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 Trichocereus terscheckii (Cactaceae): Light, temperature and gibberellic acid effects

In this paper, we evaluated the effect of light and temperature and addition of gibberellic acid (GA(3)) in the germination of seeds of Trichocerelis terscheckii in order to provide information about Germination requirements which could be use for conservation studies. The germination response within a temperature gradient was evaluated for seeds arising from two populations: La Pedrera and Cuesta del Obispo (Salta, Argentina). Seeds of T terscheckii germinated within a range from 15 to 35 degrees C. Maximum germination percentages were found under white light and no germination was recorded in darkness. GA(3) at any concentration promoted germination either in white light or darkness neither at a constant temperature nor at an alternating one. (c) 2006 Elsevier Ltd. All rights reserved