Hydraulic lift: soil processes and transpiration in the Mediterranean leguminous shrub Retama sphaerocarpa (L.) Boiss

Hydraulic lift (HL) is the process by which plants can passively transfer water from deep, moist soil layers to shallow, dry soil layers. Although it has attracted recent research interest, a mechanistic understanding and its implications for ecosystem functioning are still lacking. Here we describe HL seasonal patterns in a semi-arid shrub species and its influence on plant water dynamics. We measured soil water availability and plant water status over the course of 1 year. Soil water potential in the rhizosphere of Retama sphaerocarpa (L.) Boiss (Fabaceae) individuals and in adjacent land was recorded using soil psychrometers. Sap flow was recorded simultaneously using the stem heat balance method (SHBM). Our results show a seasonal HL trend linked to mean seasonal soil water potential with greatest HL amplitudes at moderately low water potentials (ca ?4 MPa). HL amplitude was negatively affected by nocturnal transpiration, and HL patterns were recorded in all seasons and at water potentials ranging from ?0.1 MPa to ?8.5 MPa which is consistent with R. sphaerocarpa deep rooting habit and its steady access to ground water.     

Enhancing the early performance of the leguminous shrub Retama sphaerocarpa (L.) Boiss.: fertilisation versus Rhizobium inoculation

We have investigated the effect on growth of fertilisation versus biological nitrogen fixation by rhizobial nodules in Retama sphaerocarpa(L.) Boiss, a leafless leguminous shrub native to the Iberian Peninsula and North-West Africa that has generated interest for revegation of dry Mediterranean habitats. Our main objective was to optimise the formation of root nodules under nursery conditions and to evaluate their influence on the first year of seedling growth in comparison with standard fertilisation. Seedlings of R. sphaerocarpa from two Spanish localities were grown under two levels of fertilisation, and half of each were inoculated with rhizobia isolated from adult Retama, Cytisus and Adenocarpusplants in the field. Although some promiscuity was observed, nodulation was significantly successful with specific rhizobia. At the end of the experiment, highly fertilised plants were taller and heavier and exhibited larger photosynthetic rates than either nodulated or non-nodulated plants under low fertilisation. High fertilisation enhanced seedling growth but inhibited both the nodulation and the nitrogenase activity of the nodules. Thus, physiological differences between nodulated and non-nodulated plants were observed in the low but not in the high fertilisation treatment. Nitrogen uptake and use was enhanced by root nodules, which translated into enhanced photosynthesis and growth. Since inoculation is simple, environmentally friendly and cheap, and nodulated plants are more likely to overcome transplant stress than non-nodulated ones, our results suggest that inoculation together with low, background fertilisation (instead of high fertilisation) should be used when producing high quality seedlings of this autochthonous Mediterranean shrub.     

Anaerobic processes in yellow lupin (Lupinus luteus L.) root nodules

The lupin root nodule homogenate was separated by centrifugation in the Percoll density gradient into the Rhizobium bacteroid fraction and plant subcellular components. High activities of alcohol dehydrogenase and lactate dehydrogenase in the soluble fraction of host plant, and high capability of the isolated bacteroids to oxidize ethanol, malate, lactate and acetaldehyde evidence functional interrelationship between the plant and bacteroids.     

白芥自交亲和性分析

对不同来源的8份白芥材料,采用人工自交法分析其自交亲和性。结果显示:白芥的自交亲和性存在较大幅度的变异,自交亲和指数在0.01~4.10之间,8份参试材料中,自交亲和指数小于1的材料有3个,自交亲和指数大于1的材料有5个。表明白芥中存在自交亲和材料,白芥自交亲和性变异不仅存在于材料间,而且也存在于同一材料内不同个体间。按自交亲和指数的高低,可将参试材料分为3种类型:高自交亲和类型(自交亲和指数大于3.00,如民乐洪水芥麻、04(X)等)、自交亲和类型(自交亲和指数为1.00~2.99)、自交不亲和类型(自交亲和指数0.00~1.00)。     

Beitrag zur systematik vonScilla L. subgen.Scilla (inklusiveChionodoxa Boiss.)

Zusammenfassung Die vonBoissier aufgestellte GattungChionodoxa wird auf Grund samenanatomischer und karyologischer Befunde eingezogen. Ihre nahe Verwandtschaft mitScilla bifolia agg. konnte aufgezeigt werden. Die wesentlichen Unterschiede derScilla bifolia- Gruppe (inklusiveChionodoxa-Arten) zu anderen Gruppen myrmekochorerScilla-Arten sowie zuPuschkinia undHyacinthus wurden dargelegt.Folgende neue Kombinationen werden aufgestellt:Scilla luciliae (Boiss.)Speta comb. nova,Scilla cretica (Boiss. &Heldr.)Speta comb. nova,Scilla nana (Schult. fil.)Speta comb. nova,Scilla sardensis (Barr &Sugden)Speta comb. nova,Scilla siehei (Stapf)Speta comb. nova,Scilla×allenii (Nicholson)Speta comb. nova.Weiters wurden die Chromosomenzahlen für einigeScilla- Arten überprüft und dabei fürScilla bifolia neben der bekannten diploiden auch die tetraploide Zahl 2n=36 aufgefunden.

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Summary The genusChionodoxa set up byBoissier is withdrawn due to seedanatomical and caryological statements and its species are incorporated intoScilla L. The close affinity between formerChionodoxa-species andScilla bifolia agg. could be demonstrated. The essential differences between theScilla bifolia group (including the formerChionodoxa species) and other groups of myrmecochorousScilla species,Puschkinia andHyacinthus were shown. The following new combinations are set up:Scella luciliae (Boiss.)Speta comb. nova,Scilla cretica (Boiss. &Heldr.)Speta comb. nova,Scilla nana (Schult. fil.)Speta comb. nova,Scilla sardensis (Barr &Sugden)Speta comb. nova,Scilla siehei (Stapf)Speta comb. nova,Scilla×allenii (Nicholson)Speta comb. nova.Furthermore the chromosome numbers of someScilla species were checked, and inScilla bifolia L. besides the known diploid number the tetraploid number 2n=36 was discovered.

     

Structural cost of shoot modules and its implications on plant potential fitness in a Mediterranean perennial shrub, Retama sphaerocarpa (L.) Boiss

This paper introduces a methodology to analyse the structural costs on plant potential fitness, empirically exemplified in the hierarchical shoot system of a Mediterranean perennial plant, Retama sphaerocarpa (L.) Boiss. During growing season every year (March-August), the terminal shoot (which is the basic unit of growth) develops inflorescences, flowers and fruits, as well as new shoots (first-, second- and third-order branching shoots) which have the potential to "behave" as terminal shoots in the following year. Different morphological and demographical aspects of the modules within the terminal shoot were measured in 100 terminal shoots selected from different plants of a natural population of R. sphaerocarpa. Complementary samples of 100 shoots of different branching orders were collected to obtain biomass estimations of the terminal shoots. We propose a simple procedure to estimate structural cost (biomass investment) on plant potential fitness (flowering buds) as a methodology for interpreting and comparing the consequences on fitness of different plant growth patterns. The results of this study exemplify how differential allocation patterns among plant structural modules, depending on their position within the shoot system, can be quantified to estimate their influence upon plant potential fitness.     

Cellular compartmentation of ureide biogenesis in root nodules of cowpea (Vigna unguiculata (L.) Walp.)

Cowpea (Vigna unguiculata (L.) Walp.) nodules have been investigated by means of cytochemical and immunocytochemical procedures at the ultrastructural level in order to assess the role of the uninfected cells in ureide biogenesis. Uricase activity in the nodules was shown by cytochemical methods to be localized exclusively in the numberous large peroxisomes confined to the uninfected cells; the small peroxisomes in the infected cells did not stain for uricase. Uricase was also localized in the peroxisomes of uninfected cells by immunogold techniques employing polyclonal antibodies against nodule-specific uricase of soybean. There was no labeling above background of any structures in the infected cells. The results indicate that the uninfected cells are essential for ureide biogenesis in cowpea. Although tubular endoplasmic reticulum, the presumptive site of allantoinase, increases greatly in the uninfected cells during nodule development, it virtually disappears as the nodules mature. The inconsistency between the disappearance of the tubular endoplasmic reticulum from older nodules and the high allantoinase activity reported for older plants remains to be explained.Abbreviations DAB 3,3-diaminobenzidine - ER endoplasmic reticulum - GARG goat anti-rabbit immunoglobulin G - IgG immunoglobulin G - kDa knodalton - Mr apparent molecular mass - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Nitrogen-fixing root nodules inDatisca Cannabina L.

Summary The occurrence of root nodules inDatisca cannabina is reported. The nodules are typically of the Alnus type, forming dichotomously-branched coralloid clusters. The enlarged cortical cells contain vesicle clusters of the endophyte. The nodules reduced acetylene to ethylene at a rate of 5.5 moles ethylene per g fresh wt of nodules per hour.     

The occurrence of amoeboid plastids in the actinorhizal root nodules of Alnus glutinosa (L.) Gaertn.

Abstract. The invasion of the actinomycete Frankia into the root cells of Alnus glutinosa with subsequent nodule formation effects a number of ultrastructural changes in the host cell cytoplasm. Among other changes the amyloplasts rapidly lose their starch and acquire an amoeboid or pleomorphic form. Such plastids occur predominantly in the mature vesicle-containing, nitrogen-fixing cells of the nodule. They lack starch, have an electron dense stroma and a complex lamellar system. This last would appear to be associated with a distinct membranous reticulum which can be extensive. The flexible form of these plastids is mirrored in their ability to enclose portions of host cytoplasm together with organelles and even other plastids. Their close association with cristate mitochondria suggests an active metabolic role in the nodule symbiosis.     

Ammonium effects on function and structure of nitrogen-fixing root nodules of Alnus incana (L.) Moench

Cloned plants of Alnus incana (L.) Moench were inoculated and grown without combined nitrogen for seven weeks. The effects of ammonium on the function and structure of the root nodules were studied by adding 20 mM NH₄Cl (20 mM KCl=control) for four days. Nitrogenase activity decreased to ca. 50% after one day and to less than 10% after two days in ammonium treated plants, but was unaffected in control plants. The results were similar at photon flux densities of 200 and 50 mol m^-2 s^-1. At the higher light level the effect was concentration dependent between 2 and 20 mM NH₄Cl. The recovery was slow, and more than 11 d were needed for plants treated with 20 mM ammonium to reach initial activity. The distribution of ¹⁴C to the root nodules after assimilation of ¹⁴CO₂ by the plants was not changed by the ammonium treatment. Microscopical studies of root nodules showed high frequencies of endophyte vesicles being visually damaged in nodules from ammonium-treated plants, but not in nodules from control plants. When nitrogenase activity was restored, visually damaged vesicles were again few, whereas young developing vesicles were numerous. The slow recovery, the ¹⁴C-translocation pattern, and the structural changes of the endophyte indicate a more complex mechanism of ammonium influence than simply a short-term reduction in supply of carbon compounds to the nodules.     

Physiological aspects of fungi isolated from root nodules of faba bean (Vicia faba L.)

The present study was made to isolate and assess some physiological characteristics of root nodule-colonizing fungi. During this study, 17 fungal species were isolated from root nodule samples taken from faba bean plants (Vicia faba L.) collected from different sites at Assiut area (Egypt). The growth of faba bean plants in pots was significantly promoted by soil inoculation with most fungi. Growth was checked in pots with inocula of Cladosporium cladosporioides, Fusarium moniliforme, F: oxysporium, F solani, Macrophominia phaseolina and Rhizoctonia solani which were added separately. All growth-promoting fungi were capable of producing cellulase, pectin lyase, polygalacturonase, protease, urease, amidase, acid phosphatase, alkaline phosphatase and arylsulfatase in growth medium supplemented with the corresponding substrates. Four fungal species, Aspergillus awamori, A. flavus, Penicillium chrysogenum and Trichoderma koningii showed the highest rates of enzyme formation. The effect of the addition of six trace elements to the growth media at 30 micromol/ml on enzyme production revealed some dependency on species, enzyme and metal ion. Cd2+, Hg2+ and Zn2+ generally inhibited enzyme activity. Cu(1+), Fe3+ and Al3+ showed a stimulatory effect. Fungicides (afugan and tilt) and herbicides (brominal and fusilade) at 50 ppm generally promoted enzyme activity, but insecticides (kelthane and fenvalerate) caused some inhibition to enzyme activities. Salinization of the growth media with NaCl strongly inhibited the enzymatic activity of all fungi at concentrations between 0.5 and 1.5%.     

The extrafloral nectaries of cowpea (Vigna unguiculata (L.) Walp): I. Morphology,anatomy and fine structure

The cowpea bears two distinctive types of extrafloral nectaries. One, on the stipels of trifoliolate leaves, consists of a loosely demarcated abaxial area (1–2 mm diameter) of widely-spaced trichomes (papillae) borne on a stomata-free epidermis, and lacking a specific vascular supply. Each trichome has up to eight apical (head) cells, two to four intermediate cells, and a single large stalk cell. The secretory faces of the apical cells bear wall ingrowths and an easily detached cuticle. The wall separating the stalk cell and the underlying epidermal cell(s) has a mean plamodesmatal frequency of 25/m². The second type of nectary consists of a large elliptical mound of tissue (short and long axes about 2 mm and 4 mm) formed between a pair of flowers on an inflorescence stalk. It comprises four to eight cone-shaped subnits of secretory tissue, each with a circular secretory orifice and an individual supply of phloem, but not of xylem. Cells of the secretory tissue of the nectary subunits separate as they mature, and nectar flows to the orifice through the resulting intercellular spaces. Intact secretory cells and cellular debris are extruded into the nectar. Some of the sieve elements terminating in the inner secretory tissue exhibit open sieve pores. Each mature secretory cell contains many small (2 m diameter) spherical protein bodies and one to three large (up to 2–3 m diameter 15 m long), paracrystalline bodies. These inclusions are absent or not fully developed in inner, less mature regions of the secretory tissue. Mechanisms of secretion are proposed for the two classes of nectary, including estimates of flux of sugar into the trichomes of the stipel nectary.     

Observations on the fine structure of the endophyte of the root nodules of alnus glutinosa (L.) gaertn.

Summary Electron micrographs have been prepared showing different stages in the development of the endophyte in Alnus glutinosa root nodules. Although the complete life cycle of the organism has not yet been worked out it is concluded that it is an Actinomycete. The organism can exist as a septate, branching filament of diameter 0.7–1.0 . However, under certain conditions within the nodule, the endophyte can form spherical sub-divided vesicles 4–5 in diameter and it is suggested that these vesicles are analogous to sporangia. Yet again under other conditions the organism fragments to form bacteroids. It would appear that the different forms of the organism are associated with different seasons of the year and with different metabolic patterns, of particular interest in this connection is the fixation of nitrogen which is associated with the nodule symbiosis.     

In situ localization of Paenibacillus polymyxa HKA-15 in roots and root nodules of soybean (Glycine max.L.)

Background and aims

Bacterial endophytes can colonize various plants and organs. However, endophytic bacteria (other than rhizobia) colonizing root nodules in legumes have been rarely analyzed. The present study aimed to examine the colonization and spread of gfp-tagged Paenibacillus polymyxa in soybean plants under gnobiotic conditions.

Methods

Inoculation with gfp-tagged Paenibacillus. polymyxa HKA ?15 alone and in combination with Bradyrhizobium japonicum were done on soybean seedlings. In situ localization was detected through confocal microscopy and PCR.

Results

Inoculation with P. polymyxa-gfp strain alone and in combination with B. japonicum DS-1 had a stimulatory effect on the plant growth. There was an increase in shoot (7.2 %) and root dry weights (14.5 %) when the two strains were co - inoculated over that of B. japonicum inoculation alone. In vivo simultaneous visualization using Confocal Laser Scanning Microscopy (CLSM) showed the localization of the gfp-tagged P. polymyxa cells in the root nodules and its spread in the root tissue, both tap as well as lateral roots. Systemic spread into aerial tissue did not occur as indicated by the absence of bacteria. CLSM observations of the presence of gfp-tagged P. polymyxa in the nodule and roots tissues was corroborated with PCR amplification of the gfp-gene from these tissues.

Conclusions

CLSM and PCR methods confirmed that P. polymyxa invades roots and root nodules of soybean, but the spread is restricted to root tissue only. The strain improves plant growth when inoculated singly or in combination with B. japonicum.     

La presenza di Euphorbia hyberna L. subsp. insularis (Boiss.) Briq. sull'Appennino ligure

Abstract

The presence of Euphorbia hyberna L. subsp. insularis (Boiss.) Briq. in the Ligurian Apennines. — The author studies the geographical distribution and the ecology of Euphorbia hyberna L. subsp. insularis (Boiss.) Briq. in the Ligurian Apennines, where the plant occurs in several stations which are localized in two distinct areas: in the group of Mt. Dente (province of Genoa) and near the Capanne di Marcarolo (province of Alessandria). Euphorbia insularis is recorded only in Liguria, the Apuane Alps (Tuscany), Corsica and Sardinia. The climatic, edaphic, topographic and biotic characteristics of the stations in which the plant is found in Liguria are pointed out. It grows in different environmental conditions, but occurs only in localities with northerly or north easterly exposure, at altitudes between 700 and 950 m; it attains the best development in open places, like grassland and glades, where it grows profusely. On the whole, Euphorbia insularis requires a climate characterized by a strong oceanicity, i.e. by moderate temperatures, a high amount of rainfall, and a notable atmospheric humidity throughout the year. However, the plant shows no particular edaphic requirements, and its occurrence on the serpentine soils is only due to the low competition in the plant-communities of these stations. The author emphasizes the remarkable phytogeographic interest of Euphorbia insularis, which probably represents a tertiary atlantic relict and has survived in the Ligurian Apennines owing to peculiar geo-climatic conditions.