Poster: Photosynthesis (carbon)

Abs # 233: Light regulation of starch degradation capacity

Presenter:	Lu, Yan , ylu7@wisc.edu
Authors	Lu, Yan  (A)   Gehan, Jackson P. (A)   Sharkey, Thomas D. (A)
Affiliations:	(A): University of Wisconsin-Madison

Transitory starch is stored during the day inside chloroplasts and then broken down at night for export. We found that cytosolic amylomaltase and starch phosphorylase are involved in starch breakdown. Null mutants of cytosolic amylomaltase (dpe2-1, dpe2-2) accumulated a large amount of maltose and starch. Mutation in cytosolic starch phosphorylase (pho2-1) is embryo-lethal. By using real-time RT-PCR, we found that the transcript level of these two enzymes is higher during the light period and lower during the dark period. The dramatic change of transcript level of Pho2 at the transition point of photoperiod suggests that Pho2 is under light regulation. The transcript level of DPE2 and Pho2 is also affected by the length of the photoperiod. Plants under long-day photoperiod produce more starch than plants under short-day photoperiod. We propose that under long-day photoperiod, more DPE2 and Pho2 transcripts are present during the day causing more starch metabolism enzyme to accumulate in plants grown in long days and less in plants grown in short days. Plants may sense the length of photoperiod and regulate the mRNA and proteins levels of DPE2 and Pho2, to adjust their capacity of starch breakdown. To test this hypothesis, we determined the amount of DPE2 and Pho2 transcripts before and after altering the length of photoperiod. The protein level of DPE2 and Pho2 under different treatments will also be determined.