Smyrnium perfoliatum L. (Apiaceae), an endangered forest herb with only one main locality in South-West Slovakia (Devfnska Kobyla in the Little Carpathian Mountains), is capable to recover chlorophylls at the end of the growing season. This regreening only within bracts was observed dturing two weeks before achieving the so-called "point of no return" that leads to the last stage of ontogenesis -leaf senescence. The effect not only of endogenous cytokinins on chlorophyll content and carbon dioxide exchange (photosynthesis, mitochondriaI respiration, and photorespiration) is discussed but also of other factors such as strong irradiance, high temperature or drought stress on studied parameters was considered.List of abbreviations: PN (CO2)sat -net photosynthetic rate at saturating irradiance, F -CO 2 compensation concentration, RD -mitochondrial respiration rate, RL -photorespiration rate, chl a, b, a+bchlorophylls a,b,a+b, d.m. -dry mass, SLM -specific leaf mass, SLA -specific leaf area
A b s t r a c t Smyrnium pe~, oliatum L. (Apiaceae), an endangered summer forest herb grown in the understory of dominant oak-hornbeam stands in Devinska Kobyla, Little Carpathians region in SW Slovakia, is considered to form at least five leaf types of different physiological and anatomical quality. These observation are based upon the estimated differences of photosynthetic carbon dioxide uptake, chlorophyll content, leaf anatomy, and several quantitative parameters of growth analysis. There is a further attempt to establish, to what extent the daily changing environment, especially the excess of light of fast-moving sunflecks by the photosynthetic apparatus within any leaf type, according to its dominant shade adaptation could be effectively used.Webb R.A. 1972, Use of the boundary line in the analysis of biological data. J. Hort. Sci. 47:309-319. Young D.R., Smith W.K, 1980. Influence of sunlight on photosynthesis, water relation, and leaf structure in the understory species Arnica cordifolia.
The effect of different concentrations of lead was investigated in two different ways in the leaves of Helianthus annuus plants. In the first way, removed leaf discs from 5-wceks old plants were floated in 0.05, 0.25, 2.50 and 5.00 mM PbNO3 solutions for 2, 4 and 6 days. In addition, the chlorophyll content and the activity of peroxidase enzyme which are the parameters of stress conditions in plants were also measured. In this experimental series, a decrease was determined in polyamine and chlorophyll contents and in the peroxidase activity in leaf discs which were treated with different concentrations of lead. In the second experimental series, one half of the upper leaves of 5-wceks old plants were used for lead treatments, while the other half for control. In half leaf experiments, lead in 0.05, 1.25 and 5.00 mM concentrations were sprayed to the both sides of the half leaves. According to the results of the half leaf experiments, 0.05, 1.25 and 5.00 mM lead treatments increased the putrescine content in 27, 15 and 9 % respectively. On the other hand, chlorophyll content and the activity of peroxidnse enzyme were decreased with the treatments of lead.
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