Darkness affects differentially the expression of plastid-encoded genes and delays the senescence-induced down-regulation of chloroplast transcription in cotyledons of Cucurbita pepo L. (Zucchini).

In contrast to differentiated leaves, the regulatory mechanisms of chloroplast gene expression in darkened cotyledons have not been elucidated. Although some results have been reported indicating accelerated senescence in Arabidopsis upon reillumination, the capacity of cotyledons to recover after dark stress remains unclear. We analysed the effect of two-days dark stress, applied locally or at the whole-plant level, on plastid gene expression in zucchini cotyledons.

Desiccation of the resurrection plant Haberlea rhodopensis at high temperature.

Haberlea rhodopensis plants, growing under low irradiance in their natural habitat, were desiccated to air-dry state at a similar light intensity (about 30 μmol m(-2) s(-1)) under optimal (23/20°C, day/night) or high (38/30°C) temperature. Dehydration of plants at high temperature increased the rate of water loss threefold and had a more detrimental effect than either drought or high temperature alone. Water deficit decreased the photochemical activity of PSII and PSI and the rate of photosynthetic oxygen evolution, and these effects were stronger when desiccation was carried out at 38°C.

Changes in photosynthesis, mesophyll conductance to CO2, and isoprenoid emissions in Populus nigra plants exposed to excess nickel.

Poplar (Populus nigra) plants were grown hydroponically with 30 and 200 μM Ni (Ni30 and Ni200). Photosynthesis limitations and isoprenoid emissions were investigated in two leaf types (mature and developing). Ni stress significantly decreased photosynthesis, and this effect depended on the leaf Ni content, which was lower in mature than in developing leaves.

Genotypic variation in drought stress response and subsequent recovery of wheat (Triticum aestivum L.).

Three wheat (Triticum aestivum L.) genotypes, Sadovo, Katya and Prelom, with different tolerance to drought were comparatively evaluated in terms of leaf respiratory responses to progressing dehydration and consecutive rewatering. Under drought stress, the respiration of all varieties gradually decreased, as the drought-tolerant Katya showed the most pronounced decline at earlier stages of dehydration.

Effects of foliar fertilization and arbuscular mycorrhizal colonization on Salvia officinalis L. growth, antioxidant capacity, and essential oil composition.

Background: The effect of foliar fertilization and Glomus intraradices inoculation on the growth, qualitative and quantitative pattern of essential oil in Salvia officinalis was determined. Sage plants were grown in a glass house on a soil/sand mixture (w/w = 3:1). Agroleaf total, N:P:K = 20:20:20 + microelements, was used at the whole vegetative growth stage as a 0.

Proteolytic activity and cysteine protease expression in wheat leaves under severe soil drought and recovery.

The involvement of acidic proteases in soil drought response of winter wheat (Triticum aestivum L.) at seedling stage in three cultivars differing in water stress tolerance was studied. Withholding irrigation for seven days resulted in severe drought stress corresponding to 60% leaf water deficit.

Protection of thylakoids against combined light and drought by a lumenal substance in the resurrection plant Haberlea rhodopensis.

Background And Aims: Haberlea rhodopensis is a perennial, herbaceous, saxicolous, poikilohydric flowering plant that is able to survive desiccation to air-dried state under irradiance below 30 micromol m-2 s-1. However, desiccation at irradiance of 350 micromol m-2 s-1 induced irreversible changes in the photosynthetic apparatus, and mature leaves did not recover after rehydration. The aim here was to establish the causes and mechanisms of irreversible damage of the photosynthetic apparatus due to dehydration at high irradiance, and to elucidate the mechanisms determining recovery.

Variety-specific response of wheat (Triticum aestivum L.) leaf mitochondria to drought stress.

The main objective of the present work was to examine leaf respiratory responses to dehydration and subsequent recovery in three varieties of winter wheat (Triticum aestivum L.) known to differ in their level of drought tolerance. Under dehydration, both total respiration and salicylhydroxamic acid (SHAM)-resistant cytochrome (Cyt) pathway respiration by leaf segments decreased significantly compared with well-watered plants.

Changes in the leaf polypeptide patterns of wheat flag leaves spraying with non-purine cytokinins.

The changes in the polypeptide patterns of soluble proteins of wheat flag leaves after treatment with two synthetic cytokinin-like substances 3-CP-2-PU [1-(3-chlorophenyl)-3-(2-pyridyl)urea] and 3-CP-4-MPU [1-(3-chlorophenyl)-3-(4-methyl-2-pyridyl)urea] was studied. Both compounds increased differentially in quantity and composition most individual polypeptides identified compared to the non-treated leaves. While 3-CP-2-PU increased only the polypeptide quantity, 3-CP-4-MPU led to the appearance of new polypeptide with Mw of 51 kDa.

Exogenous treatment with salicylic acid attenuates cadmium toxicity in pea seedlings.

The present study investigated the possible mediatory role of salicylic acid (SA) in protecting plants from cadmium (Cd) toxicity. The exposure of pea plants to increasing Cd concentrations (0.5, 1.

Senescence progression in a single darkened cotyledon depends on the light status of the other cotyledon in Cucurbita pepo (zucchini) seedlings: potential involvement of cytokinins and cytokinin oxidase/dehydrogenase activity.

Darkness mediates different senescence-related responses depending on the targeting of dark treatment (whole plants or individual leaves) and on the organs that perceive the signal (leaves or cotyledons). As no data are available on the potential role of darkness to promote senescence when applied to individual cotyledons, we have investigated how darkness affects the progression of senescence in either a single or both individually darkened cotyledons of young 10-day-old Cucurbita pepo (zucchini) seedlings. Strong acceleration of senescence was observed when both cotyledons were darkened as judged by the damage in their anatomical structure, deterioration of chloroplast ultrastructure in parallel with decreased photosynthetic rate and photochemical quantum efficiency of PSII.

Singlet oxygen quenching by phenylamides and their parent compounds.

This paper demonstrates for the first time that plant metabolites of the phenylamide type, conjugates of putrescine with hydroxycinnamic acids (p-coumaric, caffeic and ferulic), possess 1O2 quenching properties. Data were obtained confirming that their acidic parent compounds were also able to quench 1O2, as did polyamines (putrescine, spermidine and spermine), and that this ability depends on the number of amino groups. Potentiation of the 1O2 quenching ability of the conjugates relative to both parent components was established.

Treatment with salicylic acid decreases the effect of cadmium on photosynthesis in maize plants.

The present study investigated the possible mediatory role of salicylic acid (SA) in protecting photosynthesis from cadmium (Cd) toxicity. Seeds of maize (Zea mays L., hybrid Norma) were sterilized and divided into two groups.

The induction of microsomal NADPH:cytochrome P450 and NADH:cytochrome b(5) reductases by long-term salt treatment of cotton (Gossypium hirsutum L.) and bean (Phaseolus vulgaris L.) plants.

We studied the effect of salinity on the activity of microsomal NADPH:cytochrome P450 reductase (CPR, EC 1.6.2.

Separation and quantification of the cellular thiol pool of pea plants treated with heat, salt and atrazine.

A novel procedure for the separation of the cellular thiol pool according to the molecular weight and localization of compounds with sulphydryl groups is presented. This simple and rapid method allows the differentiation of thiols into three major fractions-low molecular weight (LMT, primarily glutathione and free cysteine), protein-bound (TPT) and pellet-bound (PBT, associated with cell walls and broken organelles). Moreover, determination of the ratio between surface (readily reactive) thiols (ATG) and those that are more or less buried in the protein structure (BTG) can be achieved.

Response of inoculated foliar fed pea plants (Pisum sativum L.) to reduced Mo supply.

The application of nutrients to the roots and leaves of inoculated pea plants grown under conditions of reduced Mo supply was studied. Pea plants (Pisum sativum L.) were grown on liquid nutrient solution excluding Mo from the media until the 35th day under glasshouse conditions.

Improved procedure for separation and purification of Arthronema africanum phycobiliproteins.

A rapid, inexpensive and reliable procedure for separation and purification of C-phycocyanin (C-PC) and allophycocyanin (APC) from Arthronema africanum based on a previously described rivanol-sulfate method for C-PC purification was developed. Exclusion of NaCl from the extraction buffer resulted in complete separation of APC and C-PC, two-fold reduction of rivanol treatments, and a higher yield and purity of C-PC. Pure C-PC (A(620)/A(280) of 4.

Methyl jasmonate is a more effective senescence-promoting factor in Cucurbita pepo (zucchini) cotyledons when compared with darkness at the early stage of senescence.

The effects of short-term darkening and methyl jasmonate (MeJA) on cotyledon senescence were studied 24h after transfer of intact 7-day-old Cucurbita pepo (zucchini) seedlings to darkness or spraying with 100 microM MeJA. The jasmonate inhibitory effect on chlorophyll content and chloroplast transcriptional activity was stronger compared with darkness. Further, MeJA reduced the photosynthetic rate whereas darkness did not affect photosynthesis.

Photosynthetic activity of homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and rehydration.

The functional state of the photosynthetic apparatus of flowering homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and subsequent rehydration was investigated in order to characterize some of the mechanisms by which resurrection plants survive drought stress. The changes in the CO2 assimilation rate, chlorophyll fluorescence parameters, thermoluminescence, fluorescence imaging and electrophoretic characteristics of the chloroplast proteins were measured in control, moderately dehydrated (50% water content), desiccated (5% water content) and rehydrated plants. During the first phase of desiccation the net CO2 assimilation decline was influenced by stomatal closure.

Control by cytokinins of the cellular behavior in the plate meristem of zucchini cotyledons.

The temporal and spatial effects of exogenous cytokinins on both cell expansion and division activity in the plate meristem of cultured zucchini cotyledons were studied. N6-benzylaminopurine (1-100 microM) and N-(2-chloro-4pyridyl)-N'-phenylurea (4PU-30) (0.1-100 microM) greatly stimulated the cell growth and division.

Comparative study on the changes in photosynthetic activity of the homoiochlorophyllous desiccation-tolerant Haberlea rhodopensis and desiccation-sensitive spinach leaves during desiccation and rehydration.

The functional peculiarities and responses of the photosynthetic system in the flowering homoiochlorophyllous desiccation-tolerant (HDT) Haberlea rhodopensis and the non-desiccation-tolerant spinach were compared during desiccation and rehydration. Increasing rate of water loss clearly modifies the kinetic parameters of fluorescence induction, thermoluminescence emission, far-red induced P700 oxidation and oxygen evolution in the leaves of both species. The values of these parameters returned nearly to the control level after 24 h rehydration only of the leaves of HDT plant.

Alterations in some oxidative parameters in susceptible and resistant wheat plants infected with Puccinia recondita f.sp. tritici.

We studied the systemic effects after infection of susceptible and resistant (expressing HSR) wheat plants with leaf rust (Puccinia recondita f.sp. tritici) on the amount of hydrogen peroxide and activity of some ROS scavenging enzymes.

Thermoluminescence study of photosystem II activity in Haberlea rhodopensis and spinach leaves during desiccation.

Thermoluminescence glow curve parameters were used to access the functional features of PS II in the Balkan endemic Haberlea rhodopensis. This representative of the higher desiccation-tolerant plants is unique for the European flora. An unusual high temperature of TL emission from Haberlea leaves after excitation by one flash at 5 degrees C was observed.

Exogenous treatment with salicylic acid leads to increased antioxidant capacity in leaves of barley plants exposed to paraquat.

Our previous study suggests that salicylic acid mediates tolerance in barley plants to paraquat (Ananieva et al. 2002). To further define the role of SA in paraquat induced responses, we analysed the capacity of the antioxidative defence system by measuring the activities of several antioxidative enzymes: superoxide dismutase (SOD, EC 1.

Cell division and cell enlargement in isolated Cucurbita cotyledons grown in darkness and in light.

The spatial and temporal patterns of post-embryonal cell growth and cell division were characterised in excised cotyledons of vegetable marrow ( Cucurbita pepo L. var. giromontia Alef.