Nitrate transport rate in the xylem of tomato plants grafted onto a vigorous rootstock

Abstract

Vigorous interspecific rootstocks increase nitrogen (N) uptake in tomato plants but limited information is available on xylem transport rate. Non-grafted and self-grafted tomato plants cv. Attiya and plants grafted onto an interspecific hybrid, Kaiser, were grown under growth chamber conditions and subjected to two light levels, 400 or 800 μmol PAR m-2 s-1. Plant water uptake, xylem sap NO3- content, and stem hydraulic conductance (ks) were measured after two weeks of growth. Xylem vessel number and diameter were evaluated in cross-sectional stem cuts and the theoretical xylem hydraulic conductance (kh) was calculated. Only the light level modified the xylem NO3- content. Grafting reduced ks by 84% in comparison to non-grafted plants. The water uptake rate and xylem sap NO3- content were 4.02 ± 0.66 g H2O kg-1 DW h-1 and 12.78 ± 1.16 mM, respectively, across all grafting treatments. The rootstock has a higher kh because the vessel diameter is 79.3 ± 14.4 μm while in non-grafted plants it is 62.0 ± 10.1 μm. Nitrate concentration and transport rate changes accordingly to the plant's growth rate. The vigorous rootstock relies on larger vessels to supply the required amounts of N.