Parenchyma-chlorenchyma water movement during drought for the hemiepiphytic cactus Hylocereus undatus.

Background And Aims: Hylocereus undatus, a hemiepiphytic cactus cultivated in 20 countries for its fruit, has fleshy stems whose water storage is crucial for surviving drought. Inter-tissue water transfer during drought was therefore analysed based on cell volumes and water potential components.

Methods: In addition to determining cell dimensions, osmotic pressures and water potentials, a novel but simple procedure leading to an external water potential of zero was devised by which cells in thin sections were perfused with distilled water.

Young daughter cladodes affect CO2 uptake by mother cladodes of Opuntia ficus-indica.

Background And Aims: Drought damages cultivated C3, C4 and CAM plants in the semi-arid lands of central Mexico. Drought damage to Opuntia is common when mother cladodes, planted during the dry spring season, develop young daughter cladodes that behave like C3 plants, with daytime stomatal opening and water loss. In contrast, wild Opuntia are less affected because daughter cladodes do not develop on them under extreme drought conditions.

Nectar: properties, floral aspects, and speculations on origin.

Although nectar is crucial for most pollinators, its evolutionary origin has received scant attention. Nectar is derived from the phloem solution. Both have high sugar concentrations (usually 10-30% solutes by fresh mass); the main solute in the phloem is sucrose, whereas nectar can also contain considerable amounts of fructose and glucose.

Carbon and water relations for developing fruits of Opuntia ficus-indica (L.) Miller, including effects of drought and gibberellic acid.

Growth, gas exchange rates, and carbohydrate content were studied for developing fruits of the cultivated cactus Opuntia ficus-indica (L.) Miller, including effects of drought and exogenous gibberellic acid (GA3). Fruit development required 110 d from the time of bud differentiation to ripening at 80 d after anthesis, when the fruit mass averaged 67 g.

Effects of benomyl and drought on the mycorrhizal development and daily net CO2 uptake of a wild platyopuntia in a rocky semi-arid environment.

The effects of drought and the fungicide benomyl on a wild platyopuntia, Opuntia robusta Wendl., growing in a rocky semi-arid environment were assessed. Cladode phosphorus content, cladode water potential and daily net CO2 uptake were measured monthly in 2000 and 2001 before, during and after the summer rainy period.

Growth and development of the arborescent cactus Stenocereus queretaroensis in a subtropical semiarid environment, including effects of gibberellic acid.

In Stenocereus queretaroensis (Weber) Buxbaum, an arborescent cactus cultivated in Jalisco, Mexico, for its fruits but studied here in wild populations, stem extension occurred in the autumn at the beginning of the dry season, flowering and fruiting occurred in the spring at the end of the dry season, and new roots grew in the summer during the wet season. The asynchrony of vegetative and reproductive growth reduces competitive sink effects, which may be advantageous for wild populations growing in infertile rocky soils. Seasonal patterns of sugars in the roots and especially the stems of S.

Tolerances and acclimation to low and high temperatures for cladodes, fruits and roots of a widely cultivated cactus, Opuntia ficus-indica.

• Opuntia ficus-indica , a cactus widely cultivated for fruits and forage/fodder, has shoots composed of flattened stem segments (cladodes) that are relatively sensitive to freezing temperatures below -6°C but extremely tolerant of high temperatures up to 65°C. Based on the uptake of the vital strain neutral red, fruits and roots were damaged by 60 min below -7°C or above 55°C. • Young (6 wk old) and mature (1-yr-old) cladodes had 1.

Plasma membrane aquaporins play a significant role during recovery from water deficit.

The role of plasma membrane aquaporins (PIPs) in water relations of Arabidopsis was studied by examining plants with reduced expression of PIP1 and PIP2 aquaporins, produced by crossing two different antisense lines. Compared with controls, the double antisense (dAS) plants had reduced amounts of PIP1 and PIP2 aquaporins, and the osmotic hydraulic conductivity of isolated root and leaf protoplasts was reduced 5- to 30-fold. The dAS plants had a 3-fold decrease in the root hydraulic conductivity expressed on a root dry mass basis, but a compensating 2.

Initial net CO2 uptake responses and root growth for a CAM community placed in a closed environment.

To help understand carbon balance between shoots and developing roots, 41 bare-root crassulacean acid metabolism (CAM) plants native to the Sonoran Desert were studied in a glass-panelled sealable room at day/night air temperatures of 25/15 degrees C. Net CO(2) uptake by the community of Agave schottii, Carnegia gigantea, Cylindropuntia versicolor, Ferocactus wislizenii and Opuntia engelmannii occurred 3 weeks after watering. At 4 weeks, the net CO(2) uptake rate measured for south-east-facing younger parts of the shoots averaged 1.

Root deployment and shoot growth for two desert species in response to soil rockiness.

Soil texture, as well as the presence of rocks, can determine the water status, growth, and distribution of plants in arid environments. The effects of soil rockiness and soil particle size distribution on shoot and root growth, root system size, rooting depth, and water relations were therefore investigated for the Crassulacean acid metabolism leaf succulent Agave deserti and the C(4) bunchgrass Pleuraphis rigida after precipitation events during the summer and winter/spring rainfall periods in the northwestern Sonoran Desert. The soils at the field site varied from sandy (<3% rocks by volume) to rocky (up to 35% rocks), with greater water availability at higher water potentials for sandy than for rocky soils.

Growth and reproductive characteristics of the columnar cactus Stenocereus queretaroensis and their relationships with environmental factors and colonization by arbuscular mycorrhizae.

Three natural populations of pitayo (Stenocereus queretaroensis (Weber) Buxbaum), a columnar arborescent cactus, were studied in their subtropical environments in western Mexico. All of the sites were characterized by shallow, nutrient-poor soils. Percentage of colonization by arbuscular mycorrhizae (AM) fungi, stem growth, fruit mass, and percentage germination were greater in S.

Plant frequency, stem and root characteristics, and CO uptake for Opuntia acanthocarpa: elevational correlates in the northwestern Sonoran Desert.

A common cylindropuntia in the northwestern Sonoran Desert, Opuntia acanthocarpa, was investigated for the following hypotheses: its lower elevational limit is set by high temperatures, so its seedlings require nurse plants; its upper elevational limit is set by freezing; spine shading is the least at intermediate elevations; and changes in plant size and frequency with elevation reflect net CO uptake ability. For four elevations ranging from 230 m to 1,050 m, the mean height of O. acanthocarpa approximately doubled and its frequency increased 14-fold.

Root-soil contact for the desert succulent Agave deserti in wet and drying soil.

To investigate the extent and size of root-soil air gaps that develop during soil drying, resin casts of roots of the desert succulent Agave deserti Engelm. were made in situ for container-grown plants and in the field. Plants that were draughted in containers for 7 and 14 d had 24 and 34% root shrinkage, respectively, leading to root-soil air gaps that would reduce the hydraulic conductivity at the root-soil interface by a factor of about 5.

Light, chlorophyll, carboxylase activity and CO fixation at various depths in the chlorenchyma of Opuntia ficus-indica (L.) Miller under current and elevated CO.

Mature cladodes of Opuntia ficus-indica (L.) Miller have a thick chlorenchyma (about 4 mm) with a relatively high chlorophyll convent (0.65 gm ), suggesting that light may be greatly attenuated and hence CO fixation negligible in the inner part of this tissue.

Hydraulic conductivity and anatomy along lateral roots of cacti: changes with soil water status.

To help understand root function for desert plants at different levels of water availability, cellular and water-conducting properties were examined for young lateral roots of Ferocactus acanthodes (Lem.) Britton & Rose and Opuntia ficus-indica (L.) Miller.

Influence of rocks on soil temperature, soil water potential, and rooting patterns for desert succulents.

At a site in the Sonoran Desert, subterranean rocks and exposed boulders affected soil water potential as well as root morphology and distribution. For Agave deserti, the number of lateral roots per unit length of main root was 11 times higher under rocks and six times higher alongside rocks than in rock-free regions. Total root length per unit soil volume for Echinocereus engelmannii averaged 3-fold higher within 1 cm of boulders than 5 cm away, where the soil was drier.

Water relations and mucopolysaccharide increases for a winter hardy cactus during acclimation to subzero temperatures.

Thickness, relative water content (RWC), osmotic pressure, water potential isotherms, and mucopolysaccharide content were measured for the photosynthetic chlorenchyma and the water-storage parenchyma of the winter hardy cactus, Opuntia humifusa, after shifting from day/night air temperatures of 25° C/15° C to 5° C/-5° C. After 14 d at 5° C/-5° C, the average fraction of water contained in the symplast decreased from 0.92 to 0.

Achievable productivities of certain CAM plants: basis for high values compared with C and C plants.

CAM species, which taxonomically are at least five times more numerous than C species, often grow-slowly, as is the case for various short-statured cacti and many epiphytes in several families, However, slow growth is not a necessary corollary of the CAM photosynthetic pathway, as can be appreciated by considering the energetics of CO fixation. For every CO fixed photosynthetically, C plants require 3 ATP and 2 NADPH, whereas the extra enzymatic reactions and compartmentation complexity for C plants require 4 or 5 ATP and 2 NADPH, and CAM plants require 5.5-6.

Temperature, water, and PAR influences on predicted and measured productivity of Agave deserti at various elevations.

To measure productivity of Agave deserti over its elevational range in the northwestern Sonoran Desert, leaf unfolding from its basal rosette was monitored on groups of 10 plants at 13 sites. Based on data from an intermediate elevation (840 m), leaf unfolding proved to be highly correlated (r =0.88) with an environmental productivity index (EPI) formed as the product of indices for water status, temperature, and photosynthetically active radiation (PAR); each of these latter indices indicated the fraction of maximum net CO uptake expected for that parameter based on laboratory measurements of gas exchange and field microclimatic data.

Productivity of Agave deserti: measurement by dry weight and monthly prediction using physiological responses to environmental parameters.

An "environmental productivity index" based on physiological responses to three environmental variables was used to predict the net productivity of a common succulent perennial of the Sonoran Desert, Agave deserti, on a monthly basis. Productivity was also independently measured in the field from dry weight changes. The index was based on soil water availability, day/night air temperatures, and photosynthetically active radiation (PAR), which were individually varied in the laboratory and the effect on net CO uptake by the leaves determined.

Extreme temperatures and thermal tolerances for seedlings of desert succulents.

Extreme temperatures near the soil surface, which can reach 70°C at the main study site in the northwestern Sonoran Desert, markedly affect seedling survival. Computer simulations indicated that for the rather spherical barrel cactus Ferocactus acanthodes (Lem.) Britt.

Experimental removal of intraspecific competitors - effects on water relations and productivity of a desert bunchgrass, Hilaria rigida.

Intraspecific competition in the C bunchgrass Hilaria rigida was examined on a Sonoran Desert site in southeastern California. Potential competition within monospecific stands was experimentally altered by removal of the aboveground portions of all plants within a 1.5 m radius of a monitored plant.

Ecophysiology of Yucca brevifolia, an arborescent monocot of the Mojave sesert.

Photosynthetic characteristics and transpiration of Yucca brevifolia, an evergreen tree endemic to the Mojave Desert of California and Nevada, were examined in the field and the laboratory. Yucca brevifolia was confirmed to be a C plant, with no CAM tendencies observed for its semi-succulent leaves. The species exhibited a maximum net CO uptake of 12 μmol m s at 22°C when grown at day/night air temperatures of 31°C/17°C (data expressed on a total area basis for these opaque leaves).

Simulation of plant temperature and water loss by the desert succulent, Agave deserti.

A simulation model has been developed to describe the thermal relations of individuals of an important group of desert succulents, the agaves, similar to previous modeling efforts on cacti. The model utilizes an energy budget approach to evaluate the effect of various morphological and microclimatic parameters on plant temperature and water loss. For an Agave deserti 0.

High temperature tolerance and heat acclimation of Opuntia bigelovii.

The tolerance of Opuntia bigelovii Engelm. (Cactaceae) to high temperature was investigated by subjecting stems to temperatures ranging from 25°C to 65°C for a 1-h period, after which various properties of chlorenchyma cells were examined. The temperatures at which activities depending on membrane integrity decreased by 50% were 60°C for electrolyte leakage, 52°C for staining by neutral red, and 51°C for plasmolysis for plants maintained at day/night air temperatures of 30°C/20°C.