CORESTA Congress, Paris, 2006, APOST 09

Growth, maturation and senescence of Oriental tobacco leaves as affected by ethephon and inhibitors of ethylene biosynthesis

Aristotle University of Thessaloniki, and Tobacco Institute, Laboratory of Agronomy, Laboratory of Pomology, Drama, Greece
Ethylene is a gaseous plant growth regulator that it has long been known to promote fruit ripening and senescence of plant tissues. In contrast, aminoethoxyvinylglycine (AVG) and aminooxyacetic acid (AOA) both inhibitors of ethylene biosynthesis are responsible for delaying maturity and ripeness in several fruits. Ethephon (2-chloroethylphosphonic acid) an ethylene releasing agent can be applied as a spray field treatment to plants and plant parts. A field experiment was established during 2002 growing season in order to determine the effect of ethephon, AVG and AOA on leaf growth, ethylene evolution, respiratory rate, maturation and senescence processes of leaves of Oriental tobacco type (Basma, cv. BZ 7). Immature leaves of tobacco plants before the completion of their expansion were sprayed with 100 ppm ethephon, 50 ppm AVG, 0.5 mM AOA or water (control). Six sequential samplings of leaves at the accurately same age and position on the stalk were carried out at 2-day intervals after the application. All samplings were replicated 4 times. Leaf samples were analyzed for chlorophyll, total carotenoids and total proteins. Ethephon application caused inhibition in dry matter accumulation of immature leaves and significant reduction in the relative growth rate (RGR), in the ratio fresh/dry weight and in the relative water content (RWC), but increased the ethylene and CO2 evolution, just 2 days after its application and throughout the whole period of samplings. In contrast to ethephon, AVG had the opposite effects on most of the characteristics recorded, but in a much weaker way, whereas the effect of AOA was not significant. In addition, chlorophyll degradation was more rapid in ethephon treated leaves than in AVG, AOA and control ones during the whole period of samplings. Total proteins and total carotenoids were significantly decreased in ethephon treated leaves, but were increased in AVG treatments in comparison to those of AOA and control. We conclude that ethephon promoted whereas AVG delayed the maturation and senescence processes and both caused significant modifications in chemical characteristics of leaves.