Effects of O₂and CO₂partial pressure on senescence of oat leaves and broccoli miniflorets

Abstract

Effects of decreased O 2 partial pressure P(<h) and increased C02 partial pressure p(C<h) on senescence of 7-day-old oat plants or excised leaves (A vena sativa L. cv. Victory) and broccoli miniflorets (Brassica oleracea L. var. italica) were studied in tetmS of chlorophyll and protein loss, proteolytic activity, and stomatal behaviour. Senescence in darkness was delayed by decreasing P(<h), an effect which in oat leaves was unaffected by the COz partial pressure, p(C<h). However, increased P(COz) at low <h levels gave the best colour and flavour retension in broccoli miniflorets. Chlorophyll level increased c. 25% during the first 2-3 days after plants or excised leaves were placed in darkness at a P(02) of 0.5 kPa. Protein and chlorophyll breakdown were inhibited when P(02) was 2 kPa or less. Excision of leaves accelerated breakdown when compared to whole plants regardless of P(<h). Modification of ubiquitin conjugates was observed in broccoli miniflorets stored at reduced P(02). The data indicates ubiquitindependent proteolysis contributed to senescence of broccoli miniflorets.