Some Aspects of Translocation in Root Nodule Plants

By the use of ¹⁶N it is shown that the removal, over a shortzone at the base of the shoot of a typical root nodule plant(alder), of the tissues external to the xylem does not interferewith the upward movement of fixed nitrogen from the nodulesinto the shoot. It is concluded that the fixed nitrogen, whichis probably in organic form, can be translocated in the xylemin the transpiration stream, and that this is most likely itsnormal route. It is also shown that in unringed plants substantialenrichment in fixed ¹⁶N is detectable in the shoot within 6hours from the commencement of the exposure of the nodules toexcess free ¹⁶N. Structural and experimental evidence showsthat the alder nodule is not a water-absorbing organ, and themechanism of transfer of fixed nitrogen from the nodule intothe transpiration stream is not obvious.     

根瘤形成过程中豆科植物根毛和根外层传递细胞的诱发

对7种豆科植物接种根瘤菌后根部的形态和内部结构进行了研究.结果表明:根瘤菌可诱发根瘤形成部位根段的根毛增生、形变和根外层传递细胞的发育.根外层传递细胞发生在根毛伸长形变时期,一直可持续到根瘤形成,传递细胞壁内突发育过程是先由根表皮细胞外切向壁一侧细胞质膜向细胞质内陷形成囊状壁傍体,次生细胞壁物质在初生壁上沉积并逐渐充满囊状体,最终形成传递细胞典型的壁内突结构.根瘤形成过程中根外层传递细胞的诱发与培养方式(水培、固培)没有直接关系.在不接菌的对照苗的根段内未发现壁内突结构,研究证明豆科植物根外层传递细胞的形成是由根瘤菌诱导所致.     

Evolutionary Geography of Root Nodule Bacteria: Speciation Directed by the Host Plants

Microbiology - Compared to free-living relatives, bacterial symbionts of plants exhibit higher rates of population diversification (microevolution), as well as of speciation and formation of...     

Root Nodule Symbiosis II

Nodule-roots of Myrica cerifera (Southern Wax Myrtle) and Casuarina cunning hamiana (Australian Pine) have a negative geotropic curvature. Studies of their endogenotts auxin content revealed a pattern of correlation: the absence of detectable auxin when the geotropisni was negative. Non-nodulated roots of Myrica exhibited a normal positive geotropic curvature and possessed an auxin content within an anticipated range (10 mg/kg). Root nodules of Alnus species, whose roots exhibit a positive geotropic curvature, contained measurable endogenous auxin (20 mg IAA/kg). The presence of an indoleaectic acid oxidase system in Myrica and Casuarina root nodules has heen described and correlations are drawn between non-detectable endogenous auxin concentrations and high enzymatic activities. It is suggested that the negative geotropic curvature of the nodule-roots of Myrica and Casuarina is due to the presence of a sub-optimal concentration of auxin which in turn results from the activity of an indoleacetic aeid destroying system.     

Alfalfa Root Nodule Carbon Dioxide Fixation : II. Partial Purification and Characterization of Root Nodule Phosphoenolpyruvate Carboxylase

A nonphotosynthetic phosphoenolpyruvate carboxylase (EC 4.1.1.31) was partially purified from the cytosol of root nodules of alfalfa. The enzyme was purified 86-fold by ammonium sulfate fractionation, DEAE-cellulose, hydroxylapatite chromatography, and reactive agarose with a final yield of 32%. The enzyme exhibited a pH optimum of 7.5 with apparent K_m values for phosphoenolpyruvate and magnesium of 210 and 100 micromolar, respectively. Two isozymes were resolved by nondenaturing polyacrylamide disc gel electrophoresis. Subsequent electrophoresis of these isozymes in a second dimension by sodium dodecyl sulfate slab gel electrophoresis yielded identical protein patterns for the isozymes with one major protein band at molecular weight 97,000. Malate and AMP were slightly inhibitory (about 20%) to the partially purified enzyme. Phosphoenolpyruvate carboxylase comprised approximately 1 to 2% of the total soluble protein in actively N₂-fixing alfalfa nodules.     

Diurnal Functioning of the Legume Root Nodule

Diurnal changes in plant and nodule performance were studiedin 28–9 d plants of Pisum sativum L. in two environments,both with a 12 h (27 000 lx):12 h::light:dark cycle, but one(A) with a fluctuating temperature-humidity regime (photoperiod18 ?C, 60 per cent relative humidity:night 12 ?C, 85 per cent),the other (B) with constant temperature (18 ?C) and humidity(75 per cent). Fixation rate (C₂H₂ reduction), respiratory output of the nodulatedroot, and nodule sugar level increased throughout the photoperiod,whereas nodule soluble nitrogen level declined steadily. Reversalof these trends in the night period led, at its end, to minimain fixation rate, sugar level and respiration, but a maximumin soluble nitrogen. The A environment produced the greaterday:night fluctuations in transpiration and nodule soluble nitrogen,but B, with its higher night temperature, induced the more pronounceddecrease in fixation at night. Slightly less nitrogen was fixed during the photoperiod thanduring the night in the A environment, yet since some fixationproducts were retained in the nodules at night and not releaseduntil the next photoperiod, the day: night difference in nitrogenexport from nodules was 1.8:1. The photoperiod of A was alsoa time of higher nodule respiration and replenishment of nodulesugar and starch, so that the nodules' requirement for translocatedcarbohydrate was more than twice that at night. Humidity decrease in the photoperiod (of A) elicited higherrates of transpiration and a more rapid than normal emptyingof soluble nitrogen from the nodules: elevation of humidityhad the opposite effects. Shoot removal (A-grown plants) causednodule sugar levels to fall rapidly below those normally encounteredin intact plants.     

The Development of Root Nodule Xylem Transfer Cells in Trifolium repens

Stereological analysis of micrographs of developing and functioningxylem transfer cells of Trifolium repens indicates that theER and dictyosomes may be involved in wall ingrowth deposition,and the ER in intracellular solute transport.     

Alfalfa Root Nodule Carbon Dioxide Fixation : III. Immunological Studies of Nodule Phosphoenolpyruvate Carboxylase

Antiserum was prepared in rabbits against purified alfalfa (Medicago sativa L.) nodule phosphoenolpyruvate carboxylase (PEPC). Immunotitration assays revealed that the antiserum recognized the enzyme from alfalfa nodules, uninoculated alfalfa roots, and from soybean nodules. Tandem-crossed immunoelectrophoresis showed that the PEPC protein from alfalfa roots and nodules was immunologically indistinguishable. The 101 kilodalton polypeptide subunit of alfalfa nodule PEPC was identified on Western blots. The PEPC polypeptide was detected in low quantities in young alfalfa roots and nodules but was present at increased levels in mature nodules. Senescent nodules appeared to contain a reduced amount of the PEPC polypeptide. PEPC was also detected by western blot in some plant- and bacterially-conditioned ineffective alfalfa nodules but was not detected in bacteroids isolated from effective nodules. Alfalfa nodule PEPC is constitutively expressed in low levels in roots. In nodules, expression of PEPC polypeptide increases several-fold, resulting in increased PEPC activity. Antiserum prepared against the C₄ PEPC from maize leaves recognized the PEPC enzyme in all legume nodules and roots tested, while the antiserum prepared against alfalfa nodule PEPC also recognized the leaf PEPC of several C₄ plant species. Neither antiserum reacted strongly with any C₃ leaf proteins. The molecular weight of the PEPC polypeptide from C₄ leaves and legume nodules appears to be similar.     

Callose-Regulated Symplastic Communication Coordinates Symbiotic Root Nodule Development

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Genetic Diversity and Phylogeny of Root Nodule Bacteria Isolated from Nodules of Plants of the Lupinaster Genus Inhabiting the Southern Urals

Russian Journal of Genetics - The genetic diversity and phylogeny of root nodule bacteria, microsymbionts of plants of the genus Lupinaster Adans. (L. albus Link and L. pentaphyllus Moench), were...     

Novel Alphaproteobacterial Root Nodule Symbiont Associated with Lupinus texensis

Phylogenetic analysis of rRNA gene, recA, nodA, nifD, and nifH sequences suggested that nitrogen-fixing symbionts from two populations of Lupinus texensis acquired the capacity for nodule symbiosis separately from other rhizobia in the alphaproteobacteria. Their closest 16S rRNA relatives were the nonsymbiotic taxa Chelatococcus, Bosea, and Balneomonas.     

Phytoextraction of Soil Cobalt Using Hyperaccumulator Plants

A greenhouse study was conducted on phytoextraction of cobalt by nickel hyperaccumulators Alyssum murale and Alyssum corsicum and by two varieties of cobalt accumulator Nyssa sylvatica compared with the nonmetal accumulator crop plant Brassica juncea. The plants were grown on Sassafras sandy loam soil (<2 mg Co and 5 mg Ni/kg dry soil), amended with 1 mmol Co/kg dry soil (58.9 mg/kg), and two Ni smelter-contaminated soils, Quarry muck with 24 mg Co and 1720 mg Ni/kg dry soil and Welland loam with 37 mg Co and 2570 mg Ni/kg dry soil. All soils were adjusted to pH 6.5 to prevent Ni phytotoxicity. Of the five plant entries tested in the study, the two Alyssum species demonstrated the most promising Co phytoextraction results. In Co-amended Sassafras soil, the maximum concentration accumulated by Alyssum murale was 1320 mg Co/kg dry weight, which was almost 60 times higher than accumulation by crop plant Brassica juncea. At a single harvest after 60 days of growth, A. murale was able to extract more than 3% of Co from Co-amended soil. As expected, both Alyssum species accumulated up to 1% Ni on dry weight basis when grown on Ni-contaminated soils.

Nyssa sylvatica showed considerable Co accumulation; foliar Co concentration in the second harvest was as high as 800 mg/kg dry weight. The first few leaves that emerged were chlorotic, both in the Co-amended soil and Ni-contaminated soils, but with growth the signs of toxicity disappeared. In the Co amended soil, Co concentration in Nyssa sylvatica leaves was 30% of that found in shoots of Alyssum species, but an order of magnitude higher than that of Brassica juncea. The leaves accumulated a higher concentration compared with the stems.

Both Alyssum species and Nyssa sylvatica offer promise for phytoextraction of Co and ⁶⁰Co from contaminated or mineralized soils.     

Symbiosis of Leguminous Plants and Nodule Bacteria: IV. The Importance of the Oxygen Factor in Nodule Formation and Function

Nodulated plants of soya-bean have been grown in culture solutionslacking combined nitrogen and in continuous contact with oxygen/nitrogengas mixtures containing 21, 12, and 5 per cent. oxygen respectively.Reductions of oxygen content led to reductions in dry weightand in fixation of nitrogen. Somewhat similar but smaller effects on dry weight were observedwith non-nodulated plants supplied with ammonium-nitrogen, butsuch plants supplied with nitrate-nitrogen grew equally vigorouslyat all three oxygen levels, a result regarded with some reservation. The weight of nodules per plant was markedly reduced by curtailmentof oxygen, but the number was unaffected, indicating that theearlier stages in nodule formation are not specially sensitiveto oxygen supply. The greater effect of oxygen reduction onnodulated plants appears to be exerted on the process of fixationor on associated processes such as nodular respiration.     

Bioproduction of Ascorbic Acid in Root Nodule and Root of the Legume Pulse Phaseolus mungo

The root nodules of Phaseolus mungo (L.), a herbaceous leguminous pulse, contain high amounts of ascorbic acid (AsA). A glucose pool present in the nodule might serve as precursor for AsA production. From root nodule, a Rhizobium sp. was isolated. The symbiont produced a large amount of AsA (290.5 μg/ml) from glucose-supplemented basal medium. The production of AsA by the symbiont was much greater than that of the control when the glucose (0.5%)-supplemented mineral medium was enriched with thiamine hydrochloride (20 μg/100 ml), biotin (20 μg/100 ml), and L-asparagine (0.2%). The possible role of the rhizobial production of AsA on rhizobia–legume symbiosis is discussed.     

Physiological Role of Leghaemoglobin Heterogeneity in Pea Root Nodule Development

Disk-gel-electrophoresis of the leghaemoglobin isolated frompea root nodules revealed two major (Lb I and Lb IV) and threeminor components. The ratio of the two major components (LbI/Lb IV) decreased with increasing age. This ratio was higherin the distal than in proximal region when nodules were cutinto distal and proximal sections. In young nodules, the incorporationof radioactive leucine into Lb I was much higher than into LbIV. In older nodules, the radioactivities were much higher inLb IV than in Lb I. These data suggest that the change in thisratio is due mainly to differences in the rates of biosynthesis. Two major components (Lb I and Lb IV) which were isolated separatelyhad different O₂-binding affinities. The O₂-binding affinityof the component synthesized mainly in older nodules (Lb IV)was higher than that of the component synthesized mainly inyoung nodules (Lb I). These results indicate that changes inthe relative contents of leghaemoglobin during nodule developmentcontribute to more effective nitrogen fixation which is mediatedby changes in the capacities of oxygen transport. (Received July 7, 1981; Accepted November 2, 1981)