"Elegy of blossoms": Decrypting the dynamics of petal senescence in Ranunculus asiaticus L.

Abstract

Petal senescence represents a crucial phase in the developmental continuum of flowers, ensuing tissue differentiation and petal maturation, yet anteceding seed formation and development. Instigation of petal senescence entails myriad of changes at the cytological, physiological and molecular dimensions, mirroring the quintessential characteristics of cell death. In the current investigation biochemical and molecular intricacies were scrutinized across various developmental stages (bud to the senescent phase). Scanning electron microscopy analysis unveiled significant changes in petal tissue morphology, evolving from tightly interwoven ridges and grooves at the bud stage to a completely flattened surface devoid of intricate patterns in the senescent stage. Throughout the developmental continuum, significant metabolic reconfigurations were discerned. The concentration of soluble proteins displayed a continuous decrement from the bud phase through the anthesis stage, culminating in a pronounced diminution during the senescent phase. This pattern was concomitant with the expression profiles of RaSAG12 (senescence-associated gene 12) and RaDAD1 (defender against cell death 1) genes. Membrane integrity exhibited a gradual decline from the bud to the open stage, attributed to diminished lipoxygenase (LOX) activity and low RaLOX1 (lipoxygenase 1) transcript levels. This deterioration was further exacerbated during senescence by increased LOX1 expression, ultimately compromising membrane stability. The developmental progression of Ranunculus asiaticus flowers is modulated by hormonal flux, with abscisic acid and ethylene concentrations escalating as senescence approaches. This upsurge is attributed to elevated mRNA transcripts of RaAAO3 (abscisic aldehyde oxidase 3) and RaACO (1-amino cyclopropane-1- carboxylic acid oxidase), concomitant with a reduction in RaIPT3 (isopentenyl transferase 3) transcript abundance during the senescent phase compared to earlier developmental phases. ROS (Reactive oxygen species) neutralizing antioxidant enzymes exhibited a marked increase from the bud to the bloom stage, leading to reduced hydrogen peroxide (H₂O₂) levels. However, during the senescent phase, the activity of these enzymes diminished markedly, resulting in the accumulation of ROS and ensuing oxidative damage.