Genetic and environmental variation in acyl glucose ester production and glandular and nonglandular trichome densities in Datura wrightii

Natural populations of Datura wrightii in southern California are dimorphic for trichome type. Some plants within populations produce greater than 85% glandular trichomes, whereas other produce mainly nonglandular trichomes, Glandular trichome exudates in D. wrightii consist of glucose esterified wi th straight chain C-6-C-9 acids. These exudates, and similar exudates in ot her species, confer resistance to several insect herbivore species. We test ed the hypothesis that water was limiting sugar ester production and examin ed the extent to which trichome density was determined by environmental fac tors by measuring the concentrations of sugar esters and the densities of t richomes on leaves of plants grown under different irrigation treatments. W ater did not limit sugar ester production, as unwatered plants produced 36% more millimoles of glucose esters per square centimeter of leaf surface th an did watered plants. Although the addition of water increased leaf size, densities of both nonglandular and glandular trichomes did not change with leaf length or area, suggesting that plants having larger leaves initiated more trichomes in order to maintain nearly constant densities. Millimoles o f sugar esters produced did not correlate with densities of glandular trich omes, suggesting that other factors in addition to glandular trichome numbe r govern the production of sugar esters for plant defense.