Transport of Salicylic Acid and Related Compounds - Salicylic Acid: Plant Growth and Development - page 51

By contrast, studies on long distance transport of SA in response to abiotic
stress are scarce. In Vitis vinifera plants 14 C-SA molecules move in part from the
non-stressed leaves to leaves exposed to high temperatures (Wang et al. 2004 ).
Predicting Phloem Mobility of SA and Related Compounds
Phloem mobility of endogenous compounds, synthetic derivatives and various
xenobiotics is often predicted using the model of Kleier (Kleier 1988 ; Hsu and
Kleier 1996 ) (Fig. 2 ) and Bromilow and coworkers (Bromilow et al. 1991 ).
Although these models are based on only two physicochemical properties of the
molecules, namely their lipophilicity (assessed as the 1-octanol/water partition
coefficient, Log K ow ) and their pKa values, the experimental data often fit rather
well with the predictions. Discrepancies between predictions and experimental
data may indicate the involvement of a carrier system instead of—or in addition
to—diffusion through the plasma membrane (Oparka 1991 ; Rocher et al. 2009 ).
Other diffusion predictors must also be taken into consideration, especially Log
D (i.e., the pH dependent Log K ow ) which indicate the true behavior of ionizable
compounds in the various cell compartments (Bhal et al. 2007 ), the polar surface
Fig. 2 Prediction of phloem mobility of salicylic acid and derivatives using Kleier map (Log Cf
as a function of Log K ow and pKa) according to Kleier et al. (1996). Plant parameters are for a
short plant. Compounds are identified with letters listed in Table 1