Carbon metabolism in leaves of micropropagated sugarcane during acclimatization phase

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The activity of the main enzymes related to the sucrose metabolism, photosynthesis, and sucrose concentration were studied in sugarcane (Saccharum spp hybrid) plantlets. Acclimatization was developed in two steps. (1) Light intensity of 1,000 μmol m−2 s−1 and 90% relative humidity during the first 21 d; followed by 2,000 μmol m−2 s−1 and approximately 80% of relative humidity. All measurements were carried out at the end of rooting phase concomitant with day 0 of acclimatization and at 7-d intervals thereafter (0, 7, 14, 21, 28, 35, 42 d). As the in vitro plantlets were transferred to the acclimatization phase, photosynthesis increased significantly during the first 7 d. After this period, the increase was constant with only a small but nonsignificant decline after being transferred to the uncontrolled external conditions. The activity of the sucrose synthase began to show a decrease, starting from day 7, and was related to the changes that began to happen in these plants from its adaptation to new ex vitro conditions. Due to the increase of fresh weight favored by the high light intensity and lower relative humidity, an increase of the sucrose phosphate synthase activity was observed. The maximum activity of the acid and neutral invertases was reached at 14 and 21 d, respectively, after 21 d of acclimatization period. There was a marked tendency for the activity of both enzymes to decrease. The sucrose content was decreased only in the first 7 d. The metabolism of sugarcane plantlets seemed to be susceptible to the environmental changes during the acclimatization phase but did not contribute to inhibitory factors for normal development.

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