Photosynthesis and Kaempferol Yields of Soy Leaves Under ABA Application and Mechanical Wounding

Environmentally sound plant treatments that can impose mild physiological stress and elicit bioaccumulation of useful phytochemicals such as kaempferols are limited. We tested ABA foliar application, 100 or 200 μM, and two types of leaf wounding, piercing or hole punching in young greenhouse-grown soy plants. Leaf gas exchange and A/Ci response, ΦPSII, pigments and antiradical activity were measured using the same leaf and kaempferols were measured in the leaf above. ABA 200 μM-treated plants had ≥ 20% less gas exchange and 17% less ETR, but greater Vcmax and Jmax compared to control. They had 55% and 100% more stomatal limitation to Pnet and ΦPSII, respectively, than control. Leaf-wounded plants showed the lowest stomatal limitation to either Pnet or ΦPSII. Leaf piercing increased chlorophylls 39% and carotenoids 38% compared to control. Six kaempferols quantified were found to be mono-, di- and triglycosides. Each leaf treatment increased total kaempferol yield ranging from 42% in ABA 100 μM to 68% in ABA 200 μM treatment compared to control. In general, kaempferol yields were positively correlated to Pnet in ABA 100 μM-treated plants and to gs in ABA 200 μM-treated plants but negatively correlated to Pnet in leaf-pierced plants. ABA application and wounding affected the association between photosynthetic primary metabolism and kaempferol accumulation differently. Both ABA application and wounding are promising leaf treatments for eliciting kaempferol accumulation in young soy leaves.