The paper gives more detailed characteristics of Arabis mosaic virus (AMV) and tomato bushy stunt virus (TBSV) isolated from lilac, the latter being identified in lilac (from plants suffering from yellow ring disease) for the first time. The isolate of TBSV from lilac, from which an antiserum with a titre of 1024 was prepared, is closely related to the artichoke strain. Information is given about two types of ringspot disease and about chlorotic ringspot of lilac. Whereas in the leaves of lilac suffering from ringspot disease (of ring mosaic type) the presence of AMV was demonstrated, the sap transmission from the leaves diseased with ringspot of linepattern (and wave-like mosaic) type failed; from the leaves affected by chlorotic ringspot a mixture of AMV and cherry leaf roll virus was identified. In addition, the polyetiological nature of "spring" mosaic and necrotic mosaic of lilac, in which bacteriumPseudomonas syringaevan Hall, was found is dealt with. The TBSV was also identified in the isolate of necrotic mosaic.Additional index words: Lilac ringspot, chlorotic ringspot, yellow ring, "spring" mosaic, necrotic mosaic, cherry leaf roll virus,Pseudomonas syringaevan Hall.

InOrobanche aegyptiaca PEES. (Orobanchaceae) the mature seed is tiny and contains a subglobose embryo which is not differentiated into radicle, hypocotyl, plumule, and cotyledons. In aseptic seed cultures on medium TB supplemented with yeast extract or coconut milk, both roots and shoot originated from the morphological radicular pole of the embryo (monopolar pattern). The bipolar mode of seedling formation, that is a shoot originating from the plumular pole and roots from the radicular pole, ensued on the basal medium THS and on TB supplemented with certain concentrations of IAA, kinetin, GA3, or strigol.

The water potential and the osmotic potential in plants which dominate Greek phryganic ecosystems (Phlomis fruticosa, Sarcopoterium spinosum, Gistus sp.) were measured from April to Nowember. Water potential decreased considerably reaching a minimum in September. Higher values of osmotic potential than that of water potential were found during dry period (i.e. negative values of pressure potential). This interesting fact was confirmed by artificial desiccation.

Three days" illumination of tissues cultured previously in darkness decreases their peroxidase activity and increases their content in phenolic compounds; conversely, when tissues cultured under continuous illumination are placed in darkness for three days, their peroxidase activity increases and their content in phenolic compounds decreases. There is an inverse relationship between the quantity of phenol compound and peroxidase activity. The isoperoxidase pattern is the same in both illuminated and not illuminated tissues.

Mycoplasma-like organisms (MLO) spread from the infectious grafts intoSolanum laciniatumAit. stock plants relatively slowly. MLO were present in all sprouts ofS. laciniatum four weeks after grafting, but the infected plants remained under glasshouse conditions mostly symptomless and flowered normally and formed fruits like healthy plants. The growth of plants with infectious tomato grafts was identical with the controls but that of plants with infectious tobacco (Nicotiana glaucaGrah.) grafts was expressively stimulated. The first flower symptoms appeared onS. laciniatum plants with tomato grafts after five and half months and on.S. laciniatum plants with tobacco grafts after seven months of graft symbiosis. Electron micrographs of ultrathin sections showed the presence of MLO in sieve tubes of potiols and midribs of the infected but symptomless plants. In the phloem parenchyma cells of the witches' broom diseased plants, highly ordered crystals were occasionally found lying in a microbody surrounded by a membrane. The possible reasons of the disease latency are discussed.

Lunulario aoid was isolated from fresh thalli ofTargionia hypophylla L. This acid was found to enhanoe the destruction of IAA by auxin-oxidase from lentil roots. Such action can explain, at least partially, its inhibitory effect on IAA-induced plant growth.

Alcohol dehydrogenase was isolated both from monocotyledons and dicotyledons, some of them with proteins (bean, pea), others with lipids (rape, sunflower) and still others with sugars (rice) as reserve substances. Molecular weights of the isolated dehydrogenases ranged from 53 000 to 80 000. Plant alcohol dehydrogenases (ADH) catalyze the oxidation of ethanol as well as the reduction of acetaldehyde. pH optimum for the oxidation is in the alkaline region, for the reduction it is near neutrality. The Michaelis constants for ethanol oxidation are, with the exception of rice, higher than those for reduction of acetaldehyde. The specificity of plant ADH toward alcohols is relatively broad and only quantitatively different in the individual plants. Inhibitors of the ADH's studied are oximes, amides and intermediates of sugar metabolism, such as malate, acetate or succinate. The degree of inhibition brought about by the inhibitors studied differs from plant to plant but the inhibition type is the same.

The alga occurring in rice fields grew in nitrogen-free medium and fixed Ca. 1.5 rng nitrogen per 50 ml of culture in 30 to 35 d of incubation period.

The evidence is presented that pollen tubes ofNicotiana tabacum L. cultivated in shaken suspension do synthesize 5S, 18S and 28S RNA. Following incubation of pollen tubes in the presence of radioactive uracil or uridine, RNA was isolated from total pollen tube material after the removal of 4S RNA, from polysomes and from 80S ribosomal particles, and fractionated by density gradient centrifugation and MAK column chromatography. The results obtained further suggest a higher rate of 5S RNA synthesis with respect to 18S+28S RNA.

The formation of polysomes in relation to RNA synthesis was investigated in tobacco (Nicotiana tabacum L.) pollen cultivated submersely for a period of 12 h. The percentage of polysomes was estimated by determining the number of ribosomes carrying nascent polypeptides using RNase and 0.8 M KC1 treatment of the ribosomal preparation. This approach showed that the proportion of ribosomes "active" in protein synthesis amounts to about 12 % in dry pollen rising to 46 % within 10 min of imbibition and to 66 % during the period 1-4 h of cultivation. The latter increase is accompanied by a rapid incorporation of uridine-¹⁴C into polysome-as-sociated RNA and is sensitive to actinomycin D.
The rapidly labelled RNA isolated from the ribosomal preparation sedirnented in the range from about 5S to 30S. Longer labelling periods led to a gradual shift of the major peak of this heterogeneous RNA from about 11.5S and 14S to about 7.5S and the development of radioactivity peaks in the position of 18S and 28S RNA. Uridine incorporated both into the active ribosomes and into the subunits of inactive ribosomes at a more or less constant rate during the whole 12-h period of cultivation.
These results present evidence that in addition to the initial combination of the existing ribosomes with the stored mRNA following imbibition, an activation of pollen tube genome and its implication in directing protein synthesis take place during the early phases of pollen tube growth. From the results on kinetics of labelling of ribosomes it appears that in pollen tubes new synthesized ribosomal subunits enter polysomes directly, the entry of 40S subunits being more rapid than that of 60S subunits.

Seed germination studies onTrichodesma amplexicaule were carried out. Seeds show abnormal behaviour of germination which is termed "Chalazal germination". This abnormal behaviour of germination is due to the presence of an obturator at the micropylar end. Seeds showed maximum (60 per cent) germination with 110 min concentrated H₂SO₄ treatment.

Photoperiodic responses of seedlings of long-day plantBrassica campestris L. cv. Ceres were investigated at different ages and varying length of inductive period. It was found that photoperiodie response increased with age. All plants flowered after one inductive cycle beginning with a light-period of 16h, but remained in the vegetative phase when kept under short-days (16h darkness, 8h light).
Both auxins (IAA and NAA) and cytokinins (kinetin and benzyladenine) inhibited flowering when applied to the plumule or via the roots immediately before the inductive photoperiod. This inhibitory effects was confined to bud formation, whereas the rate of leaf initiation remained mostly unchanged. Only high concentrations of growth substances also affected the growth of roots and leaves. These results agree, in general, with the effects of growth substances in the short-day plantChenopodium rubrum.

Epidermal conductances for water vapour transfer(gep), water vapour efflux(E), and net photosynthetic CO² uptake (P _N ) through adaxial and abaxial leaf surfaces were estimated, simultaneously during the development of water stress in primary leaves ofPhaseolus vulgaris L. Hydration level was characterized by water saturation deficit (ΔW _sat ), water potential (Τ _w ), osmotic potential (Τ₈) and pressure potential (Τ_p). The conductance of the abaxial epidermis was consistently greater than that of the adaxial epidermis, but the response of both surfaces to the increase in water stress corresponded: with increasing water stress epidermal conductances slightly increased, reached a plateau and then sharply decreased (at a rate of about 1.10x10^-6 cm s^-1 Pa^-1 and 1.55x10^-6 cm s^-1 Pa^-1 of Τ_w for adaxial and abaxial epidemics, respectively) to very low value. The curves expressing relationship between epidermal conductances and Δ W_sat, Τ_w, Τ_s, as well as Τ_p were of a similar character. E and P_N through adaxial and abaxial surfaces were practically not affected until water stress reached the "critical" value (Τ_w from - 8.2 to - 9.2 x 10⁵ Pa). With further increase in water deficit, however, they sharply decreased. The "critical" value of Τ_w was the same for both leaf surfaces.

The effect of 0.1% Metation E 50 (fenitrothion) and Fosfotion 50 (malathion) on the level of total nitrogen and that of free amino acids was investigated in juvenile and mature leaves of apple seedlings in the course of six days following treatment. Fosfotion affected both nitrogen and amino acid content to a higher degree than Metation. Fosfotion increased the total nitrogen content in all leaves, but Metation induced the change only in the leaves which were at the end of the logarithmic growth phase at the time of treatment. The level of amino acids increased on the whole, with the exception of a temporary decline in the youngest leaves as well. The treatment with both insecticides affected most the content of amides: the greatest decrease of glutamine occurred in young leaves, the highest increase in asparagine content was recorded in both juvenile and mature leaves.

Toluidine blue is known to induce gynogenic haploids in significant numbersin Populus]. Because the efficacy of a chemical in inducing gynogenesis depends largely on its effeot on pollen germination, on pollen tube growth, and on male gamete formation, the effect of toluidine blue (0, 1, 10 and 100 mgl-1) on these processes was studied in treated pistils ofSolatium nigrum (4 X), as well as on cultured pollen grains ofS. nigrum andTrigonella foenumgraecum.
Irrespective of the time of application, toluidine blue (1 and 10 mg I-1) had no effect on pollen germination or pollen tube growth in pistils ofS. nigrum; at 100 mg I-1 it invariably inhibited both the processes. Almost similar responses were elicited by cultured pollen grains. InT. foenum-graecum toluidine blue had no effeot on pollen germination and suppressed tube growth. Gamete formation was inhibited, to various degrees, at all the concentrations tested; at 100 ing I-1 hardly any pollen tube showed gamete formation. Based on our results, and those on other systems, the potentiality of toluidine blue as an inducer of gynogenesis has been analysed.

Following a 24-h exposure to a solution of polyethylene glycol 4 000 of a -12.66 bar osmotic potential the roots of maize ceased growing. The inhibition of growth was conditioned by the inhibition of cell elongation and division. The elongation of cells was substituted by their radial enlargement which took place both in the peripheral and central root parts. The cells either did not divide at all, or sporadic mitoses still occurred in the roots. The meristematic cells treated were highly vacuolized, chromatin condensation being observed in their nuclei. In contrast to growth processes, differentiation was stimulated: the formation of the secondary wall in protoxylem elements occurred at a shorter distance,i.e. 1 500-2 400 µm from the apex, in comparison with 4000-5 000 µm in the control, this evidently being caused not only by the inhibition of growth, but also by the capacity of cells to differentiate more rapidly. The changes induced by a 24-h exposure to water stress were of a reversible nature; however, a 48-h treatment brought about irreversible changes.

The water potential of wheat and barley leaves considerably decreased with the decrease of the soil moisture percentage, with the increase of the eleotrical conductivity of the soil solution and with the increase in the exchangeable sodium percentage level. Also the leaf insertion level affected the values of water potential and the most negative values were found in the top leaves.

Pretreatment with calf thymus DNA decreases the frequency of chromosomal aberrations in metaphases and anaphases induced by X-rays in barley root meristem cella. This effect is manifested in a wide range of concentrations (5% -0.001%) without any great dependence on the concentration. Calf thymus DNA alone does not induce any chromosomal aberrations in barley root meristem cells.

Epidermal features of control, 16 treated and 7 mutants ofPhysalis ixocarpa BROT. (tomatillo),Lycopersicon esculentum MILL. (tomato) andL. pimpinellifolium MILL. (currant tomato) are studied. Although the distribution, ontogenesis and mature structure of stomata in control as well as in treated and mutant plants were similar, the mutagens reduced the stomatal abnormalities which were abundant (60%) inP. ixocarpa. Maximum rectification was found after combined treatment of gamma radiation (5.16 C kg^-1 [= 20 kR]) + 1 % dimethyl sulphate. Methyl ethane sulfonate, gamma radiation and gamma radiation + DMS caused an increase in epidermal cell size irrespective of the leaf size but in DMS and diethyl sulphate treated plants, a close negative correlation between leaf size and epidermal coll size was observed. The size and frequency of stomata were also affected, the large leaf usually showed high frequency and small size stomata. The data reveal that mutagens affect the epidermal structures differently.

Irradiation of the seeds of radioresistant kohlrabi with gamma-rays causes at doses SO to 300 kR a decrease in growth and a drop in tryptophan (Try) level in seven-day-old plants. The level of glucobrassicin (GLUBR), 3-indolylacetonitrile (IAN) and gibberellic acid (GA3) in these plants increases up to a maximum with a dose of about 150-200 kR, afterwards it decreases. We assume that the specific system of auxin synthesis inBrassicaceae plants takes an important part in the reparation processes and thus in the radioresistance of these plants as well. In contrast to the divergent systems of auxin biosynthesis in other plants which are damaged by lower doses of irradiation, the specific system of auxin formation via GLUBR synthesis, under formation of IAN intermediate, is widely not. attacked by radiation. Thus, these irradiated plants are supplied with auxins and with gibberellins too, the both hormones having a radioprotective effect.

In decapitated pea plants an increased peroxidase activity ocours after the cotyledon excision in cotylars growing in axillas of cotyledons prior to the growth of excised cotylars. It was found that peroxidase plays an important role in this correlation.
Auxin applied on epicotyl stumps inhibited the growth of cotylars and the removal of this inhibition by cytokinin or ethrel was associated with an increased peroxidase activity followed by the growth of cotylars situated in axillas of treated cotyledons.