The use of laser light to enhance the uptake of foliar‐applied substances into citrus (Citrus sinensis) leaves

Abstract

Premise of the study:Uptake of foliar-applied substances across the leaf cuticle is central to world food production as well as for physiological investigations into phloem structure and function. Yet, despite the presence of stomata, foliar application as a delivery system can be extremely inefficient due to the low permeability of leaf surfaces to polar compounds.Methods:Using laser light to generate microscopic perforations in the leaf cuticle, we tested the penetration of several substances into the leaf, their uptake into the phloem, and their subsequent movement through the phloem tissue. Substances varied in their size, charge, and Stokes radius.Results:The phloem-mobile compounds 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose (2-NBDG), lysine, Biocillin, adenosine triphosphate (ATP), trehalose, carboxyfluorescein-SE, and poly(amidomine) (PAMAM) dendrimer G-4 nanoparticles (4.5 nm in size) showed a high degree of mobility and were able to penetrate and be transported in the phloem.Discussion:Our investigation demonstrated the effectiveness of laser light technology in enhancing the penetration of foliar-applied substances into citrus leaves. The technology is also applicable to the study of phloem mobility of substances by providing a less invasive, highly repeatable, and more quantifiable delivery method. The implied superficial lesions to the leaf can be mitigated by applying a waxy coating.

Determining the Size Exclusion for Nanoparticles in Citrus Leaves

“…Since both of these particles were of the same composition and charge, the lack of internal movement by the FITC-PAMAM NPs 6.7 nm in diameter must have been due to their size (Stokes radius). The fact that the free soluble forms of the fluorescent fluorophores Alexa-488 and FITC were incapable of moving through the cell wall (Etxeberria et al, 2016) demonstrates that the fluorescence observed inside the leaf and within the phloem had to be from the NP-conjugated fluorophores (Alexa-488-PAMAM G-4 and FITC-PAMAM G-5) and not from free fluorescent dyes. These observations also substantiate It should be noted that both condensed (Au-NPs, CuInS/ZnS nanocrystals) and soft (fourth to sixth generation PAMAM dendrimers) NPs were employed in the study, and these NPs possessed different surface charges (-18.1 mV for Au-NPs, -29.2 mV for CuInS/ZnS nanocrystals, and +30.7, +23.2, and +5.35 mV for cationic PAMAM dendrimers fourth, fifth, and sixth generation, respectively).…”

“…Leaves were lasered using a lowenergy carbon dioxide laser etching machine (model XY Mark-10; GPD Technologies, Peachtree City, GA) located at the University of Florida's Citrus Research and Education Center in Lake Alfred, FL. Laser specifications used were those already reported for citrus fruits ) and leaves (Etxeberria et al, 2016). We used the dot matrix pattern where the surface area of one dot was 3.14 · 10 -4 cm 2 , and the energy per surface area of one dot was 0.00785 W/dot/ 10 6 s. These energy levels had been predetermined from previous work (Etxeberria et al, 2016).…”

“…Laser specifications used were those already reported for citrus fruits ) and leaves (Etxeberria et al, 2016). We used the dot matrix pattern where the surface area of one dot was 3.14 · 10 -4 cm 2 , and the energy per surface area of one dot was 0.00785 W/dot/ 10 6 s. These energy levels had been predetermined from previous work (Etxeberria et al, 2016). Immediately after lasering, 7 mL of NP solutions were manually smeared on each lasered area.…”

Scaling of phloem hydraulic resistance in stems and leaves of the understory angiosperm shrub Illicium parviflorum

“…With a recent exception (Carvalho et al., , ), detailed evaluations of phloem architecture in leaves with reticulate venation are lacking. The paucity is in part due to the challenging manipulations required to quantify the geometry of the sieve tubes in the tapering veins, as well as difficulties in evaluating the velocity of the sap inside the sieve tubes, typically measured using a fluorescent dye tracer (Jensen et al., ; Etxeberria et al., ) or radiolabeled compounds (Knoblauch et al., ). Thus far, phloem sap velocities in leaves of adult plants (including petioles) have only been measured in a handful of species (Jensen et al., ).…”

Phloem structure and development in Illicium parviflorum, a basal angiosperm shrub

“…With a recent exception (Carvalho et al ., 2017a), detailed evaluations of phloem architecture in leaves with reticulate venation are lacking. This is in part due to the challenging manipulations required to quantify the geometry of the sieve tubes in the tapering veins, as well as difficulties in evaluating the velocity of the sap inside the sieve tubes, typically measured by a fluorescent dye tracer (Jensen et al ., 2011, Etxeberria et al ., 2016) or radiolabeled compounds (Knoblauch et al ., 2016). Thus far, phloem sap velocities in leaves (including petioles) have been measured in only a handful of adult plant species (Jensen et al ., 2011), and in the seedlings of the family Cucurbitaceae (Savage et al ., 2013).…”