Upon bolting the GTR1 and GTR2 transporters mediate transport of glucosinolates to the inflorescence rather than roots

Abstract

We recently described the glucosinolate transporters GTR1 and GTR2 as actively contributing to the establishment of tissue-specific distribution of the defense compounds glucosinolates in vegetative Arabidopsis plants. Upon bolting and thereby development of the inflorescence and initiation of seed setting, the spatial distribution of glucosinolates does undergo major changes. Here we investigate the role of GTR1 and GTR2 in establishment of glucosinolate source-sink relationships in bolting plants. By in vivo feeding the exogenous p-hydroxybenzylglucosinolate to a rosette leaf or the roots of wildtype and a gtr1 gtr2 mutant, we show that this glucosinolate can specifically translocate from the rosette and the roots to the inflorescence in a GTR1- and GTR2-dependent manner. This marks that, upon bolting, the inflorescence rather than the roots constitute the strongest sink for leaf glucosinolates compared with plants in vegetative state.

Keywords: Arabidopsis; chemical defense distribution; feeding; glucosinolate; roots; specialized/secondary metabolites; transport.

Figure 1. Distribution of leaf- and root-fed p-hydroxybenzylglucosinolate. Hydroponically grown 5-week-old wildtype (Col-0) and gtr1gtr2 plants were fed with the exogenous p-hydroxybenzylglucosinolate (pOHB) for a total timespan of 72 h. The content of pOHB was analyzed in the separate tissues by HPLC and normalized to the total content of the plant. (A) Infiltration of pOHB to a rosette leaf. (B) Feeding of pOHB to roots by addition of pOHB to the growth media. Total amount of recovered pOHB can be found in Table 1. HAF; hours after feeding, nd; none detected. Solid bars represent wild-type plants and open bars represent the gtr1gtr2 mutant. * P < 0.01 (Student t-test vs corresponding tissue at 48 h. Bars are average, ± SD, n = 10).