Paclobutrazol improves leaf carbon-use efficiency by increasing mesophyll conductance rate, while abscisic acid antagonizes this increased rate

Abstract

Our experiment was conducted to understand the effects of foliar sprays of paclobutrazol (PBZ), its mixture with abscisic acid (ABA), or water (control) on leaf carbon-use efficiency (CUEl), photosynthesis, and respiration of Euonymus japonicus seedlings. Plants were pot-grown in a greenhouse. The study revealed that elevated stomatal conductance, mesophyll conductance, and maximum rate of Rubisco carboxylation (Vcmax) in plants treated with PBZ could strongly improve net photosynthetic rate (PN). ABA could antagonize the increase of mesophyll conductance and stomatal conductance by PBZ, thereby inhibiting the improvement of photosynthesis by PBZ. The combination of PBZ and ABA significantly reduced day respiration (Rd) and dark respiration (Rdk), resulting in the increased CUEl, PN/Rd, and PN/Rdk. The increased PN in the PBZ treatment led to slightly increased PN/Rd and CUEl. Thus, the CUEl could be improved by PBZ and its mixtures with ABA by regulating leaf photosynthesis and respiration.

Keywords

• gas exchange
• leaf respiration
• photosynthetic respiration ratio
• plant growth inhibitors