SUMMARYAcid invertase (EC 3.2.1.26) is present in soluble and insoluble preparations from root and shoot tissue of Ricinus communis L. Greatest activity is found in expanding tissue, whilst very low activity is found in vascular and in phloem-enriched tissue from stem internodes. In most tissues less than 20",, of the total acid invertase activity is insoluble, the exception being extrafloral nectaries where 65-82",, is insoluble. The activity of sucrose synthase (EC 2.4.1.13) is low in leaves and apical regions of the primary root; the root stele contains greater activity than the cortex. Considerable diel variations in leaf carbohydrate content were demonstrated and the results suggest that variations lor the young sink leaves might be out of phase with those of source leaves by as much as one photoperiod. Tbe results are discussed in relation to the metabolism and transport of sucrose, particularly in roots.

S U M M A R Y' lie accumulation of exogenous D-fructose, D-glucose atid sucrose into root tips of Ricinus communis was studied. Accumulation of sucrose is biphasic with respect to substrate concentration, both saturable and non-saturable phases being discerned. Accumulation is sensitive to pH, the exogenous solute potential, PCMBS, and other sugars. Sap representative of the apoplast was collected by centrifugation and contains approximately 40 mol Tl -hexose equivalents. Plants were labelled to the steady state with respect to cotyledonary sucrose derivatives; \'hole roots were then analysed by compartmental analysis and the r-esults indicated similar apoplastic hexose concentrations. The vacuoles of roots grown in low salt solution contain most of the root soluble sugars, at a 'concentration of about 70 mol m '' hexose equivalents. The sugar content of such roots decreases with availability "f KCl to an extent which indicates that this involves a replacement of vacuolar hexose by alternative osmotica, 'supporting the results frot-n compartmental analysis.

S U M M A R yThe intercellular pathway of sugar transport within tissues of Ricinus communis roots, whicb are available to exogenous solutions, was investigated to identify the route of pbloem unloading. Less than 3",, of soluble translocate within tbe root system accumulates in root f-iathing media designed to influence the apoplastic movement of soluble sugars. Sucrose and hexoses make up 80",, of the leaked translocate. The influence of plant growth regulator substances and of amino acid analogues upon tbe accumulation of translocate into the primary root has been evaluated and is discussed in relation to the symplastic transport of carbohydrate.

Nodulated winged bean [Psophocarpus tetragonolobus (L.) DC., cv. UPS 122] were grown under constant environmental conditions and supplied with mineral nutrient solution in which nitrogen was absent or was present as nitrate (12 mg N week‐1 plant‐1). Nitrate treatment dramatically promoted plant growth, increased fruit weight 1.6 fold, was necessary for tuberisation and enhanced nodulation. The in vitro accumulation of 14C into asparagine and aspartate components of excised nodules supplied with exogenous 14CO2 and [14C]‐D‐glucose was greater for nitrate‐treated plants, whilst accumulation into ureides was reduced by nitrate treatment. Levels of amino acids in xylem sap were greater for plants supplied with a complete nutrient solution, than those grown without applied nitrate, particularly for asparagine, glutamine and proline. Xylem ureide levels were greater for plants grown in the absence of supplementary nitrate. Nitrogen accumulated in leaf, stem and petiole, and root nodule tissues for utilisation during fruit development; peak nitrogen levels and time of anthesis were retarded for plants grown without applied nitrate. The shoot ureide content increased during fruiting, coincident with decreases in the total nitrogen content, indicating that ureide pools are not utilised during the early reproductive phase. However ureide reserves, particularly allantoin, were utilised during the later stages of pod fill. Enzyme activity which metabolised asparagine was found throughout the plant and was identified as K+‐dependent asparaginase (EC 3.5.1.1) and an aminotransferase. Apart from temporal differences in developmental profiles of enzyme activity, the activity of these enzymes and of allantoinase (EC 3.5.2.5) in developing tissues were similar for both treatments. The main differences were greater asparaginase and asparagine:pyruvate aminotransferase activities in root tissues and fruit of nitrate‐supplied plants; allantoinase activity in the primary roots of plants grown without nitrate decreased during development, whilst activity in developing tubers (nitrate‐supplied plants) increased.