The effects of nitrogen and sulphur nutrition on the response of Brussels sprout plants to infestation by the aphid Brevicoryne brassicae

The effects of two levels each of nitrogen and sulphur nutrition and of infestation by Brevicoryne brassicae on the growth of Brussels sprout plants were studied in factorial experiments. All the plants receiving high nitrogen treatments grew more rapidly than those with low, but in infested plants the improvement in growth at the higher levels of nitrogen was offset by the increased size of aphid populations. Low sulphur nutrition increased the growth of plants receiving high nitrogen and of the aphids feeding on them. Leaf diffusive resistances and chlorophyll concentrations were greater with high nitrogen, but were significantly lowered by infestation in all nutrient treatments. Infestation decreased leaf total nitrogen concentration at the sites of feeding, but effects on soluble nitrogen were not significant. Removal of aphids 72 days after initial infestation did not cause marked plant recovery during the next 22 days. It is concluded that the benefits of increased yield resulting from high nitrogen levels must be balanced against the greater potential for damage by aphids.     

Effect of Ethylene and Ethylene Precursors on Protein Phosphorylation and Xylogenesis in Tuber Explants of Helianthus tuberosus (L.)

Koritsas, V. M. 1988. Effect of ethylene and ethylene precursorson protein phosphorylation and xylogenesis in tuber explantsof Helianthus tuberosus (L.).J. exp. Bot. 39: 375–386. The role of ethylene in protein phosphorylation and xylem-celldifferentiation was studied in explant cultures of Jerusalemartichoke, Helianthus tuberosus (L.). Explants on xylem-inducingmedium growing at 25 °C developed more xylem elements andproduced more ethylene gas within 3 d of culture than controlcultures growing and developing at similar rates. L-methionineand 1-aminocdopropane-1-carboxylic acid (ACC) incorporated intoboth xylem-inducing and control media enhanced xylem differentiation,increased protein levels and stimulated protein kinase activityin the explants. Inhibitors of the ethylene biosynthetic pathway,cobalt nitrate and aminoethoxyinyl glycine (AVG), depressedxylem differentiation, protein phosphorylation and polypeptidesynthesis. Ethylene gas or ACC reversed the effects of the inhibitors.Ethylene production, protein phosphoryilation and xylem-celldifferentiation were all linked. Ethylene thus promotes xylem-celldifferentiation in Jerusalem artichoke explants, the processprobably being regulated by protein phosphorylation. Key words: Ethylene, phosphorylation, xylem differentiation, Jerusalem artichoke explants     

Glucosinolate responses of oilseed rape, mustard and kale to mechanical wounding and infestation by cabbage stem flea beetle (Psylliodes chrysocephala)

Mechanical wounding of the petioles of six laboratory-grown rapeseed ( Brassica napus ) cultivars induced physiological changes in the plant, markedly affecting the levels of individual glucosinolates. Greatest increases were observed for the indole glucosinolates, glucobrassicin and neoglucobrassicin. Such changes were usually associated with large decreases in the levels of aliphatic glucosinolates. The total glucosinolate content of the wounded plant was thus a reflection of these two opposing trends and wounding produced a greater relative indole glucosinolate content in this total figure. Thus increasing wounding was associated with an increase in indole glucosinolates and a decrease in aliphatic compounds.
Infestation of field- and laboratory-grown rapeseed with cabbage stem flea beetle ( Psylliodes chrysocephala ) produced similar effects, which were observed in various parts of the plant. Differences in response between field- and laboratory-grown infested plants are attributed to the different physiological ages of the harvested material.
Laboratory-grown kale and mustards also showed wound-induced glucosinolate changes. The kale, cv. Fribor, produced elevated levels of both indoles and aliphatics after wounding. Total glucosinolate content in the mustards, which, unlike rape and kale, normally contain only traces of indole glucosinolates in the unstressed state, was increased following wounding. This was, however, not associated with elevated levels of indole glucosinolates, but with accumulation of aliphatic ( Brassica nigra, B. juncea ) and aromatic ( Sinapis alba ) glucosinolates. The significance of these findings is discussed.