INVESTIGATIONS ON THE CONTRIBUTION OF THE STOMATAL PATHWAY TO FOLIAR UPTAKE
The main uptake pathways for foliar-applied substances such as nutrients are the cuticle and the stomata.
However, the relative importance of each of these uptake routes is still unclear.
The cuticular pathway consists of two size-selective routes, the lipophilic cuticular pathway and polar cuticular pores.
In contrast to the cuticular pathway, uptake through stomata should not be size-selective and should not discriminate large molecules.
Hence, it is hypothesized that large polar molecules are almost exclusively taken up via stomata.
Foliar uptake of small polar molecules (15N-labeled urea, ammonium or nitrate) into leaves of Vicia faba was studied, each applied together with equimolar concentrations of a larger polar molecule (13C-labeled sucrose). Mean N uptake was independent of N species.
Both N and sucrose uptake were strongly affected by the aperture of stomata.
N uptake into individual leaves was positively correlated with sucrose uptake.
Linear regression (y = ax + b) of N uptake (y) vs. sucrose uptake (x) yielded similar equations for all N species.
All intercepts (b) were significantly positive, i.e. when uptake of sucrose was extrapolated to zero, N uptake apparently continued.
Positive intercepts indicate the existence of at least two independent uptake pathways, one of them excluding the large sucrose molecules.
Slopes (a) of regression lines resembled the ratios of diffusion coefficients of the respective N-species and sucrose in water, suggesting that both sucrose and N were taken up predominantly by free diffusion without steric restrictions.
Taken together, these results strongly support the conclusion that stomata play an important role in the uptake of foliar applied substances.
Eichert, T., Kurtz, A. and Goldbach, (2006). INVESTIGATIONS ON THE CONTRIBUTION OF THE STOMATAL PATHWAY TO FOLIAR UPTAKE. Acta Hortic. 721, 307-312
DOI: 10.17660/ActaHortic.2006.721.43
https://doi.org/10.17660/ActaHortic.2006.721.43
DOI: 10.17660/ActaHortic.2006.721.43
https://doi.org/10.17660/ActaHortic.2006.721.43
stomata, cuticle, foliar nutrition, polar pores, Vicia faba
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