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Characterisation of ethylene pathway components in non-climacteric capsicum.

Aizat WM, Able JA, Stangoulis JC, Able AJ - BMC Plant Biol. (2013)

Bottom Line: Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green.Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit.The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Agriculture, Food and Wine, Waite Research Institute, The University of Adelaide, Glen Osmond SA 5064, Australia. amanda.able@adelaide.edu.au.

ABSTRACT

Background: Climacteric fruit exhibit high ethylene and respiration levels during ripening but these levels are limited in non-climacteric fruit. Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green. However, ripening progresses normally in capsicum fruit when they are harvested during or after what is called the 'Breaker stage'. Whether ethylene, and components of the ethylene pathway such as 1-aminocyclopropane 1-carboxylate (ACC) oxidase (ACO), ACC synthase (ACS) and the ethylene receptor (ETR), contribute to non-climacteric ripening in capsicum has not been studied in detail. To elucidate the behaviour of ethylene pathway components in capsicum during ripening, further analysis is therefore needed. The effects of ethylene or inhibitors of ethylene perception, such as 1-methylcyclopropene, on capsicum fruit ripening and the ethylene pathway components may also shed some light on the role of ethylene in non-climacteric ripening.

Results: The expression of several isoforms of ACO, ACS and ETR were limited during capsicum ripening except one ACO isoform (CaACO4). ACS activity and ACC content were also low in capsicum despite the increase in ACO activity during the onset of ripening. Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit. Some of the ACO, ACS and ETR isoforms were also differentially expressed upon treatment with ethylene or 1-methylcyclopropene.

Conclusions: ACS activity may be the rate limiting step in the ethylene pathway of capsicum which restricts ACC content. The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato. Ethylene independent pathways may also exist in non-climacteric ripening as evidenced by the up-regulation of CaACO4 during ripening onset despite being negatively regulated by ethylene exposure. However, some level of ethylene perception may still be needed to induce ripening especially during the Breaker stage. A model of capsicum ripening is also presented to illustrate the probable role of ethylene in this non-climacteric fruit.

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Gene expression of CaACO (A), CaACS (B) and CaETR (C) isoforms during capsicum ripening as determined by qPCR. G, Green; B, Breaker; BR1, Breaker Red 1; BR2, Breaker Red 2; LR, Light Red; DR, Deep Red. Bars represent the mean ± SE of n = 3 biological replicates. The same letter indicates no difference between means as determined using the Least Significant Difference (P < 0.05). Gene expression was normalised relative to CaGAPdH expression according to the Methods. Note that the relative expression axis was set at a similar value for CaACO, CaACS and CaETR, respectively. For CaACO1, CaACO2, CaACO3, CaACO5 and CaACO6, inset figures are shown with respect to their relative expression values corresponding to the ripening stages (G, B, BR1, BR2, LR, DR) and the double slash on both DR stage bars of CaACO1 and CaACO3 indicate values higher than the maximum (A).
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Figure 1: Gene expression of CaACO (A), CaACS (B) and CaETR (C) isoforms during capsicum ripening as determined by qPCR. G, Green; B, Breaker; BR1, Breaker Red 1; BR2, Breaker Red 2; LR, Light Red; DR, Deep Red. Bars represent the mean ± SE of n = 3 biological replicates. The same letter indicates no difference between means as determined using the Least Significant Difference (P < 0.05). Gene expression was normalised relative to CaGAPdH expression according to the Methods. Note that the relative expression axis was set at a similar value for CaACO, CaACS and CaETR, respectively. For CaACO1, CaACO2, CaACO3, CaACO5 and CaACO6, inset figures are shown with respect to their relative expression values corresponding to the ripening stages (G, B, BR1, BR2, LR, DR) and the double slash on both DR stage bars of CaACO1 and CaACO3 indicate values higher than the maximum (A).

Mentions: Throughout capsicum ripening, the transcript expression of most ACO isoforms was limited except CaACO4 (Figure 1A). CaACO4 relative expression (normalised by CaGAPdH) was significantly greater during ripening onset (approximately seven to 12 times at B and BR1 compared to G) with minimal expression during the full red stages (LR and DR). Even though CaACO1 and CaACO3 transcripts were significantly increased at the DR stage and CaACO2 was increased at the G stage, their relative expression levels throughout capsicum ripening stages were still very low compared to CaACO4. The relative transcript expression of CaACO5 and CaACO6 was also extremely low but constant during ripening.


Characterisation of ethylene pathway components in non-climacteric capsicum.

Aizat WM, Able JA, Stangoulis JC, Able AJ - BMC Plant Biol. (2013)

Gene expression of CaACO (A), CaACS (B) and CaETR (C) isoforms during capsicum ripening as determined by qPCR. G, Green; B, Breaker; BR1, Breaker Red 1; BR2, Breaker Red 2; LR, Light Red; DR, Deep Red. Bars represent the mean ± SE of n = 3 biological replicates. The same letter indicates no difference between means as determined using the Least Significant Difference (P < 0.05). Gene expression was normalised relative to CaGAPdH expression according to the Methods. Note that the relative expression axis was set at a similar value for CaACO, CaACS and CaETR, respectively. For CaACO1, CaACO2, CaACO3, CaACO5 and CaACO6, inset figures are shown with respect to their relative expression values corresponding to the ripening stages (G, B, BR1, BR2, LR, DR) and the double slash on both DR stage bars of CaACO1 and CaACO3 indicate values higher than the maximum (A).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4219378&req=5

Figure 1: Gene expression of CaACO (A), CaACS (B) and CaETR (C) isoforms during capsicum ripening as determined by qPCR. G, Green; B, Breaker; BR1, Breaker Red 1; BR2, Breaker Red 2; LR, Light Red; DR, Deep Red. Bars represent the mean ± SE of n = 3 biological replicates. The same letter indicates no difference between means as determined using the Least Significant Difference (P < 0.05). Gene expression was normalised relative to CaGAPdH expression according to the Methods. Note that the relative expression axis was set at a similar value for CaACO, CaACS and CaETR, respectively. For CaACO1, CaACO2, CaACO3, CaACO5 and CaACO6, inset figures are shown with respect to their relative expression values corresponding to the ripening stages (G, B, BR1, BR2, LR, DR) and the double slash on both DR stage bars of CaACO1 and CaACO3 indicate values higher than the maximum (A).
Mentions: Throughout capsicum ripening, the transcript expression of most ACO isoforms was limited except CaACO4 (Figure 1A). CaACO4 relative expression (normalised by CaGAPdH) was significantly greater during ripening onset (approximately seven to 12 times at B and BR1 compared to G) with minimal expression during the full red stages (LR and DR). Even though CaACO1 and CaACO3 transcripts were significantly increased at the DR stage and CaACO2 was increased at the G stage, their relative expression levels throughout capsicum ripening stages were still very low compared to CaACO4. The relative transcript expression of CaACO5 and CaACO6 was also extremely low but constant during ripening.

Bottom Line: Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green.Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit.The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Agriculture, Food and Wine, Waite Research Institute, The University of Adelaide, Glen Osmond SA 5064, Australia. amanda.able@adelaide.edu.au.

ABSTRACT

Background: Climacteric fruit exhibit high ethylene and respiration levels during ripening but these levels are limited in non-climacteric fruit. Even though capsicum is in the same family as the well-characterised climacteric tomato (Solanaceae), it is non-climacteric and does not ripen normally in response to ethylene or if harvested when mature green. However, ripening progresses normally in capsicum fruit when they are harvested during or after what is called the 'Breaker stage'. Whether ethylene, and components of the ethylene pathway such as 1-aminocyclopropane 1-carboxylate (ACC) oxidase (ACO), ACC synthase (ACS) and the ethylene receptor (ETR), contribute to non-climacteric ripening in capsicum has not been studied in detail. To elucidate the behaviour of ethylene pathway components in capsicum during ripening, further analysis is therefore needed. The effects of ethylene or inhibitors of ethylene perception, such as 1-methylcyclopropene, on capsicum fruit ripening and the ethylene pathway components may also shed some light on the role of ethylene in non-climacteric ripening.

Results: The expression of several isoforms of ACO, ACS and ETR were limited during capsicum ripening except one ACO isoform (CaACO4). ACS activity and ACC content were also low in capsicum despite the increase in ACO activity during the onset of ripening. Ethylene did not stimulate capsicum ripening but 1-methylcyclopropene treatment delayed the ripening of Breaker-harvested fruit. Some of the ACO, ACS and ETR isoforms were also differentially expressed upon treatment with ethylene or 1-methylcyclopropene.

Conclusions: ACS activity may be the rate limiting step in the ethylene pathway of capsicum which restricts ACC content. The differential expression of several ethylene pathway components during ripening and upon ethylene or 1-methylclopropene treatment suggests that the ethylene pathway may be regulated differently in non-climacteric capsicum compared to the climacteric tomato. Ethylene independent pathways may also exist in non-climacteric ripening as evidenced by the up-regulation of CaACO4 during ripening onset despite being negatively regulated by ethylene exposure. However, some level of ethylene perception may still be needed to induce ripening especially during the Breaker stage. A model of capsicum ripening is also presented to illustrate the probable role of ethylene in this non-climacteric fruit.

Show MeSH
Related in: MedlinePlus