Seed germination of Agave species as influenced by substrate water potential

BACKGROUND: Plants of Agave spp. perform Crassulacean acid metabolism (CAM) and are highly drought-tolerant, but little is known concerning seed germination under low water availability. The aim of this study was to assess the effect of substrate water potential (ΨW) on seed germination and contrast hydrotime parameters of seven valuable and commercially-important Agave species from different geographical distributions and climatic regions of Mexico. Our hypothesis was that seed germination of Agave species is not affected by low water availability independently of seed biomass and the climate of their distribution area. RESULTS: Seed germination (at 25°C and in the dark) between 85 and 100% for all species occurred within 80 - 180 h at -0.03 MPa and 250 - 430 h at -1.0 MPa. Seed germination at -1.5 MPa declined to less than 50% (p < 0.05) for A. asperrima and A. cupreata but did not change significantly for A. americana var. marginata, A. lechuguilla and A. striata, although they showed the lowest mean base water potential (-2.01 to -2.64 MPa). Seed germination of 40% Agave species, from arid and semi-arid climates in this study, was not affected by the lower ΨW. CONCLUSION: Germination of seeds of Agave species is moderately affected by low water availability, is partially dependent of their ecological distribution, and is independent of seed mass.

Anatomical root variations in response to water deficit: wild and domesticated common bean (Phaseolus vulgaris L)

Root anatomical responses to water deficit are diverse and regulation of water uptake strongly depends on plant anatomy. The ancestors of common bean (Phaseolus vulgaris L.) cultivars are the wild common beans. Because wild beans adapt and survive well in theon atural environment, it is hypothesized that wild common bean roots are less affected than those of domesticated beans at low substrate water potential (ψW). A wild common bean accession from Chihuahua Mexico and cv. Bayomex were studied. Seedlings with a mean root length between 3 and 4 cm were maintained for 24 h in vermiculite at ψW of -0.03 (well hydrated), -0.65, -1.48 and -2.35 MPa (partially dry). Ten anatomical characteristics of differentiation and cell division in root regions were evaluated. Thickness of epidermis and protoderm diminished similarly in wild and domesticated beans growing at low substrate ψW (between -0.65 and -2.35 MPa). At the same time, parenchymatic cell area diminished by 71 percent in the domesticated variety, but by only 32 percent in the wild bean at -2.35 MPa. Theon umber of cells in the cortex and the thickness of the xylem wall increased in both wild and domesticated beans at low substrate ψW;on evertheless, the effect was significantly lower in the wild bean. Theon umber of xylem vessels increased in the cultivar (up to 40 percent) while in the wild bean it decreased (up to 33 percent). The diameter of xylem vessels and transverse root area diminished (15 and 57 percent, respectively) in the cultivar, but in the wild common bean wereon ot affected. Anatomical root characteristics and their modifications in both differentiation and cell division in root regions demonstrated that the wild bean reacted quite differently to substrate ψW than the domesticated common bean.

Effects of substrate water potential in root growth of Agave salmiana Otto ex Salm-Dyck seedlings

The objective of this study was to test the hypothesis that root of maguey (Agave salmiana Otto ex Salm-Dyck) seedlings reacts during the first 24 h to low substrate water potential (Yw), by anatomical modifications. Three-4 cm root length seedlings were planted in vermiculite for 24 h at Yw between -0.03 and -2.35 MPa. Root dimensions, proline content and anatomy were evaluated. Substrate ψw between -0.65 and -2.35 MPa did not significantly affect longitudinal root growth. However, proline content significantly increased from 1.6 to 2.1 emoles mg-1. Significant reductions of transverse root area (41 percent), thickness of mucilage covering the epidermis (47 percent), thickness of epidermis (between 15 and 46 percent), area of the parenchyma (between 35 and 41 percent) and number of vessels (up to 28 percent) were observed with Yw of -2.35 MPa. In contrast, thickness of xylem wall, diameter of xylem vessels and the number of cells of the cortex of the differentiation root region significantly increased (64, 17, and 97 percent, respectively). The anatomical changes associated with low substrate Yw indicate a net increase of root apoplatic paths; structures involved in water conduction increased their diameter under low substrate Yw conditions and anatomical changes occurred during the first 24 h of water stress.

Efectos del potencial de agua en el crecimiento radical de plántulas de agave salmiana otto ex salm-dyck / Effects of the potential of water in the radical growth of plántulas of agave salmiana otto former salm-dyck

El objetivo de este estudio fue determinar el efecto del potencial de agua del substrato en las características fisiológicas y biofísicas de la raíz de plántulas de Agave salmiana Otto ex Salm-Dyck en condiciones de laboratorio. Las plántulas con raíz de 3 a 4 cm de longitud se mantuvieron por 24h en vermiculita con psi A de -0,03: -0,65; -,148 y -2,35MPa. Un lote de plántulas fue rehidratado y de otro las raices se recolectaron y se cuantificó el crecimiento, contenido de prolina, así como la conductividad eléctrica, pH, Cu, Fe, K, Mn, Na y Zn en el medio de resuspensión de las raices. Se calculó el índice de daño y se evaluó el efecto de la rehidratación en el crecimiento. Los psi A bajos del substrato no afectaron significativamente la longitud, pero afectaron significativamente el peso fresco (entre 23,5 y 49,2 por ciento) y el índice de daño incrementó 36,0 por ciento; los elementos liberados al medio no se modificaron significativamente y el contenido de prolina de la raíz se incrementó de 1,6 a 2,14 moles.mg1 de materia seca. Con la rehidratación la raíz continuó su crecimiento