Changes in Structure and Hydraulic Conductivity for Root Junctions of Desert Succulents as Soil Water Status Varies

Variations in hydraulic conductivity (L_P) and the underlying anatomical and morphological changes were investigated for main root-lateral root junctions of Agave deserti and Ferocactus acanthodes under wet, dry, and rewetted soil conditions. During 21 d of drying, L_P and radial conductivity (L_R) increased threefold to fivefold at junctions of both species. The increase in L_R was accompanied by the formation of an apoplastic pathway for radial water movement from the surface of the junction to the stele for A. deserti and by the rupture of periderm by emerging primordia of secondary lateral roots for F. acanthodes. During 7 d of rewetting, L_R decreased for junctions of A. deserti, as apoplastic water movement was not apparent, but L_R was unchanged for F. acanthodes. Axial conductance (K_h) decreased during drying for both species, largely because of embolism related to the degradation of unlignified cell wall areas in tracheary elements at the root junction. The resulting apertures in the cell walls of such elements would admit air bubbles at pressure differences of only 0.12-0.19 MPa. Rewetting restored K_h for both species, but not completely, due to blockage of xylem elements by tyloses. About 40% of the primary lateral roots of the monocotyledon A. deserti abscised during 21 d of drying. For the dicotyledon F. acanthodes, which can form new conduits in its secondary xylem, only 10% of the primary lateral roots abscised during 21 d of drying, consistent with the much greater frequency of lateral roots that persist during drought in the field compared with the case for the sympatric A. deserti.     

Past and present role of the Indian-fig prickly-pear (Opuntia ficus-indica (L.) Miller,Cactaceae) in the agriculture of sicily

Of prickly-pear cacti occurring in Sicily, the most widespread and economically important isOpuntia ficus-indica (L.) Miller. In Sicily it has, since its introduction, played an important role in the exploitation of marginal areas. The Sicilian experience is described with reference to the historical outlines and the present intensive production of late fruit. Information on historical and actual uses of the plant and its products (flowers, cladodes, fruits) is given.     

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. Stomatal conductance and net CO2 uptake rates for fruits were higher during the night; they were maximal at 7 d before anthesis and decreased as development progressed. Fruits undergoing drought, imposed by detaching terminal stems bearing fruits, were 50% smaller than the control at 80 d after anthesis and did not ripen. Fruits injected with 2 ml of 500 ppm GA3 were 30% smaller than the control at 80 d after anthesis; they contained a large proportion of aborted seeds that produced a weak sink signal for dry mass accumulation. Gas exchange was higher at 21 d after anthesis for fruits treated with GA3. Total soluble sugars represented 40% of the fruit's dry mass until 45 d after anthesis, when the sugar content rapidly increased, reaching 90% at 73 d after anthesis. Such an increase was not observed for fruits treated with GA3, and the sugar content for fruits undergoing drought remained low throughout development. Starch content increased for developing fruits of O. ficus-indica until 14 d after anthesis and, except for the fruits undergoing drought, decreased thereafter. Fruit development for O. ficus-indica is apparently regulated by water availability as well as hormonal signals originating both within and outside the fruit.     

Vegetative Parthenocarpy in the Cactus Pear Opuntia ficus-indica (L.) Mill.

The dependence of fruit development on fertilization was studiedin two clones of Opuntia ficus-indica, Ofer and BSI. Fruitsof the clone Ofer bear fully developed seeds, whereas fruitsof the clone BSI contain only degenerated seeds and it was suspectedthat BSI is parthenocarpic. The two clones differed in theirpattern of fruit development. The increase in fruit fresh weightin Ofer was a result of both peel and pulp growth, whereas inBSI fruit growth was mainly due to pulp growth and the peelhad reached its final weight almost at anthesis. Pulp growthin BSI commenced earlier and was faster than in Ofer, but thefinal pulp weight in BSI was only 64% of that in Ofer. Seedgrowth in BSI was limited to the development of semilignifiedand lignified seed coats, whereas in Ofer 43·5% of theseeds were completely developed, the remainder being similarto those found in BSI. Fruits bearing well-developed seeds werealso found in a 'mutant' of BSI that, like Ofer, contained smallerovules at anthesis than flower of the regular BSI genotype.Germination in vivo and in vitro were similar in BSI and Ofer,but pollen tubes failed to reach the ovules in the regular BSIgenotype, while penetrating the ovules in Ofer and the small-ovuledgenotype of BSI. Good-quality fruits similar to Ofer fruitsin weight but with a higher peel to pulp ratio developed inBSI after flower-sterilization in the spring and in the autumn.In Ofer, sterilized flowers failed to develop fruits in springand partially set fruit in the autumn; the fruits consistedalmost exclusively of peel tissue. It was concluded that BSIis a vegetative parthenocarpic clone, i.e., that pollinationis not required for fruit set and development.Copyright 1993,1999 Academic Press Opuntia ficus-indica, cactus pear, fruit development, parthenocarpy, pollen-tube-growth, fluorescence microscopy     

Lactic Acid Fermentation of Cactus Cladodes (Opuntia ficus-indica L.) Generates Flavonoid Derivatives with Antioxidant and Anti-Inflammatory Properties

Cactus pear (Opuntia ficus-indica L.) is widely distributed in the arid and semi-arid regions throughout the world. In the last decades, the interest towards vegetative crop increased, and cladodes are exploited for nutraceutical and health-promoting properties. This study aimed at investigating the capacity of selected lactic acid bacteria to increase the antioxidant and anti-inflammatory properties of cactus cladodes pulp, with the perspective of producing a functional ingredient, dietary supplement or pharmaceutical preparation. Preliminarily, the antioxidant activity was determined through in vitro assays. Further, it was confirmed through ex vivo analysis on intestinal Caco-2/TC7 cells, and the profile of flavonoids was characterized. Cactus cladode pulp was fermented with lactic acid bacteria, which were previously selected from plant materials. Chemically acidified suspension, without bacterial inoculum and incubated under the same conditions, was used as the control. Lactobacillus plantarum CIL6, POM1 and 1MR20, Lactobacillus brevis POM2 and POM4, Lactobacillus rossiae 2LC8 and Pediococcus pentosaceus CILSWE5 were the best growing strains. Fermentation of cladode pulp with L. brevis POM2 and POM4 allowed the highest concentration of γ-amino butyric acid. Lactic acid fermentation had preservative effects (P<0.05) on the levels of vitamin C and carotenoids. Two flavonoid derivatives (kaemferol and isorhamnetin) were identified in the ethyl acetate extracts, which were considered to be the major compounds responsible for the increased radical scavenging activity. After inducing oxidative stress by IL-1β, the increased antioxidant activity (P<0.05) of fermented cladode pulp was confirmed using Caco-2/TC7 cells. Fermented cladode pulp had also immune-modulatory effects towards Caco-2 cells. Compared to the control, fermented cladode pulp exhibited a significantly (P<0.05) higher inhibition of IL-8, TNFα and prostaglandins PGE2 synthesis. The highest functional effect was found using ethyl acetate extracts. In conclusion, fermentation, especially with L. plantarum strains and L. brevis POM4, enhanced the antioxidant and immune-modulation features of cladode pulp.     

Effect of polysaccharides from Opuntia ficus-indica (L.) cladodes on the healing of dermal wounds in the rat.

In traditional medicine extracts of polysaccharide-containing plants are widely employed for the treatment of skin and epithelium wounds and of mucous membrane irritation. The extracts of Opuntia ficus-indica cladodes are used in folk medicine for their antiulcer and wound-healing activities. The present study describes the wound-healing potential of two lyophilized polysaccharide extracts obtained from O. ficus-indica (L.) cladodes applied on large full-thickness wounds in the rat. When topically applied for 6 days, polysaccharides with a molecular weight (MW)>10(4)Da from O. ficus-indica cladodes induce a beneficial effect on cutaneous repair in this experimental model; in particular the topical application of O. ficus-indica extracts on skin lesions accelerates the reepithelization and remodelling phases, also by affecting cell-matrix interactions and by modulating laminin deposition. Furthermore, the wound-healing effect is more marked for polysaccharides with a MW ranging 10(4)-10(6)Da than for those with MW>10(6)Da, leading us to suppose that the fine structure of these polysaccharides and thus their particular hygroscopic, rheologic and viscoelastic properties may be essential for the wound-healing promoter activity observed.     

Influence of Soil Water Matric Potential and Hydraulic Conductivity on the Germination of Rape (Brassica napus L.)

The influence of matric potential and hydraulic conductivityon the water absorption and germination of rape (Brassica napusL.) was investigated by comparative studies in three seed-soilwater systems. In all systems the rate of germination and totalgermination were substantially retarded with decreasing matricpotential. Hydraulic conductivity of the soil system was demonstratedto be a limiting factor in the germination process. The effectsof matric potential and hydraulic conductivity on water absorptionfollowed closely those demonstrated for germination. The influenceof matric potential was shown to be comparable to that of osmoticpotential provided consideration was given to the hydraulicproperties of the soil-seed system.     

Water Transport in Onion (Allium cepa L.) Roots (Changes of Axial and Radial Hydraulic Conductivities during Root Development)

The hydraulic architecture of developing onion (Allium cepa L. cv Calypso) roots grown hydroponically was determined by measuring axial and radial hydraulic conductivities (equal to inverse of specific hydraulic resistances). In the roots, Casparian bands and suberin lamellae develop in the endodermis and exodermis (equal to hypodermis). Using the root pressure probe, changes of hydraulic conductivities along the developing roots were analyzed with high resolution. Axial hydraulic conductivity (Lx) was also calculated from stained cross-sections according to Poiseuille's law. Near the base and the tip of the roots, measured and calculated Lx values were similar. However, at distances between 200 and 300 mm from the apex, measured values of Lx were smaller by more than 1 order of magnitude than those calculated, probably because of remaining cross walls between xylem vessel members. During development of root xylem, Lx increased by 3 orders of magnitude. In the apical 30 mm (tip region), axial resistance limited water transport, whereas in basal parts radial resistances (low radial hydraulic conductivity, Lpr) controlled the uptake. Because of the high axial hydraulic resistance in the tip region, this zone appeared to be "hydraulically isolated" from the rest of the root. Changes of the Lpr of the roots were determined by measuring the hydraulic conductance of roots of different length and referring these data to unit surface area. At distances between 30 and 150 mm from the root tip, Lpr was fairly constant (1.4 x 10-7 m s-1 MPa-1). In more basal root zones, Lpr was considerably smaller and varied between roots. The low contribution of basal zones to the overall water uptake indicated an influence of the exodermal Casparian bands and/or suberin lamellae in the endodermis or exodermis, which develop at distances larger than 50 to 60 mm from the root tip.     

Aluminium and the Hydraulic Conductivity of Quercus rubra L. Root Systems

Two hydroponic experiments were conducted to determine the effectsof brief and prolonged AI³⁺ exposures on the hydraulic conductivity(Lp) of northern red oak (Quercus rubra L.) root systems. RootLp was determined using the pressure chamber method of Fiscus(1977). In the first experiment, 28- to 40-d-old seedlings weretreated for 4 d with complete nutrient solutions containingone of three Al concentrations (0.04, 1.85 or 3.71 mol m^–3)and either 0 or 50 mmol m^–3 P. Neither Lp nor daily transpirationwas affected by treatment. In Experiment II, seedlings were grown for 48–63 d incomplete solutions containing one of three Al concentrations(0, 0.75 or 2.00 mol m^–3) and either 10 or 250 mmol m^–3Ca. Lp and leaf area to root length ratio (LA/RL) were reducedwhen (AI³⁺/ Ca²⁺), the solution activity ratio, was 2.9 andhigher. Lp and LA/RL were also negatively correlated with Alconcentration and Al/Ca concentration ratio in the roots. Lpwas positively correlated with LA/RL in both experiments. Itis unclear whether Lp in the second experiment was reduced directlyby solution and root chemistry or whether Lp changed in responseto altered leaf/root balance. Key words: Al phytotoxicity, Al x Ca interaction, Quercus rubra, root hydraulic conductivity     

Axial and Radial Hydraulic Resistance to Roots of Maize (Zea mays L.)

A root pressure probe was employed to measure hydraulic properties of primary roots of maize (Zea mays L.). The hydraulic conductivity (Lp_r) of intact root segments was determined by applying gradients of hydrostatic and osmotic pressure across the root cylinder. In hydrostatic experiments, Lp_r was constant along the segment except for an apical zone of approximately 20 millimeters in length which was hydraulically isolated due to a high axial resistance. In osmotic experiments, Lp_r decreased toward the base of the roots. Lp_r (osmotic) was significantly smaller than Lp_r (hydrostatic). At various distances from the root tip, the axial hydraulic resistance per unit root length (R_x) was measured either by perfusing excised root segments or was estimated according to Poiseuille's law from cross-sections. The calculated R_x was smaller than the measured R_x by a factor of 2 to 5. Axial resistance varied with the distance from the apex due to the differentiation of early metaxylem vessels. Except for the apical 20 millimeters, radial water movement was limiting water uptake into the root. This is important for the evaluation of Lp_r of roots from root pressure relaxations. Stationary water uptake into the roots was modeled using measured values of axial and radial hydraulic resistances in order to work out profiles of axial water flow and xylem water potentials.     

A Stereological Analysis of the Succulent Tissue 5Opuntia ficus-indica (L.) Mill.: I. DEVELOPMENT OF MUCILAGE CELLS

A correlated stereological and developmental analysis of thesucculent tissue of Opuntia ficus-indica was carried out. Thestereological parameters related to mucilage cells were describedas a function of their distance from the apical meristem. Polynomesof the second and third degree were found to describe the developmentalprocess. Three zones of development could be distinguished.The relation of the structure of the tissue to its physiologicalfunction and mucilage secretion is discussed.     

Evaluation of three varieties ofOpuntia ficus-indica (L.) Miller as hosts of the Cochineal insectDactylopius coccus costa (Homoptera: Dactylopiidae) in a semiarid area of northeastern Mexico

Three varieties of prickly pearOpuntia ficus- indica (Villanueva, Copena, and Jalpa varieties) were evaluated in their capacity to be host of the cochineal insect (Dactylopius coccus Costa) in two localities of northeastern Mexico. The experiment was carried out for two seasons, winter and summer, in 1998. Variables under evaluation were: fresh weight of grana, dry weight of grana, and number of insects. The Villanueva variety showed the highest production for the three variables and there were no differences between the other two varieties. Iturbide locality was superior to Linares for the three variables. Higher production (both dry and fresh weight of grana) was obtained during winter and there were no differences between seasons for number of insects. Figures obtained for the Villanueva variety are slightly higher than those reported in literature for the most productive cochineal areas in Mexico.     

A Stereological Analysis of the Succulent Tissue 5Opuntia ficus-indica (L.) Mill.: II. ULTRASTRUCTURAL DEVELOPMENT OF THE MUCILAGE CELLS

Five stages of the development of the cytoplasm of mucilagecells were followed by stereological analysis and analysed togive numerical (N_v), volumetric (V_v) and surface (S_v) densitiesof organelles and membranes. A quantitative evaluation of membrane areas, membrane sites,and mucilage secretion was obtained based on morphological andhistochemical data. The developmental process from early differentiationto complete degeneration of the cytoplasm is discussed in quantitativeterms.     

Root Hydraulic Conductivity of Two Cactus Species in Relation to Root Age, Temperature, and Soil Water Status

The effects of root age, temperature, and soil water statuson root hydraulic conductivity (L_P) were investigated for twocactus species, Ferocactus acanthodes and Opuntia ficus-indica.The volumetric flux density of water was measured for excisedroot segments, either using negative hydrostatic pressures appliedto the proximal end or using reverse flow of water from theroot to the soil. For both species, L_P at 20 ?C increased withroot age, average values reaching a maximum of 3.9 ? 10^–7m s^–1 MPa^–1 for F. acanthodes and 5.2 ? 10^–7m s^–1 MPa^–1 for O.ficus-indica at 11 to 17 weeksof age; L_P subsequently declined with increasing root age forboth species. L_P was maximal at a temperature of about 10 ?Cfor the youngest roots (1–3 weeks), this optimum shiftingto 40 ?C for 8-week-old roots of both species. For older roots(up to 1.5-years-old), L_P increased with temperature from 0?C to 50 ?C, with a Q₁₀ of 1.3 between 20 ?C and 30 ?C. At asoil water potential (_soil) of –0.016 MPa, root L_P wasindependent of the direction of water flow for both species.Depending on root age, L_P declined 45- to 500-fold for F. acanthodesand 90- to 800-fold for O.ficus-indica as _soil was reduced from–0.016 to –1.06 MPa, consistent with a rectifier-likebehaviour with respect to water movement between soil and roots.Incorporation of such responses into water uptake models shouldlead to a better understanding of root function. Key words: Ferocactus acanthodes, Opuntia ficus-indica, water potential, tension, reverse flow     

Development of Golgi Apparatus in the Root Cap Cells of Maize (Zea mays L.) as Affected by Compacted Soil

Effects of soil mechanical impedance on the development of Golgiapparatus in the root cap cells of maize were studied undercontrolled soil-water conditions Heavily compacted soil (bulkdensity = 1.50 g cm^–2) had 3.3 to 3.4 times greater mechanicalimpedance than control soil (bulk density = 1.33 g cm^–3),but their oxygen diffusion rates were not significantly differentThe number of dictyosomes and the number and area of secretoryvesicles per unit area of tangentially sub-peripheral root capcells in the heavily compacted soil increased compared to thosein the control These results suggest that secretory activityof the root cap cells is promoted by soil mechanical impedance Dictyosome, Golgi apparatus, maize, mucilage, root cap, secretory activity, secretory vesicles, soil mechanical impedance, Zea mays L     

Comparative Effects of Soil Moisture Stress and Restricted Root Zone Volume on Morphogenetic and Physiological Responses of Soybean [Glycine max (L.) Merr.]

Significant differences in response to soil moisture stress(SMS) and restricted root zone volume (RRZV) were found in twocultivars of soybean [Glycine max (L.) Merr.] (‘Forrest’and ‘Williams’) plants grown under controlled-environmentconditions. Leaf water potentials of SMS-treated plants were0·4-0·6 MPa lower than those of controls and stomata1conductances 23-56% lower. In the case of RRZV treatment, however,there were no differences in either parameter. Initiation ofnew leaves as reflected in the plastochron index was stronglyreduced by SMS but was unaffected by RRZV. Photosynthetic rates(CO₂ fixation dm² of leaf) of plants given SMS were reducedby 11-21% while those of RRZV-treated plants were unaffected.SMS caused a strong preferential allocation of dry matter tothe root at the expense of the shoot in both cultivars. RRZV,however, had no effect on assimilate distribution in ‘Forrest’and only slightly favoured root growth in ‘Williams.’Carbohydrate concentrations of both alcohol-soluble and insolublefractions were increased significantly by SMS, especially inthe leaves, but were little affected by RRZV. Nitrogen concentrationin the root fraction was reduced by 22-24% and that in the leafand stem fractions by 7-14% under SMS but was not affected appreciablyby RRZV. Phosphorus concentration in the leaf, stem, and rootfractions was reduced by 45-65% under SMS but was relativelyunaffected by RRZV. These findings suggest that SMS and RRZVare basically different in their mechanism of action and thatthe impairment of growth resulting from these two stresses mayinvolve different physiological processes. Our results alsoindicate that the suppressive effects of small containers onplant growth do not necessarily result from inadvertent SMS. Key words: Drought, Container effects, Glycine max (L.) Merr     

薄荷根内生及根际细菌多样性探究

采用传统的培养方法和基于分子生物学技术的非培养方法对我国常用中药之一的薄荷植物的根内生及根际细菌进行研究,从而了解其中细菌群落的多样性。对分离得到的细菌菌株进行16S rDNA扩增和系统发育分析,结果表明,利用培养方法与非培养方法分离得到薄荷根内生细菌及根际细菌一些共有的细菌种类,但前者优势种群为g-变形杆菌,后者优势种群为芽孢杆菌,说明土壤细菌,特别是根际细菌是植物内生细菌的重要来源,但植物对其内生细菌具有选择压。首次报道了薄荷根内和根际具有丰富的微生物群落多样性,为进一步探索植物根系微生态环境中微生物群落的形成和生态功能提供了基础信息。在今后探讨植物与微生物相互作用关系时,有必要考虑土壤环境,特别是根际对其的影响的同时,更加重视植物与其相关联的细菌种类的选择作用。     

Effects of Soil Nutrients and Moisture on Root/Shoot Ratios in Lolium perenne L. and Trifolium repens L

The dry weights of foliage and roots (excluding stembases) werecompared in a 3³x2² factorial experiment with Lolium perenneL. and Trifolium repens L. grown in pots with three nitrogen(0–300 ppm N), phosphorus (0–300 ppm P), and soilmoisture (pF 3.2, pF 2.4, and waterlogged) treatments, eachduplicated. Root/shoot ratios were influenced significantly (P < 0.001)by N, P, and W (soil moisture), but these main effects werequalified by highly significant first-order interactions andsecond-order interactions which included N and P. The lowestR/S ratios occurred where N, P, and W were all non-limiting,and the highest where there was an imbalance of these factors. The explanation suggested is that a decrease in the availabilityof N, P, or W causes an increase in the relative weight of roots,but in the presence of N, P, or W deficiency an increase inany one of these factors causes a further increase in the R/Sratio by increasing the relative efficiency of the foliage.