Abstract
Plant growth regulators play a key role in cell wall structure and chemistry of woody plants. Understanding of these regulatory signals is important in advanced research on wood quality improvement in trees. The present study is aimed to investigate the influence of exogenous application of 24-epibrassinolide (EBR) and brassinosteroid inhibitor, brassinazole (BRZ) on wood formation and spatial distribution of cell wall polymers in the xylem tissue of Leucaena leucocephala using light and immuno electron microscopy methods. Brassinazole caused a decrease in cambial activity, xylem differentiation, length and width of fibres, vessel element width and radial extent of xylem suggesting brassinosteroid inhibition has a concomitant impact on cell elongation, expansion and secondary wall deposition. Histochemical studies of 24-epibrassinolide treated plants showed an increase in syringyl lignin content in the xylem cell walls. Fluorescence microscopy and transmission electron microscopy studies revealed the inhomogenous pattern of lignin distribution in the cell corners and middle lamellae region of BRZ treated plants. Immunolocalization studies using LM10 and LM 11 antibodies have shown a drastic change in the micro-distribution pattern of less substituted and highly substituted xylans in the xylem fibres of plants treated with EBR and BRZ. In conclusion, present study demonstrates an important role of brassinosteroid in plant development through regulating xylogenesis and cell wall chemistry in higher plants.
Highlights
Xylogenesis represents one of the dynamic developmental processess by which xylem elements are produced from the vascular meristem [vascular cambium] through a complex coordination of cell division, differentiation, tissue patterning and growth across tissues and organs (Larson 1994; Du et al 2020)
EBR induced enhancement of xylogenesis was evident from the increase in radial extent of xylem with increase in concentration of exogenously applied hormone (Fig. 1d, Table 2)
The present study demonstrated that the exogenous application of 24-epibrassinolide (EBR) have a predominant effect on xylogenesis and anatomical structure of xylem elements of L. leucocephala
Summary
Xylogenesis represents one of the dynamic developmental processess by which xylem elements are produced from the vascular meristem [vascular cambium] through a complex coordination of cell division, differentiation, tissue patterning and growth across tissues and organs (Larson 1994; Du et al 2020). Brassinosteroids (BRs) are plant-specific steroid hormones demonstrated to have an important function in many aspects of plant growth and development (Divi and Krishna 2009; Nolan et al 2020). These are reported to play a role in photomorphogenesis (Song et al 2009), leaf angle inclination (Wada et al 1984), seed germination (Steber and McCourt 2001), leaf senescence and abscission (Fedina et al 2017), stomatal development (Tae-Wuk et al 2012), root gravitropism (Retzer et al 2019), regulation of cell elongation and division (Minami et al 2019; Liu et al 2019) and vascular differentiation (Tian et al 2018). Yamamoto et al (1997) demonstrated the role of BRs on secondary cell wall formation and cell death during tracheray element differentiation in Zinnia system
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