Latencia secundaria en especies de la tribu Cacteae (Cactaceae)

En ambientes impredecibles como las zonas áridas, los mecanismos de latencia que presentan las semillas que habitan estos ambientes son importantes para el mantenimiento de las poblaciones vegetales. Muchas especies vegetales tienen requerimientos de luz para poder germinar y se ha asociado al fotoblastismo y a la latencia con la formación de bancos de semillas. En las zonas áridas el agua es un factor que limita la germinación y el establecimiento de las plantas por lo que lo que la formación de un banco de semillas es una estrategia que puede incrementar las posibilidades de una semilla de coincidir con un evento de precipitación.  Por ello, se determinó la respuesta fotoblástica de cinco especies de la tribu Cacteae y el desarrollo de latencia secundaria. Se encontró que las especies estudiadas presentan fotoblastismo positivo y que Mammillaria compressa y Turbinicarpus gielsdorfianus desarrollaron eskotolatencia, después de haber estado incubadas en la oscuridad durante un mes. Se discute la importancia del desarrollo de este tipo de latencia y su posible relación con el banco de semillas.

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

Influence of aerial seed banks on germination response in three desert plant species

© The Author 2016. Aims To determine if the germination response of desert plant species to a period of aerial storage in field conditions (i.e. mature seeds that remain attached to the parent plant) is comparable to seeds harvested at maturity and stored in ambient laboratory conditions, to better understand the role of aerial seed bank in the germination ecology of desert plants, using one annual and two perennial species. Methods Seeds of three desert plants (Anastatica hierochuntica, Blepharis ciliaris and Scrophularia deserti) that matured in June 2014, were collected from wild plants in June and November 2014, and germinated under two photoperiods (0, 12 hours light) and three thermoperiods (night/day temperatures of 15/25, 20/30 and 25/35°C). Important Findings Seeds of B. ciliaris and S. deserti had significantly higher germination percentages when harvested and stored for five months, compared to being stored in the aerial seed bank. Germination percentages of these two species increased with decreasing temperature and in the presence of light. These results indicate that these species use a combination of aerial and soil seed banks to maintain a percentage of viable seeds through favourable germination periods. Germination percentages of A. hierochuntica were high under all tested circumstances, indicating that this species relies mainly on the aerial seed bank to maintain a percentage of viable seeds through favourable germination periods. This study shows that the population survival strategies of an aerial seed bank are species-specific. These results have practical implications for conservation and habitat restoration for these species, and also for their propagation since early collection of mature fruits and ex situ storage will result in greater germination percentages of some species