RESPIRATORY METABOLISM OF ORCHID FLOWER

Abstract

1) A respiratory drift has been demonstrated in cells isolated from petals of Aranda flowers at different stages of development. Tight bud had a respiratory quotient of 0.58, this increased to 0.7 in the first flower and reached 1.0 in the mature flower. There appeared to be a non-glycolytic pathway contribution in addition to the EMP pathway in tight bud and newly opened flower stages. Carbohydrate metabolism in the mature flower proceeds predominantly via the EMP pathway. Cyanide-insensitive respiration was demonstrated in the tight bud. There was a shift towards cyanide-sensitive respiration as the flower developed. 2) Respiration of isolated Aranda orchid petal cells increased markedly after cut flowers were treated with ethylene. An increase in respiration was observed 15 to 20 hours after treatment which was further enhanced in the presence of oxygen and ethylene. Ethylene induces the development of a cyanide resistant pathway in fully opened orchid flower tissues where the cyanide resistant capacity is negligible. However, there appears to be a shift back to the cyanide sensitive pathway some time after induction. 3) Mitochondrial respiration of developing Aranda orchid flower has been studied. State 3 and state 4 mitochondrial respiration rated were different at different stages of floral development. The rates also varied when different substrates were used. Bud mitochondria exhibited prominent cyanide resistant and rotenone resistant pathways. This is reflected in the low ADP:O and R.C. ratio in bud mitochondria and greater capacity of bud mitochondria to oxidise NADPH added exogenously. 4) There appears to be a correlation between ethylene production and bud opening and the development of cyanide resistant pathway in orchid flowers. A high rate of ethylene production was observed during bud growth, reaching a high value in half opened flower. This was followed by a gradual decline but it increased again when the flowers showed sign of senescence. Aminooxyacetic acid (AOA) inhibited ethylene production and bud expansion of Aranda buds.