Effect of elevated CO[sub 2] and temperature on sucrose phosphate synthase activity and carbohydrate metabolism in rice
The kinetics of sucrose phosphate synthase (SPS) activity were studied in leaf extracts of rice (Oryza sativa L. cv. IR-3-). The SPS activity showed hyperbolic and sigmoidal response, respectively, as a function of concentration for its two substrates, UDPG and F6P. The K[sub m] (UDPG) and S[sub 0.5] (F6P) were 2.7 and 2 mM, respectively. The enzyme was activated in an allosteric manner by G6P at low F6P concentrations, while P[sub i] inhibited it. Diel profiles indicated SPS was light activated and the activation was greatest under limiting assay conditions. Leaves were pretreated either with mannose to sequester endogenous P[sub i] or with exogenous P[sub i]. Mannose pretreatment made the enzyme relatively insensitive to p[sub i] inhibition, whereas P[sub i] pretreatment enhanced the inhibitory effect. These data suggest that the rice SPS enzyme exists in two states, a light-active, P[sub i]-insensitive form, and a dark form that is more P[sub i]-sensitive. Based on these kinetic analysis, leaf SPS activity was examined as a function of CO[sub 2]-enrichment and growth temperature for rice plants grown under natural irradiance at 330 and 660 [mu]L CO[sub 2] L[sup [minus]1] and growth temperatures ranging from 25 to 37[degrees]C. CO[sub 2]-enrichment at 28[degrees]C caused a season-long increase (18%) in SPS activity measured under limiting or saturating assay conditions. It is also increased the leaf starch and sucrose content, but lowered the total nitrogen. Sucrose content was higher than starch, suggesting rice is a sucrose and starch storer. In CO[sub 2]-enriched plants, SPS activity increased with growth temperature up to 34[degrees]C, but declined at 38[degrees]C. The increasing temperature caused a significant linear decrease in starch content, whereas sucrose was only slightly decreased, while fructose was increased. The data suggest that up-regulation of SPS activity is an acclimation response of rice to elevated CO[sub 2] and temperature.
- Research Organization:
- Florida Univ., Gainesville, FL (United States)
- OSTI ID:
- 5437939
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CARBOHYDRATES
METABOLISM
CARBON DIOXIDE
BIOLOGICAL EFFECTS
ECOLOGICAL CONCENTRATION
RICE
CARBON COMPOUNDS
CARBON OXIDES
CEREALS
CHALCOGENIDES
GRAMINEAE
LILIOPSIDA
MAGNOLIOPHYTA
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PLANTS
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