Maltose is the major form of carbon exported from the chloroplast at night

Abstract

Transitory starch is formed in chloroplasts during the day and broken down at night. We investigated carbon export from chloroplasts resulting from transitory-starch breakdown. Starch-filled chloroplasts from spinach ( Spinacia oleracea L. cv. Nordic IV) were isolated 1 h after the beginning of the dark period and incubated for 2.5 h, followed by centrifugation through silicone oil. Exported products were measured in the incubation medium to avoid measuring compounds retained inside the chloroplasts. Maltose and glucose made up 85% of the total exported products and were exported at rates of 626 and 309 nmol C mg(-1) chlorophyll h(-1), respectively. Net export of phosphorylated products was less than 5% and higher maltodextrins were not detected. Maltose levels in leaves of bean ( Phaseolus vulgaris L. cv. Linden), spinach, and Arabidopsis thaliana (L.) Heynh. were low in the light and high in the dark. Maltose levels remained low and unchanged during the light/dark cycle in two starch-deficient Arabidopsis mutants, stf1, deficient in plastid phosphoglucomutase, and pgi, deficient in plastid phosphoglucoisomerase. Through the use of nonaqueous fractionation, we determined that maltose was distributed equally between the chloroplast and cytosolic fractions during darkness. In the light there was approximately 24% more maltose in the cytosol than the chloroplast. Taken together these data indicate that maltose is the major form of carbon exported from the chloroplast at night as a result of starch breakdown. We hypothesize that the hydrolytic pathway for transitory-starch degradation is the primary pathway used when starch is being converted to sucrose and that the phosphorolytic pathway provides carbon for other purposes.

EST-analysis of the thermo-acidophilic red microalga Galdieriasulphuraria reveals potential for lipid A biosynthesis and unveils the pathway of carbon export from rhodoplasts

“…Up to 50% of the carbon dioxide assimilated during the day is stored as transitory starch within chloroplasts and exported to the cytosol during the night in the form of glucose and maltose (Niittyla et al, 2004;Weise et al, 2004). However, as outlined above, red algae store starch in the cytosol and produce floridosides as soluble sugars.…”

Leaf Starch Turnover Occurs in Long Days and in Falling Light at the End of the Day

“…Maltose is a major product of leaf starch degradation, and levels provide an indication of whether starch degradation is occurring (Weise et al, 2004;Niittylä et al, 2004;Smith and Stitt, 2007;Stitt and Zeeman, 2012). Levels are low during the day and elevated at night when plants are grown in daynight cycles (Niittylä et al, 2004;Weise et al, 2006;Pal et al, 2013).…”

Lipid Exchange Envelope Penetration (LEEP) of Nanoparticles for Plant Engineering: A Universal Localization Mechanism

“…To study the effect of surface charges of the nanoparticles on their entry into chloroplasts isolated chloroplasts were first obtained from commercially procured baby spinach leaves (Spinacia oleracea) using protocols modified from Weise et al 26 ss(AT) 15 -SWCNT (3 nm diameter and zeta potential of approximately −45 mV) were prepared by tip sonication of ss(AT) 15 with HiPCO SWCNTs (Unidym) in a 2:1 wt ratio (see SI for details). Gold-cysteine-AF405 nanoparticles (GNPCys-AF405) (30 nm diameter and zeta potential of ∼ −38 mV) were prepared using gold nanoparticles purchased from Nanocomposix.…”