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.

The translocation of¹⁴C-ABA from roots into other parts of the plant was followed in intact and decapitated pea seedlings. In intact plants ABA from roots was translocated above all into the apical part of epicotyl. In decapitated plants the regulative ability of intact apex can be partly simulated by exogenous IAA. The growth of lateral buds occurring after decapitation was associated with an intensive flow of¹⁴C-ABA from roots into released lateral buds as late as 72 h after decapitation,i.e. in the stage of intensive elongation growth of buds.

Crystal-containing organelles in cells of virus infected plants lying at chloroplasts and mitochondria are identical with single membrane-bound microbodies containing crystals of catalase described in healthy plants. Massive complex inclusions caused by turnip mosaic virus very frequently contain the same microbodies with crystal inclusions; that phenomenon may be related to some pathophysiological changes of virus infected plants. Comparable proteinaceous crystals, but not lying within microbodies limited by a membrane, may also be found in cytoplasm of infected cells. These crystals are sometimes surrounded by a substance resembling the microbody matrix. Disintegrated cytoplasm of virus infected cells may also contain the same crystals lying free in "empty spaces". Cytopathological effects responsible for this phenomenon and possible artifacts as well are discussed.

Acid-soluble chromosomal proteins were extracted from purified nuclei, isolated from 3 - 4 h, 12 -14 h and 24 -26 h maize embryos, as well as from nuclei isolated from meris-tematic, elongating and differentiated cells, from 2 and 3-day-oldZea mays seedlings primary roots.
Using polyacrylamide gel electrophoresis (urea-acetic acid in the cylindrical gels and slab-SDS-electrophoresis), it was established that germination and root cell differentiation induced changes in some nuclear acid-soluble chromosomal proteins, especially in histone H1.
The results of proteins belonging to the high-mobility group proteins (HMG) and some other acid-soluble proteins with unknown nature for the plants, based on the electrophoretic mobility, were discussed.

Starch was determined by means of IKI reaction in shoot apices ofChenopodium rubrum plants induced to flowering by two short days and in non-induced plants. Small starch grains were already observed in the meristematic cells at an age of four days after sowing. Larger grains were found in the subapical region of the apex. Heterogeneity increases during further growth of the plants in induced, as well as in non-induced vegetative plants. Starch disappears from the cells potentially giving rise to axillary buds, while the number and size of starch grains increase in cells from which leaf primordia will be formed. This metabolic specifity of leaf and bud primordia is preserved during morphological differentiation and applies to vegetative, as well as to prefloral apices of photoperiodically induced plants. The amount of starch in the different regions of the apex is linked rather with organogenesis than with the quantitative growth in the apex.

Three short-day inductive cycles bring about inhibition followed by transitional enhancement of growth, not only in roots and leaves but also in different zones of shoot apical meristem, as shown by measurement of DNA synthesis using³H-thymidine autoradiography. The first inductive cycle resulted in marked inhibition of the cells of the central zone (CZ), rib meristem (RM), and peripheral zone (PZ). Subsequent enhancement of DNA synthesis occurs in RM during the second inductive cycle, but in CZ only in the third cycle. The growth activation in PZ is counteracted by decrease in apical dominance which results in further inhibition of leaf primordia and increases in bud primordia. In plants induced only by one cycle, which later reverse the vegetative pattern of growth and differentiation, increased DNA synthesis in RM and CZ was not observed. The significance of inhibitory and stimulatory processes in particular zones of the shoot apex is discussed considering flower morphogenesis.

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.

GA₃, cyclic AMP as well as 3'-AMP and 5'-AMP induced the formation of floral buds inImpatiens balsamina under strictly non-inductive photoperiods. While photoperiods and treatments with GA₃ or AMPs did not much affect acid phosphatase activity, AMPs increased the activity of alkaline phosphatase both in the stem and the leaves under both photoperiods. The phosphatase activity of the water- and GA₃-treated plants under inductive photoperiods was higher than that of the plants of the respective treatments under non-inductive photoperiods. GA₃ as well as all the three AMPs induced both in the stem and the leaves the formation of new isoenzymes of both these enzymes under both photoperiods.

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.

On squash preparations of anthers from pollen fertile and sterile plants of sweet pepper (Capsicum annuum L. cv. Severka) callose envelopes of microsporocytes, stained specifically with resorcin blue, were investigated microscopically. During normal course of microsporogenesis in fertile plants the envelopes remained intact up to the stage of microspore tetrads. Then callose begins to dissolve, and that from individual microspores towards the envelope periphery. In sterile analogues of the same cultivar the callose breakdown occurred precociously, usually in the course of the second, but sometimes as early as the first meiotic division of PMCs. Having completed meiosis sporadic microsporocytes formed microspore tetrads. Most PMCs contained an undivided four-nucleate protoplast rimmed with a narrow or wider unstained zone of dissolved callose. In certain cases more condensed callose septa pointing to the furrows on the surface of the PMC protoplast were well-observable in this lytic zone, as a residuum of normal mechanism of tetradogenesis.

Protein content, total and specific peroxidase activity and isoperoxidase patterns were determined in crude protein preparations from individual parts of field-grown wheat (Triticum aestivum L., cv. Jubilar). Protein content in roots, leaves, and stalks increased at the beginning of ontogenesis and then decreased from 6th, 9th, and 10th development phase (according to Feekes), respectively. Steady increase of the protein content in the ears was observed.
Highest peroxidase activity was found in the roots; it diminished from the onset of ontogenesis till maturity of the plants. In the leaves and stalks a slight decrease of peroxidase activity till the 10th development phase and then an increase till maturity was found. The ears exhibited a gradual increase of peroxidase activity. The course of specific peroxidase activity was found to be very similar to that of total activity.
Isoperoxidase patterns did not change significantly. In the leaves, a decrease of activity of C₄ and C₅ isoperoxidases was recorded. In the stalks, C l isoenzyme emerged at the end of ontogenesis. A gradual increase of A₁ and A₅ isoperoxidase intensity took place both in the leaves and stalks.

The morphoregulatory effect of FeEDTA chelating complex was verified in an androgenically more productive cultivar of tobacco White Burley and inDatura innoxia Mill. The presence of EDTA in Nitsch (1969) medium (N medium) was sufficient for the conversion of isolated embryoids and embryoids in anthers into complete plants. The androgenic development was most rapid in N medium with FeEDTA. In N medium with EDTA, the cultures developed more slowly and remained vital for a long time. In the medium without EDTA, new embryoids developed continuously. The embryoids arose and developed also in closed anthers. All embryoids which arose in anthers cultured on N medium were capable of forming complete plants. The threshold morphoregulatory concentration of FeEDTA was 40 μM FeEDTA per 1 litre of medium for embryoids in anthers and 30 μM FeEDTA per 1 litre for isolated embryoids. The dark brown colour of the anthers of tobacco andD. innoxia was due to the presence of iron (FeEDTA) in the culture medium. The morphoregulatory effect of EDTA in N medium is explained by the formation of a complex with iron present in the form of pollution of chemicals and agar. This amount of iron in complex with EDTA is sufficient for the conversion of embryoids into plants, but it is insufficient for the browning of anthers.

Different types of stress, such as hypersensitive reaction to viruses or necrotic response induced by chemical and mechanical injuries, caused similar patterns in early electrolyte leakage from discs of cowpea leaves. The electrolyte leakage, suggestive of permeability alterations, always occurred in advance of cell death. Altered permeability can therefore be considered as an aspecific response to stress and a marker of necrogenesis. No correlation was found between permeability alterations and the mechanism for virus localization, the main characteristic of the hypersensitive reaction, because tobacco rattle virus induced similar alterations in either incompatible cowpea or compatible tobacco plants. Early Ca²⁺ losses occurred following viral and abiotic necrogenic stresses. The external supply of Ca²⁺ to cowpea during the course of the hypersensitivity to viruses failed to effect pathogenesis, assessed as the number and size of the resulting necrotic local lesions, and the release of electrolyte leakage from the infected leaves. However, the external supply of Ca²⁺ counteracted the negative effect of EDTA, a chelating agent, on the resistance of cowpea leaves to cell-to-cell spread of viruses, suggesting that a Ca²⁺-deficiency may weaken the mechanism of defense of the cells against the localized viral infection.

Field trials on the effect of chlorocholinechloride (CCC) on rye plants of the cultivar Danae and of a selected population "WRS" proved that rye principally shows as reaction analogous to wheat. The CCC-induced decrease of stalk length is due to the reduction of elongation growth of the 4th internode. This shortening effect is mainly the result of decreased cell extension and, in the middle internode, additionally of inhibited cell division in longitudinal direction. The shape of internodes is changed under the influence of CCC. Walls of parenchyma cells of CCC-treated plants are thinner and those of sclerenchyma cells are thicker compared with cell walls of control plants.

The net photosynthetic rate (F), transpiration rate (Q) and water use efficiency (F/Q) of oilseed rape (Brassica campestris L. cv. Span) was studied under a range of atmospheric conditions by gas exchange techniques. The plants were at the full bloom/pod initiation stage of development at the time of measurement. The environmental conditions consisted of various levels of photosynthetically active radiation (100 to 2800 (μmol m^-2 s^-1 PAK: 400-700 nm), air temperature (10 to 42°C) and vapour pressure deficit (0.7 to 2.1 kPa VPD). The peak values ofF were recorded at 1600 μmol m^-2 s^-1 PAR, 20°C air temperature and 1.2 kPa VPD of air in the chamber.
Q increased with increasing PAR, air temperature and VPD. However, theF/Q remained high and almost constant from 600 to 1600 μmol m^-2 s^-1 PAR, but declined at the low and high photon flux densities.F/Q decreased progressively with increase in air temperature and VPD of air in the chamber.

Chlorosis induced with a supraoptimum dose of phosphorus in nutrient solution (69 mg P l^-1) was reverted by spraying of leaves of chlorotio maize plants (Zea mays L.) with FeEDTA. Biomass formation, chlorophyll and iron content were decreased in the above-ground parts of plants grown under chlorosis-inducing conditions. Spraying always decreased content of inorganic phosphorus (P_i/Fe ratio was significantly changed), increased chlorophyll content in old plants and stimulated dry mass formation at supraoptimum phosphorus doses. FeEDTA application improved phosphate utilization (portion of phosphate in organic bonds was increased). This may be the basis of chlorosis-reverting effect of FeEDTA.

The rooting response to exogenous auxin of cuttings in a juvenile phase of growth from plants ofCastanea sativa Mill. was determined and simultaneously the rooting potential of the water extracts was evaluated in presence of IAA by a bean rooting test. The level of the extractable rooting promoters was high in the cuttings which exhibited the highest percentage of rooting. An inhibition of the effect of IAA on rooting was detected in the cuttings which showed the lowest rooting response, the histogram differing not much from that of the adult plant. The results indicate that in chestnut the juvenile condition, easy rooting, is associated with high levels of endogenous rooting promoters.

Polyethylene glycol (PEG-4000) solution in concentration from 7.5 to 200 g 1-¹ rapidly induced water stress of the desirable level in primary leaves of bean plants. At the same water saturation deficit, however, the water potential as well as the osmotic potential were considerably lower in leaves of PEG - treated plants than those in leaves of plants naturally wilting due to a gradual decrease in substrate moisture.

Using differential staining of cell walls the anatomy of microsporogenesis was investigated on cross-sections of anthers of fertile plants of the sweet pepperCapsicum annuum L. cv. Severka, as well as of its sterile analogues. The lignin-like staining as observed in the microsporocyte primary walls of fertile plants disappears with their getting independent in the course of meiosis. On the contrary, in sterile plants the stain increases in intensity, the thick-walled microsporocytes usually form a continuous block up to the period of tetradogenesis, and so far as microspores originate, they are not dissociated outwards. Moreover, in sterile anthers the external tapetum is usually not differentiated.

Amaranthus viridis is a quantitative SD plant in which inflorescence primordia are initiated under both 24- and 8-h photoperiods after 12 and 10 days, when 8 and 7 leaves are differentiated, respectively. Photoperiod plays a non-determinate role, whereas the maturity of plants linked with the attainment of minimum leaf number is significant and of primary importance in floral induction. This is further confirmed by the more or less identical nature of changes in the total enzyme activity and isoenzyme patterns of peroxidase, esterase and alkaline and acid phosphatase under the two photoperiods. These changes occur once the minimum vegetative growth has been achieved prior to the reproductive transformation, irrespective of the photoperiod, pointing to the activation of a general common pathway of events leading to floral induction.

In field-grown sugar beet plants (Beta vulgaris L. cv. Dobrovická A), each of66 successive leaves produoed in the course of the vegetation period was different with respect to its photosynthetic capaoity (P_c), life span, duration of leaf area expansion, and longevity after its maximum leaf area (A_max) has developed. The proportionality between the seasonal changes in these characteristics was not the same if the sequential senescence of leaves was taken into account. With aging of individual leaves, P_c increased with the leaf area expansion having attained the peak value between 75% to 100% of A_max The rate of ontogenetic changes in P_c of each leaf was specified by the rate of its growth and development so that even at comparable ages the successive leaves constituted a series of different physiological units.
The seasonal changes in quantum irradiance (PAR) were found to be responsible for differences in the growth characteristics between the successive leaves: Leaf expansion period was related with daily integrals of the incoming PAR (Io), while leaf longevity, after the A_max had been attained, was closely linked with PAR intercepted by the canopy (I). P_c expressed per the total leaf area of the plant was significantly correlated withI, while P_c calculated per unit leaf area of the plant was related toI _o Leaf potential to adapt P_c correspondingly to changes in PAR was greatest during leaf blade expansion; after the leaf had ceased to expand, changes in P_c were independent of differences in leaf irradiance.
The results stress, at least for field conditions, the inadmissibility of the extrapolation of attributes from one leaf to the other ones sequentially senescing on the plant.

Intact maize seedlings were examined for the uptake and leakage of labelled sulphate and phosphate anions affected by temperature. Control plants, grown at 25 °C were compared from the aspects of uptake capacity and leakage with plants incubated in nutrient solutions cooled to 15 °C and 5 °C, respectively. Short time intervals as well as 1-7 d exposure to cooling were used. Already after 1 h exposure at 5 °C and 5 h cooling at 15 °C and at 5 °C, considerable changes were manifested in anion uptake and leakage.
The uptake of³²P declined more than that of³⁵S. So, after a 30 min uptake interval the uptake of³⁵S decreased at 15 °C to 49.84% and at 5 °C to 6.05% comparing with the uptake at 25 °C, while the uptake of³²P declined to 28.64% at 15 °C and to 4.45% at 5 °C. The leakage of both anions was the highest at 25 °C in absolute rates, but relatively most of the uptaken³⁵S and³²P was released at 5 °C. Longer exposure to a chilling temperature of 5 °C (1-7 days) resulted in two patterns of sulphate and phosphate uptake.

Uptake of potassium by rice plants at different stages of growth can be described by a biphasic isotherm in the range of 5 × 10^-5 M and is probably mediated bya multiphasic mechanism in the plasmalemma.

The increased activity of GOT (E.C.2.6.1.1.) and GPT (E.C.2.6.1.2.) transaminases in maize seedlings found as a marker of genotype opaque-2, was investigated in extirped sprouts of both genotypes, normal and opaque-2. The enzymatic activity was determined in three maize samples from breeding experiments, each sample consisting of a genotype pair, normal and opaque-2, collected from segregating ears of maize plants in the S₁ generation. The seedlings were aseptically grown for 7 days in two variants of cultivation, intact seedlings and sprouts extirped after 4 days of germination.
In the intact seedlings of genotype opaque-2 an increased activity of GOT and GPT, as compared to the intact normal plants, was observed. The extirpation of the sprouts enhanced GOT and GPT activity in the sprouts of both genotypes. However, in extirped sprouts the GOT and GPT activity was found to be still higher in the genotype opaque-2 as compared with the sprouts of normal genotype. Thus it seems that the increased transaminase activity in the sprouts of genotype opaque-2 is genetically determined. The increase does not result from an induction of enzyme synthesis through the supply of amino acids translocated from the endosperm to the sprouts. The absolute level of transaminases in the different breeding samples is dependent on the parenteral lines, the relative level of GOT and GPT activities is higher in the genotype opaque-2.

White mustard (Sinapis alba L.) plants, susceptible to 2,4-D, and scentless mayweed (Tripleurospermum maritimum L.) plants, resistant to 2,4-D, markedly differ in the distribution and metabolism of 2,4-D. When 2,4-D-¹⁴C was applied onto the leaf, radioactivity was found in mustard after 8 days in the entire plant, whereas in scentless mayweed radioactivity occurred mainly in the leaf onto which it was applied and in another one or two leaves, with the roots showing only traces of radioactivity. The two plant species differed both in the character and in the number and amount of metabolites detected in aqueous and ether fractions. The metabolite with R_f 0.63 -0.65, soluble in ethylether (39% of the total radioactivity applied), and that with R_f 0.35 -0.36 (23% of the total radioactivity) were present exclusively in the roots of scentless mayweed plants. The R_f values established indicate that the former metabolite may be a conjugate with the amino acids alanine and valine and the latter a hydroxylated derivate of 2,4-D. In the shoots of both plants, 2,4-D-¹⁴C was metabolized to identical metabolites with R_f 0.59 -0.61, which occurred in mustard plants only in trace amounts. Free 2,4-D-¹⁴C occurred in the shoots of both plants and in considerable amounts also in mustard roots; it could not be demonstrated in the roots of scentless mayweed. The two species did not differ in the uptake rate or in the amount of absorbed 2,4-D-¹⁴C.

In intact, decapitated and decapitated indole-3-acetic acid (IAA) treated pea seedlings the translocation of benzyl-8-^l4C-adenin (¹⁴C-BA) from the roots was studied with regard to the release of lateral buds from apex-induced inhibition. In intact plants (controls) a substantial part of the activity was found in the apical part of the epicotyl. Decapitation resulted in the initiation of growth of lateral buds. As early as 24 h after decapitation and application of¹⁴C-BA a significantly higher activity was found in growing lateral buds (cotylars) of decapitated plants than in inhibited ones of intact or IAA-treated decapitated plants. The accumulation of¹⁴C-activity in stump tops of decapitated plants treated with IAA was associated with the thickening growth.

The study was concerned with the effects of irradiation of the sodium humate on its biological activity, which was assessed by the elongation of the hypocotyl and root in young plants of lettuce (Lactuca sativa L. cv. Rapid and cv. Smaragd) growing in the solution of the tested preparation. It was found that its stimulative action on hypocotyl and root elongation in lettuce was changed due to irradiation. However, the degree was dependent on concentration; stimulation mostly decreased, only at some higher concentrations did it increase. Further, experiments showed that there was some interaction between the irradiation of the humate and the cultivar used for testing, but none between the irradiation and the light exposure of plants during the test. The response of the experimental plants to the concentration of the humate depends on the light exposure.

Shoots have been produced in the explants from flower head receptacles cultured on BDS medium with BAP and/or NAA. The shoots produced could be regenerated to form the whole plants and transplanted into soil. No morphological or cytological variations were observed in mature plants. The histological analysis of adventive bud formation is presented. The importance of this method for clonal propagation ofAllium porrum plants is discussed.