Effects of Mannose on Photosynthetic Gas Exchange in Spinach Leaf Discs

Self Cite

150

ABSTRACIIn spinach (Spinacia okracea) and barley (Hordeum vulgare) leaves, chlorophyll a fluorescence and 02 evolution have been measured simultaneously following re-illumination after a dark interval or when steady state photosynthesis has been perturbed by changes in the ps phase. In high CO2 concentrations, both O°and fluorescence can display marked dampening oscillations that are antiparallel but slightly out of phase (a rise or fall in fluorescence anticipating a corresponding fall or rise in 02 by about 10 to 15 seconds). Infrared gas analysis measurements showed that CO2 uptake behaved like 2 evolution both in the period ofoscillation (about 1 minute) and in its relation to fluorescence. In the steady state, oscillations were initiated by increases in CO2 or by increases or decreases in 02. Oscillations in 02 or CO2 did not occur without associated oscillations in fluorescence and the latter were a sensitive indicator of the former. The relationship between such oscillations in photosynthetic carbon assimilation and chlorophyl a fluorescence is discussed in the context of the effect of ATP or NADPH consumption on known quenching mechanisms.In 1949, Van der Veen (23) described what he called 'irregularities in photosynthesis' during the period when a leaf is suddenly illuminated after a period in darkness. These irregularities during the induction period, i.e. the lag before maximal photosynthesis is achieved following re-illumination (28), included 'secondary peaks' (or increases and decreases in rate which finally gave way to a more or less steady rate of CO2 uptake). Similar but somewhat simpler irregularities associated with re-illumination had already been observed by McAlister and Myers (16) and by Aufdemgarten (2). They were immediately apparent when renewed attempts were made to follow 02 evolution from leaf discs by polarographic methods (26 studied for many years, and many attempts have been made to relate these relatively slow changes (that normally occur after the first few s of illumination), with changes in 02 evolution and/or CO2 uptake (see e.g. Ref. 16). Surprisingly, Van der Veen (24) did not follow the fluorescence changes associated with the more dramatic secondary peaks in CO2 fixation which he had observed (cf Refs 23 and 24) but nevertheless concluded that 'nearly always increase of photosynthesis during adaptation (induction) is correlated with a decrease of fluorescence.' In algae, the relationship seems less clear and Chl fluorescence has been found to rise in parallel with 02 evolution in some circumstances (3) but not in others (18) and Ogawa (19) has recently reported that fluorescence yield and 02 evolution oscillate in phase (in parallel) in Vicia faba leaves under anaerobic conditions. In preliminary experiments with spinach, antiparallel, dampening oscillations in 02 and fluorescence were observed (29). These observations have now been confirmed and further characterization of these phenomena is reported.

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Simultaneous Measurement of Oscillations in Oxygen Evolution and Chlorophyll a Fluorescence in Leaf Pieces

Walker¹,

Sivak²,

Prinsley³

et al. 1983

Self Cite

150

“…We decided to measure the concentration of phosphate in the stroma and cytosol of leaves exhibiting feedback-limited photosynthesis. This condition can be induced by feeding the phosphate sequestering agent mannose (9) and can also occur under natural conditions ( 13,20).…”

mentioning

confidence: 99%

Stromal Phosphate Concentration Is Low during Feedback Limited Photosynthesis

Sharkey¹,

Vanderveer²

1989

161

125

It has been hypothesized that photosynthesis can be feedback limited when the phosphate concentration cannot be both low enough to allow starch and sucrose synthesis at the required rate and high enough for ATP synthesis at the required rate. We have measured the concentration of phosphate in the stroma and cytosol of leaves held under feedback conditions. We used nonaqueous fractionation techniques with freeze-clamped leaves of Phaseolus vulgaris plants grown on reduced phosphate nutrition.Feedback was induced by holding leaves in low 02 or high CO2 partial pressure. We found 7 millimolar phosphate in the stroma of leaves in normal oxygen but just 2.7 millimolar phosphate in leaves held in low oxygen. Because 1 to 2 millimolar phosphate in the stroma may be metabolically inactive, we estimate that in low oxygen, the metabolically active pool of phosphate is between negligible and 1.7 millimolar. We conclude that halfway between these extremes, 0.85 millimolar is a good estimate of the phosphate concentration in the stroma of feedback-limited leaves and that the true concentration could be even lower. The stromal phosphate concentration was also low when leaves were held in high C02, which also induces feedback-limited photosynthesis, indicating that the effect is related to feedback limitation, not to low oxygen per se. We conclude that the concentration of phosphate in the stroma is usually in excess and that it is sequestered to regulate photosynthesis, especially starch synthesis. The capacity for this regulation is limited by the coupling factor requirement for phosphate.During photosynthesis, phosphate is required by the coupling factor for the production of ATP from ADP. At the same time, phosphate inhibits starch (15) and so the phosphate level need not fall to such low levels to limit photosynthesis.The concentration of phosphate in the stroma has been measured in the past (3, 21, 36), but it has never been measured in feedback-limited leaves, that is leaves which exhibit 02-insensitive photosynthesis. We decided to measure the concentration of phosphate in the stroma and cytosol of leaves exhibiting feedback-limited photosynthesis. This condition can be induced by feeding the phosphate sequestering agent mannose (9) and can also occur under natural conditions ( 13,20).The measurement of stromal phosphate concentration is difficult because plants grown on luxuriant levels of phosphate, as is common practice in research, usually have a large amount of metabolically inactive phosphate in the vacuole (4, 39). This problem can be overcome by growing plants with more realistic phosphate nutrition. When the phosphate supply is restricted, the phosphate concentration in the vacuole can be substantially reduced with little or no effect on photosynthesis (5, 22

“…Since these two stresses provoke similar responses in the plant, we examined the response of a leaf disc to an external osmotic stress which would cause water movements, such as might be induced by exposure to air pollutants. We utilized an IRGA' system as described by Harris et al (5) to measure transpiration, photosynthesis, and Chi fluorescence. This system simultaneously measures CO2 and H20 changes in the vapor phase passing over the surface of a leaf disc.…”

mentioning

confidence: 99%

Effects of Polyethylene-Glycol-Induced Osmotic Stress on Transpiration and Photosynthesis in Pinto Bean Leaf Discs

Heath

Furbank²,

Walker³

1985

Self Cite

A new leaf disc chamber allows measurements of chlorophyll fluorescence and CO2 and H20 vapor exchanges during infusion of solution into the cut edge of the disc. Polyethylene glycol (molecular weight, 6000) was used to apply a mild external osmotic stress to the leaf disc within this chamber. This stress rapidly caused a temporary increase in transpiration. This increase was reversed (5-6 minutes later) and after 20 to 25 min, the stomates nearly completely closed. Internal CO2 (calculated) and leaf temperature followed the transpiration measurements. However, chlorophyll fluorescence (small rise) followed internal CO2 (small rise). This complete sequence of events resembles those caused by exposure of leaves to certain air pollutants which have been seen to cause such a transient increase followed by a decrease in stomatal closure.The role ofstomata in the control ofpollutant entry into plants remains a subject of debate (6, 7). When stomates are closed, the only possible path of pollutant entry is through the leaf cuticle.When stomates are open initially, the course of entry is more difficult to analyze since both the degree to which pollutants affect stomatal behavior and the nature of this interaction are presently unclear (7).A prevalent theory (6) suggests that pollutants directly affect stomatal aperture either by inducing an increase in ion permeability (e.g. ozone) or increasing cellular osmotic potential (e.g. weak acids like hydrated SO2) by the accumulation of ions in the guard cells. The characterization of these processes has been sketchy; questions as to response times, threshold levels, and reversibility have not been answered satisfactorily.Stomatal response to air pollutants and stomatal response to water stress share some common features (3, 6). Since these two stresses provoke similar responses in the plant, we examined the response of a leaf disc to an external osmotic stress which would cause water movements, such as might be induced by exposure to air pollutants. We utilized an IRGA' system as described by Harris et al. (5) to measure transpiration, photosynthesis, and Chi fluorescence. This system simultaneously measures CO2 and H20 changes in the vapor phase passing over the surface of a leaf disc. In addition, various solutions can be infused into the tissue through the cut edges ofthe disc, permitting the application of an osmotic agent at the cut edge. This provides the ability to manipulate leaf water potential. These measurements are used to analyze the effects of leaf water potential on the leaf gas exchange properties.