Programmed Cell Death Progresses Differentially in Epidermal and Mesophyll Cells of Lily Petals

Abstract

In the petals of some species of flowers, programmed cell death (PCD) begins earlier in mesophyll cells than in epidermal cells. However, PCD progression in each cell type has not been characterized in detail. We separately constructed a time course of biochemical signs and expression patterns of PCD-associated genes in epidermal and mesophyll cells in Lilium cv. Yelloween petals. Before visible signs of senescence could be observed, we found signs of PCD, including DNA degradation and decreased protein content in mesophyll cells only. In these cells, the total proteinase activity increased on the day after anthesis. Within 3 days after anthesis, the protein content decreased by 61.8%, and 22.8% of mesophyll cells was lost. A second peak of proteinase activity was observed on day 6, and the number of mesophyll cells decreased again from days 4 to 7. These biochemical and morphological results suggest that PCD progressed in steps during flower life in the mesophyll cells. PCD began in epidermal cells on day 5, in temporal synchrony with the time course of visible senescence. In the mesophyll cells, the KDEL-tailed cysteine proteinase (LoCYP) and S1/P1 nuclease (LoNUC) genes were upregulated before petal wilting, earlier than in epidermal cells. In contrast, relative to that in the mesophyll cells, the expression of the SAG12 cysteine proteinase homolog (LoSAG12) drastically increased in epidermal cells in the final stage of senescence. These results suggest that multiple PCD-associated genes differentially contribute to the time lag of PCD progression between epidermal and mesophyll cells of lily petals.

Spatial and temporal transcriptome changes occurring during flower opening and senescence of the ephemeral hibiscus flower,Hibiscus rosa-sinensis

“…Moreover, the transcriptional signatures of flower ageing in hibiscus share common features with the conserved core of developmentally regulated programmed cell death signatures in plants recently reported by Olvera-Carrillo et al (2015). In fact, transcripts for ribonuclease 3, calcium-dependent nuclease 1, metacaspase, cysteine proteases, aspartic proteases, cysteine endopetidases, and vacuolar processing enzymes were more abundant in senescing petals and S-S+S, defining the transcriptional regulation that leads to the rapid execution of cell death observed in many systems (Coll et al , 2014; Hatsugai et al , 2015; Mochizuki-Kawai et al , 2015; Olvera-Carrillo et al , 2015). …”

Plant proteases during developmental programmed cell death

“…However, none of the three inhibitors affect flower longevity or the progression of senescence (Battelli et al, 2011). In another study on lily flowers, signs of PCD including decreasing protein content and DNA degradation have been described in mesophyll and epidermal cells (Mochizuki-Kawai et al, 2015). During early senescence, mesophyll cells show an upregulation of the KDEL-tailed cysteine protease LoCYP and display signs of PCD.…”

“…During early senescence, mesophyll cells show an upregulation of the KDEL-tailed cysteine protease LoCYP and display signs of PCD. Only during later flower senescence, epidermal cells start to undergo PCD, with the simultaneous upregulation of the lily SAG12 homolog, LoSAG12 (Mochizuki-Kawai et al, 2015). In this review, we aim to provide an overview of existing data on proteases in the context of dPCD and cover a selection of relatively well-described PCD processes in which the functional involvement of proteases has been demonstrated ( Figure 2).…”

Morphological, biochemical and molecular hallmarks of programmed cell death in stigmatic papillae of Brassica oleracea L.

“…Parallel to these literatures, it was remarkable that the vacuoles were large and covered the large part of the cell at the post-anthesis stage which we detected the dPCD. Researchers have been reported the decrease in the protein content of cytoplasm in petals of Nicotiana tabacum (Serafini-Fracassini et al 2002), in tepals of Iris and Alstroemeria (Wagstaff et al 2005) and Lilium candidum (Mochizuki-Kawai et al 2015) during dPCD. Similar to these findings, we detected the decrease in the protein content of papillae at the post-anthesis stage which we detected the dPCD.…”