Induction and growth properties of carrot roots with different complements of Agrobacterium rhizogenes T-DNA

Single and multiple infections of carrot discs were carried out with Agrobacterium strains harbouring different segments of pRi1855 TL-DNA cloned in the binary vector Bin 19 and with a strain carrying the TR-DNA from the same Ri plasmid. Roots induced by the various co-inoculations were cultured and their growth patterns were followed. Abundant roots could be induced by TL-DNA rol genes A, B and C as a single insert (rolA+B+C) and by rolB alone provided an extended segment beyond its 5 noncoding region was included in the construction. A depression of rooting capability was caused by the inclusion of rolC together with rolB (rolB+C). In all cases co-inoculation with the Agrobacterium carrying TR-DNA-borne auxin genes was necessary for root induction since none of the rol constructions was in itself capable of eliciting any response; an exceeding majority of these roots were however shown to contain rol genes but no TR-DNA. Rooting was also elicited if rol constructions were co-inoculated with a strain carrying TL-DNA genes 13 and 14 (ORF13+14) instead of the TR-DNA strain. These roots were shown to contain both rol genes and ORF13+14. Striking differences in growth properties were shown by roots containing different complements of TL-DNA genes. Typical hairy root traits, high growth rate, branching and, most noticeably, absence of geotropism, were shown by roots containing rolB alone, while roots with rolA+B+C were geotropic as normal carrot roots. Hairy root traits were conferred to rolA+B+C roots by the concomitant presence of ORF13+14 and by the addition of auxin to the culture medium. A model is presented which attempts to rationalize the growth patterns by assigning interplaying roles to the various TL-DNA genes involved.     

New motile anaerobic bacteria growing by succinate decarboxylation to propionate

Three strains of new anaerobic, gram-negative bacteria which grew with succinate as sole source of carbon and energy were isolated from anoxic marine and freshwater mud samples. Cells of the three strains were small, non-spore-forming, motile rods or spirilla. The guanine-plus-cytosine content of the DNA of strain US2 was 52.6±1.0 mol%, of strain Ft2 63.5±1.4 mol%, and of strain Ft1 62.6±1.0 mol%. Succinate was fermented stoichiometrically to propionate and carbon dioxide. The growth yields were 1.2–2.6 g dry cell mass per mol succinate degraded. Strains US2 and Ft2 required 0.05% w/v yeast extract in addition to succinate for reproducible growth. Optimal growth occurred at 30°–37°C and pH 6.8–8.0. Addition of acetate as cosubstrate did not stimulate growth with any strain. Strain Ft2 grew only under strictly anaerobic conditions, whereas strains US2 and Ft1 tolerated oxygen up to 20% in the headspace. Strains US2 and Ft2 grew only with succinate. Strain Ft1 also converted fumarate, aspartate, and sugars to propionate and acetate. This strain also oxidized propionate with nitrate to acetate. Very low amounts of a c-type cytochrome were detected in propionate plus nitrate- or glucose-grown cells of this strain (0.4 g x g protein^-1). Moderate activities of avidin-sensitive methylmalonyl-CoA decarboxylase were found in cell-free extracts of all strains.     

Use of a root assessment tray for the detection of take-all on lateral roots of wheat seedlings

A root assessment tray was designed for the meticulous assessment of take-all on wheat seedling roots from soil bioassays. Subsequently, the detection of lateral root infections (in addition to the more obvious infections on main axes of seminal roots) resulted in increased estimates of propagule numbers of the take-all fungus (Gaeumannomyces graminis var.tritici) for 196 of the 368 soil samples bioassayed in a field study conducted in Western Australia between 1984 and 1986.     

Microbeam analysis of Ca exchange and uptake in the fine roots of spruce: influence of pH and aluminum

Summary A novel stable isotope labelling procedure for microbeam analysis was developed to monitor exchange and uptake of nutrients, primarily Mg, K and Ca, by root tips at the cellular level. Initially root samples were analysed from 2-year-old spruce trees, originating both from a nursery and from a polluted forest site, (1) for the cortex cell wall accessibility and nutrient binding properties, (2) for the influence of low pH and elevated aluminum concentrations on Ca binding to cortex cell walls, and (3) for long-range transport into the secondary xylem, proximal to the labelled root tip. In nursery control plants, Ca is localized mainly in the apoplast of the cortex. Exchange of Mg, K, Ca in the cell wall of the cortex and the primary xylem with label in incubation solutions is almost completed to equilibration within 30 min. In the secondary xylem we could detect Mg, K, and Ca from labelling solutions in minute amounts after 30 min, and as a major fraction after 48 h. This indicates that stable isotope labelling can be used to study both ion-exchange properties of the apoplast and long-range transport. Slight acidification of the labelling incubation media to pH 4.5 reduced Ca binding to the cortex cell walls slightly, but acidification to the extreme value of pH 2.3 reduced binding 41%. A combination of pH 4.5 and increased free aluminum reduced the binding by 83%. In a preliminary attempt to analyse the nutrient binding capability of the root-tip apoplast from pollution affected trees, we exposed fine roots of 2-year-old spruce from an acidified and polluted site showing typical low levels of Ca and Mg in the cortical cell walls to Ca-enriched media. Under these conditions the Ca content of cortex cell walls doubled upon incubation at pH 4.7, reaching 40% of the total binding capacity of our nursey control plants.     

The aluminium signal: New dimensions to mechanisms of aluminium tolerance

The physiological basis of plant reaction to and tolerance of aluminium (Al) is poorly understood. We review the results of investigations into Al toxicity and root physiology to develop a theoretical basis for explaining the reaction of the root to Al, including suggested roles for Ca²⁺, mucilaginous cap secretions and endogenous growth regulators in mediating a transmitted response between Al-damaged cap cells and the interacting cell populations of the cap and root. This information is used to identify possible mechanisms of Al tolerance, notably involving signal transduction, Al uptake pathways and root morphogenesis; and to briefly discuss how procedures selecting for Al tolerance may be improved by incorporating the concept of stimulus-response coupling. Similarities in the responses of roots to Al and other signals (e.g. gravity, light, mechanical impedance) are used to develop the hypothesis that roots respond to environmental signals by way of a common regulatory system. New research prospects for extending our perception of Al tolerance mechanisms are identified.     

Clerodane diterpenoids from the roots of Portulaca pilosa

Three trans-clerodane diterpenoids, pilosanol A, B and C, the last compound being a glucoside, have been isolated from the roots of Portulaca pilosa. They show a marked contrast in skeletal type with the constituents of aerial part. Evolutionary changes in the biosynthetic abilities of Portulaca species is discussed.     

Contribution of organic acids to the acidification of the rhizosphere of maize seedlings

The participation of organic acids in the process of soil acidification was related to other H⁺ pumping processes. The ratio between efflux of organic acids and proton secretion of maize roots was determined with the use of a pH-stat combined with a collecting system for organic acids. Changes in the composition of carboxylic acids influenced by nitrogen supply were monitored by HPLC and via enzymatic conversion. The following substances were found to be secreted by maize roots: glycolate, glyoxylate, fumarate, 2-oxoglutarate and oxalate. Malate, however, could not be detected. There is no organic acid dominantly secreted by the roots, but changes are observed during aging which might result from deficiencies of nutrients e.g. P. Fertilization of N-deficient plants with urea leads to a significant change in the composition of acids secreted. In this case, oxalate was additionally detected with a concomitant increase in glyoxylate, indicating important changes in metabolism. Acidification of the rhizosphere is predominantly maintained by secretion of protons, not by efflux of organic acids, which contributed 0.2 to 0.3% to this process only. The role of organic acids in nutrient uptake is discussed.     

Cytochemical localization of plasma membrane ATPase activity in plant cells

Summary The cytochemical localization of ATPase activity has been investigated in maize root cells using both lead and cerium-based capture methods. With both methods, staining at the plasma membrane was observed in all cells of the root, although the precipitate obtained with cerium was more uniform and granular than that with lead. Controls using no substrate or no magnesium, -glycerophosphate to replace ATP, vanadate or boiled tissue generally showed little or no staining. However, biochemical studies on purified plasma membrane fractions showed that ATPase activity was markedly inhibited by fixation, particularly by glutaraldehyde, and also by lead and cerium ions. Non-enzymic hydrolysis of ATP by cerium was greater than that by lead. The value and limitations of these procedures for the localization of plasma membrane H⁺-ATPase activity are summarized in relation to previous criticisms of these methods.Abbreviations DTT dithiothreitol - EDTA ethylene diaminetetraacetic acid - GP B-glycerophosphate - PCMBS p-chloromercuribenzene sulphonic acid - PMSF phenylmethylsulphonyl fluoride