Cecilia B. Peña-Valdivia

Diversity of unavailable polysaccharides and dietary fiber in domesticated nopalito and cactus pear fruit (Opuntia spp.).

The aim of this study was to quantify mucilages, pectins, hemicelluloses, and cellulose of nopalitos (edible, as vegetable, young cladodes of flat‐stemmed spiny cacti) of most consumed Mexican cultivars, and sweet and acid cactus pear fruits of Opuntia spp. The hypothesis is that, regardless of their unavailable polysaccharides diversity, nopalitos and cactus pear fruits are rich sources of soluble and insoluble dietary fiber. Twelve cultivars of Opuntia spp. were used. Nopalitos had a significant variation in structural polysaccharides among the cultivars: mucilages (from 3.8 to 8.6% dry matter (DM)) averaged near a half of pectins content (from 6.1 to 14.2% DM) and tightly bound hemicelluloses (from 2.2 to 4.7% DM), which were the less abundant polysaccharides, amounted 50% of the loosely bound hemicelluloses (from 4.3 to 10.7% DM). Acid fruits (or ‘xoconostle’) had significantly higher unavailable polysaccharides content than sweet fruit, and contain similar proportions than nopalitos. Unavailable polysaccharides represent a high proportion of dry tissues of nopalitos and cactus pear fruits, composition of both of these soluble and insoluble polysaccharides (total dietary fiber) widely vary among cultivars without an evident pattern. Nopalitos and cactus pear fruit can be considered an excellent source of dietary fiber.

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 the natural 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 % in the domesticated variety, but by only 32 % in the wild bean at -2.35 MPa. The number of cells in the cortex and the thickness of the xylem wall increased in both wild and domesticated beans at low substrate ψW; nevertheless, the effect was significantly lower in the wild bean. The number of xylem vessels increased in the cultivar (up to 40 %) while in the wild bean it decreased (up to 33 %). The diameter of xylem vessels and transverse root area diminished (15 and 57 %, respectively) in the cultivar, but in the wild common bean were not 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.

Root growth and proline content in drought sensitive and tolerant maize (Zea mays L.) seedlings under different water potentials

The effect of substrate water potential (Ψ W ) in root growth and proline content of maize seedlings of Tuxpeno Sequia C0 (TSC0) and Tuxpeno Sequia C8 (TSC8), sensitive and resistant to drought respectively, were evaluated. Seventy two hours old seedlings, with 5 cm root length, were maintained for 24 h in vermiculite at Ψ W between −0.03 and −2.35 MPa. Root length, fresh and dry weight, number of lateral roots and proline content were evaluated. Root enlargement of TSC0 was significantly higher than TSC8 at −0.03 MPa, but the response was opposite at low substrate Ψ W . The number of lateral roots was reduced in 23% in TSC8 at the lowest substrate Ψ W (−2.35 MPa) but it was not significantly affected in TSC0. A higher proline content was quantified in the cell division root region than in differentiation root region in both maize populations (5.64 and 6.96 μmol 100 mg −1 of dry weight in TSC0 and TSC8, respectively); and Ψ W between −0.65 and −2.35 MPa induced a drastic and significant increase of prolin...

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 (PsiW), by anatomical modifications. Three-4 cm root length seedlings were planted in vermiculite for 24 h at PsiW between -0.03 and -2.35 MPa. Root dimensions, proline content and anatomy were evaluated. Substrate PsiW 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 micromoles mg(-1). Significant reductions of transverse root area (41%), thickness of mucilage covering the epidermis (47%), thickness of epidermis (between 15 and 46%), area of the parenchyma (between 35 and 41%) and number of vessels (up to 28%) were observed with PsiW 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%, respectively). The anatomical changes associated with low substrate PsiW indicate a net increase of root apoplatic paths; structures involved in water conduction increased their diameter under low substrate PsiW conditions and anatomical changes occurred during the first 24 h of water stress.

Root anatomy of drought sensitive and tolerant maize ( Zea mays L.) seedlings under different water potentials

The effect of substrate water potential (ψW) in anatomical characteristics of root seedlings of maize Tuxpeno Sequia C0 (TSC0), drought sensitive, and Tuxpefto Sequia C8 (TSC8), drought resistant, were evaluated. Seventy two hours old seedlings, having an average root length of 5 cm, were maintained for 24 h in vermiculite at ψW of −0.03, −0.65, −1.48 and −2.35 MPa. Anatomical characteristics from both differentiation and cell division root regions were evaluated. Lowest ψW diminished significantly (P=0.0020) transverse root area, number of cells in the cortex parenchyma, thickness of epidermis, exodenmis and cortex, and number of metaxylem vessels in both maize populations. Number of metaxylem vessels and cortex thickness was affected only in TSC0 (15% in both cases); in contrast, the number of cortex cells in the differentiation root region increased 25%, independently of the ψW, and the thickness of the xylem wall from the differentiation root region increased 93% at ψW of −2.35 MPa, in both maize populations. Results suggest that the recurrent selection for drought tolerance induced a significant thinning of the protoderm (78%), endodermis (17%), and xylem vessels (14%) in Tuxpefto maize root and modified the response of root to substrate ψW, including several anatomical changes.

Chemical Composition of Cacti Wood and Comparison with the Wood of Other Taxonomic Groups

The aims of this study were to determine the wood chemical composition of 25 species of Cactaceae and to relate the composition to their anatomical diversity. The hypothesis was that wood chemical components differ in relationship to their wood features. The results showed significant differences in wood chemical compounds across species and genera (P < 0.05). Pereskia had the highest percentage of lignin, whereas species of Coryphantha had the lowest; extractive compounds in water were highest for Echinocereus, Mammillaria, and Opuntia. Principal component analysis showed that lignin proportion separated the fibrous, dimorphic, and non‐fibrous groups; additionally, the differences within each type of wood occurred because of the lignification of the vascular tissue and the type of wall thickening. Compared with other groups of species, the Cactaceae species with fibrous and dimorphic wood had a higher lignin percentage than did gymnosperms and Acer species. Lignin may confer special rigidity to tracheary elements to withstand desiccation without damage during adverse climatic conditions.