Developmental Reaction Norms for Water Stressed Seedlings of Succulent Cacti

Succulent cacti are remarkable plants with capabilities to withstand long periods of drought. However, their adult success is contingent on the early seedling stages, when plants are highly susceptible to the environment. To better understand their early coping strategies in a challenging environment, two developmental aspects (anatomy and morphology) in Polaskia chichipe and Echinocactus platyacanthus were studied in the context of developmental reaction norms under drought conditions. The morphology was evaluated using landmark based morphometrics and Principal Component Analysis, which gave three main trends of the variation in each species. The anatomy was quantified as number and area of xylem vessels. The quantitative relationship between morphology and anatomy in early stages of development, as a response to drought was revealed in these two species. Qualitatively, collapsible cells and collapsible parenchyma tissue were observed in seedlings of both species, more often in those subjected to water stress. These tissues were located inside the epidermis, resembling a web of collapsible-cell groups surrounding turgid cells, vascular bundles, and spanned across the pith. Occasionally the groups formed a continuum stretching from the epidermis towards the vasculature. Integrating the morphology and the anatomy in a developmental context as a response to environmental conditions provides a better understanding of the organism's dynamics, adaptation, and plasticity

Seed germination of Echinopsis schickendantzii (Cactaceae): the effects of constant and alternating temperatures

The effects of constant and alternating temperatures on seed germination in the Cactaceae have been reported to vary, probably as a result of the different temperature regimes used and the species considered. We determined the cardinal temperatures for, and evaluated the effects of a wide range of constant and alternating temperatures on, seed germination of the South American cactus, Echinopsis schickendantzii Web. The base, optimum and maximum temperatures were 7°C, 26.8°C and 49°C, respectively. The proportion of seeds that germinated and the germination rates were not only significantly different at constant and alternating temperatures but also among all temperature regimes considered. The highest proportion of seeds to germinate occurred at 15°, 20°, 30° and 30/15°C whereas the highest germination rates occurred at 25°, 30°, 30/20°, 35/20° and 40/25°C, with no significant differences between the highest values at constant and alternating temperatures. In the suboptimal temperature range for germination rate, the thermal time to 50% germination was 98°C-days. The results indicate that the seeds have no obligate requirement for alternating temperature for germination.Fil: Ortega Baes, Francisco Pablo. Universidad Nacional de Salta. Facultad de Cs.naturales. Escuela de Agronomia. Laboratorio de Investigaciones Botanicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Galindez, Guadalupe. Instituto Nacional de Tecnología Agropecuaria. Centro Nacional de Investigaciones Agropecuarias. Centro de Investigación de Recursos Naturales. Instituto de Recursos Biológicos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Sühring, Silvia Susana. Universidad Nacional de Salta. Facultad de Cs.naturales. Escuela de Agronomia. Laboratorio de Investigaciones Botanicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rojas Aréchiga, Mariana. Universidad Nacional Autónoma de México; MéxicoFil: Daws, M. I.. Royal Botanic Gardens; Reino UnidoFil: Pritchard, H. W.. Royal Botanic Gardens; Reino Unid