DEVELOPMENTAL PROFILE OF SINALBIN (P-HYDROXYBENZYL GLUCOSINOLATE) IN MUSTARD SEEDLINGS, SINAPIS-ALBA L, AND ITS RELATIONSHIP TO INSECT RESISTANCE

Sinalbin was identified as a chemical component of insect antixenosis and antibiosis resistance mechanisms in seedlings of Sinapis alba by DEAE-Sephadex chromatography, HPLC, treatment with sulfatase and myrosinase, various feeding tests using artificial and natural substrates, and by measuring sinalbin concentrations in cotyledons and leaves during seedling development. The effects of sinalbin on feeding were dependent upon the insect species and upon the rapidly changing profile of sinalbin concentrations in the developing seedling. The high concentrations of sinalbin found in young cotyledons (up to 20 mM) and leaves (up to 10 mM) deterred the feeding of the flea beetle, Phyllotreta cruciferae Goeze and larvae of the bertha armyworm, Mamestra configurata Walker. The protection that sinalbin confers upon the vulnerable, newly emerged seedling (and upon tiny, young leaves) appears critical for the first few days of survival of S. alba under feeding pressure from flea beetles in the field. The lower concentrations of sinalbin found in older cotyledons and leaves (2-3 mM) offer little or no protection against P. cruciferae and may actually stimulate the feeding of this crucifer specialist. These concentrations of sinalbin, however, are still effective in reducing the level of feeding by larvae of the more generalist feeder M. configurata.