Regulation of Harvest-induced Senescence in Broccoli (Brassica oleracea var. italica) by Cytokinin, Ethylene, and Sucrose

  • Nigel E. Gapper
  • Simon A. Coupe
  • Marian J. McKenzie
  • Ben K. Sinclair
  • Ross E. Lill
  • Paula E. Jameson
Original Article

Abstract

Broccoli (Brassica oleracea var. italica) deteriorates rapidly following harvest. The two plant hormones ethylene and cytokinin are known to act antagonistically on harvest-induced senescence in broccoli: ethylene by accelerating the process, and cytokinin by delaying it. To determine the level at which these hormones influenced senescence, we isolated and monitored the expression of genes normally associated with senescence in broccoli florets treated with exogenous 6-benzyl aminopurine (6-BAP), 1-aminocyclopropane-1-carboxylic acid (ACC), a combination of 6-BAP and ACC, and sucrose, in the five days following harvest. Exogenous 6-BAP caused both a reduction (BoACO) and an increase (BoACS) in ethylene biosynthetic gene expression. The expression of genes used as senescence markers, BoCP5 and BoMT1, was reduced, whereas BoCAB1 levels were maintained after harvest in response to exogenous 6-BAP. In addition, the expression of genes encoding sucrose transporters (BoSUC1 and BoSUC2) and carbohydrate metabolizing enzymes (BoINV1 and BoHK1) was also reduced upon 6-BAP feeding. Interestingly, the addition of ACC prevented the 6-BAP-induced increase in expression of BoACS, but 6-BAP negated the ACC-induced increase in expression of BoACO. The culmination of these results indicates a significant role for cytokinin in the delay of senescence. The implication that cytokinin regulates postharvest senescence in broccoli by inhibiting ethylene perception and/or biosynthesis, thus regulating carbohydrate transport and metabolism, as well as senescence-associated gene expression, is discussed and a model presented.

Keywords

Cytokinin Ethylene Sucrose Senescence Broccoli Brassica oleracea Postharvest 

Notes

Acknowledgments

The authors acknowledge Duncan Hedderley for carrying out statistical analyses and the New Zealand Foundation for Research, Science and Technology (FRST) for funding this work.

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Copyright information

© Springer Science+Business Media, Inc. 2005

Authors and Affiliations

  • Nigel E. Gapper
    • 1
    • 2
    • 3
  • Simon A. Coupe
    • 1
    • 4
  • Marian J. McKenzie
    • 1
  • Ben K. Sinclair
    • 1
  • Ross E. Lill
    • 1
  • Paula E. Jameson
    • 1
    • 2
  1. 1.New Zealand Institute for Crop & Food Research LimitedFood Industry Science CentreNew Zealand
  2. 2.Institute of Molecular BioSciencesMassey UniversityNew Zealand
  3. 3.Produce Quality and Safety LaboratoryBeltsville Agricultural Research Center, USDA/ARSBeltsvilleUSA
  4. 4.Marks and SpencerLondon WZUK

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