This paper describes the hitherto unreported aspects of orchid mycorrhizae. The host cells harbour upto 4 generations of fungal pelotons which are formed after each peloton is digested. There are two types of hyphae in a host cell, one forming the pelotons, and the other which lies close to the host cell wall and separated from the former by a callosic wall. The later, called non-pelotonic hyphae form the fresh peloton when the former is digested. Consequently, there are also cytochemical differences between these two types of hyphae.

Two wheat cultivars, Hesheng 2 with large grain yield potential, and Shannong 505 with small grain yield potential, were used for investigating the responses of postanthesis photosynthesis, dry matter accumulation and allocation, and grain growth to source/sink changes. At the initial grain filling stage, Hesheng 2 was sensitive to source reduction leading to an increase of net photosynthetic rate (P_N) by 10 %; however, little effect of sink reduction was observed. In Shannong 505, P_N was obviously decreased by sink reduction, and changed a little after source reduction. At the rapid grain filling stage, Hesheng 2 was sensitive to both source and sink reduction resulting in the increase or decrease of P_N, respectively. However, the response of P_N in Shannong 505 to source/sink changes was similar to that in previous stage. The dry matter (DM) accumulation after anthesis was affected by source/sink changes. In Hesheng 2, the decrease in DM was higher than that in Shannong 505 after the same source or sink reduction. Source reduction caused a decrease in the allocation of DM to the sheath and stem, and promoted the reserve photosynthates to be reallocated to grain. The effect of sink reduction was contrary. The grain mass of Hesheng 2 was more easily regulated by source/sink changes than that of Shannong 505. The effect source/sink changes on grain mass was in order upper > basal > middle spikelets on spike. As for a spikelet, the effect was found mainly in the grain mass at the positions 3 and 4 from base of the spikelet.

A novel approach for simultaneous localization of two DNA sequences on plant chromosomes is described. The approach is based on a combined use of primed in situ DNA labelling (PRINS) with fluorescent in situ hybridization (FISH). Traditionally, this has been done using FISH with two probes labelled by two different marker molecules. Compared to this method, the combined PRINS-FISH procedure is faster. Furthermore, because one of the DNA sequences is localized by PRINS with specific primers, only one labelled probe is needed.

The role of plant antioxidant systems in stress tolerance was studied in leaves of three contrasting wheat genotypes. Drought imposed at two different stages after anthesis resulted in an increase in H2O2 accumulation and lipid peroxidation and decrease in ascorbic acid content. Antioxidant enzymes like superoxide dismutase, ascorbate peroxidase and catalase significantly increased under water stress. Drought tolerant genotype C 306 which had highest ascorbate peroxidase and catalase activity and ascorbic acid content also showed lowest H2O2 accumulation and lipid peroxidation (malondialdehyde content) under water stress in comparison to susceptible genotype HD 2329 which showed lowest antioxidant enzyme activity and ascorbic acid content and highest H2O2 content and lipid peroxidation. HD 2285 which is tolerant to high temperature during grain filling period showed intermediate behaviour. Superoxide dismutase activity, however, did not show significant differences among the genotypes under irrigated as well as water stress condition. It seems that H2O2 scavenging systems as represented by ascorbate peroxidase and catalase are more important in imparting tolerance against drought induced oxidative stress than superoxide dismutase alone.

Acetylsalicylic acid, which applied to cotyledons of the short day plant Pharbitis nil prior to an inductive 16-h dark period inhibits flowering by 90 %, is converted to salicylic acid and to a lesser extent to gentisic acid in the cotyledons during this 16-h dark period. Our results confirmed that salicylic acid and gentisic acid are responsible for the inhibition of flowering. They also inhibit prostaglandin biosynthesis.

Experiments were conducted to determine the interactive effects of salinity and certain growth regulators on growth and nitrogen assimilation in maize (Zea mays L. cv. GS-2). 100 mM NaCl inhibited the biomass accumulation, chlorophyll and carotenoid contents in leaves, nitrate content and uptake and nitrate reductase activity. The application of kinetin, ascorbic acid and 10 and 50 µM abscisic acid in the first experiment and 50 and 100 µM abscisic acid in the second experiment induced a substantial increase in the above parameters, the effect was highest with abscisic acid in salinized as well as non-salinized plants.

Primed in situ labelling (PRINS) of nucleic acids was developed as an alternative to traditionally used fluorescence in situ hybridization (FISH). Compared to FISH, PRINS is faster and does not require preparation of labelled probes. Nevertheless, the number of applications for physical mapping of DNA sequences on plant chromosomes remains low. This is due to the fact that there are a number of factors which influence the specificity and sensitivity of the reaction. The purpose of this work was to analyse the effect of some of them, including the age of slides, type of Taq DNA polymerase, number and concentration of primers, the presence and concentration of bovine serum albumine and MgCl₂ in the reaction mixture. Furthermore, the effect of various pre-treatments on signal intensity and non-specific fluorescence was studied. A consensus Arabidopsis-type telomeric sequence and Vicia faba mitotic chromosomes were used as a model system. We have found that the age of slides was critical and that under optimal conditions it was possible to achieve relatively high signal to noise ratio.

A single degenerate glutamine synthetase (GS)-specific primer was used to amplify the 3' end of cDNAs derived from different GS genes that are expressed in leaves and roots of sunflower (Helianthus annuus L. cv. Peredovic). Four types of GS cDNA (I, II, III and IV) were simultaneously amplified from leaves and five types (I, II, V, VI, VII) from roots with a minimum investment of time and experimental work. cDNAs II, III and IV encode chloroplastic isoforms as deduced by the presence of chloroplastic GS-specific features in their sequences. The rest of cDNAs codifies cytosolic isoforms. Using cDNA-specific probes and primers, homologous sequences to all GS cDNAs amplified from cv. Peredovic, except to cDNAs III and IV, were detected in the inbred line R41. This result strongly suggests that the three cDNAs for chloroplastic isoform are allelic sequences from the same locus, and since cDNA type IV contains sequences derived from cDNAs II and III, it indicates a recombinational origin. The results presented are consistent with the existence of a GS gene family in sunflower with at least five members. Four of them, named ggs1.1 to ggs1.4, codify for the cytosolic isoforms (cDNAs I, V, VI and VII). A fifth member, named ggs2, from which three allelic sequences (cDNAs II, III and IV) have been cloned, encodes the chloroplastic isoform.

Accumulation of the pathogenesis-related (PR) proteins localised in intercellular spaces of barley primary leaves, chlorophyll content, structure of chloroplasts, and photosynthesis were examined during natural and in vitro induced leaf senescence (cultivation of whole plants in the dark or detached leaves under nutrient deficiency). Some of PR proteins accumulated during natural senescence, but their accumulation pattern was different from those of pathogen-induced as well as during in vitro-induced senescence, which indicate different molecular bases of these processes. Photosynthetic rate and chlorophyll content indicate that natural senescence of barley primary leaves began from 15th day after sowing. In 35-d-old first leaves, the chloroplasts showed typical characteristics of senescence as significant decrease of size, greater grana, and prominent plastoglobuli. The chloroplasts contained more grana under in vitro induced senescence and they had reduced length in the dark. Correspondingly, accumulation of PR proteins was detectable on about the 15th day but the content of some PR proteins increased in later stages of senescence.

The impact of increased solar UV-B radiation on photosynthetic characteristics of rice (Oryza sativa L.) cultivars ADT36, IR20, IR50, J13 and MDU4 has been studied. In all the cultivars concentrations of photosynthetic pigments decreased under increased UV-B radiation. Even low enhancement of UV-B reduced the photochemical activities in all the cultivars except MDU4 and changed chlorophyll a fluorescence. Enhanced UV-B radiation caused a dose-dependent changes in chloroplast proteins in most of the cultivars.

The inoculation of mycorrhizal maize plants with three isolates of microaerophilic diazotrophic bacteria obtained from the mycelium of arbuscular mycorrhizal fungi associated with three grasses (Arrhenatherum elatius - bacterial isolate ARR, Agropyrum repens - isolate AGR and Poa annua - isolate POA) caused no increase in nitrogen content in plant biomass. The inoculation with bacterial isolate ARR resulted in the decreased plant growth. Bacterial isolate AGR decreased the percentage of the root length colonized by arbuscular mycorrhizal fungus Glomus fistulosum. The inoculation with both mycorrhizal fungus and isolate POA increased significantly the concentration of phosphorus in plant shoots compared to uninoculated control.

In wheat seedlings (Triticum aestivum L. cv. 2329) oxidative stress caused by UV-B radiation led to lipid peroxidation of thylakoid membrane; it was expressed in term of malondialdehyde (MDA) formation. The peroxidation of lipids of thylakoid membrane in isolated chloroplasts was prevented when flavonoids quercetin and rutin were supplied into the incubation medium. The activities of superoxide dismutase, ascorbate peroxidase, and catalase increased during the first hours of UV-B exposure. A comparative study of UV-B and temperature effects showed different profiles of the antioxidant enzymes and MDA, suggesting that these two stresses have distinct sites of action. In addition to quantitative increase in flavonoids, qualitative change in flavonoid composition was also marked during UV-B stress, and a new peak at 330 nm was found as compared to control.

The Vigna radiata L. plants were grown in greenhouse at moisture content of sand (SMC) of 12.0 ± 0.5 %. At flower bud initiation stage, i.e. 45 - 50 d after sowing, the SMC was decreased to 3.5 ± 0.5 %, and the effects of applied potassium (0, 2.56 and 3.84 mmol dm-3) were studied. During water stress, K-fed plants maintained higher leaf water potential and relative water content (RWC) of leaves and nodules and lower osmotic potential as compared to untreated plants. The proline content was higher in nodules than in leaves showing their difference in degree of stress. A partial recovery was found after re-irrigation. When subjected to drought, carbon was accumulated in the leaves and declined in nodules and roots. K-fed plants showed higher C and N content in stem, roots and nodules than untreated plants. The content of K significantly increased in stem and nodules in K-fed plants, irrespective of SMC. Dry masses of different plant parts were also increased in K-fed plants.

Nitrate content, activities of nitrate reductase and glutamine synthetase, soluble protein content, and proportion of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) protein in total proteins were measured in leaves of Beta vulgaris L. plants affected by nickel, cadmium, and molybdenum in concentrations of 10^-4, 10^-2, and 1 mM. The most harmful effect on the above mentioned parameters had Cd, less harmful Ni, whereas Mo stimulated the investigated parameters. The proportion of RuBPCO protein showed a high tolerance to heavy metals.

Soybean (Glycine max Merrill) and maize (Zea mays L.) plants were exposed for 5 to 48 h to the herbicide diquat under "white light" (WL) or far-red radiation (FR) (photon fluence rate of 30 µmol m^-2 s^-1). The WL enhanced diquat effect on chlorophyll content in soybean plants, while FR had the same effects on maize plants. After 5 h, diquat increased the content of polypeptides bound to light-harvesting proteins in both plants.

Two approaches were used to detect variability within 23 pea cultivars. Eight random amplified polymorphic DNA (RAPD) primers produced 163 bands (114 polymorphic), whereas five isoenzyme systems produced 25 bands (20 polymorphic). Both methods provided good results in finger-printing and identified all cultivars tested. Genetic similarity analysis (UPGMA) gave different results from RAPD and isoenzyme data. This could reflect different properties of both marker types. These data were also analysed using the bootstrap method, which supported the idea of one common progenitor of cultivated peas.

The role of potassium nutrition in microtuber production was investigated in two potato cultivars belonging to different maturity groups. Alterations were made in Murashige and Skoog (MS) medium to obtain seven concentrations of potassium (10, 15, 20, 25, 30, 35 and 40 mM), and their effects were studied on microtuber number, microtuber mass and harvest index. In late cultivar Kufri Sindhuri, an increase in potassium concentration beyond 25 mM decreased the number of microtubers. Whereas, potassium did not show any inhibitory effect on microtuber number in early cultivar Kufri Ashoka. Potassium showed promoting effect on microtuber mass in both the cultivars. Maximum microtuber mass and harvest index were observed when the medium was supplemented with 40 mM potassium. Therefore, large size potato microtubers amenable to direct field planting can be induced in MS medium containing 40 mM potassium.

Growth of Sesbania rostrata was decreased gradually with increase in root medium salinity (mixed salts or NaCl alone). Soil moisture or anoxia did not affect plant growth significantly. Higher K⁺/Na⁺ ratios in plant tissues compared to those in the root medium were found under different salinities. This indicated a high K⁺-Na⁺ selectivity, a characteristic generally considered unique to halophytes. S. rostrata is moderately salt tolerant and may be utilized as forage crop and green manure on saline land.

French bean (Phaseolus vulgaris L. cv. Contender) plants at five developmental stages (4, 8, 12, 16 and 20 d after sowing) were exposed to one of three treatments: 1 - 25 °C (control), 2 - exposure to chilling at 10 °C only for 2 d prior to sampling, and 3 - long-term exposure to chilling at 10 °C. Short- and long-term chilling decreased plant growth. Higher concentrations of ascorbate and glutathione were found in the chilling-treated plants throughout the different period of growth in comparison with those in the control plants. The activities of superoxide dismutase, ascorbate peroxidase, and glutathione reductase increased in the chilling-treated seedlings while activities of catalase and peroxidase and of β-carotene content decreased in young chilling-treated plants and slightly increased in older ones.

Five wild herb legumes (Trifolium resupinatum, Melilotus indica, Medicago intertexta, Trigonella hamosa, and Alhagi murarum) were collected from cultivated lands of the Nile Valley, and compared with clover (Trifolium alexandrinum), a cultivated forage legume. The wild herb legumes exhibited great variation in nodulation percentage, nodule number, nodule mass and acetylene reduction activity with regard to locality. Nodulation of T. resupinatum and M. indica ranged between 50 - 100% and 33 - 100%, respectively, compared to 50 - 100% for T. alexandrinum. The number of nodules formed on T. resupinatum was 9 - 128 and that of M. indica 6 - 39, compared to 13 - 122 nodule per plant for T. alexandrinum. Nodule mass was correlated with nodule number. In M. indica, a small number of nodules was compensated with high specific nitrogenase activity. The herb legumes formed nodules of small size, varying shape (globose, cylindrical, branched, etc.), and of different types (crotalaroid and astragaloid). Microscopic examination of root-nodules from T. resupinatum, M. indica and M. intertexta, showed that these legumes formed indeterminate and effective nodules, containing apical meristems, central symbiotic tissue with characteristic zonation and peripheral vascular bundles. The nodules harboured bacteroids with pleiomorphic morphology.