Abscisic Acid stimulates elongation of excised pea root tips

Excised Pisum sativum L. root tips were incubated in a pH 5.2 sucrose medium containing abscisic acid. Elongation growth was inhibited by 100 mum abscisic acid. However, decreasing the abscisic acid concentration caused stimulation of elongation, the maximum response (25% to 30%) occurring at 1 mum abscisic acid. Prior to two hours, stimulation of elongation by 1 mum abscisic acid was not detectable. Increased elongation did not occur in abscisic acid-treated root tips of Lens culinaris L., Phaseolus vulgaris L., or Zea mays L.     

Electropotential in excised pea epicotyls

In contrast to intact etiolated pea seedling tissue (Pisum sativum L.), excised segments immersed in a complete nutrient solution show marked increases in ion content, largely of K⁺ and NO₃⁻, over a 72-hour period. During this time there is increase in cell electropotential difference, PD. During the initial 6 to 8 hours there is a lag in ion uptake; cell PD, however, increases rapidly from approximately −50 to −100 mv then increases more slowly. The increase in PD precedes and thus may be a prerequisite for the rapid ion accumulation phase. Cell PD increases in either water or nutrient solution but eventually reaches higher levels in the latter. Following water pretreatment of sufficient duration K⁺ accumulation shows no lag period. The lag phase noted here appears dissimilar to that of storage tissues.     

Polysome formation and stability in pea stem and root tissue

Polysome stability and the formation of various polysomal populations in pea stem and root tissue were examined. Both total ribosomal fraction and four polysome populations were isolated: FP (free polysomes), MBP (membrane-bound polysomes), CBP (cytoskeleton-bound polysomes) and CMBP (cytoskeleton-membrane-bound polysomes). The content of above mentioned populations decreased in roots and stems during germination. In both roots and stems a gradual decrease of FP participation in the total polysomal population was also observed during germination. On the other hand, an obvious increase in participation of CMBP population in the total polysomes pool was observed in later stages of germination. Increase of CMBP participation in pea root and stem tissues in later stages of germination is probably due to intensive enzymatic protein synthesis taking place in them. These proteins may participate in elongating growth of cells. The results of investigation on polysomes stability showed that total polysomes isolated from pea roots appeared to be more resistant to digestion by exogenous ribonuclease (EC 3.1.27.5) than polysomes isolated from stems. As protein-mRNA interactions are widely known and ribosomes are also very adhesive structures, numerous non-ribosomal proteins are present in the polysome preparations. We suppose that changes in proteins bound to polysomes indicated by us previously, significantly influence both the stability and also translatability of polysomes isolated from different plant organs.     

Differential effects of the sulfonylurea herbicides chlorsulfuron and sulfometuron methyl on microorganisms

The sulfonylurea herbicides exert their effects on cells via their inhibition of the acetohydroxy acid synthase (AHS) enzymes. Although chlorsulfuron and sulfometuron methyl often affected microbial growth differently their effects on the AHS activities of toluenised cells were similar. Sulfometuron methyl was always a more potent inhibitor than chlorsulfuron. We have postulated that sulfometuron methyl penetrated into microbial cells more readily then did chlorsulfuron. The effect of the herbicides on microbial growth was altered by the composition of the medium and in particular by valine or valine plus isoleucine. Different microorganisms had different complements of AHS isoenzymes which together with differences in permeability were the most likely explanations for the different responses observed. It was pointed out that application of these sulfonylurea herbicides would have significant effects on the microbial ecological balance of soil, and particularly so in alkaline soils. The consequences would be most evident in agricultural situations where the microbial population played an important role in maximising the productivity of crops.     

Genetic variability in nodulation and root growth affects nitrogen fixation and accumulation in pea

BACKGROUND AND AIMS: Legume nitrogen is derived from two different sources, symbiotically fixed atmospheric N(2) and soil N. The effect of genetic variability of root and nodule establishment on N acquisition and seed protein yield was investigated under field conditions in pea (Pisum sativum). In addition, these parameters were related to the variability in preference for rhizobial genotypes. METHODS: Five different spring pea lines (two hypernodulating mutants and three cultivars), previously identified in artificial conditions as contrasted for both root and nodule development, were characterized under field conditions. Root and nodule establishment was examined from the four-leaf stage up to the beginning of seed filling and was related to the patterns of shoot dry matter and nitrogen accumulation. The genetic structure of rhizobial populations associated with the pea lines was obtained by analysis of nodule samples. The fraction of nitrogen derived from symbiotic fixation was estimated at the beginning of seed filling and at physiological maturity, when seed protein content and yield were determined. KEY RESULTS: The hypernodulating mutants established nodules earlier and maintained them longer than was the case for the three cultivars, whereas their root development and nitrogen accumulation were lower. The seed protein yield was higher in 'Athos' and 'Austin', the two cultivars with increased root development, consistent with their higher N absorption during seed filling. CONCLUSION: The hypernodulating mutants did not accumulate more nitrogen, probably due to the C cost for nodulation being higher than for root development. Enhancing exogenous nitrogen supply at the end of the growth cycle, by increasing the potential for root N uptake from soil, seems a good option for improving pea seed filling.     

Electrical resistance and ion movement through excised discs of sugar beet root tissue

Electrical and tracer techniques were used to investigate the movement of Na⁺, K⁺ and Cl^? through discs of a range of thicknesses cut from the root tissue of sugar beet, Beta vulgaris L. cv. Amono. At low external concentration the electrical resistance across a discs is less than that of an equivalent volume of solution. This does not appear to be due to a low resistance symplastic pathway but rather, to an enhanced concentration of cation in the apoplast. The resistance is proportional to the thickness of tissue. Although measurement of diffusion potential gives about 25 mV difference across the disc for a ten-fold change in cation concentration, there is little discrimination between K⁺ and Na⁺. The observed tracer kinetics of ⁸⁶Rb through the disc are consistent with those of diffusion, with a coefficient of diffusion, D, of 0.19 × 10^?9 m² s^?1 and a tissue partition coefficient, k, of 0.27 (or of 2.7 if referred to the cell wall phase only). ³⁶Cl gives a similar value for D, but has a k reduced by a factor of 3.3, a result that is consistent with the diffusion potential observation. However, a much larger discrimination would have been expected from the chemically measured cation exchange capacity.     

Lectin-enhanced accumulation of manganese-limited Rhizobium leguminosarum cells on pea root hair tips.

The ability of Rhizobium leguminosarum 248 to attach to developing Pisum sativum root hairs was investigated during various phases of bacterial growth in yeast extract-mannitol medium. Direct cell counting revealed that growth of the rhizobia transiently stopped three successive times during batch culture in yeast extract-mannitol medium. These interruptions of growth, as well as the simultaneous autoagglutination of the bacteria, appeared to be caused by manganese limitation. Rhizobia harvested during the transient phases of growth inhibition appeared to have a better attachment ability than did exponentially growing rhizobia. The attachment characteristics of these manganese-limited rhizobia were compared with those of carbon-limited rhizobia (G. Smit, J. W. Kijne, and B. J. J. Lugtenberg, J. Bacteriol. 168:821-827, 1986, and J. Bacteriol. 169:4294-4301, 1987). In contrast to the attachment of carbon-limited cells, accumulation of manganese-limited rhizobia (cap formation) was already in full progress after 10 min of incubation; significantly delayed by 3-O-methyl-D-glucose, a pea lectin haptenic monosaccharide; partially resistant to sodium chloride; and partially resistant to pretreatment of the bacteria with cellulase. Binding of single bacteria to the root hair tips was not inhibited by 3-O-methyl-D-glucose. Whereas attachment of single R. leguminosarum cells to the surface of pea root hair tips seemed to be similar for both carbon- and manganese-limited cells, the subsequent accumulation of manganese-limited rhizobia at the root hair tips is apparently accelerated by pea lectin molecules. Moreover, spot inoculation tests with rhizobia grown under various culture conditions indicated that differences in attachment between manganese- and carbon-limited R. leguminosarum cells are correlated with a significant difference in infectivity in that manganese-limited rhizobia, in contrast to carbon-limited rhizobia, are infective. This growth-medium-dependent behavior offers and explanation for the seemingly conflicting data on the involvement of host plant lectins in attachment of rhizobia to root hairs of leguminous plants. Sym plasmid-borne genes do not play a role in manganese-limitation-induced attachment of R. leguminosarum.     

Uptake of benzyladenine by excised watermelon cotyledons

The uptake of 8-[¹⁴C]N⁶-benzyladenine (BA) was studied in excised watermelon (Citrullus vulgaris Schrad.) cotyledons 24 hours after the start of imbibition. The passive nature of this uptake is suggested by the following evidence: (a) no sign of saturation on increasing external concentration of BA; (b) no decrease in uptake under conditions that inhibit ATP synthesis; (c) no change in amount of radioactivity absorbed when cotyledons are frozen and thawed before the uptake test. About two-thirds of the radioactivity taken up is released after 12 hours of washing. If the washing is performed at 2 C very little radioactivity is released.     

Changes in sulphate uptake and accumulation along the primary root during tissue differentiation

Experiments were made with the uptake of 35-S sulphate along the axis of the intact seminal root of maize seedlings. Using short exposures the most intensive sulphur uptake was found in the apical 10 mm long region of the root. In the differentiating cells the maximum of sulphur uptake was in the first two 1-mm segments of the elongation zone immediately behind the meristem and then in the zone of the root hairs. Apart from the high activity in the area of the root hairs, two and three peaks, respectively, of increased sulphur accumulation were found in the area of the formation of laterals in case of longer exposure.     

Purification and properties of two ribonucleases in different intracellular compartments in pea root tissue.

Two RNases in bound forms associated with the microsomal membrane and with the ribosomes or unknown particles in pea root tissue were solubilized by subjecting the membrane to sonic oscillation in the presence of EDTA and KC1 and by treating the particles with EDTA, respectively. The RNases were than purified by DEAE-cellulose and Sephadex G-75 column chromatographies. The elution profiles of RNases from the columns were very similar. No significant differences were observed in their electrophoretic mobilities in polyacrylamide gels, in molecular weight, in activation by inorganic ions, urea or phospholipid micelles or in the dependence of their activities upon pH. The purified RNASES were not different from the bound enzymes as regards activation by inorganic ions and urea and the dependence of the activity upon pH. Triton X-100 stimulated the activity only if RNase was in a bound form associated with the microsomal membrane. We propose that the two RNases may be the same molecular species and differ only in the form of association with intracellular structures.     

Sites of accumulation in excised Phloem and vascular tissues

Excised pieces of vascular bundle and phloem tissue were allowed to accumulate radioactive phosphate and sulfate, and were then sectioned and autoradiographed so as to detect the sites of accumulation. Special methods were needed to prevent any diffusion of the radioisotope. Some autoradiographs obtained are presented. In excised celery vascular bundles, the most radioactive area and hence the most actively accumulating tissue was the young secondary phloem at the sides of the bundle. In intact plants, the same tissue was the most active in translocating. In excised apple phloem there was some variation in behavior, but again the young secondary phloem was generally the most actively accumulating tissue. Accumulation activities of individual cells in the phloem and vascular tissue were compared. It appeared that all cell types, ray, phloem and xylem parenchyma, cambial cells and sieve tubes, accumulated at least 5 times more actively than did the cortical parenchyma cells. The sieve tubes were among the most actively accumulating cells present, accumulating 20 times more actively than the cortical parenchyma cells. It is concluded that accumulation processes have a primary role to play in the mechanism of phloem transport.     

Effects of fluorinated pyrimidines on the growth of excised pea embryos

The effects of some fluorinated pyrimidines on the growth ofexcised pea embryos {Pisum sativum var. Alaska) in sterile culturewere studied. Even the lowest concentrations of the compoundstested inhibited growth in length of the embryos. In order ofdecreasing activity, the compounds tested were : 5-fluorodeoxyuridine,5-fluorodeoxycytidine, 5-fluorouridine, 5-fluoroorotic acidand 5-fluorouracil. Inhibition of growth in length of the rootprimordia was found to be mainly due to inhibition of cell divisionwith no effect on cell elongation. Reversal of fluoropyrimidineinduced inhibition of growth by pyrimidine bases and their relatedmetabolites indicated that the analogues primarily inhibitedDNA synthesis. ¹Part of a thesis submitted by the senior author for the degreeof M.Sc. of the University of Malaya ²Present address: Department of Botany, University College ofWales, Aberystwyth, U.K. (Received October 27, 1969; )