Emeritus Professor John Patrick

The significance of the osmotic potential of the seed apoplast sap as a regulator of assimilate transfer to and within coats of developing seed of Vicia faba (cv. Coles Prolific) was assessed using attached empty seed coats and intact developing seed. Following surgical removal of the embryos, through windows cut in the pod walls and underlying seed coats, the resulting attached ¿empty¿ seed coats were filled with solutions of known osmotic potentials (¿0. 02 versus ¿0. 75 MPa). Sucrose efflux from the coats was elevated at the higher osmotic potential (high osmotic concentration) for the first 190 min of exchange. Thereafter, this efflux was depressed relative to efflux from coats exposed to the low osmotic potential (high osmotic concentration) solution. This subsequent reversal in efflux was attributable to an enhanced diminution of the coat sucrose pools at the high external osmotic potential. Indeed, when expressed as a proportion of the current sucrose pool size, relative efflux remained elevated for coats exposed to the high osmotic potential solution. Measurement of potassium and sucrose fluxes to and from their respective pools in the coat tissues demonstrated that the principal, fluxes, sensitive to variative in the external osmotic potential, were phloem import into and efflux from the ¿empty¿ coats. Phloem import, consistent with a pressure-driven phloem transport mechanism, responded inversely with changes in the external osmotic potential. In contrast, sucrose and potassium efflux from the coats exhibited a positive dependence on the osmotic potential. Growth rates of whole seed were approximately doubled by enclosing selected pods in water jackets held at temperatures of 25°C. compared to 15°C. The osmotic potential of sap collected from the seed apoplast remained constant and independent of the temperature-induced changes in seed growth rates and hence phloem import. Based on these findings, it is proposed that control of phloem import by changes in the external osmotic potential observed with ¿empty¿ seed coats has no significance as a regulator of assimilate import by intact seed. Rather, maintenance of the seed apoplast osmotic potential, independent of seed growth rate, suggests that the observed osmotic regulation of efflux from the coats may play a key role in integrating assimilate demand by the embryo with phloem import. Copyright © 1993, Wiley Blackwell. All rights reserved

Until recently a suitable experimental system to study sugar unloading from the phloem was not available. Now it is possible to gain a greater insight into this important process using excised seed-coat halves of bean. The technique is described along with three experiments illustrating important characteristics of sugar unloading. Full details of methods are given although the article can be used simply to introduce students to current terminology in phloem physiology, typical 14CO2-dosing techniques in plant studies, and the complex nature of sugar transport across the plasma membrane. Abbreviations: BAP = 6-benzylaminopurine; CCCP = carbonyl cyanide m-chlorophenylhydrazone; MES = 2N-morpholino]ethanesulfonic acid; PPO = 2, 5-diphenyloxazole; TRIS = tris (hydroxymethyl) methylamine. © 1989, Taylor & Francis Group, LLC. All rights reserved.

Phloem transport in stems of Phaseolus vulgaris was found to be sensitive to treatment with the auxin transport inhibitor, 2,3,5-triidobenzoic acid (TIBA). The response was dependent on the concentration of TIBA applied. A concentration of TIBA (0·5% in lanolin) which did not interfere with normal phloem transport proved inhibitory to both basipetal transport of IAA and the acropetal component of IAA-promoted metabolite transport. In contrast, both acropetal IAA transport and basipetal IAA-promoted metabolite transport were unaffected by TIBA treatment. The inhibitory effect of TIBA on acropetal IAA-promoted transport was overcome by providing IAA below the point of TIBA application. Both acropetal and basipetal IAA-promoted transport in stem segments were unaccompanied by any corresponding changes in the accumulation of [14C]sucrose by the segments. © 1978 Oxford University Press.

The hypothesis that indol-3yl-acetic acid (IAA) stimulates solute mobilization in stems by increasing metabolite utilization (i.e. sink strength) and/or sieve tube unloading mechanisms was investigated using seedlings of Phaseolus vulgaris L. Sink strength was assessed by obtaining estimates of rates of growth, 14C incorporation into protein, sucrose metabolism, and sucrose uptake. The data obtained suggest that, whilst enhancing assimilate mobilization, IAA had no short term effect on the sink strength of the treated stumps. In several experiments involving long distance transport of 14C-assimilates, the magnitude of auxin-promoted transport was found to be insensitive to potential changes in sink strength. Furthermore, 14C transport profiles demonstrated that the site of hormone action was not confined to its point of application. © 1976 Oxford University Press.

Indol-3yl-acetic acid (IAA) applied to sterns of Phaseolus vulgaris seedlings, decapitated above primary leaves, enhanced the mobilization of 14C-metabolites to the treated stumps and this effect was apparent within 3-6 h of applying the hormone. More than 90 per cent of the total 14C-activity transported to the stumps was detected in the alcohol-soluble extracts. In all treatments, less than 5 per cent of the 14C-photosynthate exported from the primary leaves was translocated upwards. Accumulation of 14C-activity was also increased when the IAA was applied laterally to intact internodes. This effect was obtained when 14C was supplied either above or below the point of hormone application. By selective heat girdling, it was shown that the auxin affected 14C transport when either the root 'sink' was removed or transpiratory flow of water through the treated internode was maintained. Decapitated stems treated with plain lanolin for 3 d were found to retain their responsiveness to auxin in terms of enhanced metabolite transport. Heat-girdling experiments and estimates of 14C transport velocity suggested that most of the 14C movement was restricted to the phloem of treated stumps. Similar effects of IAA on a transport in excised stem segments of Phaseolus vulgaris were observed. © 1973 OXFORD UNIVERSITY PRESS.

Physiological amounts of indol-3yl-acetic acid (IAA) were accumulated by decapitated stems of Phaseolus vulgaris L. seedlings from lanolin pastes, containing 0.1 per cent IAA, applied to the cut surfaces of the stumps. Both the levels and gradients of extractable and diffusable IAA detected in the treated stumps compared favourably with those reported for the whole plants. A considerable portion of IAA that entered the tissue was metabolized to a compound that had chromatographic properties similar to indol-3yl-acetylaspartic acid. Two other metabolities were tentatively identified as indol-3yl-acetylaspartic acid indol-3yl-acetylglucose. The accumulated IAA appears to be transported as indol-3yl-acetic acid at an apparent velocity of 28 mm/h down the decapitated internodes. © 1973 OXFORD UNIVERSITY PRESS.

The sequence of vascular differentiation in the shoot of the main tiller of Triticum aestivum L. was reconstructed from seriai transverse sections of shoot apices made at various stages of development. The pattern of initiation and development of the procambial strands was confirmed. The provascular bundles of the pith plexus arose independently and developed acropetally from the base of the future node. Early differentiation of proto-phloem and -xylem in the main procambial strands proceeded bidirectionally up the leaf primordia and down the stem from a site of initiation isolated from other differentiated vascular elements. Further development was basipetal from the tip of the primordia, and the rate of differentiation of the sieve elements was sufficient to maintain phloem continuity across the intercalary meristems of the laminae, sheaths, and internodes. Within the developing nodes sieve tube differentiation in the cross-linking strands lagged behind that of the leaf traces they interconnected, and this may influence the movement of photoassimilate from a recently expanded leaf to the apex. © 1972 CSIRO. All Rights Reserved.

The courses of the various vascular bundles in the nodes of the main tiller of Triticum aestivum L. have been reconstructed from anatomical observations of consecutive serial transverse sections. Of the bundles entering a node (n) from its attached leaf, the first-formed and largest, the median, passes directly through the node to the second node below (n-2), where it bifurcates and fuses with other strands. These continue to node n-3 before fusing completely with the nodal plexus. The next six bundles to form (laterals) establish some links with bundles from higher leaves in the node of entry, much more extensive connections in node n-1, and fuse completely with the nodal plexus in node n-2. The next four lateral bundles to differentiate are more extensively linked in node n and fuse completely with the nodal plexus in node n - I. The remaining 16-20 bundles from the leaf (intermediates) follow much the same course but develop more extensive connections with other bundles. The extensive plexus which develops in each node ensures vascular connections between most bundles. The significance of these in transport is briefly discussed. © 1972 CSIRO. All Rights Reserved.

For a series of metallurgical cokes covering the range encountered in industrial practice, the tensile strength, as determined by the diametral-compression test, has been considered in relation to aspects of the porous structure. By means of reflected light microscopy and a computerised image analysis system a quantitative characterisation of the porous structure was made in terms of the number, shape and size of the pores in chosen size categories. It is found that for metallurgical cokes in general, no single structural parameter gives a good correlation with the tensile strength. More complex relationships using composite terms involving several of the structural parameters can be derived and these lead to correlations of high statistical significance. The data are discussed with reference to other published work on the relation between the strength and structure of similar materials.