Ethylene biosynthesis, ripening and senescence behavior of Oriental tobacco leaves
Ethylene is a plant growth regulator found in many plants and plant parts. It has long been known to promote fruit ripening and senescence of plant tissue. The rate of ethylene production by intact, attached leaves of tobacco plants (Nicotiana tabacum L.), Oriental type, during ripening and senescence was studied with a field experiment in 2002. In addition, as the degree of leaf ripeness at harvest is an important factor determining the suitability of cured leaves for use in smoking products, the process of ripeness and senescence of Oriental tobacco leaves were investigated in order to evaluate their effects on yield and quality of tobacco. Ethylene production of lower leaves declined progressively up to 76 DAT (days after transplanting). Since the color changes are usually the principal guides in judging ripeness, senescence of lower leaves began around 78 DAT when leaves began to loss their chlorophyll and a progressively increase of ethylene production appeared. In addition, during this period leaf dry weight began to decrease. Ethylene production is reached in a peak, a climacteric-like surge, within 6 days after the beginning of increase and after the beginning of rapid chlorophyll breakdown and dry matter loss. This peak involved a 5-6 fold increase in the rate of ethylene production. The subsequent rise of ethylene production appears to be associated with the rapid phase of chlorophyll and protein nitrogen breakdown, and may indicate the final stage of senescence process.