Acclimation of Photosynthesis to Low Leaf Water Potentials

Matthews, Mark A.; Boyer, John S.

doi:10.1104/pp.74.1.161

Cited by 123 publications

(86 citation statements)

References 17 publications

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“…Instead, the inhibition of chloroplast function was entirely attributable to direct effects of water deficits. It has been shown previously that both the quantum yield for CO2 fixation and the light-and C02-saturated capacity of photosynthesis are strongly inhibited at low 41, in sunflower (20,21). The present study shows that the inhibition occurs even when leaves are exposed to very low PFD during dehydration.…”

Section: Discussionmentioning

confidence: 49%

“…In sunflower, photosynthesis at low 4/1 is limited more by losses in chloroplast activity than by decreases in the diffusive conductance to CO2 entry into the leaf resulting from stomatal closure, as shown in the present study and in previous reports from this laboratory (6,20). Therefore, we could explore the inhibition of the chloroplast capacity for CO2 fixation at low A, directly with measurements of leaf gas exchange, avoiding all artifacts of chloroplast isolation.…”

Section: Discussionmentioning

confidence: 80%

“…Decreases in the capacity for both light-limited and light-saturated CO2 fixation are generally observed during photoinhibition (27). Moreover, decreases in these capacities are characteristic of the inhibition of photosynthesis at low tP, (6,7,20,21,33,34). …”

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confidence: 99%

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Photosynthesis at Low Water Potentials in Sunflower: Lack of Photoinhibitory Effects

Sharp

Boyer²

1986

Plant Physiol.

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The losses in chloroplast capacity to fix CO2 when photosynthesis is reduced at low leaf water potential (#,) have been proposed to result from photoinhibition. We investigated this possibility in soil-grown sunflower (Helianthus annuus L. cv IS894) using gas exchange techniques to measure directly the influence of light during dehydration on the in situ chloroplast capacity to fix CO2. The quantum yield for CO2 fixation as well as the rate of light-and CO2-saturated photosynthesis were strongly inhibited at low C1. The extent of inhibition was the same whether the leaves were exposed to high or to low light during dehydration. When intercellular partial pressures of CO2 were decreased to the compensation point, which was lower than the partial pressures resulting from stomatal closure, the inhibition of the quantum yield was also unaffected. Photoinhibition could be observed only after high light exposures were imposed under nonphysiological low CO2 and 02 where both photosynthesis and photorespiration were suppressed. The experiments are the first to test whether gas exchange at low #1 is affected by potentially photoinhibitory conditions and show that the loss in chloroplast capacity to fix CO2 was entirely the result of a direct effect of water availability on chloroplast function and not photoinhibition.

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Section: Discussionmentioning

confidence: 49%

Section: Discussionmentioning

confidence: 80%

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Photosynthesis at Low Water Potentials in Sunflower: Lack of Photoinhibitory Effects

Sharp

Boyer²

1986

Plant Physiol.

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“…The half-time for CO2 equilibration was determined by injecting a known amount of CO2 into the system and measuring the time to reach a new stable reading. The effect of cup attachment on leaf photosynthesis was measured with a gas exchange system (18) when P/L covered an area the size of the cup to simulate cup attachment or covered the entire underside. The ability of the method to give expected pi was determined by monitoring pi in an otherwise untreated intact sunflower leaf continuously during the day/night conditions in the growth environment.…”

Section: Tests Of the Methodsmentioning

confidence: 99%

“…The diffusive resistance of the stomata was estimated in relative terms from the square root of the time required for sufficient movement of air through the leaf to permit the pressure to increase from -0.47 to -0.27 kPa. The square root of the time gave the relative resistance that matched most closely the changes in diffusive resistance measured in the gas exchange system (18) …”

Section: Iw and Relative Resistancementioning

confidence: 99%

Internal CO₂ Measured Directly in Leaves

Lauer¹,

Boyer²

1992

Plant Physiol.

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Observations of nonuniform photosynthesis across leaves cast doubt on intemal CO2 partial pressures (p) calculated on the assumption of uniformity and can lead to incorrect conclusions about the stomatal control of photosynthesis. The problem can be avoided by measuring pi directly because the assumptions of uniformity are not necessary. We therefore developed a method that allowed pi to be measured confinuously in situ for days at a time under growth conditions and used it to investigate intact leaves of sunflower (Helianthus annuus L.), soybean (Glycine max L. Merr.), and bush bean (Phaseolus vulgaris L.) subjected to high or low leaf water potentials (I,) or high concentrations of abscisic acid (ABA). The leaves maintained a relatively constant differential (Ap) between ambient CO2 and measured pi throughout the light period when water was supplied. When water was withheld, ', decreased and the stomata began to close, but measured p increased until the leaf reached a *w of -1.76 (bush bean), -2.12 (sunflower) or -3.10 (soybean) megapascals, at which point Ap = 0. The increasing pi indicated that stomata did not inhibit CO2 uptake and a Ap of zero indicated that CO2 uptake became zero despite the high availability of CO2 inside the leaf. In contrast, when sunflower leaves at high Iw were treated with ABA, pi did not increase and instead decreased rapidly and steadily for up to 8 hours even as I, increased, as expected if ABA treatment primarily affected stomatal conductance. The accumulating CO2 at low Iw and contrasting response to ABA indicates that photosynthetic biochemistry limited photosynthesis at low Iw but not at high ABA.Water deficits have a large impact on plant growth and productivity by reducing leaf turgor, cell expansion, stomatal conductance, and photosynthesis and increasing ABA and solute concentrations in the tissues (2, 4). Among these responses, the inhibition of photosynthesis is central and often thought to be caused by reduced stomatal conductance, perhaps because of high ABA, that limits the availability of CO2 inside the leaf (8-10, 29, 32, 33). However, the '

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