Immunoprofiling of Cell Wall Carbohydrate Modifications During Flooding-Induced Aerenchyma Formation in Fabaceae Roots

Abstract

Understanding plant adaptation mechanisms to prolonged water immersion provides options for genetic modification of existing crops to create cultivars more tolerant of periodic flooding. An important advancement in understanding flooding adaptation would be to elucidate mechanisms, such as aerenchyma airspace formation induced by hypoxic conditions, consistent with prolonged immersion. Lysigenous aerenchyma formation occurs through programmed cell death (PCD), which may entail the chemical modification of polysaccharides in root tissue cell walls. We investigated if a relationship exists between modification of pectic polysaccharides through de-methyl esterification (DME) and the formation of root aerenchyma in select Fabaceae species. To test this hypothesis, we first characterized the progression of aerenchyma formation within the vascular stele of three different legumes-Pisum sativum, Cicer arietinum, and Phaseolus coccineus-through traditional light microscopy histological staining and scanning electron microscopy. We assessed alterations in stele morphology, cavity dimensions, and cell wall chemistry. Then we conducted an immunolabeling protocol to detect specific degrees of DME among species during a 48-hour flooding time series. Additionally, we performed an enzymatic pretreatment to remove select cell wall polymers prior to immunolabeling for DME pectins. We were able to determine that all species possessed similar aerenchyma formation mechanisms that begin with degradation of root vascular stele metaxylem cells. Immunolabeling results demonstrated DME occurs prior to aerenchyma formation and prepares vascular tissues for the beginning of cavity formation in flooded roots. Furthermore, enzymatic pretreatment demonstrated that removal of cellulose and select hemicellulosic carbohydrates unmasks additional antigen binding sites for DME pectin antibodies. These results suggest that additional carbohydrate modification may be required to permit DME and subsequent enzyme activity to form aerenchyma. By providing a greater understanding of cell wall pectin remodeling among legume species, we encourage further investigation into the mechanism of carbohydrate modifications during aerenchyma formation and possible avenues for flood-tolerance improvement of legume crops.

Possible Role of High Temperature and Soil Biological Fertility on Kiwifruit Early Decline Syndrome

“…The presence of numerous canals in the phloem layer of roots from plants showing strong KEDS symptoms (Figures 4, 5) could represent the plant response to hypoxic conditions through aerenchyma formation to facilitate oxygen diffusion from leaves to root tips (Bailey-Serres and Voesenek, 2008). Lysogenic aerenchyma formation occurs through programmed cell death, mediated by ethylene-induced increase of cytoplasmic Ca 2+ (Bouranis et al, 2006;Bailey-Serres and Voesenek, 2008;Pegg et al, 2020). This involves the death, and often complete lysis, of cells with the disappearance of all cell components, including the cell walls (He et al, 1994).…”

A Spatial-Temporal Analysis of Cellular Biopolymers on Leaf Blight-Infected Tea Plants Using Confocal Raman Microspectroscopy

“…To prevent pathogens from progressing further, lignin forms cork layers around the site of infection. Additionally, tylose is also an important structure found in the infected tissues of the vascular bundle, which consists of hemicellulose, cellulose, and pectin ( Pegg et al, 2020 ; Kashyap et al, 2021 ). Tylose can affect the vascular bundle by blocking it, thereby preventing infection.…”

Aerenchyma formation in the root of leaf‐vegetable sweet potato: Programmed cell death initiated by ethylene‐mediated H2O2 accumulation

“…Primary aerenchyma is lysigenous, schizogenous or expansigenous. Lysigenous aerenchyma utilizes the programmed cell death (PCD) of specific cells to form a new cavity, while schizogenous is formed through the separation of middle lamella between cells (Grandis et al 2019; Pegg et al 2020). Expansigenous aerenchyma is a new discovered type of aerenchyma, lacunae originate only from cell division and cell expansion, without cell separation (Flores‐Borges et al 2016).…”

“…This further increases the susceptibility of the tissues to hydrolytic enzymatic degradation of the pectin backbone from polygalacturonase and pectin lyase activity, which destabilizes the cell wall matrix resulting in cell death (Boger et al 2019). In legumes, for example, pectin DME occurs in specific cell regions prior to or during the formation of lysigenous aerenchyma, and it significantly results in cavity formation (Pegg et al 2020).…”