Tephrosia purpurea Pers. was found to accumulate high proline content in dry habitat. The proline content was higher in shoots, especially in leaves, than in roots. Pod walls and young seeds showed the highest proline content. The proline content of young leaves was higher than that of mature and old leaves. During leaf senescencein vitro proline content increased rapidly upto 6 h and further decreased in leaves as well as in leachate. High proline content seems to be positively related with 'survival capability' of this plant.

In seedlings of the tropical tree speciesErythrina variegata Lam. andHardwickia binata Roxb. exposed to different acidic mist (H₂SO₄, pH 5, 3 and 2) for 5 d significant reduction in seedling growth, biomass accumulation and¹⁴CO₂ fixation were determined. In isolated chloroplasts a decrease in the activities of photosystem 2 and whole electron transport chain was observed only at pH 3 and 2, but no significant change in photosystem 1 activity was observed. SDS-PAGE analysis of crude leaf extracts of ribulose 1,5-bisphosphate carboxylase (RuBPC) indicated a significant loss of 55 and 15 kDa polypeptides at pH 2 inErythrina. The reduction in the RuBPC activity in seedlings grown under acidic mists correlated well with CO₂ fixation.

Rates of whole chain and photosystem 2 activities in chloroplasts isolated fromVigna unguiculata L. seedlings grown under ultraviolet-B (UV-B) enhanced radiation were less affected by 3, 6 and 9 mM CdCl₂ for 60 min at 0 °C in the dark than the rates in chloroplasts from control plants grown under normal irradiation. The results are in agreement with changes in contents of chloroplast 55, 47, 43, 33, 29, 27-25, 23 and 17 kDa polypeptides that were significantly lowered at 3, 6 and 9 mM CdCl₂ only in chloroplasts from control plants. On the other hand, in the simultaneous treatment of chloroplast isolated from control plants the UV-B supported the inhibitory effect of all applied concentrations of CdCl₂. The photosystem 1 activity was only marginally affected in the all experimental variants.

A field experiment was carried out to investigate the effects of presoaking the wheat grains (Triticum aestivum L.) in 33 or 66 mM NaCl and indolyl-3-acetic acid (IAA at 50 g m^-3), gibberellic acid (GA₃ at 100 g m^-3) or kinetin (100 g m^-3) on some tolerance criteria in wheat flag leaf at different stages of development. At various stages of flag leaf development pretreatment with 33 or 66 mM NaCl decreased degree of succulence (particularly 66 mM), relative growth rate, net assimilation rate, relative water content, K⁺ content and K⁺/Na⁺ ratio and at the same time induced accumulation of abscisic acid and Na⁺. In the majority of cases grain pretreatment with GA₃ or kinetin and to a lesser extent with IAA alleviated either partially or completely the deleterious effect of salinity on the above mentioned parameters.

Addition of different concentrations of heavy metal ions (Hg²⁺, Cu²⁺, Ni²⁺ and Pb²⁺) inhibited the photosystem 2 catalyzed electron transport activity (H₂O→p-benzo-quinone) of the cyanobacteriumSpirulina platensis. Hg²⁺ caused the inhibition in electron transport activity in very low concentrations compared to the other metal ions. Hg²⁺ at this low concentration specifically altered the spectral properties of phycocyanin of the phycobilisomes in the intact cells ofSpirulina, whereas other heavy metal ions were ineffective in this sense.

Influence of inoculation with efficient rhizobia or nitrate fertilization in alleviating salinity (NaCl, CaCl₂ and Na₂SO₄) stress was investigated in sand culture experiments. Shoot dry mass declined beyond salinity level corresponding to electrical conductivity (EC) 5.6 dS m^-1 in control or in inoculated plants and after EC 7.4 dS m^-1 in nitrate fed ones. Root growth was more sensitive and decreased at EC 3.3 dS m^-1. Nitrate reductase activity in leaves reduced at EC 3.3 dS m^-1 but in inoculated and nitrate fed plants it reduced at EC 5.6 dS m^-1. Na⁺ accumulation increased at EC 5.6 and 7.4 dS m^-1 in roots and, shoots, respectively. In inoculated and nitrate fed plants Na⁺ content in roots increased at EC 7.4 dS m^-1. Content of Ca²⁺ increased slightly only in shoots and content of K⁺ was unaffected. Besides inoculation, application of small doses of nitrogen should prove beneficial for legume cultivation in saline soils.

The effects of 4 or 8 drought cycles on four grass species,Cenchrus pennisetiformis, Leptochloa fusca, Panicum turgidum, andPennisetum divisum were assessed in a pot experiment. There were significant differences between the species in biomass production under water stress.C. pennisetiformis andP. turgidum produced significantly greater fresh and dry matter thanP. divisum and especially thanL. fusca. L. fusca had the lowest andP. divisum highest osmotic potentials compared with the other species after the completion of 4 or 8 drought cycles. Osmotic adjustment (difference between osmotic potential of droughted/rehydrated plants and control plants) was highest inL. fusca. The stomatal conductance was significantly decreased with increased drought stress inC. pennisetiformis. The elasticity ofC. pennisetiformis, P. turgidum andP. divisum increased with increase in number of drought cycles, whereas that ofL. fusca remained unchanged.L. fusca andP. turgidum had the lowest leaf hydration of all species after 8 drought cycles. The chlorophyllsa andb in all species remained unaffected by drought treatments. The proline content ofC. pennisetiformis andL. fusca increased significantly with increased drought stress, whereas that ofP. turgidum remained unaffected after 4 or 8 drought cycles.L. fusca synthesized great amount of leaf soluble proteins during 8 drought cycles, whereasP. divisum had low protein content after 4 drought cycles. The protein contents ofC. pennisetiformis andP. turgidum remained unaffected after 8 drought cycles. The leaf epicuticular wax ofL. fusca increased consistently with increased drought stress, but leaf wax ofP. divisum increased only at the highest drought stress and that ofC. pennisetiformis andP. turgidum increased after 4 drought cycles. On the basis of these results it was established thatC. pennisetiformis andP. turgidum were the most tolerant,P. divisum intermediate, andL. fusca the most sensitive to drought stress. The osmotic adjustment did not positively correlate with the degree of drought resistance.

Limitations on photosynthesis, characterized by leaf CO₂ exchange, chlorophyll fluorescence, and thylakoid structure, were studied under environmental conditions simulating culturein vitro. These were simulated by growingPhaseolus vulgaris plants in nutrient solution under high relative humidity of air (>90%), and CO₂ concentrations (c_a) that decreased with the development of photosynthetic activities during plant ontogeny (1200 to 300 mg m^-3). The ontogeny of such model plants was more rapid, primary leaves reached photosynthetic maturity 2 to 3 d earlier and their life span was 7 to 14 d shorter than in control plants. Their photosynthetic activityin situ was limited, after reaching "photosynthetic maturity", similarly to plants grownin vitro. When measured under optimal conditions, however, 50 to 70% higher net photosynthetic rates (P_N) were found in leaves of different ages as compared with plants grown under c_a of 700 mg m^-3 and a lower air humidity (30-35%). This increase in P_N was associated with a high conductance for CO₂ transfer by adaxial and abaxial epidermes. In model plants, the dark respiration rate (R_D) was almost twice that in the control, while the photorespiration rates were similar to controls; CO₂ compensation concentration was about 50% of that in controls. The ratios P_N/R_D were similar in control and in model plants. Chlorophylla+b content in leaves of the model plants was lower than that in the control plants. Grana extent increased with plant age in the model plants while it decreased in the control ones. In both the stromal and granal membranes of the chloroplasts in model plants, a marked accumulation of carotenoids occurred independent of age. The ratio of variable to maximal fluorescence, F_v/F_m, did not differ in the model and the control plants. In the control plants, photochemical quenching (q_P) slightly increased with plant age and was not affected by CO₂ concentration present during measurement. In the model plants, q_P increased with elevated CO₂ concentration in young plants and decreased in saturating CO₂ concentrations in older plants. Nonphotochemical quenching (q_NP) was lower in the model plants and increased under CO₂ saturating conditions. Vitality index, Rfd, was markedly lower in the model plants than in the control ones and a decline was found in saturating CO₂ concentration.

Supply of 100 μM spermidine (Spd) in the nutrient solution containing 10 mM nitrate as the sole nitrogen source, increased growth of roots and shoots, total nitrogen content andin vivo orin vitro nitrate reductase (NR) activity of leaves of 10-d oldLeucaena leucocephala seedlings. Spd and the cytokinins benzyladenine or kinetin also increased growth, total nitrogen andin vivo NR activity of isolated cotyledons. The synergistic effects of nitrate, kinetin and Spd in increasing NR activity, indicate that the Spd acted at different level than the nitrate or cytokinin.

The addition of NaCl to cadmium had significant synergistic effect on the wheat root and shoot fresh mass, relative growth rate and net assimilation rate, while showed no significant effects on the dry mass production, leaf area, leaf area ratio, leaf mass ratio and specific leaf area. Additive depression of the rate of photosynthesis and the stomatal conductance was recorded, while no significant effect on the transpiration rate was observed. The Cd stress disturbed the mineral nutrition of the wheat plants either directly or indirectly, NaCl markedly reduce the uptake and internal concentration of K and Ca in the shoot. The combination of cadmium and NaCl showed no additive effects on the content of ions in the root as well as in the shoot of wheat plants.

Hybridization between the nearly extinct speciesDiplotaxis siettiana andBrassica juncea is prevented because of strong prefertilization barriers. Use of mentor pollen ofD. siettiana irradiated with 1000 Gy gamma radiation before the incompatible pollination led to fertilization. 5 d after pollination 17% ovules showed entry of pollen tubes, 10 d after pollination 27% ovules showed small globular embryos which grew no further. No embryos were found in control pollinations. Thus , use of irradiated mentor pollen brings about fertilization in this difficult cross and hybrids can be obtained if embryos are rescued.

The short term uptake of phosphate involving 10 min absorption followed by 5 min desorption, both at 30 °C, in the concentration range 1.0×10^-9 to 7.5×10^-2 M KH₂PO₄ by fresh and washed maize (Zea mays L. cv. Ganga Safed-2) roots can be described by a single isotherm having five phases (0 and I-IV) with regularly spaced kinetic constants. Almost identical kinetics were observed in both fresh and washed maize roots. The kinetics of phase 0 in the concentration range 1.0×10^-9-3.0×10^-5 M. was sigmoidal in fresh maize roots, however, in washed tissue exhibited 2 phases termed here as 0a and 0b. 0a covered the concentration range 1.0×10^-9-5.0×10^-6 M and 0b 6.0×10^-6-3.0×10^-5 M. In the concentration range 1.0×10^-4-7.5×10^-2 M four distinct phases, termed as I, II, III and IV were evident in both fresh and washed maize roots. Each phase obeyed Michaelis-Menten kinetics. The values of K_m and V_max have been estimated for each phase. The uptake isotherm was accompanied by discontinuous transitions.

Triazine treatment of thylakoid membranes isolated from the primary leaves ofZea mays L. showed an 80% inhibition of photosystem (PS) 2 activity. No detectable change of PS 1 activity was found. The inhibited membranes showed a selective reduction of the most unsaturated linolenic acid (C_18∶3) biosynthesis by about 15% coupled with a corresponding increase in stearic (C_18∶0), oleic (C_18∶1) and linoleic (C_18∶2) acids. Thus the inhibition of electron transfer of PS 2 induced by triazine treatment was followed by lipid peroxidation and changes in the thylakoid membrane fluidity.

The induction of sister chromatid exchanges (SCEs) inVicia faba root-tip cells after short-term (2 h) and long-term (24 h) treatments with alkylating agents (N-methyl-N-nitrosourea, ethyl methanesulphonate) and maleic hydrazide was studied. The primary roots were treated with mutagens before or after 5-bromodeoxyuridine (BrdU) incorporation into DNA and the influence of mutagen application on SCE induction in the cells with non- and BrdU-substituted chromosomal DNA. On the contrary, application of maleic hydrazide after the incorporation of BrdU into DNA strongly increased the rate of SCEs. The lowest limit concentrations of mutagens capable of significantly increasing SCE frequency in the cells with non-substituted DNA after the long-term treatment were estimated.

The interaction between native and introduced fungi and their effect on plant growth and mineral uptake were studied. The host plants wereLygeum spartum andAnthyllis cytisoides, the introduced fungus wasGlomus fasciculatum. The four soils used were selected from disturbed and contaminated by mining activities areas. Inoculated and uninoculated plants were grown in the unsterilized and sterilized soils (with and withouth native microflora, respectively). Plants inoculated withG. fasciculatum were higher and had higher tissue P concentration than uninoculated plants, especially inA. cytisoides. However, this inoculation was not effective in unsterilized substrates, suggesting a competition between introduced and native fungi. Concentration of mineral elements other than P varied depending on the host plant and soil. Decrease in Fe, Cu, Mn, Zn and Pb was observed in mycorrhizalA. cytiosides plants and a slight increase in Zn concentration was noted in mycorrhizalL. spartum plants. The study showed that the type of soil and their populations of native endophytes have a considerable effect on plant response to mycorrhizal symbiosis, especially in disturbed soils.

The effect of L-proline, glycinebetaine, L-and D-asparagine on rice seedling growth under NaCl stress was investigated. Glycinebetaine and L-asparagine were not effective in reducing NaCl inhibition in shoot growth of rice seedlings. L-Proline and D-asparagine were found to be able to reduce shoot growth inhibition under NaCl stress. However, L-proline, glycinebetaine, D- and L-asparagine further enhanced NaCl inhibition of root growth.

The barley (Hordeum vulgare L.) seeds were germinated in the non-saline conditions after 12 h imbibition in 2 % of NaCl solution. The results of treatment were: (l) the membrane system in meristematic cells of root tips developed well; (2) many profiles of endoplasmic reticulum and Golgi bodies appeared; and (3) the quantities of amoeboid plastids and amoeboid mitochondria increased. Thus the inhibitory effects of short-term NaCl stress on plants were reversible, and simultaneously NaCl treatment enhanced the metabolic activities in cells. The amoeboid form may be an adaptive form of plastids or mitochondria to an enhanced metabolic activity.

Decapitated pending vines are the most responsive parts of vanilla plants. Inflorescence localization along training vines showed a decreasing gradient from the decapitated end to the base in sun locality and was irregular and showed opposite gradient in shade locality. Soluble and ionic peroxidase activities, determined in the leaves and in the internodes, showed a marked peak during the end of June and a gradient along training vines which was inverse to the gradient of inflorescence localization and opposite between sun or shade conditions, supporting the utility of peroxidases as spatial and temporal biochemical markers of flowering processes.

Experiments were conducted to study the effect of plant type on canopy photosynthesis under field conditions. A chamber made of aluminium frame covered with clear plastic material was used to estimate canopy CO₂-exchange rates over a land area of 1.33 m². The plant type of maize "Shendan 7" [planophile type, original-type (OT)] was changed to erectophile type [altered-type (AT)] at silking stage. The rates of canopy apparent photosynthesis (CAP) were measured in both types of maize grown at five plant densities during the reproductive phase. It was shown that AT canopies had greater rates (about 17.2%) of CAP than did OT canopies and the yield increased by about 5.9-8.6% in AT canopies. The vertical distribution of photosynthetic photon flux density and CO₂ concentration in AT canopies were more uniform than those in OT ones. It was suggested that the compact architecture of maize canopy was excellent for photosynthesis and yield formation.

To determine some physiological parameters implicated in somatic embryogenesis in date palm (Phoenix dactylifera L.), peroxidases have been studied. Activated charcoal commonly used in date palm tissue culture as an essential antibrowning factor decreased cellular protein contents and peroxidase activities. During the first months of culture, the conventionally used medium (100 mg dm^-3 of 2,4-dichlorophenoxyacetic acid, 3 g dm^-3 charcoal) reduces 2 to 3 and 4 to 6 times protein contents and peroxidase activities, respectively, in comparison with the same one containing only 5 mg dm^-3 of 2,4-D and with or without 150 mg dm^-3 charcoal. In addition, the standard procedure decreased the embryogenic potential which is positively related to the intra- and extracellular (excreted into culture medium) peroxidase activities. In medium with embryogenic calli, extracellular peroxidase activity was three times as high as the activity determined in the same medium with non-embryogenic calli. There were two basic isoforms and four to five acidic bands characterizing the embryogenic calli. It can be suggested that peroxidases play a key role in somatic embryogenesis of date palm and the charcoal used at 3 g dm^-3 constitute a perturbating factor for this process.

The effect of 80 mM NaCl on the structure and ultrastructure of root cells ofPhaseolus vulgaris plants has been investigated. Roots of plants treated with NaCl were shorter and had less secondary roots than control plants. In control plants, epidermal cells were isodiametric and uniformly placed forming a thin layer, whereas in stressed plants, the shape and disposition of epidermal cells was less regular. The cortical cells of control plant were round-shaped and distributed allowing large and well defined intercellular spaces, whereas stressed plants presented irregular cells, which were interdigitated, thus decreasing the volume of the intercellular spaces. Presence of 80 mM NaCl did not result in significant differences in the number, shape or distribution of the cell organelles. Membrane vesiculation was often observed in cells of NaCl treated plants. Addition of 80 mM NaCl to the growth medium considerably increased the leakage of solutes from intact plant roots back to the solution especially K⁺ and Ca²⁺.