Ozone-induced microscopical changes and quantitative carbohydrate contents of hybrid poplar (Populus � euramericana)

Abstract

Summary. Cuttings of hybrid poplar (Populus • euramericana var. "Dorskamp") were exposed to ozone (80 ]xg/m 3 from 2100 hours to 0700 hours, 180 [.tg/m 3 from 0700 hours to 2100 hours) for 3 months. Ozone reduced the starch content in leaves and stem bark, whereas starch granules accumulated in bundle sheath cells along small leaf veins. At the same time, sucrose and inositol content increased in the leaves. Mesophyll cells in the vicinity of the stomata were injured first, and droplet-like material appeared on their walls. In the sieve plates of fumigated trees, the pores showed a higher degree of narrowing than those of the control treatment. Cell collapse in the leaves was accompanied by water loss and an increase in air space. In the stems, the ozone treatment led to a reduced radial width, particularly in the xylem tissue. These results are discussed in relation to reduced or inhibited phloem loading and ozone-induced drought stress. The plants injured by ozone showed quite distinct patterns of metabolite responses as well as enzyme activities (PEP-and RubPcarboxylase) in the leaves from the top to the bottom. There were also remarkable differences in the reaction of sucrose and inositol between leaves and stem bark. Future research should therefore increasingly follow a whole-plant approach for a better understanding of complex plant reactions.

Nonstructural Carbon in Woody Plants

“…Ozone damage typically reduces leaf sucrose and has little effect on leaf starch (147). There is no clear effect of ozone on stem NSC, with some studies showing increases and others decreases, but most found reductions in phloem sugars or translocation (71,81). In the roots there was a general trend of reduced starch concentrations, but impacts on root sugars are mixed (81,115,129).…”

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

“…Although the exact mechanism of the injur}^ process is still poorly understood, changes in carbon allocation and a decline of net photosynthesis are well documented and can affect plant growth (for reviews see Darrall, 1989;Hampp, 1992;Heath, 1994;Matyssek et al, 1995;Schmieden & Wild, 1995). In many fumigation experiments reduced C export and an accumulation of carbohydrates in mature leaves were found (Ito, Mitsumori & Totsuka, 1985;Kuppers & Klumpp, 1988;LuethyKrause & Landolt, 1990;Biicker & Ballach, 1992;Matyssek et al, 1992;Willenbrink & Schatten, 1993;Landolt et al, 1994). Accumulation of carbohydrates or disturbances of C flux can lead to regulatory changes of metabolism: A feedback control of sucrose synthesis reduces activities of key enzymes such as sucrose phosphate synthase and fructose 1,6-bisphosphatase, and induces enzyme activities of sucrose breakdown (sucrose synthase and invertase) thus favouring glycolysis (for review see Koch, 1996).…”

Responses of Leaf Processes in a Sensitive Birch (Betula pendulaRoth) Clone to Ozone Combined with Drought

“…Earlier experiments in birch have shown deleterious cellular ozone responses to different low (from ambient to double ambient) ozone concentrations : structural collapse and disintegration of mesophyll cells, discoloration, decreased photosynthetic capacity, and ultrastructural chloroplast and membrane injuries (Matyssek et al, 1991(Matyssek et al, , 1992Gu$ nthardt-Goerg et al, 1993 ;Pa$ a$ kko$ nen et al, 1995 a, b) and also in hybrid poplar (Landolt et al, 1994 ;Gu$ nthardtGoerg, 1996). The ozone responses were dependent on genetical predisposition (Pa$ a$ kko$ nen, a, 1997a, 1997 AOT 00 ( µl l −" h) 43n8 6 7 n 6 AOT 40 ( µl l −" h) 0n5 1 0 n 7 24 h mean (nl l −" ) 2 4 n 3 p 5 n 7 3 7 n 0 p 8 n 2 7 h mean (nl l −" ) 3 1 n 7 p 7 n 2 4 8 n 7 p 9 n 7 Maximum 1 h concentration (nl l −" ) 48n1 7 5 n 2 and Frey et al, 1996 ;Gu$ nthardt-Goerg et al, 1997, 1998, or on climatic factors (Pa$ a$ kko$ nen et al, et al, 1998).…”