Cortical Bundles in the Persistent, Photosynthetic Stems of Cacti

We examined 62 species in 45 genera of the cactus subfamilyCactoideae; all had collateral cortical bundles that permeatedthe broad, water-storing inner cortex and extended to the baseof the outer, photosynthetic palisade cortex. Mean distancebetween cortical bundles was 0.75 mm, similar to the mean spacing(0.74 mm) of veins in leaves of Pereskia, a genus of relictleaf-bearing cacti. In 16 species, both young and extremelyold stem cortex was available for study: in all of these, olderbundles had larger amounts of phloem than did younger bundles,indicating that phloem had been produced for many years. Inten species, older bundles also had more xylem than youngerbundles. In two genera (Rhipsalis and Selenicereus) there werecaps of primary phloem fibres, and in a single species (Pilosocereusmortensenii) cortical bundle xylem contained libriform fibres.All cortical bundle tracheary elements were narrow (radius range,0.91–8.2 µm; mode, 1.8–2.7 µm), similarto Pereskia leaf vein elements (radius range, 1.8–2.7µm); this was much narrower than stem wood vessels (radiusrange, 10–42 um; mode, 23–28 µm). Longitudinalconduction of water and nutrients probably occurs predominantlyin stem wood, with cortical bundles maintaining the broad, voluminouscortex, the outer part of which is the plant's photosynthetictissue and the inner part of which stores water and starch.The cortex of the Cactordeae contains numerous leaflike characters;homeotic genes may be involved in its morphogenesis. Cactaceae, cortical bundles, homeotic, xylem, phloem, evolution     

Variable Photosynthetic Metabolism in Leaves and Stems of Cissus quadrangularis L

By measuring titratable acidity, gas exchange parameters, mesophyll succulence, and ¹³C/¹²C ratios, we have shown that Cissus quadrangularis L. has C₃-like leaves and stems with Crassulacean acid metabolism (CAM). In addition, the nonsucculent leaves show the diurnal fluctuations in organic acids termed recycling despite the fact that all CO₂ uptake and stomatal opening occurs during the day. Young succulent stems have more C₃ photosynthesis than older stems, but both have characteristics of CAM. The genus Cissus will be a fruitful group to study the physiology, ecology, and evolution of C₃ and CAM since species occur that exhibit characteristics of both photosynthetic pathways.     

Population Genetic Structure of Two Columnar Cacti with a Patchy Distribution in Eastern Brazil

The genetic variability and population genetic structure of six populations of Praecereus euchlorus and Pilosocereus machrisii were investigated. The genetic variability in single populations of Pilosocereus vilaboensis, Pilosocereus aureispinus, and Facheiroa squamosa was also examined. All of these cacti species have a patchy geographic distribution in which they are restricted to small areas of xeric habitats in eastern Brazil. An analysis of genetic structure was used to gain insights into the historical mechanisms responsible for the patchy distribution of P. euchlorus and P. machrisii. High genetic variability was found at the populational level in all species (P=58.9–92.8%, A_p=2.34–3.33, H_e=0.266–0.401), and did not support our expectations of low variability based on the small population size. Substantial inbreeding was detected within populations (F_IS=0.370–0.623). In agreement with their insular distribution patterns, P. euchlorus and P. machrisii had a high genetic differentiation (F_ST=0.484 and F_ST=0.281, respectively), with no evidence of isolation by distance. Accordingly, estimates of gene flow (N_m) calculated from F_ST and private alleles were below the level of N_m=1 in P. machrisii and P. euchlorus. These results favored historical fragmentation as the mechanism responsible for the patchy distribution of these two species. The genetic distance between P. machrisii and P. vilaboensis was not compatible with their taxonomic distinction, indicating a possible local speciation event in this genus, or the occurrence of introgression events.     

昆明海口早寒武世澄江生物群中叶状红藻化石

主要报道了采自云南省昆明市海口马房村鞍山早寒武世筇竹寺组玉案山段澄江生物群中的叶状红藻-似红叶藻(新属、新种)(Paradelesseria sanguinea Xu,gen.et sp.Nov.).通过比较形态学研究,探讨了该宏观化石藻类的分类归属与亲缘关系,进一步丰富了澄江生物群生物物种多样性的认识,并为研究早寒武世生物演化及其古环境提供了新的化石证据.同时,通过对现生红藻的比较研究,进一步证明了澄江生物群在云南海口地区发生于一个水深在30 m以上的亚潮带和下潮间带的海水环境.     

Salt Tolerance in the Succulent, Coastal Halophyte, Sarcocornia natalensis

The effects of 0, 50, 100, 200, 300, 400 and 500 mol m^–3NaCl on growth and ion accumulation in the succulent, coastalhalophyte Sarcocornia natalensis (Bunge ex Ung.-Sternb.) A.J. Scott were investigated. Increase in salinity from 0 to 300 mol m^–3 NaCl stimulatedproduction of fresh, dry, and organic dry mass, increased succulenceand shifted resource allocation from roots to shoots. Growthwas optimal at 300 mol m^–3 and decreased with furtherincrease in salinity. Water contributed to a large proportion of the increase in freshmass. Inorganic ions, especially Na⁺ and Cl– contributedsubstantially to the dry mass. At 300 mol m^–3 NaCl inorganicions contributed to 37% of total dry mass and NaCl concentrationin the shoots was 482 mol m^–3. Expressed sap osmotic potentialsdecreased from –2.10 to –3.95 MPa as salinity increasedfrom 0 to 300 mol m^–3 NaCl. Massive accumulation of inorganicions, especially Na⁺ and Cl^–, accounted for 86% of theosmotic adjustment at 300 mol m^–3 NaCl. Salinity treatments decreased the concentrations of K+ in shoots.Plant Na+ :K+ ratios increased steadily with salinity and reacheda maximum of 16.6 at 400 mol m3 NaCl. It is suggested that the exceptional salt tolerance of S. natalensisis achieved by massive inorganic ion accumulation which providessufficient solutes for osmoregulation, increased water fluxand turgor-induced growth. Key words: Sarcocornia natalensis, salt tolerance, halophyte     

昆明海口早寒武世澄江生物群中叶状红藻化石

主要报道了釆自云南省昆明市海口马房村鞍山早寒武世筇竹寺组玉案山段澄江生物群中的叶状红藻-似红叶藻(新属、新种)(Paradelesseria sanguinea Xu,gen.et sp.Nov.)。通过比较形态学研究,探讨了该宏观化石藻类的分类归属与亲缘关系,进一步丰富了澄江生物群生物物种多样性的认识,并为研究早寒武世生物演化及其古环境提供了新的化石证据。同时,通过对现生红藻的比较研究,进一步证明了澄江生物群在云南海口地区发生于一个水深在30m以上的亚潮带和下潮间带的海水环境。     

Photosynthetic Characteristics of Portulaca grandiflora, a Succulent C(4) Dicot : CELLULAR COMPARTMENTATION OF ENZYMES AND ACID METABOLISM

The succulent, cylindrical leaves of the C₄ dicot Portulaca grandiflora possess three distinct green cell types: bundle sheath cells (BSC) in radial arrangement around the vascular bundles; mesophyll cells (MC) in an outer layer adjacent to the BSC; and water storage cells (WSC) in the leaf center. Unlike typical Kranz leaf anatomy, the MC do not surround the bundle sheath tissue but occur only in the area between the bundle sheath and the epidermis. Intercellular localization of photosynthetic enzymes was characterized using protoplasts isolated enzymatically from all three green cell types.     

Effects of Multispecies Clumping on Survival of Three Succulent Plant Species Translocated onto Mine Spoil in the Succulent Karoo Desert, South Africa

Salvaging from premining areas and translocation of succulent plants has been investigated for the revegetation of gypsiferous mine spoil in an arid region of South Africa. Given that facilitation effects are thought to outweigh competition effects in harsh environments, we hypothesized that the survival of translocated succulents would be higher when planted in multispecies clumps than alone and that the growth rate (measured as stem extension) and fruit‐set would be greater for plants in clumps than for those planted alone. Two leaf‐succulent species (Aridaria noctiflora ssp. noctiflora and Drosanthemum deciduum) and one stem‐succulent species (Psilocaulon dinteri) were salvaged from the area destined for mining and translocated onto the mine spoil. These plants were planted either in a multispecies clump of the three species together or alone. One year after translocation, 67% of the plants survived. It was also found that the succulents used in these experiments survived in higher numbers when planted alone. Due to the similar root morphology of D. deciduum and P. dinteri, they competed for resources instead of facilitating each other's establishment. The results were variable for each of the species used, and neither growth nor seed‐set was improved by clumping. These findings would also possibly vary from year to year with different abiotic conditions.     

Salt Requirement for Crassulacean Acid Metabolism in the Annual Succulent, Mesembryanthemum crystallinum

In experiments with the facultative Crassulacean acid metabolism (CAM) species, Mesembryanthemum crystallinum, only plants which received high levels of inorganic salts fixed substantial amounts of CO₂ by the CAM pathway. Equivalent osmolarities of polyethylene glycol 6000 did not yield any CAM fixation. Plant water potential and turgor pressure had no detectable influence on the amount of CAM fixation. These observations rule out the possibility that the inorganic ions were acting as osmotic agents.     

Status of succulent shrubs in the southern Namib Desert, Succulent Karoo Biome

The ratio of dead to alive succulent shrubs as an indicator of turnover was investigated to test whether the accepted notion of rapid turnover rates and cyclic succession in the Succulent Karoo Biome are applicable in the southern Namib. Based on counts of dead and alive plants, twelve species in two habitat types were investigated. These short‐term data which could not incorporate recruitment rates or changes over time, generated, however, some hypotheses. (i) Rapid turnover rates are likely not supported by all succulent plants at the Succulent Karoo Biome's northern boundary. With the exception of one species, mortality rates in succulent shrubs across a range of plant functional types were lower than reported in other parts of the biome. (ii) Sand plains appeared to support some transient species, indicating that there may be differences in vegetation dynamics between habitats. (iii) Species of different plant functional types showed no differences in ratio of dead to alive plants related to habitat. These species may have broad ecological tolerance limits and are perhaps less affected by changes in their environment. (iv) Shrubby Mesembryanthemaceae have high turnover rates and hence a short live span in the investigated area, but are longer lived than elsewhere in the Succulent Karoo Biome. As these hypotheses have implications for management and conservation of succulent species in this global biodiversity hotspot, a detailed evaluation of vegetation turnover, balancing mortality versus recruitment, should be investigated over a longer time span.     

Evaluation of Restoration Techniques for the Succulent Karoo, South Africa

Abstract Possible constraints on the passive recovery of bare areas in the Karoo, a semiarid region in South Africa, include inadequate supply of seed, availability of suitable microsites for plant establishment, altered soil properties, and the truncation of key soil biotic processes. Here we investigate the possibility of initiating the restoration of bare areas by soil surface treatments with gypsum (CaSO₄) and/or organic mulch. We also apply an exogenous seed source to test the hypothesis that seed availability limits autogenic recovery. Both gypsum and mulch improved rain water infiltration, gypsum more so than mulch, and both treatments resulted in significantly higher numbers of reseeded seedlings compared with controls. Gypsum also improved the survival of the cohorts of seedlings of the larger seeded Tripteris sinuata. Tripteris showed the highest number of seedlings (maximum count of 150 seedlings/1,000 viable seeds sown) and surviving plants of the three reseeded species, which included two small‐seeded species, Ruschia spinosa and Chaetobromus dregeanus. Throughout the study period significantly higher plant volumes of naturally seeded annuals and perennials were recorded in the gypsum and/or mulch treatments compared with the controls. Germination and emergence of reseeded and naturally seeded plants appears to be determined by the availability of cool season (autumn to spring ) soil moisture, whereas follow‐up rainfall during this time is important for plant survival. Mulching of bare areas in the Succulent Karoo has the potential to re‐create vegetated areas that will further capture and conserve water, soil, and nutrients. Gypsum also showed positive results but might not be a cost‐effective option because of transport costs to these remote arid areas.     

光合膜膜脂的结构、特性与分子组装

本文就叶绿体光合膜中主要膜脂的分子结构及其特性和在膜中的分子组装进行了综述,并指出了目前膜脂研究的趋势和存在的问题     

光合膜膜脂的结构、特性与分子组装

本文就叶绿体光合膜中主要膜脂的分子结构及其特性和在膜中的分子组装进行了综述,并指出了目前膜脂研究的趋势和存在的问题。     

Water-storing and Cavitation-preventing Adaptations in Wood of Cacti

Ancestral cacti presumably had abundant, fibrous, heavily lignifiedwood, similar to that present in the relictual, leaf-bearinggenus Pereskia. During the evolutionary radiation of the subfamilyCactoideae, diverse types of bodies and woods arose. Severalevolutionary lines have retained an abundant, fibrous wood:all wood cells, even ray cells, have thick lignified walls,and axial parenchyma is only scanty paratracheal. Aside froma diversity of vessel diameters, there seems to be little protectionagainst cavitation during water-stress, and little water-storagecapacity. This strong wood permits the plants to be tall andto compete for light in their tree-shaded semi-arid habitats.In other evolutionary lines, the wood lacks fibres, and almostall cells have thin, unlignified walls. Vessels occur in anextensive matrix of water-storing parenchyma, and tracheidsare also abundant, constituting over half the axial tissue insome species. There is excellent protection against cavitation,but little mechanical support for the plant body; however, theseplants are short and occur in extremely arid, unshaded sites.Scandent, vinelike plants of two genera produce a dimorphicwood—while their shoots are extending without externalsupport, they produce fibrous, lignified wood, but after leaningagainst a host branch, they produce a parenchymatous, unlignifiedwood.Copyright 1993, 1999 Academic Press Cactaceae, cactus, water-stress, wood, evolution, xylem     

福建厦门地区龙舌兰科多肉植物资源及其园林应用

龙舌兰科多肉植物种类繁多,共约400余种,在整个多肉植物大家族中具有举足轻重的地位。本文报道厦门地区引种的龙舌兰科多肉植物资源,并就其栽培状况、园林应用以及发展前景作一简明阐述。     

Factors affecting fruit set in Aizoaceae species of the Succulent Karoo

By reducing the number of flowers and fruits, intense grazing activities of domestic livestock are considered to have negative effects on the plant recruitment of perennial plants in the Succulent Karoo, South Africa. In the present study, the fruit set of six perennial species belonging to the Aizoaceae was investigated under two different grazing intensities. Two species (Cheiridopsis imitans and Leipoldtia schultzei) were examined more closely to determine whether factors other than grazing impact fruit production of these plants. Apart from reproductive output, the population structure of these two species was explored in heavily and slightly grazed areas.For all investigated species, heavy livestock grazing was identified as a major threat to fruit production. Deviations from this pattern were recorded in a drought year, when harsh weather conditions reduced herd sizes dramatically and the usually high grazing pressure was alleviated. However, detailed analyses revealed that also other biotic factors can cause severe fruit and flower losses even exceeding that caused by grazing. Caterpillars of the noctuid moth, Diaphone eumela, and two rodent species, Otomys unisulcatus and Rhabdomys pumilio, proved to be further important herbivores of flowers and fruits. Experiments with caged plants, excluding livestock from grazing, confirmed though that livestock grazing definitely accounts for a continuous reduction of fruit production. Insufficient pollination success was another parameter reducing fruit set; however, this was almost exclusively observed under low grazing pressure.     

The Influence of Wind on the Behaviour of Stomata of Photosynthetic Stems of Cytisus scoparius (L.) Link

Potted transplants of Cytisus scoparius (L.) Link sub-speciesmaritimus (Rouy) Heywood (prostrate) and sub-species scoparius(erect) were subjected to an abrupt increase in wind speed.Following this change, stomata of the prostrate plants closedquite markedly to an equilibrium conductance within 60 min andremained substantially closed for at least the next 8 h. Stomatalconductance of erect plants increased slightly in the hour followingthe increase in windspeed but decreased gradually in the next8 h. These changes resulted in changes in transpiration andplant water status but stomatal responses to wind were not directresponses to changes in the bulk water status of the plants.It is suggested that the occurrence of sub-species maritimuson exposed sea cliffs and the limitation of the erect sub-speciesscoparius to relatively more sheltered habitats may be relatedto the stomatal responses to wind and the plant-water relationshipsof the two sub-species. Cytisus scoparius, broom, stomata, wind     

Fine Structure Aberrations in the Movement of 11C and 13N in the Stems of Plants

¹¹CO₂ was offered to leaves of sunflower, corn and ryegrassand ¹³N₂ to root nodules of alfalfa and alder. Movement of thetracers out of the feed region was monitored along stems orpetioles using geiger tubes. Fluctuations in radioactivity werenot detected as statistically significant from random tracerdecay in the ‘background’ section of the time-activityprofiles before mass-flow commenced, but became highly significantin the mass-flow sections. These pulses of radioactivity couldbe followed from one detector to the next over 1–3 cmand were analysed for periodicity by cross-correlation and auto-correlationcomputer programmes. Periodicity was only rarely detected in¹¹C runs, but was evident in many ¹³N experiments. Speed ofpulse movement (microfronts) were measured, both visually andby computer cross-correlations, and compared with rates foundby the ‘moving intercept’ of mass flow. Microfrontspeeds were faster. Speeds of ¹¹C movement were comparable withthose reported for phloem, but ¹³N movements were often muchhigher, suggesting xylem movements. Fine structure pulses indicatethat movements of ¹¹C photosynthate or ¹³N compounds are rapid,erratic and far more complex than expected by a simple Münchpressure flow mechanism. Key words: ¹¹C, ¹³N, plant stems, radioactive pulse     

Photosynthetic Assimilation of 14CO2 by Mature Brown Stems of the Tea Plant (Camellia sinensis L.)

The fixation of ¹⁴CO₂ by mature brown stems of the tea plantwas studied by supplying ¹⁴CO₂ to selected stems of pruned andintact plants for 24 h under field conditions. Utilization of¹⁴C assimilates for the production of new shoots was also examined.The photosynthetic nature of the fixation of ¹⁴CO₂ is demonstrated.The efficiency of this fixation was very low compared with thattaking place in leaves. The movement of labelled assimilatesfrom stem bark to the roots was inappreciable, whereas newlyemerged shoots on the pruned frame drew labelled assimilatesfrom stem bark.