Absorption of foliar-applied Zn fertilizers by trichomes in soybean and tomato.

Cui Li,Peter M Kopittke,Caixian Tang,Daryl L Howard,Peng Wang,Enzo Lombi,Neal W Menzies,Miaomiao Cheng

doi:10.1093/jxb/ery085

Abstract

The present study investigated the role of trichomes in absorption of foliar-applied zinc fertilizers in soybean and tomato. Using synchrotron-based X-ray fluorescence microscopy for in situ analyses of hydrated leaves, we found that upon foliar application of ZnSO4, Zn accumulated within 15 min in some non-glandular trichomes in soybean, but not in tomato. However, analyses of cross-sections of soybean leaves did not show any marked accumulation of Zn in tissues surrounding trichomes. Furthermore, when near-isogenic lines of soybean differing 10-fold in trichome density were used to compare Zn absorption, it was found that foliar Zn absorption was not related to trichome density. Therefore, it is suggested that trichomes are not part of the primary pathway through which foliar-applied Zn moves across the leaf surface in soybean and tomato. However, this does not preclude trichomes being important in other plant species, as they are known to be highly diverse. We also compared the absorption of Zn when supplied as either ZnSO4, nano-ZnO, or bulk-ZnO, and found that absorption from ZnSO4 was about 10-fold higher than from nano- and bulk-ZnO, suggesting that it was mainly absorbed as soluble Zn. This study improves our understanding of the absorption of foliar-applied nutrients.

Highlights

Zinc (Zn) is an essential micronutrient for the nutrition of both plants and humans
Using synchrotron-based X-ray fluorescence microscopy (μ-XRF) for in situ analysis of Zn distribution within hydrated leaves we found that, for both soybean and tomato, Zn moved rapidly across the leaf surface, and it was observed in the mesophyll within only 15 min of application (Fig. 3 and Supplementary Fig. S2)
Given that Zn absorption was not related to trichome density in the four soybean near-isogenic lines (NILs), we examined stomatal density; this did not differ between the four NILs (Fig. 6), and it could not account for the observed changes in foliar absorption of Zn (Fig. 8).We considered whether the differences in absorption of Zn between the four NILs could be due to differences in contact between the leaves and the droplets, given that trichomes are known to alter leaf surface wettability (Brewer et al, 1991; Fernández et al, 2014)

Summary

Introduction

Zinc (Zn) is an essential micronutrient for the nutrition of both plants and humans. it has been estimated that 49% of the world’s agriculturally important soils have inadequate levels of Zn and that one-third of the world’s human population suffers from Zn deficiency (Sillanpää, 1990; Cakmak et al, 2010). Much remains unknown regarding the underlying processes whereby foliar-applied nutrients move across the leaf surface into the underlying plant. Tissue (Fernández et al, 2017; Li et al, 2017).This poor understanding of the physiological processes involved in the absorption of foliar-applied nutrients hinders efforts to increase the effectiveness of foliar fertilizers (Fernández et al, 2013). Of particular interest, it is unclear how nutrients move across the hydrophobic cuticle covering the leaf surfaces (Riederer and Schreiber, 2001; Fernández and Eichert, 2009; Fernández et al, 2017). The importance of the stomata, cuticle, and trichomes in foliar nutrient absorption remains unclear (Schönherr, 2006; Fernández et al, 2013)

Methods

Results

Discussion

Conclusion