encoded by At3g14310). PMEs play an important role in plant development, including seed germination. The aim of this study was to evaluate the function of the DUF642 gene At4g32460 during seed germination and plant development and to determine its relation to PME activity regulation.ResultsOur results indicated that the DUF642 proteins encoded by At4g32460 and At5g11420 could be positive regulators of PME activity during several developmental processes. Transgenic lines overexpressing these proteins showed increased PME activity during seed germination, and improved seed germination performance. In plants expressing At4g32460 antisense RNA, PME activity was decreased in the leaves, and the siliques were very short and contained no seeds. This phenotype was also present in the SALK_142260 and SALK_054867 lines for At4g32460.ConclusionsOur results suggested that the DUF642 family contributes to the complexity of the methylesterification process by participating in the fine regulation of pectin status during plant development.