Gibberellin Enhances the Anisotropy of Cell Expansion in the Growth Zone of the Maize Leaf

Abstract

Although plant organ shapes are defined by spatio-temporal variations of directional tissue expansion, this is a little characterized aspect of organ growth regulation. Although it is well known that the plant hormone gibberellin increases the leaf length/with ratio, its effects on cell expansion in the growing leaf are largely unknown. To understand how variations in rate and anisotropy of growth establish the typical monocotelydonous leaf shape, we studied the leaf growth zone of maize (Zea mays) with a kinematic analysis of cell expansion in the three directions of growth: proximo-distal, medio-lateral, and dorsoventral. To determine the effect of gibberellin, we compared a gibberellin-deficient dwarf3 mutant and the overproducing UBI::GA20OX-1 line with their wild types. We found that, as expected, longitudinal growth was dominant throughout the growth zone. The highest degree of anisotropy occurred in the division zone, where relative growth rates in width and thickness were almost zero. Growth anisotropy was smaller in the elongation zone, due to higher lateral and dorso-ventral growth rates. Growth in all directions stopped at the same position. Gibberellin increased the size of the growth zone and the degree of growth anisotropy by stimulating longitudinal growth rates. Inversely, the duration of expansion was negatively affected, so that mature cell length was unaffected, while width and height of cells were reduced. Our study provides a detailed insight in the dynamics of growth anisotropy in the maize leaf and demonstrates that gibberellin specifically stimulates longitudinal growth rates throughout the growth zone.

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“…R significantly impacts endogenous action of gibberellic acid which is involved in cell elongation, root inhibition, and stimulating mitosis in meristematic cells ( Manivannan et al, 2015 ) for replication. Gibberellic acid action is known to trigger anisotropic responses for leaf expansion in monocots ( Xu et al, 2016 ; Sprangers et al, 2020 ), though R can impart different effects on leaf morphology for different plants in vitro . B increased leaf thickness, leaf numbers and leaf areas compared to R, which reduced leaf thickness and area in cultured Alternanthera brasiliana ( Macedo et al, 2011 ).…”

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“…In GA-treated plants, the shoots or leaves were significantly elongated, as other studies showed (Fig. S2) (Achard & Genschik, 2009; Xu et al ., 2016; Sprangers et al ., 2020). In addition to promoting plant growth, GA treatment has been reported to induce transcriptional changes (Cheng et al ., 2015).…”

Integrated Physiological and Metabolomic Analyses of the Effect of Potassium Fertilizer on Citrus Fruit Splitting

“…However, further exploration is needed to study the regulatory mechanism and function involved in fruit splitting. In addition, gibberellin is a plant hormone that is responsible for promoting cell division and expansion [25,26]. Thus, spraying gibberellin is an important technical measure to increase fruit size, firmness, peel strain and reduce the fruit splitting rate in many woody fruit plants, such as grape (Vitis vinifera) and cherry (Prunus avium) [27,28].…”