The wax constituents of forage grasses: Cocksfoot and perennial ryegrass

Two sides of a leaf blade: Blumeria graminis needs chemical cues in cuticular waxes of Lolium perenne for germination and differentiation

Plant surface characteristics were repeatedly shown to play a pivotal role in plant-pathogen interactions. The abaxial leaf surface of perennial ryegrass (Lolium perenne) is extremely glossy and wettable compared to the glaucous and more hydrophobic adaxial surface. Earlier investigations have demonstrated that the abaxial leaf surface was rarely infected by powdery mildew (Blumeria graminis), even when the adaxial surface was densely colonized. This led to the assumption that components of the abaxial epicuticular leaf wax might contribute to the observed impairment of growth and development of B. graminis conidia on abaxial surfaces of L. perenne. To re-assess this hypothesis, we analyzed abundance and chemical composition of L. perenne ab- and adaxial epicuticular wax fractions. While the adaxial epicuticular waxes were dominated by primary alcohols and esters, the abaxial fraction was mainly composed of n-alkanes and aldehydes. However, the major germination and differentiation inducing compound, the C26-aldehyde n-hexacosanal, was not present in the abaxial epicuticular waxes. Spiking of isolated abaxial epicuticular Lolium waxes with synthetically produced n-hexacosanal allowed reconstituting germination and differentiation rates of B. graminis in an in vitro germination assay using wax-coated glass slides. Hence, the absence of the C26-aldehyde from the abaxial surface in combination with a distinctly reduced surface hydrophobicity appears to be primarily responsible for the failure of normal germling development of B. graminis on the abaxial leaf surfaces of L. perenne.

Isolation and identification of the high molecular weight saturated fatty acids of butterfat

Butterfat has been shown to contain the normal odd-numbered saturated acids n-nonadecanoic acid (C19), n-heneicosanoic acid (C21), and n-tricosanoic acids (C23).

The presence of the normal even-numbered acids n-octadecanoic acid (C18), n-docosanoic acid (C22), n-tetracosanoic acid (C24) and n-hexacosanoic acid (C26) is conclusively established.

n-Eicosanoic acid (C20) formerly assumed to be present in butterfat has been isolated and identified by its physical and chemical properties.