Developmental and seasonal changes of stress responsiveness in beech leaves (Fagus sylvatica L.)

Abstract

The development of beech leaves ( Fagus sylvatica L.) was characterized by determination of the pigment and electrolyte concentrations as well as the accumulation of dry mass and specific leaf mass from bud break to senescence. To test the hypothesis that stress tolerance and responsiveness of defences show developmental and/or seasonal changes, leaf discs were either incubated in the absence (control) or presence of paraquat to induce oxidative stress. Controls displayed developmental changes in stress susceptibility ranging from less than 15% of maximum electrolyte leakage in mature leaves to more than20% leakage in senescent and 36-46% in immature leaves. Paraquat concentrations were chosen to result in about 95% of maximum electrolyte conductivity within 24 h in all developmental stages. Paraquat accumulation was about two-fold lower in senescent as compared with immature leaves, whereas stress susceptibility, as characterized by the kinetics of the increase in relative leakage, was similar in these developmental stages with 50% of maximum electrolyte conductivity (EC 50 ) = 6·5 h in immature and 7·5 h in senescent leaves. In mature leaves with intermediate paraquat accumulation rates, two classes of stress-sensitivity were distinguished, namely stress-resistant and stress-susceptible leaves with EC 50 = 9·5 and 5·2 h, respectively. Stress-resistance of mature leaves was accompanied by a rapid, approximately two-fold induction of superoxide dismutase activity. Stresssensitive mature leaves initially contained high superoxide dismutase activities but showed a rapid, more than sixfold loss in activity in 24 h. Correlation of meteorological data with leakage rates suggested that high air temperatures and low precipitation might have been predisposing for loss of resistance against oxidative stress in beech leaves.

Resorption Protection. Anthocyanins Facilitate Nutrient Recovery in Autumn by Shielding Leaves from Potentially Damaging Light Levels

“…The reductions in LMA observed in WT plants within each treatment are comparable with other studies where decreases in LMA ranged from 16% to 42% (Oland, 1963;Adams et al, 1990;Collier and Thibodeau, 1995;Polle et al, 2001). Senescencerelated reductions in LMA may be expected because senescence activity normally results in an increasingly carbon-starved environment within the leaf (Buchanan et al, 2000).…”

“…This hypothesis is based on the ideas that senescence-related processes lead to increased vulnerability to damage from visible light, resulting in reduced photosynthetic capacity (photo-inhibition) and that severe photo-inhibition during senescence can significantly affect a plant's ability to resorb foliar nutrients. The capacity of anthocyanins to reduce susceptibility to photo-inhibition via light attenuation is well documented (for recent review, see Steyn et al (2002), and increased light sensitivity during senescence appears to be common (Kar et al, 1993;Bukhov, 1997;Kö niger et al, 2000;Polle et al, 2001). However, the existence of a direct association between anthocyanic photoprotection and enhanced nutrient resorption has yet to be established.…”

Ozone symptoms in leaves of woody plants in open‐top chambers: ultrastructural and physiological characteristics

“…This means that, because of the low photosynthetic activity, the ozone uptake by the opened stomata is not balanced by the production of defence metabolites (Fredericksen et al 1996). Moreover, the detoxifying ability changes during the leaf lifespan, reaching a maximum at full maturity prior to the onset of senescence processes (Polle et al 2001). Thus, within the same tree crown, the sensitivity of leaves differs according to their position on the branch and their relative age.…”

Immature leaves ofWeinmannia racemosaare more heat tolerant than mature leaves based on differences in chlorophyllafluorescence and solute leakage

“…The observation that the 18:2 lipid class (the precursor to 18:3) was higher in IM or IME leaf stages compared with M leaves ( Table 2) may indicate that the expression of omega-3 fatty acid desaturase, the enzyme responsible for the 18:2 to 18:3 conversion (Murakami et al 2000) was limited during leaf expansion. Another possibility is that IME leaves have higher photorespiration and associated oxygen radical scavenging rates, as has been observed in other young leaves (Polle et al 2001). For example, young leaves of hybrid poplar (Bagard et al 2008) and a heatresistant Acer rubrum genotype (Weston & Bauerle 2007) had higher photorespiration rates and more resistance to heat stress when compared with mature leaves.…”