GROWTH AND TISSUE SENESCENCE IN PRUNUS-AVIUM SHOOTS GROWN IN-VITRO ATDIFFERENT CO2 O-2 RATIOS/

The rate of metabolism and biosynthetic processes make in vitro cultur es very sensitive to environmental changes, and therefore subject to p hysiological and morphological alterations leading to senescence in th e short term. The effects of three different calibrated atmospheric co mpositions were studied during in vitro culture of Prunus avium shoots . At 0.034% CO2-21% O-2 (vol/vol), which stimulate the natural atmosph ere, the highest growth rate and chlorophyll content were recorded. Wh en grown at 0.09% CO2-8% O-2 (vol/vol), a favorable condition for phot osynthesis and growth, cultures showed a higher percentage of dry matt er and elevated ethylene production, but total chlorophyll was lower. These shoots were also highly lignified and fibrous with red pigmentat ion along the leaves and stems. At 0% CO2-21% O-2 (vol/vol), in contra st, growth and ethylene formation were inhibited; chlorophyll content was lowest in comparison with the other two environmental conditions, hut regreening of tissues was observed after the first half of the cul ture period. Senescence symptoms, as indicated by decreased chlorophyl l, appeared after about 18 d of culture for tissues grown in CO2-conta ining atmospheres. These experiments provided evidence that in CO2-enr iched cultures biomass production steadily increased even when chlorop hyll decreased. A possible role of CO2 in promoting tissue-senescence through activation of photooxidative events and ethylene synthesis is discussed.