IMPACT OF SUGAR CONCENTRATION IN-VITRO ON PHOTOSYNTHESIS AND CARBON METABOLISM DURING EX-VITRO ACCLIMATIZATION OF SPATHIPHYLLUM PLANTLETS

Photosynthesis and carbon metabolism were followed during the acclimat ization of micropropagated Spathiphyllum cv. Petite shootlets cultured with two different sucrose concentrations (3 and 6%). Increased sugar supply resulted in inhibition of photosynthesis, nonfunctional photos ynthetic reaction centers, a more mixotrophic metabolism and higher st arch and sucrose reserves at the end of the in vitro period. During th e first days of acclimatization, net photosynthesis and adenosine diph osphoglucose (ADPG) pyrophosphorylase (EC 2.7.7.27) activity decreased for both treatments. In this period, sucrose was mainly used as nutri ent reserve by plants cultured on 6% sucrose, as evidenced by a strong increase in sucrose synthase (EC 2.4.1.13) activity together with a s evere decline in sucrose content. In the same period, sucrose breakdow n and synthesis were in balance for plants cultured on 3% sucrose and the starch content increased slightly. After one week plants started t o recover and full photosynthetic capacity developed. Two weeks after ex vitro transplantation, no differences between plants micropropagate d with 3 or 6% sucrose could be found for photosynthesis, carbohydrate pools or enzyme activities. At the end of acclimatization the starch content increased again.