Ozone‐induced accumulation of carbohydrates changes enzyme activities of carbohydrate metabolism in birch leaves

Abstract

SUMMARYBirch cuttings {Betula pendula Roth) were grown in a sand-culture system with two concentrations (0-05, HF and 0-005%, LF) of fertilizer containing macronutrients and micronutrients, and were exposed to 90/40 nll"^ O3 (day/night) and < 3 nl T^ O3 (control) for one growing season in the field fumigation chambers at Birmensdorf (Switzerland). Leaves of different ages were analysed for gas exchange, contents of chlorophyll, protein, and for metabolites as well as enzyme activities of carbohydrate metabolism.Ozone reduced net photosynthesis and chlorophyll contents in mature leaves of both fertilization treatments, whereas that of protein was only reduced in high-fertilized plants (HF). However, net photosynthesis, chlorophyll, and protein increased in young leaves of low'-fertilized plants (LF). The effects of ozone on enzyme activities of carbohydrate metabolism were most pronounced in leaves of LF plants. Specific activities of the sucrose-cleaving enzymes, sucrose synthase and alkaline invertase, were induced, whereas acid invertase was unchanged. Extractable activity of sucrose phosphate synthase, which is a key enzyme of sucrose synthesis, was reduced. Levels of fructose 2,6-bisphosphate, an inhibitor of sucrose synthesis, were increased in leaves of O3/LF plants, but reduced in O3/HF plants. In addition, activities of enzymes involved in starch metabolism, ADP-glucose pyrophosphorylase and starch phosphorylase, were lowered in ozone-treated samples and the ratio of ATP: ADP was increased.It is concluded that chronic ozone exposure leads to an inhibition of sucrose synthesis and favours sucrose degradation. This effect is modulated by the nutrient status of the plants, indicating higher O3 tolerance in HF plants. Furthermore, as the metabolic responses in the ozone-treated samples resemble very closely those observed under end-product inhibition of photosynthesis, we assume that the O3 effect is mainly due to reduced photosynthate export.

Biomass, reproductive output, and physiological responses of rapid‐cycling Brassica (Brassica rapa) to ozone and modified root temperature

“…However, the estimates made here might not be valid since photosynthesis measurements taken from young leaves were used to determine C gain. Ozone tends to decrease chlorophyll levels and photosynthesis in older leaves (Einig et al, 1997), but our estimate was based on the photosynthesis of the first fully expanded leaves, so C gain might be overestimated for plants in the O $ treatments. A study with Plantago major showed that plants may acclimate to O $ with only 14 d of exposure (Lyons & Barnes, 1998).…”

“…Future research should include studies with perennials and woody species. Because other studies have shown both that O $ responses are mediated by nutrient levels (Einig et al, 1997) and that nutrient uptake is affected by root temperature (Hood & Mills, 1994), adding differing nutrient treatments to O $ and root temperature would provide a more thorough understanding of how these factors affect plant growth in the field. …”

The effect of ozone fumigation and different Brassica rapa lines on the feeding behaviour of Pieris brassicae larvae

“…The ozone exposure also caused a significant increase in the amount of the soluble sugars in the sensitive line. Ranieri et al (2000) and Einig et al (1997) report accumulation of starch in ozone-fumigated leaves of poplar (Populus deltoides × maximowiczii) clones and birch (Betula pendula), respectively.…”

The effect of sulphite on chlorophyll fluorescence and sucrose metabolism in poplar leaves

“…1994, Alaoui-Sosse etal. 1996, Einig et al 1997). On the other hand, Kingston-Smith et al (1998) showed that in source leaves of poplar (Populus alba x tremula L.), as well as in other plant species, AI was not directly involved in sucrose degradation.…”

“…Sucrose breakdown catalysed by invertase or SuSy is associated with the differential induction of ATP-and PPi-dependent phosphofructokinases (Stitt 1998). The effects of sulphite on catabolic sucrose metabolism are absent in the literature and there are also only a few studies describing sucrolytic activity in source leaves in woody species (Alaoui-Sosse et al 1996, Einig et al 1997, Kingston-Smith et al 1998. Therefore, the question raised in this study is whether disturbances in sucrose synthesis in leaves treated with sulphite are also associated with changes in sucrolytic activities.…”