Tamara Chadzinikolau

The invasive pest Cameraria ohridella annually colonizes trees of the genus Aesculus across Europe, causing dark brown damage called mines that gradually cover the leaf surface. This study aimed to compare the VOC profiles emitted by chestnut tree leaves with varying susceptibility to the pest and assess whether these profiles change due to larval feeding. The research involved a susceptible tree (Ae. turbinata) and resistant trees (Ae. glabra and Ae. parviflora). Over three growing seasons (2014, 2015, 2016), leaf damage and the profile of VOCs were analyzed biweekly from May to September. Leaf damage increased progressively in Ae. turbinata during all seasons. The VOC profiles differed both qualitatively and quantitatively among the trees and across years. More VOCs were identified in 2014 and 2015 than in 2016. The susceptible Ae. turbinata exhibited the highest VOC diversity in 2014, aligning with severe leaf damage—profiles of VOCs in Ae. turbinata were different from resistant trees. Statistical analysis revealed that in 2014 and 2015, differences in the profile of VOCs between susceptible and resistant trees were apparent near pest-feeding dates. In 2016, VOCs significantly distinguished the profile of susceptible trees that were present before the appearance of the first generation of the pest.

Evergreen conifers thrive in challenging environments by maintaining multiple sets of needles, optimizing photosynthesis even under harsh conditions. This study aimed to investigate the relationships between needle structure, photosynthetic parameters, and age along the light gradient in the crowns of Abies alba, Taxus baccata, and Picea abies. We hypothesized that: (1) Needle structure, photochemical parameters, and photosynthetic pigment content correlate with needle age and light levels in tree crowns. (2) The photosynthetic capacity of ageing needles would decline and adjust to the increasing self-shading of branches. Our results revealed a non-linear increase in the leaf mass-to-area ratio. The maximum quantum yield of photosystem II photochemistry decreased linearly with needle age without reaching levels indicative of photoinhibition. Decreased maximum electron transport rates (ETR_max) were linked to declining values of saturating photosynthetic photon flux density and increasing non-photochemical quenching of fluorescence (NPQ), indicating energy losses as heat. The chlorophyll a to chlorophyll b ratio linearly decreased, suggesting older needles sustain high light capture efficiency. These findings offer new insights into the combined effects of needle ageing and self-shading on photochemistry and pigment content. This functional needle balance highlights the trade-off between the costs of long-term needle retention and the benefits of efficient resource utilization. In environments where air temperature is less of a constraint on photosynthesis due to climate warming, evergreen coniferous trees could sustain or enhance their photosynthetic capacity. They can achieve this by shortening needle lifespan and retaining fewer cohorts of needles with higher ETR_max and lower NPQ compared to older needles.

The aim of this study was to investigate the effects of maleic acid (MA), salicylic acid (SA), and citric acid (CA) on alleviating the drought stress of a lettuce (Lactuca sativa L.) hydroponic culture. The effect of these organic acids was tested under stress conditions induced by polyethene glycol (PEG 6000) at 5% and 7.5% concentrations. Drought stress reduced the fresh and dry matter yields of plants. The acid treatment caused increasing tendencies in the fresh weight yield:control (SA, MA), PEG 7.5% (SA, MA, CA)) and dry weight yield (control (SA, MA), PEG 5% (MA), PEG 7.5% (SA, MA)). The acid treatment also enhanced the nutrient uptake of stressed plants: SA: N (PEG 7.5%), K (PEG 5 and 7.5%); MA: N, P, K, Ca (PEG 5 and 7.5%). This work found that chlorophyll a and b amounts did not change under applied experimental conditions. Most parameters of chlorophyll fluorescence did not depend on either the level of applied water stress (PEG level) or the type of spraying. Drought stress increased leaf superoxide anion (O₂^•−) and malondialdehyde (MDA) levels but decreased H₂O₂. Proline (Pro) and phenolic compounds (TFC), including flavonols (Fla), accumulated more in stressed plants. Drought stress also affected the chlorophyll fluorescence. Our results suggest that acids can improve plant tolerance to drought stress by boosting the antioxidant defence system and reducing the oxidative damage caused by reactive oxygen species.

The study aimed to determine the level of selected indicators of nitrogen metabolism in vegetables from organic (organic food store) and conventional (supermarket and local market) crops. Nitrates, total chlorophyll content, and the activity of the nitrate biosynthesis pathway enzymes—nitrate reductase (NR) and glutamine synthetase (GS)—were determined in the leaves of selected species from different plant families. The research material consisted of dill, carrot, celery, beet, onion, Chinese and white cabbage, and rocket. The nitrate content was within the permissible limits, except for vegetables bought at a local market. In most cases, no significant differences in the level of nitrates between organic and conventional farming were observed. The analyses revealed the highest nitrate content in dill [2.16 mg × g⁻¹] and the lowest in onions [0.06 mg × g⁻¹] from conventional crops. The enzyme activities were related to the level of nitrates. The analysed species differed in phenolic compounds, ascorbate levels, and total antioxidant capacity (TCA). Positive correlations were found between TCA and antioxidants.

The effects of short-term 48 h long NaCl-stress and spermidine level modification on polyamines level and antioxidant status in cucumber (Cucumis sativus cv. Dar) leaves were investigated. Seedlings kept in nutrient solutions treated with 50 mM NaCl for 48 h exhibited reduced relative water content and accumulation of free polyamines, especially spermidine. Salinity stress caused an increase in superoxide radicals and hydrogen peroxide generation during the salinity-induced increase in antioxidant enzyme activities. Spermidine application before stress resulted in a marked increase in spermidine and spermine contents in the leaves of salt-stressed cucumber seedlings. Additionally, increased spermidine/spermine level mobilised the antioxidant enzyme’s activity and limited reactive oxygen species content. Polyamine synthesis inhibitor (MGBG) slightly decreased spermidine and spermine levels during salinity and reversed the antioxidant activity mobilisation. These results showed that Spd modifications significantly improved PAs, enhancing salinity stress tolerance by detoxifying ROS. Our findings determined the implication of PAs for improving the salinity tolerance of important vegetable species.

Soluble sugars such as sucrose, glucose and fructose in plant host cells not only play the role as donors of carbon skeletons, but they may also induce metabolic signals influencing the expression of defense genes. These metabolites function in a complex network with many bioactive molecules, which independently or in dialogue, induce successive defense mechanisms. The aim of this study was to determine the involvement of sucrose and monosaccharides as signaling molecules in the regulation of the levels of phytohormones and hydrogen peroxide participating in the defense responses of Lupinus luteus L. to a hemibiotrophic fungus Fusarium oxysporum Schlecht f. sp. lupini. A positive correlation between the level of sugars and postinfection accumulation of salicylic acid and its glucoside, as well as abscisic acid, was noted. The stimulatory effect of sugars on the production of ethylene was also reported. The protective role of soluble sugars in embryo axes of yellow lupine was seen in the limited development of infection and fusariosis. These results provide evidence for the enhanced generation of signaling molecules both by sugar alone as well as during the crosstalk between sugars and infection caused by F. oxysporum. However, a considerable postinfection increase in the level of these signaling molecules under the influence of sugars was recorded. The duration of the postinfection generation of these molecules in yellow lupine was also variable.