Brassinosteroids as Metahormones: Evidence for their Specific Influence during the Critical Period in Sorghum Development

Abstract

In Sorghum bicolor, the effect of brassinosteroid (BR) treatments on blade elongation depends both on concentration and on the stage of development. A specific period of increase in sensitivity to BR is reported during early vegetative development. It coincides with emergence of a critical period during which the between-organs relationship is readjusted as a function of new developmental events or new environmental conditions. Accordingly, the influence of BR cannot be completely understood without separating its effects during stable phases (phenophases) and during critical periods. A high level of redundancy exists in networks of regulation, so that modifications due to BR treatments generally remain cryptic. Nevertheless, it is shown that BR affects the pattern of relationships between organs, confirming its involvement in emergence of a new network of regulation. It is suggested that, during critical periods, brassinosteroids act as “metahormones” integrating the new emerging regulation network by triggering changes in cellular sensitivity to PGRs.

Abbreviations

BL: blade length

BR: brassinosteroid

CV: coefficient of variation

DW: dry weight

FW: fresh weight

GA: gibberellic acid

MRV: multiple residual value

SH: sheath length

PGR: plant growth regulators

Brassinosteroid - critical period - networks of regulation - sensitivity to hormones - developmental regulation of growth

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Section Editor: U. Lüttge