Abstract
Chloroplast stromal volume and pH influenced the phosphate (Pi)-dependence of photosynthesis of spinach (Spinacia oleracea L.) chloroplasts. Decreasing the sorbitol concentration in the reaction mixture from 0.35 to 0.25 M, or decreasing the external pH from 8.3 to 7.3, extended the induction period of photosynthesis and decreased both the optimal [Pi] and the minimal [Pi] required to inhibit O2 evolution completely. At least part of the effect of external pH was attributable to changes in stromal pH on the basis of effects of NH4Cl and sodium acetate at a constant external pH. When the external pH was increased from 7.3 to 8.3, the stromal pH changed only about 0.6 pH units. Hence, the pH gradient across the envelope was diminished and the efflux of phosphoglycerate relative to dihydroxyacetone phosphate was enhanced. Calvin-cycle activity, varied with light intesity or electron transport inhibitors, affected the rate of photosynthesis but not the induction period or the Pi optimum for photosynthesis. Relatively low Calvin-cycle activity was apparently sufficient to fill metabolite pools and thus terminate the induction period. The results indicate that pH does not affect the Pi dependence of photosynthesis by reducing Calvin-cycle activity. Rather, it is postulated that at low stromal pH, larger metabolic pools are required to maintain maximum rates of photosynthesis because of changes in substrate affinity of some Calvin-cycle enzymes. Consequently, chloroplast photosynthesis would be more sensitive to exogenous Pi.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 485-492 |
| Number of pages | 8 |
| Journal | Planta |
| Volume | 149 |
| Issue number | 5 |
| DOIs | |
| State | Published - Oct 1 1980 |
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Keywords
- Chloroplasts (isolated)
- Metabolite efflux
- O evolution
- Phosphate
- Photosynthesis (isolated chloroplasts)
- Spinacia
- Stromal pH
ASJC Scopus subject areas
- Genetics
- Plant Science
Cite this
Effects of pH and other factors on the phosphate dependence of photosynthesis in spinach chloroplasts. / Huber, Steven C.
In: Planta, Vol. 149, No. 5, 01.10.1980, p. 485-492.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Effects of pH and other factors on the phosphate dependence of photosynthesis in spinach chloroplasts
AU - Huber, Steven C
PY - 1980/10/1
Y1 - 1980/10/1
N2 - Chloroplast stromal volume and pH influenced the phosphate (Pi)-dependence of photosynthesis of spinach (Spinacia oleracea L.) chloroplasts. Decreasing the sorbitol concentration in the reaction mixture from 0.35 to 0.25 M, or decreasing the external pH from 8.3 to 7.3, extended the induction period of photosynthesis and decreased both the optimal [Pi] and the minimal [Pi] required to inhibit O2 evolution completely. At least part of the effect of external pH was attributable to changes in stromal pH on the basis of effects of NH4Cl and sodium acetate at a constant external pH. When the external pH was increased from 7.3 to 8.3, the stromal pH changed only about 0.6 pH units. Hence, the pH gradient across the envelope was diminished and the efflux of phosphoglycerate relative to dihydroxyacetone phosphate was enhanced. Calvin-cycle activity, varied with light intesity or electron transport inhibitors, affected the rate of photosynthesis but not the induction period or the Pi optimum for photosynthesis. Relatively low Calvin-cycle activity was apparently sufficient to fill metabolite pools and thus terminate the induction period. The results indicate that pH does not affect the Pi dependence of photosynthesis by reducing Calvin-cycle activity. Rather, it is postulated that at low stromal pH, larger metabolic pools are required to maintain maximum rates of photosynthesis because of changes in substrate affinity of some Calvin-cycle enzymes. Consequently, chloroplast photosynthesis would be more sensitive to exogenous Pi.
AB - Chloroplast stromal volume and pH influenced the phosphate (Pi)-dependence of photosynthesis of spinach (Spinacia oleracea L.) chloroplasts. Decreasing the sorbitol concentration in the reaction mixture from 0.35 to 0.25 M, or decreasing the external pH from 8.3 to 7.3, extended the induction period of photosynthesis and decreased both the optimal [Pi] and the minimal [Pi] required to inhibit O2 evolution completely. At least part of the effect of external pH was attributable to changes in stromal pH on the basis of effects of NH4Cl and sodium acetate at a constant external pH. When the external pH was increased from 7.3 to 8.3, the stromal pH changed only about 0.6 pH units. Hence, the pH gradient across the envelope was diminished and the efflux of phosphoglycerate relative to dihydroxyacetone phosphate was enhanced. Calvin-cycle activity, varied with light intesity or electron transport inhibitors, affected the rate of photosynthesis but not the induction period or the Pi optimum for photosynthesis. Relatively low Calvin-cycle activity was apparently sufficient to fill metabolite pools and thus terminate the induction period. The results indicate that pH does not affect the Pi dependence of photosynthesis by reducing Calvin-cycle activity. Rather, it is postulated that at low stromal pH, larger metabolic pools are required to maintain maximum rates of photosynthesis because of changes in substrate affinity of some Calvin-cycle enzymes. Consequently, chloroplast photosynthesis would be more sensitive to exogenous Pi.
KW - Chloroplasts (isolated)
KW - Metabolite efflux
KW - O evolution
KW - Phosphate
KW - Photosynthesis (isolated chloroplasts)
KW - Spinacia
KW - Stromal pH
UR - http://www.scopus.com/inward/record.url?scp=34250250796&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=34250250796&partnerID=8YFLogxK
U2 - 10.1007/BF00385753
DO - 10.1007/BF00385753
M3 - Article
C2 - 24306478
AN - SCOPUS:34250250796
VL - 149
SP - 485
EP - 492
JO - Planta
JF - Planta
SN - 0032-0935
IS - 5
ER -