Spatial and temporal patterns of net nitrate uptake regulation and kinetics along the tap root of Citrus aurantium

Abstract

Spatial-temporal variation of the regulation and the kinetics of net nitrate (NO 3 -) uptake rate (NNUR) along the tap root of Citrus aurantium L. were analysed. Suberin incrustation in the peripheral cell layers and plasma membrane (PM) H ? -ATPase localisation, anatomical and physiological factors involved in NO 3 -uptake were also investigated. The results clearly indicated a spatially uniform distribution of the regulation process, accompanied by a temporal heterogeneous pattern of the kinetics of NO 3 -uptake along citrus tap root. In particular, kinetic analysis had a biphasic pattern, saturating (high affinity transport system) and linear (low affinity transport system), in response to increasing external NO 3 -concentrations in each root region, where 200 lM NO 3 -represented the threshold separating these two systems. Kinetic parameters, K m and V max , clearly indicated that apical segments reached the maximum value of induction before basal segments. Hence, the apical root zones, early exhibiting the maximum of potential capacity to absorb the NO 3 -, could be considered more efficient than basal root segments for acquiring NO 3 -from external solution. Suberin incrustations in the hypodermal cell layer, characterised by uniform fluorescence intensity among the root segments, could be responsible for the unchanged NNUR, while the PM H ? -ATPase could explain the temporal pattern of NNUR.

Ectomycorrhizas with Paxillus involutus enhance cadmium uptake and tolerance in Populus × canescens

“…; Sorgona et al . , ). In addition to PM H + ‐ATPases genes, several other genes including ZIP2 , NRAMP1.1 , PCS , ABCC1 , MTP1 , ATM3 and HMA4 play fundamental roles in Cd 2+ transport and detoxification in plant roots (Kim et al .…”

Nitrogen in Citrus: Signal, Nutrient, and Use Efficiency

“…The authors demonstrated that the half-time of the induction phase was negatively correlated ( r 2 = 0.855) with the number of root tip (Sorgonà and Cacco 2002 ) , suggesting that the root systems of citrus rootstocks characterized by elevated numbers of root tips showed a rapid induction in NNUR. The role of root tip as NO 3 − -sensing region for the early soil exploration and belowground competition was recently con fi rmed by Sorgonà et al ( 2010 ) which observed an earlier maximum induction of the iHATS of N-nitrate of the apical root segments of tap root compared to basal ones in Sour orange. The comparison of cHATS and iHATS pattern for nitrate among citrus rootstocks characterized by different root morphology and architecture could provide useful information on the diverse physiological basis of NUE.…”

“…Like the herbaceous species, the citrus rootstocks take up the nitrate by at least two different transport systems, a low af fi nity (LATS) and high af fi nity transport system (HATS) (Cerezo et al 1997(Cerezo et al , 2000Sorgonà and Cacco 2002 ;Sorgonà et al 2005Sorgonà et al , 2006 . The LATS has a low af fi nity for nitrate and is activated by external nitrate concentrations higher than 1,000 m M in Troyer citrange and Cleopatra mandarin (Cerezo et al 1997(Cerezo et al , 2000 or 200 m M in Sour orange (Sorgonà et al 2010 ) . The HATS showed a high af fi nity for nitrate, operating at external concentrations up to 1,000 m M (Cerezo et al 1997 ) or 200 m M (Sorgonà et al 2010 ) .…”

“…The LATS has a low af fi nity for nitrate and is activated by external nitrate concentrations higher than 1,000 m M in Troyer citrange and Cleopatra mandarin (Cerezo et al 1997(Cerezo et al , 2000 or 200 m M in Sour orange (Sorgonà et al 2010 ) . The HATS showed a high af fi nity for nitrate, operating at external concentrations up to 1,000 m M (Cerezo et al 1997 ) or 200 m M (Sorgonà et al 2010 ) . This nitrate transport system, more interesting in N-de fi cient soils, is highly regulated and made up by the constitutive (cHATS) and the inducible (iHATS) high af fi nity transport systems.…”

“…This nitrate transport system, more interesting in N-de fi cient soils, is highly regulated and made up by the constitutive (cHATS) and the inducible (iHATS) high af fi nity transport systems. The cHATS is constitutively expressed in NO 3 − -starved roots, mediating a constant nitrate uptake rate, while the iHATS is induced by NO 3 − and feedback regulated by downstream N metabolites (Sorgonà and Cacco 2002 ;Sorgonà et al 2005Sorgonà et al , 2010 . Sorgonà and Cacco ( 2002 ) showed that N-starved Citrus volkameriana seedlings exhibited a net nitrate uptake rate (NNUR) of cHATS by 0.085 m mol NO 3 − g −1 FW h −1 which increased (induction phase of iHATS) reaching, after 24 h of nitrate contact, the complete induction with 0.29 m mol NO 3 − g −1 FW h −1 NNUR.…”