Abstract
The activity of several photosynthetic enzymes was unaltered by exposure of sorghum or maize to low temperatures (10 C) and light (170 w m(-2)). Two light-activated C(4)-pathway enzymes, NADP-malate dehydrogenase and pyruvate Pi dikinase, were reduced in activity, and this was largely attributable to a loss of enzyme rather than to incomplete enzyme activation. Loss of NADP-malate dehydrogenase was more marked in sorghum than in maize, and in both species no loss occurred at 10 C when light levels were reduced from 170 to 50 w m(-2). A light-dependent, low temperature-induced loss of catalase activity was also observed in maize leaves.The rate of in vivo activation of pyruvate Pi dikinase following illumination was reduced at 10 C compared with that at 25 C, but no immediate effect of low temperature on the in vivo activation of NADP-malate dehydrogenease could be measured. A similar differential effect of temperature on the rates of activation of these two enzymes was found in vitro. Arrhenius type plots of pyruvate Pi dikinase from sorghum and maize demonstrated a further sensitivity to low temperature. A sharp increase in the activation energy of this enzyme was observed below 12 C, both in the presence and absence of Triton X-100. No change in the activation energy of maize leaf malic enzyme, NADP-malate dehydrogenase, fructose-1, 6-diphosphate aldolase, or NADP-glyceraldehyde 3-P dehydrogenase occurred over a temperature range of 6 to 30 C.The postillumination time course of pyruvate Pi dikinase activation, net photosynthesis and stomatal opening was followed. Reduction in the rate of response that occurred with decreasing temperature was similar in all cases, and at any one temperature, pyruvate Pi dikinase activation slightly preceded increasing photosynthesis rates. Causal relationships could not, however, be proved.
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Claims 15
Claim · model-written summary
Several photosynthetic enzymes were unaltered by low temperature and light in sorghum or maize.
- Treatment
- low temperatures (10 C) and light (170 w m(-2))e0
- Outcome
- activity of several photosynthetic enzymese0
- Direction
- unalterede0
Sorghum
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The activity of several photosynthetic enzymes was unaltered by exposure of sorghum or maize to low temperatures (10 C) and light (170 w m(-2))”
Claim · model-written summary
NADP-malate dehydrogenase activity was reduced under low temperature and light.
Not reportedTaxonTreatmentComparator
Verbatim
e0“Two light-activated C(4)-pathway enzymes, NADP-malate dehydrogenase and pyruvate Pi dikinase, were reduced in activity”
Claim · model-written summary
Pyruvate Pi dikinase activity was reduced under low temperature and light.
Not reportedTaxonTreatmentComparator
Verbatim
e0“Two light-activated C(4)-pathway enzymes, NADP-malate dehydrogenase and pyruvate Pi dikinase, were reduced in activity”
Claim · model-written summary
The reduction in enzyme activity was largely attributed to loss of enzyme.
Not reportedTaxon
Verbatim
e0“this was largely attributable to a loss of enzyme rather than to incomplete enzyme activation”
Claim · model-written summary
NADP-malate dehydrogenase loss was greater in sorghum than maize.
- Gene
- NADP-malate dehydrogenasee0
- Outcome
- Loss of NADP-malate dehydrogenasee0
- Direction
- more markede0
- Comparator
- maizee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Loss of NADP-malate dehydrogenase was more marked in sorghum than in maize”
Claim · model-written summary
No NADP-malate dehydrogenase loss occurred in either species at 10 C with reduced light.
- Treatment
- light levels were reduced from 170 to 50 w m(-2)e0
- Outcome
- no losse0
- Direction
- no losse0
- Comparator
- 170e0
Not reportedTaxon
Verbatim
e0“in both species no loss occurred at 10 C when light levels were reduced from 170 to 50 w m(-2)”
Claim · model-written summary
Maize leaf catalase activity declined with low temperature in light.
- Organ / stage
- leavese0
- Treatment
- low temperaturee0
- Gene
- catalasee0
- Outcome
- catalase activitye0
- Direction
- losse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A light-dependent, low temperature-induced loss of catalase activity was also observed in maize leaves”
Claim · model-written summary
Pyruvate Pi dikinase activation after illumination was slower at 10 C than 25 C.
- Treatment
- 10 Ce0
- Gene
- pyruvate Pi dikinasee0
- Outcome
- rate of in vivo activation of pyruvate Pi dikinasee0
- Direction
- reducede0
- Comparator
- 25 Ce0
Not reportedTaxon
Verbatim
e0“The rate of in vivo activation of pyruvate Pi dikinase following illumination was reduced at 10 C compared with that at 25 C”
Claim · model-written summary
Low temperature had no immediate measurable effect on NADP-malate dehydrogenease activation in vivo.
- Treatment
- low temperaturee0
- Outcome
- in vivo activation of NADP-malate dehydrogeneasee0
- Direction
- no immediate effecte0
Not reportedTaxonComparator
Verbatim
e0“no immediate effect of low temperature on the in vivo activation of NADP-malate dehydrogenease could be measured”
Claim · model-written summary
In vitro tests showed a similar differential temperature effect on the two enzymes.
- Outcome
- differential effect of temperaturee0
Not reportedTaxon
Verbatim
e0“A similar differential effect of temperature on the rates of activation of these two enzymes was found in vitro”
Claim · model-written summary
Arrhenius plots revealed further low temperature sensitivity of pyruvate Pi dikinase in sorghum and maize.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Arrhenius type plots of pyruvate Pi dikinase from sorghum and maize demonstrated a further sensitivity to low temperature”
Claim · model-written summary
Activation energy of pyruvate Pi dikinase sharply increased below 12 C with or without Triton X-100.
Not reportedTaxonComparator
Verbatim
e0“A sharp increase in the activation energy of this enzyme was observed below 12 C, both in the presence and absence of Triton X-100”
Claim · model-written summary
Activation energies of five other maize leaf enzymes did not change from 6 to 30 C.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“No change in the activation energy of maize leaf malic enzyme, NADP-malate dehydrogenase, fructose-1, 6-diphosphate aldolase, or NADP-glyceraldehyde 3-P dehydrogenase occurred over a temperature range of 6 to 30 C”
Claim · model-written summary
Lower temperature similarly slowed pyruvate Pi dikinase activation, photosynthesis and stomatal opening responses.
Not reportedTaxon
Verbatim
e0“Reduction in the rate of response that occurred with decreasing temperature was similar in all cases”
Claim · model-written summary
Pyruvate Pi dikinase activation slightly preceded rising photosynthesis rates.
- Outcome
- pyruvate Pi dikinase activation slightly preceded increasing photosynthesis ratese0
Not reportedTaxon
Verbatim
e0“pyruvate Pi dikinase activation slightly preceded increasing photosynthesis rates”
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