Root xylem transport of amino acids in the root hemiparasitic shrub Olax phyllanthi (Labill) R.Br. (Olacaceaea) and its multiple hosts

The amino acid compositions of the root xylem saps of Olax phyllanthi and a range of its common hosts were examined in native coastal heath in Western Australia and in pot cultures of Olax reliant on single hosts. When hosts specializing in the xylem transport of one major solute (asparagine, glutamine, histidine, arginine or proline) were exploited, the endophytic tissue of haustoria and the xylem sap of Olax showed much lower proportions of this than of other solutes, suggesting pronounced metabolic transformation prior to xylem loading by the parasite. However, the xylem sap of Olax did partly reflect the compositions of its hosts; for example, djenkolic acid and pipecolic acid were present when Olax was parasitic on species of Acacia, and levels of citrulline and aspartic acid were higher than normal when it exploited hosts transporting large amounts of these compounds. Back-flow of S-ethenyl cysteine, a novel amino acid specific to Olax, was observed to another root hemiparasite (Exocarpos sparteus) in native habitat and to certain non-parasitic hosts in water-stressed pot cultures. Haustoria exhibited high levels of glutamine synthetase but showed appreciable in vivo nitrate reductase activity only when on hosts with high xylem levels of nitrate.     

Factors Affecting Polyamine Accumulation in Barley (Hordeum vulgare L.) Leaf Sections during Osmotic Stress

Turner, L. B. and Stewart, G. R. 1988. Factors affecting polyamineaccumulation in barley (Hordeum vulgare L.) leaf sections duringosmotic stress.-J. exp. Bot. 39: 311–316. Polyamine concentrations in peeled leaf sections of Hordeumvulgare were unaffected by decreases in leaf water potentialif osmotic adjustment took place and leaf turgor was maintained.Putrescine accumulation occurred concomitantly with a decreasein leaf turgor. Increases in the order of 3-to 4-fold were observed.An apparently greater putrescine accumulation (7-fold) occurredwhen leaf sections were osmotically stressed in the presenceof exogenous phosphate ions. This was the result of water lossfrom the tissue and the large decline which occurred in theputrescine levels of control tissue sections incubated withphosphate ions. Putrescine accumulation was at its maximum after4 h osmotic stress. In contrast, proline accumulation took placebetween 4 h and 24 h after the imposition of osmotic stress. Key words: Hordeum vulgare, osmotic stress, polyamine