The permeation barrier of plant cuticles: uptake of active ingredients is limited by very long‐chain aliphatic rather than cyclic wax compounds

Abstract

BACKGROUND The barrier to diffusion of organic solutes across the plant cuticle is composed of waxes consisting of very long‐chain aliphatic (VLCA) and, to varying degrees, cyclic compounds like pentacyclic triterpenoids. The roles of both fractions in controlling cuticular penetration by organic solutes, e.g. the active ingredients (AI) of pesticides, are unknown to date. We studied the permeability of isolated leaf cuticular membranes from Garcinia xanthochymus and Prunus laurocerasus for lipophilic azoxystrobin and theobromine as model compounds for hydrophilic AIs. RESULTS The wax of P. laurocerasus consists of VLCA (12%) and cyclic compounds (88%), whereas VLCAs make up 97% of the wax of G. xanthochymus. We show that treating isolated cuticles with methanol almost quantitatively releases the cyclic fraction while leaving the VLCA fraction essentially intact. All VLCAs were subsequently removed using chloroform. In both species, the permeance of the two model compounds did not change significantly after methanol treatment, whereas chloroform extraction had a large effect on organic solute permeability. CONCLUSION The VLCA wax fraction makes up the permeability barrier for organic solutes, whereas cyclic compounds even in high amounts have a negligible role. This is of significance when optimizing the foliar uptake of pesticides. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Leaf Cuticular Transpiration Barrier Organization in Tea Tree Under Normal Growth Conditions

“…As a chemical group, triterpenoids did not show a significant correlation with the cuticular transpiration rate or resistance ( Table 1 ), which is in accordance with previous studies ( Jetter and Riederer, 2016 ; Staiger et al, 2019 ). However, at the individual chemical level, betulin, a triterpenoid from the abaxial surface, showed significant and negative correlations with the abaxial cuticular transpiration rate ( Table 2 ).…”

“…The cuticular transpiration barrier is mainly contributed by aliphatic compounds, which are located on the intracuticular waxes (Jetter and Riederer, 2016;Zeisler-Diehl et al, 2018;Cheng et al, 2019;Zhang et al, 2020). Recently, there were controversial reports suggesting that cyclic compounds are negatively correlated with cuticular transpiration rates of developing fruits or under drought stress (Schuster et al, 2016;Romero and Rose, 2019;Lino et al, 2020;Zhang et al, 2020); however, other studies found that the cyclic compounds do not contribute to the transpiration barrier or even are positively correlated with the cuticular transpiration rate (Buschhaus and Jetter, 2012;Jetter and Riederer, 2016;Staiger et al, 2019). Jetter and Riederer (2016) chose eight different plant species of which cuticles belong to two major groups based on the presence and contents of alicyclic compounds of the adaxial leaf surface.…”

Building a Barrier: The Influence of Different Wax Fractions on the Water Transpiration Barrier of Leaf Cuticles

“…Jetter and Riederer (2016) postulated that cuticular waxes are arranged in a VLCA layer associated with the outer surface of the cuticle and a TRP layer in its interior. This view was supported by a previous study (Staiger et al, 2019) describing that no TRPs could be extracted when dipping whole leaves into MeOH. This indicates that the external VLCA layer prevents MeOH from penetrating into deeper layers of the cuticle from the outside and extracting TRPs from these locations.…”

Presentation_1.PPTX

“…Aliphatic compounds from adaxial IWs are correlated mainly with cuticular transpiration barrier (Jetter and Riederer, 2016), while the alicyclic compounds did not contribute to cuticular transpiration barrier (Buschhaus and Jetter, 2012). Consistent with this conclusion, the permeation of active ingredients is limited by very long-chain aliphatic compounds rather than alicyclic wax compounds (Staiger et al, 2019). Recently, we demonstrated that abaxial cuticle showed different transpiration barrier organization from its adaxial counterpart: the abaxial EWs is another major transpiration barrier while the abaxial IWs contribute minorly (Zhang et al, 2020).…”