Genetic and isotope ratio mass spectrometric evidence for the occurrence of starch degradation and cycling in illuminated Arabidopsis leaves.
Although there is a great wealth of data supporting the occurrence of simultaneous synthesis and breakdown of storage carbohydrate in many organisms, previous 13CO2 pulse-chase based studies indicated that starch degradation does not operate in illuminated Arabidopsis leaves. Here we show that leaves of gwd, sex4, bam4, bam1/bam3 and amy3/isa3/lda starch breakdown mutants accumulate higher levels of starch than wild type (WT) leaves when cultured under continuous light (CL) conditions. We also show that leaves of CL grown dpe1 plants impaired in the plastidic disproportionating enzyme accumulate higher levels of maltotriose than WT leaves, the overall data providing evidence for the occurrence of extensive starch degradation in illuminated leaves. Moreover, we show that leaves of CL grown mex1/pglct plants impaired in the chloroplastic maltose and glucose transporters display a severe dwarf phenotype and accumulate high levels of maltose, strongly indicating that the MEX1 and pGlcT transporters are involved in the export of starch breakdown products to the cytosol to support growth during illumination. To investigate whether starch breakdown products can be recycled back to starch during illumination through a mechanism involving ADP-glucose pyrophosphorylase (AGP) we conducted kinetic analyses of the stable isotope carbon composition (δ13C) in starch of leaves of 13CO2 pulsed-chased WT and AGP lacking aps1 plants. Notably, the rate of increase of δ13C in starch of aps1 leaves during the pulse was exceedingly higher than that of WT leaves. Furthermore, δ13C decline in starch of aps1 leaves during the chase was much faster than that of WT leaves, which provides strong evidence for the occurrence of AGP-mediated cycling of starch breakdown products in illuminated Arabidopsis leaves.
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Marouane
M
Baslam
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Edurne
E
Baroja-Fernández
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Adriana
A
Ricarte-Bermejo
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Ángela María
ÁM
Sánchez-López
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Iker
I
Aranjuelo
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Abdellatif
A
Bahaji
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Francisco José
FJ
Muñoz
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Goizeder
G
Almagro
Servicio de Apoyo a la Investigación, Universidad Pública de Navarra, Campus de Arrosadia, Iruña, Nafarroa, Spain.
Pablo
P
Pujol
Servicio de Apoyo a la Investigación, Universidad Pública de Navarra, Campus de Arrosadia, Iruña, Nafarroa, Spain.
Regina
R
Galarza
Centres Científics i Tecnològics, Universitat de Barcelona, C/ Lluís Solé I Sabarís 1-3, Barcelona, Spain.
Pilar
P
Teixidor
Instituto de Agrobiotecnología (CSIC/UPNA/Gobierno de Navarra). Iruñako etorbidea 123, Mutiloabeti, Nafarroa, Spain.
Javier
J
Pozueta-Romero
D017360:Arabidopsis / Q000378:metabolism*; D015153:Blotting, Western; D002247:Carbon Isotopes; D008027:Light; D008320:Maltose / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism* / Q000528:radiation effects; D013213:Starch / Q000378:metabolism*
D002247:Carbon Isotopes; D008320:Maltose; D013213:Starch