Influence of Low Temperature on Respiration and Contents of Phosphorylated Intermediates in Darkened Barley Leaves

Abstract

The aim of this work was to examine the effect of exposure of leaves to low temperatures (5°C) upon the contents of phosphorylated intermediates and respiration in darkened barley (Hordeum vulgare L.) plants which differed in their carbohydrate status. In leaves that had previously been illuminated for 24 hours, there was a large increase in amounts of phosphorylated metabolites at 50C during the first 3 hours of darkness, compared with control plants kept at 30°C. Hexose phosphates accounted for about two-thirds of this increase, which reached a peak after about 3 hours. At higher temperatures, there was a peak in the amount of fructose 2,6-bisphosphate and the rate of respiration which accompanied the transient increase in phosphorylated intermediates. At 50C the increase in phosphorylated intermediates was not accompanied by appreciable changes in fructose 2,6-bisphosphate, and there was a rapid decline in the rate of respiration. Leaves that had previously been darkened for 24 hours and that were low in carbohydrate failed to accumulate phosphorylated intermediates when exposed to low temperatures. The results are discussed with respect to the acclimation of carbohydrate metabolism to low temperatures. The results suggest that respiratory carbohydrate metabolism is strictly controlled even when the carbohydrate supply and glycolytic intermediates are abundant. The possibility that accumulation of hexose phosphates may be involved in acclimation of metabolism to low temperature is discussed.Low temperatures will influence carbohydrate metabolism in leaves in a number of different ways. In the whole plant, low temperatures will both diminish sink activity and export of carbohydrate from leaves, disrupting the balance between supply of, and demand for, assimilated carbon. Such temperature-dependent decreases in the utilization of photosynthate have been shown to lead to end-product inhibition of photosynthesis (1, 2, 4). (14). Exposure to low temperatures will also have consequences which occur purely at the metabolic level. For example, during photosynthesis the balance between sucrose synthesis and carbon fixation is perturbed when leaves are suddenly transferred to low temperatures because sucrose synthesis runs too slowly at lower temperatures (9,12). A number of temperature-dependent metabolic factors may act to bring about this imbalance between the capacity to fix CO2 and to synthesize sucrose. First, low temperatures raise thresholds for the metabolism of triose-P to sucrose because of large decreases in the affinity of the cytosolic Fru 1,6-P2ase3 for its substrate as the temperature is decreased (21). There is also the possibility that inactivation of the cytosolic Fru 1,6-P2ase occurs in vivo at low temperatures (23). The consequence of either change would be that more phosphorylated intermediates would be required in the cytosol in order to drive sucrose synthesis. Second, it is likely that more orthophosphate is required in the cytosol at low temperatures (1 1, 12, 21) to allow export of t...

A Comparison of Dark Respiration between C3 and C4 Plants

“…1, inset) and then declined markedly. The reason for this transient rise was not known, though it may be related to carbohydrate metabolism, as suggested by Heichel (11), or increases in Fru-2,6-P2 (17). In contrast, Rn of C album leaves declined immediately after darkening.…”

Cold-hardening results in increased activity of enzymes involved in carbon metabolism in leaves of winter rye (Secale cereale L.)

“…Photosynthesis at 5~ results in large increases to all hexose-phosphate pools in both CH and NH leaves, except glucose-l-phosphate (GlclP) and UDPGlc in NH leaves. In CH leaves, the increases at saturating PPFDs is particularly pronounced and ranged from ~75-130% for Glc6P, GlclP, Fru6P and UDPGlc to a ninefold increase for Frul,6BP, with the result that total hexosephosphates increased by 120% relative to the levels found at 20~ Previous studies have shown that phosphorylated metabolites accumulate to higher levels after exposure of leaves to low temperatures, and this has been related to low-temperature inhibition of photosynthesis resulting from reduced availability Pi in the stroma (M/ichler et al 1984;Labate and Leegood 1989;Labate et al 1990). However, although the Glc6P/Fru6P ratio of CH leaves at 5~ decreased to around 3 for all PPFDs tested (Table 3), this is still consistent with most of the hexose-phosphates being in the cytosol supporting continued sucrose synthesis.…”

Carbon Metabolism and Photorespiration: Temperature Dependence in Relation to Other Environmental Factors

“…By contrast, leaves from plants which were low in carbohydrate and hexosephosphate showed no photosynthetic acclimation (Labate and Leegood, 1989). It was suggested that high carbohydrate reserves may potentiate the system for the achievement of high rates of photosynthesis at low temperatures by accumulation of photosynthetic intermediates, such as hexose-phosphate, and that this partially overcomes Pi limitation of photosynthesis (Labate and Leegood, 1989). This interaction between carbohydrate reserves and acclimation to low temperature may also be related to observations that chilling sensitivity in plants such as tomato is partly dependent upon their carbohydrate status (King et al, 1988).…”

“…Primary leaves of barley plants which contained large carbohydrate reserves and high hexose-phosphate showed photosynthetic acclimation to low temperature. By contrast, leaves from plants which were low in carbohydrate and hexosephosphate showed no photosynthetic acclimation (Labate and Leegood, 1989). It was suggested that high carbohydrate reserves may potentiate the system for the achievement of high rates of photosynthesis at low temperatures by accumulation of photosynthetic intermediates, such as hexose-phosphate, and that this partially overcomes Pi limitation of photosynthesis (Labate and Leegood, 1989).…”