(383f) Modeling of Mass Transfer of Floral Volatiles across the Plant Cell Wall

Plants synthesize and release a variety of volatile organic compounds (VOCs) that are important for their reproduction, defense, and communication. These low-molecular-weight, lipophilic molecules also serve as practical products in industries such as food additives and fragrances. In addition, they have agricultural applications such as sustainable methods for pest control. Therefore, identifying the biological mechanisms involved in volatile emission could help researchers develop new ways to control the timing and release of volatiles, defend against pests, and engineer the production of perfumes and flavors.

While progress has been made in understanding plant volatile biosynthesis, their release from the cell remains incomplete. For plant VOCs to be emitted into the environment, they must move from their site of biosynthesis through the cytosol, transverse the plasma membrane, hydrophilic cell wall, and sometimes cuticle to exit the cell. It was previously shown by mathematical modeling that to achieve observed emission rates solely by diffusion, VOCs would accumulate in the cellular membranes to levels that are likely detrimental to the membrane integrity and function. Hence, it was proposed that there are biological mechanisms additionally involved to lower VOC concentrations in membranes. In this work, we focus on the aqueous cell wall, the thickest layer among the three subcellular barriers that should act as a barrier for the diffusion of VOCs. We hypothesize that the transport of VOCs across the cell wall is facilitated by lipid transfer proteins (LTPs) which enhance the solubility of hydrophobic volatiles in the aqueous environment, prevent their back partition into the plasma membrane after entering the cell wall, and hence enhance their net diffusion. To investigate if the presence of LTPs has influence on the total VOC efflux, a facilitated diffusion model was built to quantify the flux difference. Modeling of the steady state system revealed the facilitation of VOC flux by LTPs is greatest when the VOC concentration gradient across the cell wall is small, which is a physiologically relevant condition. In addition, there exists an optimal protein dissociation constant value for maximal facilitated flux, indicating the balance between the binding and the unloading of VOC is critical. We are currently obtaining and integrating the remaining unknown parameters, such as the binding constant of candidate LTPs with VOCs, into the model. With this information, we can quantify physiological impact LTPs have on VOC transport.