ALBERT

Notes: Summary The water-extractable and ion-exchangeable fractions of the free space of maize roots for sodium ions has been determined. The free space of whole roots, excised roots and isolated stelar and cortical tissues, has been compared and the results examined for any evidence of a barrier between the cortex and the stele. Similarly the free space of whole roots and excised roots, from which the epidermal and outer cortical cells have been removed by shaving, has been compared and the results examined for any evidence of an epidermal barrier. Whole roots gave a free space value some 20% lower than excised roots. It was calculated that this difference could be accounted for if the cortical tissues only were considered in estimating the whole root value, that is if the stele was considered as participating in the excised root but not in the whole root. Samples in which isolated cortical and stelar material were measured together, or separately and the value calculated, gave similar values to those obtained for excised roots. These results are interpreted as evidence that a barrier to free diffusion exists between the cortical and the stelar tissues at or near the endodermis. Shaving both whole and excised roots increased the free space by about 35%. However, as this value was similar for both, it was concluded that the increase was due to the contribution of damaged cortical cells and does not indicate that the epidermis is an effective barrier to the diffusive entry of sodium ions into the root.

Notes: Summary The chemical composition of exudate obtained from incisions made in the bark of the stem of actively growing Ricinus plants has been determined. The exudate had a high dry matter content (100–125 mg/ml), a high sugar content (80–106 mg/ml) which was solely sucrose, reducing sugars being absent. The amino acid composition was mainly glutamic and aspartic acids and threonine with a total amino acid concentration of 35.2 mM. The exudate had a pH of 8.0–8.2. Potassium was the major cation (60–112 mM) with sodium present at a lower concentration (2–12 mM). Of the divalent cations, calcium was at a low concentration (0.5–2.3 mM) and magnesium relatively higher (4.5–5.4 mM). Chloride was the major inorganic anion (10–19 mM). Phosphate concentration was relatively high (3.7–5.7 mM) and low concentrations of sulphate (0.3–0.5 mM) and bicarbonate (1.7 mM) were also present. Nitrate was absent. The ionic balance was maintained by the presence of relatively large quantities (30–47 meq/l) of organic anions, mainly malate. Bioassays revealed auxin, gibberellin and cytokinin activities in chromatographed exudate. Adenosine triphosphate was found in the exudate (0.40–0.60 mM). The analysis is dicussed with respect to the composition of phloem sap reported for other plant species.

Notes: Abstract Over sixty syntectonic deformation experiments in uniaxial compression have been done on fine-grained limestones in the stability fields of calcite I, calcite II and aragonite. X-ray techniques and spherical harmonic analysis of the data were used to determine preferred orientation quantitatively, and inverse pole-figures were derived for these axially symmetric specimens. They display in most cases strong preferred orientation which varies as a function of the experimental conditions, mainly temperature and pressure. At temperatures below 350° C recrystallization is lacking and flattened grains indicate that translation, twin gliding and kinking have been the dominant deformation mechanisms. The inverse pole-figure shows a maximum at c with a shoulder towards or a second maximum at e. This is in agreement with preferred orientation observed in experimentally deformed Yule marble and can be explained as the product of dominant twin gliding on e and translation gliding on r (Turner et al., 1956). At high temperatures (900–1000° C) strong grain growth (from 4 to 50 microns) indicates that the fabric recrystallized. Grains are equidimensional and clear with a marble-like texture. The inverse pole-figure shows a single maximum at r, and c-axes are oriented in a small circle around the axis of compression, σ 1. Such a pattern of preferred orientation would be expected on thermodynamic grounds assuming that recrystallized grains will be oriented in such a way that the strain energy is a maximum (e.g. MacDonald, 1960). Decrease in confining pressure caused a decrease of the maximum at c and the formation of a secondary maximum at highangle positive rhombs in the inverse pole-figure. This can be interpreted as r translation dominating over e twinning. In all deformation experiments an equilibrium in preferred orientation was reached after 20 percent shortening. The strength of preferred orientation decreased with increasing temperature. Aragonite was produced within its hydrostatic stability field at temperatures above 500° C. Close to the phase boundary, coarse-grained textures showed preferred orientation with poles to (010) parallel to σ 1. At higher pressures the fabric is fine-grained and [001] is aligned parallel to σ 1. Evidence is given that the phase change from calcite to aragonite in these deformation experiments is a diffusive and not a martensitic transformation.

Notes: Summary Steles isolated from maize roots grown under non-sterile conditions showed an increase in ion absorption capacity and in the rate of oxygen uptake when washed for 24 h, although the levels of protein and of several hydrolytic and respiratory tnzymes fell over the same period. Fresh isolated cortex showed higher activity than fresh steles in relation to both ion absorption and respiration. The large increase with washing in the ion absorption capacity of the steles was not observed when the tissue was isolated from roots grown under sterile conditions. These results are discussed in relation to proposed mechanisms for the radial transport of ions across the root and to the effect of micro-organisms on ion absorption studies in higher plant cells.

Notes: Summary Exudate can be obtained from incisions made in the bark of the stem of actively growing Ricinus plants. 14C-labelled assimilates from a fed leaf are rapidly detected in the exudate. This movement was both acropetal and basipetal from the fed leaf, at rates of over 100 cm h-1. Estimated rates within intact plants were 80–84 cm h-1. In contrast with xylem sap obtained from the same plant, the exudate obtained had an alkaline pH (8.2), a high dry matter content (10–12.5%), high sugar content (8–10%) which was predominantly sucrose; high potassium content (60–80 mM) and low calcium content (0.5–1.0 mM). It is concluded, on the basis of the present evidence, that the exudate is a true sample of the sieve tube sap undergoing translocation.

Notes: Summary A mathematical analysis of the relationship between the flux of water, f H2O, and the flux of potassium f K, to the xylem of exuding root systems of Ricinus communis, is presented. Previous analyses (Baker and Weatherley, 1969; Minchin and Baker, 1969) have indicated the presence of a water dependent and a water independent f K both of which vary with the external concentration of potassium, Cm, supplied as potassium nitrate. The present analysis reveals that whereas at Cm values〈1 mM both components of f K contribute ions to the osmotically active solutions within the osmotic barrier, at Cm values〉1 mM only the water dependent f K is responsible for the osmotic work. This suggests that the ions are released within different regions of the stele. It is proposed that at cm values〈1 mM both components are released from the inner stelar tissues whilst at higher Cm values the water dependent f K is released from the outer stelar tissues. This requires that the solute permeability of the plasmalemma of the outer stelar tissues increases markedly at or about Cm values of 1 mM. It is postulated that the required separation of the two f K components within the stelar symplasm at Cm values〉1 mM is due to the water independent f K being in a bound state, possibly being transported along a chain of binding sites whilst the water dependent f K is in a free state within the aqueous phase of the cytoplasm.

Notes: Summary The accumulation of 86Rb labelled potassium by isolated stelar and cortical tissues from 7-day-old roots of Zea mays has been compared with the levels accumulated by these tissues in the intact root. Cortical tissues have similar uptake eapacities in these two conditions whereas stelar tissues only exhibit an uptake capacity in the intact root system. The uncoupler carbonylcyanide m-chlorophenylhydrazone caused a considerable decrease in the uptake of potassium by these tissues. In the intact root system it prevented ions from the bathing medium reaching the stelar tissues. The efflux pattern from preloaded isolated stelar and cortical tissues was considerably altered by the inhibitor, a promotion of the efflux occurring in both of these tissues. It is concluded that stelar tissues only accumulated ions when these are supplied through the root symplasm and that the stelar plasmalemma has only a limited uptake capacity per se. Stelar uptake is thus a reflection of vacuolar accumulation across the tonoplast. There is no evidence in the present study of a carrier-mediated active secretion of ions across the stelar plasmalemma. The fact that the efflux was promoted rather than depressed by the uncoupler supports the postulate that a passive leakage is the final stage in the transport of ions across the plant root.

Notes: Summary The effect of calcium on the flux of potassium to the exudate of detached root systems of Ricinus communis has been investigated. Previous analyses have indicated the presence of a water dependent and a water independent flux of potassium which vary with the concentration of potassium in the bathing medium, in the presence of 0.1 mM CaCl2. In the present study it has been observed that at a higher concentration of calcium in the bathing medium (2.5 mM CaCl2) the water dependent flux of potassium is greatly reduced while the water independent flux is not affected. It is proposed that the differential effect of calcium on these two fluxes is a reflection of the degree of dependence of these fluxes on the permeability of the plasmamembranes within the root.