Boron uptake by the root cortex symplast of tomato and pea plants: evidence for low-boron-induced active transport

Abstract

The objective of this research was to test the hypothesis of the existence of an active boron (B) uptake into the cortical cells induced by low B supply. The uptake of B was characterised in two tomato (Lycopersicon esculentum Mill.) genotypes: B-efficient FER and B-inefficient mutant T3238. In addition, pea (Pisum sativum L.) was used as an anatomically appropriate model for obtaining intact root cortex. Time course uptake studies in tomato indicate that the B-inefficient mutant was defective by the absence of an active low-B-induced uptake system in the cortex. Pea roots showed up to 10-fold higher accumulation of B into the cortex symplast at low (0.5 µm) external B supply in comparison to adequate B (10 µm) supply. Also, low-B-induced uptake of B was strongly inhibited by 2,4-dinitrophenol, indicating a metabolic energy-derived active component of B uptake at low external supply. Uptake of B by the cortical cells of tomato and pea plants appears to be a combination of both passive and active components, with a passive component prevailing at higher external B. An active component of B uptake suppressed by either adequate or high B supply might indicate a downregulation of plasma membrane-associated B transporter(s) in root cortical cells.

Acclimation of eggplant (Solanum melongena) to low boron supply

“…Plant roots were able to concentrate boron 2.7-fold compared to the external nutrient solution indicating the existence of a B-concentrating mechanism located in root cortex cells, xylem parenchyma cells of the stele, or both, according to previous reports (Takano et al, 2008). Active transport of boron, induced by low external boron concentration, has been recently shown for tomato (Savic et al, 2007) in which B was concentrated up to 4-fold in the cell sap of the root cortex compared to the external solution (0.5 lM). However, the concentrating mechanism showed a saturable uptake pattern, similarly to other studies, which resulted in a lower concentration factor at higher external concentrations (ca.…”

“…Bellaloui and Brown (1998) reported that a low-B-tolerant tomato cultivar was more capable of translocating B from roots to leaf tissues resulting in higher B content in the aerial parts compared to a low-B-sensitive cultivar. A tomato B-efficient cultivar also showed enhanced B uptake by the root cortex cells based on low-B-induced active transport (Savic et al, 2007).…”

Boron transport mechanisms: collaboration of channels and transporters

“…In tomato (Lycopersicon esculentum), early studies using two genotypes showed that the B-inefficient genotype T3238 has a defect in xylem loading compared to the B-efficient genotype FER [43,44]. In addition, a recent study using these genotypes revealed that the B-efficient genotype FER showed B accumulation in the root cell sap at concentrations higher than in the external medium when precultured with a low B supply (0.5 mM), whereas the B-inefficient genotype T3238 did not [45]. Low-B-inducible accumulation of B in root cell sap and xylem sap was also described in sunflower plants [33,34].…”

“…However, accumulation of B was also observed in cortical cells of pea (Pisum sativum), which does not develop exodermal cells. The B concentration in pea root cortical cell sap was tenfold higher than in the external medium under conditions of low B supply (0.5 mM), but was similar with adequate B supply (10 mM) [45]. As-yet-unknown B importers might transport B against concentration gradients across plasma membranes in some plant species.…”

Effect of silicon on sunflower growth and nutrient accumulation under low boron supply

“…Widespread opinion that B uptake by plant roots is mainly passive process at sufficient supply as well as different mechanisms proposed for low supply, including active uptake by root cortex cells as shown for pea and tomato (Savić et al, 2007) should be also taken under consideration. Sunflower was also often used in studies on B uptake, xylem loading and compartmentation.…”