Morphogenesis, volume and number of hop (Humulus lupulus L.) glandular trichomes, and their influence on alpha-acid accumulation in fresh bracts of hop cones

The ESEM investigations revealed the morphogenesis of peltate glandular trichomes, which was divided into five phases. In phase one, new peltate glandular trichomes were initiated; in phase two, they were differentiated; in phase three trichomes grew vigorously; in phase four they were determined; in the fifth and final phase they came to maturity. Volume of glandular trichome during the different phases of morphogenesis varied from 0.25 × 10-2 mm3 in phase 1, to 1.95 × 10-2 mm3 in phase 5. More glandular trichomes are placed on the base of the adaxial side of bracts (average 7 mm-2) than on the base of abaxial side (average 5.8 mm-2). In this research, positive Spearman's rank order correlations were found between the average number of glandular trichomes and content of α-acids as well as between the average volume of glandular trichomes and content of α-acids.