Transport of¹⁴C-IAA was studied in apple spurs of a 20-year-old McIntosh with one fruit and one shoot. Water solutions of IAA were applied to intact, pricked or scratched leaf blades, to decapitated shoots or to petioles (leaf-blade removed) at the end of June, July and August.¹⁴C-IAA (in an unknown form) was transported from intact leaves and shoots to pedicel, pericarp and seeds. Radioactivity of the pedicels increased every month while that of seeds reached maximum at the end of July and then markedly decreased in August. Total radioactivity of whole fruit doubled, at least, with every month due to enlargement of the pericarp. Pedicels deprived of fruits had their retention prolonged on spurs with leaves or shoots treated with 1% IAA in lanoline. It is assumed that auxin delivered from shoots or still growing leaves at the time of its deficiency in seeds, restrains fruits from premature dropping. At the same time seeds seem to be protected by a regulatory system in pedicel against too massive flow of auxin from outside.

Cell walls of two strains ofChlorella vulgaris (from fresh water, F, and saline water, S) and ofKirchneriella lunaris contained various proportion of saccharides and proteins (highest percentage in dry matter was found inK. lunaris). They differed also in presence of individual monosaccharides (5 inC. vulgaris F, 8 inC. vulgaris S and 6 inK. lunaris) and amino acids (11 in C.vulgaris F, 6 in C.vulgaris S and 7 inK. lunaris). Common substances were rhamnose, cystine, proline, glutamic acid and leucine.

Callus formation by fragments of cauliflower hypocotyls was favoured by raising culture medium osmolarity above -0.38 MPa. Increase in sucrose concentration while diminishing macronutrients inhibited callus initiation and growth. Root formation by the same material required a low medium osmolarity (-0.19 MPa). Reducing sucrose concentration in the classical Murashige and Skoog rooting culture medium favoured root formation. Adventitious bud formation was also depending upon medium osmolarity besides the need for a cytokinin. Reducing too much the osmotic potential of the medium had an unfavourable effect on bud neoformation. The importance of sucrose in all these processes is pointed out.

We followed the effect of storage conditions on the serological activity of the potato virus A (PVA) in the ELISA test. Storage of the purified PVA in 0.05 M borate buffer, pH 8.3 at -70°C represents the optimum conditions. The activity decreased 40% in comparison to the original activity after four months. Lyophilization of infected leaves or the leaf homogenate in the extraction buffer were found to be the best methods for the storage of the PVA in natural conditions. After 12 months, the activity of PVA decreased to 80% and 50% of the original activity in the case of lyophilized leaves and leaf homogenates, respectively.

The rates of canopy apparent photosynthesis (P_C) and canopy respiration (R_c) were studied during vegetation season in two erectophile and two planophile hybrids of maize (Zea mays L.) grown at two canopy densities [7.5 plants m^-2 (HD) and 4.5 plants m^-2 (LD)]. Large differences in P_C, R_c, R_C/P_C, leaf area index (LAI), dry matter accumulation and grain yield were found among hybrids and plant densities. Variations in P_C and R_C were associated mainly with changes in LAI. There was also found change in P_C per unit LAI with time. The average R_C/P_C was 28.9 % for all treatments throughout the vegetation season. P_C and R_C per unit dry matter were higher in LD than in HD and decreased throughout the measurement period. The HD stand had higher P_C and yield in hybrids with erectophile foliage, whereas LD stand had higher P_C after male tetrad and got higher yield in hybrids with planophile foliage. Only R_C in hybrids of the two foliage types was higher under HD than under LD throughout the vegetation period.

Sugar uptake by potato tuber discs was studied. Discs were used "fresh" or after a 24-h ageing period. It was shown that ageing increases (by 3 to 4 times) the rate of glucose and sucrose uptake. Sucrose uptake by fresh tissues was insensitive to the presence of glucose or fructose while a competitive effect was observed after ageing. This indicates the development of an invertase activity, which was inhibited by tris-buffer. Sucrose and glucose uptake by aged discs was dependent on cellular metabolism as shown by the sensitivity to low temperature and metabolic inhibitors (NaCN, DNP, CCCP). Involvement of thiol groups was demonstrated by the inhibition with NEM and PCMBS. Orthovanadate, which decreases phosphate uptake by 85 % (Poderet al. 1986) did not produce any effect on glucose and sucrose uptake by aged tissues. Fusicoccin produced only a slight stimulation (15 %). These results argue in favour of the involvement of specific ATPases in ion and sugar uptake. No involvement of a redox system was observed. ABA and BAP inhibited the uptake induced by ageing but had no effect on the endogenous sugar content. BAP would act by its effect on the amount of ATP while ABA would act at the membrane level. The results are discussed in relation to the mechanisms of transfer of glucosyl groups and to the transport of sucrose by the symplasmic pathway. Reçule

Inclusion of cadmium as cadmium chloride and nickel as nickel chloride in media differentially induced dry matter mobilisation from cotyledons of germinating pigeon pea seeds. Cadmium depressed the activities of total amylase, protease, acid phosphatase and peroxidase in germinating seeds. The activities of these enzymes were stimulated at the lower concentrations of nickel and suppressed at the higher ones. This dual response of hydrolytic enzymes to cadmium and nickel is postulated to account for the promotory and inhibitory effects of these heavy metals on dry matter mobilisation.

SC₂ and SC₃ progenies of nineteenin vitro regenerated barley plants (SC₁) from resistant calli selected against purified culture filtrate ofHelminthosporium sativum and one parent 'Dissa' genotype were studied for stability of resistance and protein, soluble protein, maltose and saccharose contents. Cytological studies were also carried out on the SC₃ generation. Stability of resistance toHelminthosporium sativum was found in 50% of the somaclonal lines. Significant variation among different somaclonal lines and among different callus lines from which the plants were regenerated were found for yield, disease score and biochemical characters assessed except saccharose content in the somaclonal lines. Significant increase and decrease over the donor parent for most of the characters were obtained. Cytological abnormalities such as multilobed nuclei, multinucleate cells, abnormal anaphase and mixoploidy were also observed.

The dependence of luciferase activity in the homogenate of leaves of transgenic tobacco plants with chimeric firefly luciferase gene on ATP concentration and temperature was studied. The optimum ATP concentration was between 0.625 mM and 2.5 mM. The activity rapidly decreased if the homogenate was kept in 25°C and is completely lost during 30 min.

The rates of uptake of exogenous L[U-¹⁴C] aspartate and glutamate into tissues of vegetative growing tips ofFucus serratus and their metabolism were studied in the dark. In these non-photosynthetic conditions, aspartate was fixed and metabolically converted more rapidly than glutamate. Radioactivity from¹⁴C-aspartate was principally transferred into glutamate. On the other hand, metabolism of absorbed¹⁴C-glutamate was very slow and its rate did not increase during incubation time, but produced more diversified soluble radioactive compounds. Thus inF. serratus, glutamate principally seems to be in the dark more a temporary¹⁴CO₂ storage product coming from β-carboxylation than a rapidly turned over intermediate.

Water and K⁺ fluxes were examined in detopped plants ofZea mays L. (cv. White Horse Tooth), which were grown and exuded on half-strength Long Ashton nutrient solution containing the appropriate concentration of Zn²⁺ at 20 °C. In light-grown plants, 100 and 500 μM Zn²⁺ increased both water and K⁺ fluxes in detopped maize plants whereas 1 000 μM Zn²⁺ inhibited both fluxes. In the dark-pretreated plants, 1 000 μM Zn²⁺ in the medium stimulated K⁺ flux. The fluxes of K⁺, Zn²⁺, Ca²⁺ and Mg²⁺ were usually higher in detopped plants than in intact ones. At 1 000 μM Zn²⁺ in the exudation medium, Zn²⁺ concentration was higher in the xylem exudate of dark-pretreated plants than in roots of plants maintained in light. The results are discussed in relation to the influence of Zn²⁺ on the membrane permeability and transport in plants.

Chlorophyll (Chl) synthesis in isolated Scots pine embryos depended on exogenous application of cytokinin (CK) and Ca²⁺. At a constant benzyladenine (BA) level (4.4×10^-5 M) 10^-4 to 10^-2 M Ca²⁺ concentrations in mineral medium were optimum for Chl biosynthesis under both light and dark. At a zero or very low (10^-6 M) concentration of external Ca²⁺, Chl synthesis was relatively more Ca²⁺-dependent in embryos cultured in darkness than in the light, which suggested that the light: (a) stimulated the transport of Ca²⁺ from external sources to cytosol, and/or (b) interacted with Ca²⁺ directly in the pathway of Chl biosynthesis. The need of external Ca²⁺ was evidenced in experiments with modulators of Ca²⁺-transport systems. The reduction of the inward current of Ca²⁺ from readily accessible external sites by chelating agent (ethylene glycol-bis (beta-aminoethyl ether-N,N,N'N'-tetraacetic acid, EGTA) and Ca²⁺-channel blockers canceled the formation of Chl. The effect of EGTA depended on the level of external Ca²⁺. Inhibitory action of Ca²⁺-channel blockers depended on their kind and concentration: at the 10^-5 M concentration La³⁺>verapamil>nifedipine inhibited Chl formation. In the presence of Ca²⁺, the Ca²⁺-agonist A 23187 mimicked the BA effect and about 92% of Chl was synthesized as compared with the BA variant. Low concentrations of calmodulin antagonists reduced the amounts of Chl. Calmodulin was included in a second messenger system for BA action in promoting Chl biosynthesis in isolated Scots pine embryos.

The protein coding region of theE. coli DNA repair geneada combined with the CaMV 35S promoter has been transferred to tobacco by means ofAgrobacterium tumefaciens Ti plasmid. In transgenic plants having theada gene in a sense orientation, detectable amounts of O⁶-alkylguanine-DNA-alkyltransferase has been found whereas in non-transformed plants this activity is absent. Cell suspension cultures derived from the former plants showed lower sensitivity to the toxic (growth inhibiting) effects of the bifunctional alkylating agent 1-(2-chloroethyl)-1-nitroso-3-(aminomethyl-1,3-diazinylo)-methylurea compared with cell cultures derived from a control non-transformed plant or from transgenic plants harbouring theada gene in an opposite, non-sense orientation.

Increasing salinity induced a marked reduction in the plant growth, thoughPhaseolus seedlings tolerated salinity up to 120 mM NaCI. A great reduction in sugar and protein contents occurred with increasing salinity, whereas soluble nitrogen compounds and the relative contents of the photosynthetic pigments were increased in the treated plants. Increasing Ca concentration in the salinized medium appeared to improve the plant growth and to increase the contents of saccharides and proteins in the NaCl-treated plants. This suggests that Ca could be added to salinized media to overcome the deleterious effects of salinity on the growth and productivity of leguminous crop plants.

The antagonistic effects of some growth regulators [i.e. indol-3-yl-acetic acid (IAA), gibberellic acid (GA₃) or kinetin] on stress imposed by sea water on leaf area, pigment and photosynthetic activity in leaves of broad bean plants at different stages of development were investigated. Seed priming with GA₃ alleviated either partially or completely the effects induced by the two levels of sea water (10 and 25 %) used on leaf area at all experimental stages. However, IAA, GA₃ and kinetin inhibited leaf growth by themselves in almost all measurements. Seed pretreatment with kinetin alleviated the inhibition of pigment production in sea water-irrigated plants. Furthermore, GA₃ or kinetin nullified the deleterious effects imposed by irrigation with sea water particularly the high level (25 %) on photosynthetic¹⁴CO₂ fixation.

Following harvest, Kinnow mandarin (Citrus nobilis × Citrus deliciosa) fruits were variously treated with gibberellins (GA) and cytokinins. Ethylene caused marked chlorophyll (Chl) degradation and its effect was partially reversed by kinetin and benzylaminopurine (BAP) and to a lesser extent by GA₃ and GA₄₊₇. No appreciable accumulation of carotenoids (Car) occurred in these fruits irrespective of treatment. The loss of Chl during natural maturation was significantly reduced by cytokinins. Treatments with gibberellins alone or in combination with cytokinins were much less effective. The reduced loss of Chl in response to exogenously applied cytokinins may be probably related to a decline in its endogenous levels.

Ovules ofMelandrium album, attached to the placentas and containing immature embryo sacs, were culturedin vitro. The embryo sacs developed according to thePolygonum type but about 70% of them degenerated during the culture. Gametophytes of a non-typical structure were found in a few ovules,i.e. there appeared more nuclei or cells as in thePolygonum type and the arrangement of nuclei or cells was not true to type. Several-celled structures observed in some embryo sacs were recognized as gynogenetic embryoids.

Selected factors affecting somatic embryogenesis efficiency have been studied, namely genotype, explant type and its orientation in the medium, different basal media, different auxins for somatic embryo induction, and two ways of donor plant cultivation. The key role is played by genotype and auxin used, the minimum effect was observed due to basal media. In the series of subsequent experiments we have found the best combination of individual factors as follows: cv. Altona, 10 uM 2,4-D, L2 basal medium, central part of immature cotyledon as initial expiant oriented by adaxial side down on the agar medium, and field grown donor plants. This combination exhibited 100 % embryogenic explants with 5.43 ± 0.65 somatic embryos per expiant,i.e. somatic embryogenesis efficiency 5.43.

Multiple shoots (16-20 shoots per expiant) were induced from cotyledonary node region ofAnogeissus acuminata (Roxb. ex DC.) Guill. & Perr. on Murashige and Skoog's (MS) medium containing IAA 0.1 mg 1^-1 + BAP 1.5 mg 1^-1 and ascorbic acid 50 mg 1^-1, citric acid 25.0 mg 1^-1, arginine 25 mg 1^-1 and adenine sulphate 25 mg 1^-1. From the first node of seedling only 4-6 shoots per expiant were proliferated. Segments ofin vitro produced shoots were used as expiants for further multiplication of shoots upto 16 successive cultures at an interval of 4 week on MS medium with IAA 0.1 mg 1^-1 + BAP 1.0 mg 1^-1 and additives. The original cotyledonary expiant was repeatedly subcultured upto 4 times after harvesting crop of shoots, each time.In vitro produced shoots were rooted on half strength MS medium containing 0.5 mg 1^-1 IBA. Plantlets were transferred to pots. Other expiants (cotyledons, hypocotyl, and leaf) produced callus on medium containing auxins and cytokinins. The calluses differentiated into embryo like structures or roots on MS medium.

Floral induction in the long day plant spinach (Spinacia oleracea) has been shown to be accompanied by a thickening of plasmalemma. This change was observed at early evocation, in both shoot apices and leaves, as well as after inducing GA₃ treatment. To get further information on this thickening, plasma membranes from spinach leaves were isolated, in the present study, using aqueous two phase partitioning and the effect of variousin vitro treatments on their thickness was investigated. The average plasmalemma thickness was unaffected by Na⁺ and K⁺ ions. It was increased upon the effect of either Ca²⁺ or gibberellic acid. A thickening of plasmalemma was also observed when plasma membranes from vegetative plants were incubated with a cytosolic preparation from photoinduced plants. The results were discussed in relation with the plasmalemma modifications previously reported in spinach.

The fungal colonization of the angiosperm root parasiteCynomorium coccineum and the halophytic hostsLimonium delicatulum andArthrocnemum glaucum were investigated in a Mediterranean salt marsh in March 1992. The main fungal inhabitants on the leaves or shoot surface of the test plants wereAspergillus niger, Penicillium chrysogenum andCladosporium herbarum. The qualitative analysis of the fungal species associating the parasite, the hosts and the non-infected plants showed similar pattern. However, the total population exhibited quantitative differences coupled with the amount and the chemical composition of the exudates on plant surface and the quantity of transpired water. The fungal catch from the aerial shoot (inflorescence) of the parasite was higher than that collected from either the leaves or aerial shoots of non-infected or host plants. The fungal density on the leaves ofL. delicatulum was higher than those isolated from the aerial shoots ofA. glaucum. Infection byC. coccineum caused a marked drop in the total fungal population on leaves or shoot surfaces of the hosts as compared to the corresponding non-infected individuals. The stimulative effect of washings on spore germination of some isolated fungal species was matched with the density of fungi on the target plants.

The effect of salinity on vacuolar pH was studied in carrot (Daucus carota L.) cells grown in liquid suspension culture either in the absence or presence of 150 mM NaCl. Both vacuolar and cytoplasmic pH were determined by several independent techniques. These techniques were NMR spectrometry, distribution of radioactive probes and spectrophotometric measurement of the absorbance changes of a naturally occurring vacuolar pH indicator. There was no difference in the cytoplasmic pH between cells grown in the presence or the absence of NaCl, but the vacuolar pH of cells grown in the presence of NaCl was higher by 0.38 to 1.05 pH units (depending on the technique that was used) than the vacuolar pH of cells grown in the absence of NaCl.