The respiration of young coho Oncorhynchus kisutch at gradually declining oxygen levels and during recovery from oxygen deprivation

The respiration of coho salmon, Oncorhynchus kisutch , weighing between 15 and 50 g was measured at gradually declining oxygen levels and at temperatures ranging between 14 and 17°C. The maximum and minimum oxygen concentrations tested were 250 and 40 μmol L⁻¹, respectively. Respiration rates were measured for 1 h periods before oxygen concentration was lowered by 12.5 or 25.0 μmol oxygen L⁻¹. At the end of these endurance tests the oxygen level was returned to normoxic conditions and respiration rates were determined for the recovery period. Under normoxic conditions (> 200 μmol L⁻¹) the respiration of coho levelled around 5.1 μmol g⁻¹ wet weight h⁻¹. At intermediate levels between 150 and 200 μmol oxygen L⁻¹, the average rate increased to 5.8 μmol g⁻¹ h⁻¹, which could be attributed to higher spontaneous activity of the test animals. At low oxygen levels (< 150 μmol⁻¹) average respiration rates dropped to values between 5.5 and 5.7 μmol g⁻¹ h⁻¹, reaching a minimum of 3.8 μmol g⁻¹ h⁻¹ at oxygen levels below 50 μmol L^μ. First mortality was observed in this range. After exposure to reduced oxygen levels the fish maintained a higher respiration rate when again exposed to normoxic oxygen levels above 200 μmol L⁻¹. Increased respiration rates were observed for a recovery period of 6 h.     

Polyamines in marine macroalgae: Levels of putrescine, spermidine and spermine in the thalli and changes in their concentration during glycerol-induced cell growth in vitro

The levels of putrescine (Put), spermidine (Spd) and spermine (Spm) were analyzed in naturally collected samples of the marine macroalgae Dyctiota dichotoma, Gelidium canariensis and Grateloupia doryphora . Polyamines (PAs) appeared in free (35–134 μg g⁻¹ fresh weight) and bound TCA-insoluble form (1 667–2 624 μg g⁻¹ fresh weight). Axenic in vitro cultures of sporelings from G. doryphora were established in the medium containing glycerol. This medium promoted growth and morphogenesis and also increased the free and bound PA levels in the sporelings. Tracer experiments using 70 kBq [U-¹⁴C]-glycerol showed significant quantities of radioactivity in Put, Spd and Spm after 20 h of incubation. The effects of glycerol on growth were inhibited by the ornithine decarboxylase (EC 4.1.1.17) inhibitor α -difluoromethylornithine (DFMO). The presence of DFMO in the incubation medium with [U-¹⁴C]-glycerol also reduced the radioactivity in PAs.     

Biochemical changes associated with the ripening of hot pepper fruit

Hot pepper ( Capsicum annuum L. cv. Chooraehong) fruit underwent a respiratory climacteric during ripening. However, the rate of ethylene production was low, reaching a maximum of approximately 0.7 μl kg⁻¹ h⁻¹ at the climacteric peak when the surface color was 30 to 40% red. Ripening was accompanied by a loss of galactose and arabinose residues from the cell wall. The content of uronic acid and cellulose in the wall changed only slightly during ripening. The average molecular weight of a cell wall hemicellulosic fraction shifted progressively toward a lower molecular weight during ripening. Total β-galactosidase (EC 3.2.1.23) activity increased 50-fold from the immature green to the red ripe stage. No polygalacturonase (EC 3.2.1.15) activity was detected at any stage of ripeness. Thus, the loss of galactose and arabinose residues from the cell wall, as well as the observed modification of hemicelluloses during ripening, seem to be unrelated to active polygalacturonase. Soluble polyuronide content remained relatively constant at approximately 60 μg (g fresh weight)⁻¹ as fruit ripended.     

The effects of water hardness upon the uptake, accumulation and excretion of zinc in the brown trout, Salmo trutta L.

The effects of water hardness (9 and 220 mgl⁻¹ as CaCO₃) upon zinc exchange in brown trout exposed to 0.77 μmol Zn 1⁻¹ have been investigated using artificial soft water (<49.9 μmol Ca ^l-1, <40.1 μmol Mg 1⁻¹) and mains hard water (1671.7 μmol Ca 1⁻¹, 493.6 μmol Mg 1⁻¹) of known composition. Both hard and soft water-adapted fish exhibited a bimodal pattern of net zinc influx. Net zinc influxes during both fast and slow uptake phases were significantly greater ( P <0.001) in soft (82.9 and 6.2 μmol Zn 100 g⁻¹ h⁻¹) than in hard water (46.3 and 2.4 μmol Zn 100 g h⁻¹). Zinc efflux (- 0.2 μmol Zn 100 g⁻¹ h⁻¹) was enhanced only in hard water during the slow net influx phase.
Brown trout exposed to zinc in hard water and placed in metal-free media exhibited a greater net efflux (- 25.6 μmol Zn 100 g⁻¹ h⁻¹) of the metal than did fish in soft water (-4.2 μmol Zn 100 g⁻¹ h⁻¹) treated in the same manner. Tissue ⁶⁵Zn activities reflected both the differences in uptake and excretion rates of the metal between hard and soft water fish. During zinc exposure (0.77 μmol Zn 1⁻¹) high water hardness reduced tissue burdens of the metal by reducing net branchial influx, and enhancing efflux of the metal in hard water fish.     

Polyamines in normal and auxin-induced strawberry fruit development

The possible involvement of polyamines during strawberry ( Fragaria × ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g⁻¹ fresh weight at pollination to a minimum of 55 nmol g⁻¹ fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g⁻¹ fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re-initiation of growth by application of 1 m M α-naphtaleneacetic acid (α-NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased >3-fold in normally developing receptacles and in de-achened, auxin-treated receptacles 10 days after removal of achenes, but did not increase during this period in de-achened receptacles not treated with exogenous auxin. α-NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β-NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de-achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.     

Polyamines in normal and auxin-induced strawberry fruit development

The possible involvement of polyamines during strawberry ( Fragaria x ananassa Duch.) fruit development was investigated. Putrescine, spermidine, and spermine were identified in strawberry receptacles and achenes at all stages of development. Total (free) polyamine levels decreased from a maximum of 485 nmol g⁻¹ fresh weight at pollination to a minimum of 55 nmol g⁻¹ fresh weight in ripe receptacles. Total polyamine concentrations during corresponding stages of development were consistently higher in achenes than in receptacles, and ranged from 891 to 203 nmol g⁻¹ fresh weight. Removal of achenes from the surface of developing receptacles 10 days after pollination reduced receptacle growth, and re-initiation of growth by application of 1 m M α-naphtaleneacetic acid (α-NAA) was accompanied by a rapid increase in polyamine concentrations 24 h after treatment. Polyamine content per receptacle increased >3-fold in normally developing receptacles and in de-achened, auxin-treated receptacles 10 days after removal of achenes, but did not increase during this period in de-achened receptacles not treated with exogenous auxin. α-NAA increased growth and polyamine levels to a greater extent than the structurally related, but less effective auxin, β-NAA. Polyamine concentrations in receptacles with intact achenes remained similar to those of auxin depleted (de-achened) receptacles, implying that the concentration of these compounds may not be limiting following achene removal.     

Cytokinins and fruit development in the kiwifruit (Actinidia deliciosa). I. Changes during fruit development

The cytokinin content in fruit tissue of the kiwifruit ( Actinidia deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv. Hayward) was monitored during fruit development to identify which cytokinins were present and if they were linked with specific stages of fruit growth. Cytokinins were isolated and purified by column chromatography and high-performance liquid chromatography and quantified by radioimmunoassay. A novel HPLC step utilising an amine column was successfully introduced as a preparative step in the separation of the O - and 9-glucosides from the free bases and ribosides. The radioimmunoassay results were validated, and the different cytokinins identified, by gas chromatography-mass spectrometry. Cytokinins detected in fruit included the cytokinin free bases, zeatin and isopentenyladenine, their ribosides, nucleotides and both O - and 9-glucosides. Both qualitative and quantitative changes of the cytokinins occurred during fruit development. A decrease in cytokinin concentration occurred after anthesis (from 342 pmol g⁻¹ fresh weight at anthesis to 41 pmol g⁻¹ fresh weight 27 days after anthesis). A large increase in cytokinin concentration and content per fruit occurred as the fruit reached commercial maturity (to 1900 pmol g⁻¹ fresh weight). Individual cytokinins showed quite different patterns. Zeatin, in particular, showed a peak in concentration (13 pmol g⁻¹ fresh weight) 11 days after anthesis that correlated with the beginning of the cell division phase of fruit growth. The accumulation of cytokinin (mostly zeatin riboside or zeatin nucleotide) in mature fruit may be of significance for the postharvest storage of kiwifruit fruit.     

Ethylene synthesis and growth in embryogenic tissue of Norway spruce: Effects of oxygen, 1-aminocyclopropane-1-carboxylic acid, benzyladenine and 2,4-dichlorophenoxyacetic acid

Ethylene production from an embryogenic culture of Norway spruce ( Picea abies L.) was generally low. ca 2.5 nl g⁻¹ h⁻¹, whereas 1-aminocyclopropane-1 -carboxylic acid (ACC) concentration was high, fluctuating between 50 and 500 nmol g⁻¹ during the 11-day incubation period. Hypoxia (2.5 and 5 kPa O₂) rapidly inhibited ethylene production without subsequent accumulation of ACC. Exogenous ACC (1, 10 and 100 μ M ) did not increase ethylene production, but the highest concentrations inhibited tissue growth. Ethylene (7 μl I⁻¹) did not inhibit growth either when supplied as ethephon in the medium or in a continuous flow system. Benzyladenine (BA) had little effect on ethylene production, although it was necessary for sustaining the ACC level. Omission of 2.4-dichloro-phenoxyacetic acid (2.4-D) from the medium caused ethylene production to increase from about 2.5 to 7 nl g⁻¹ h⁻¹ within the 11-day incubation period. Although 2.4-D did not specifically alter the endogenous level of ACC, the lowest ACC level, 33 nmol g⁻¹, was observed in tissue treated with 2.4-D (22.5 μ M ) and no BA for 11 days. Data from this treatment were used to estimate the kinetic constants for ACC oxidase, the apparent K_m was 50 μ M and V_max 2.7 nl g⁻¹ h⁻¹. Growth of the tissue was strongly inhibited by 2.4-D in the absence of BA, but weakly in the presence of BA (4.4 μ M ). The results suggest that ethylene or ACC may be involved in the induction of embryogenic tissue and in the early stages of embryo maturation.     

Phenolic compounds in peach (Prunus persica) cultivars at harvest and during fruit maturation

Six peach and six nectarine cultivars were evaluated for the phenolic content in their pulp and peel tissues. Chlorogenic acid, catechin, epicatechin, rutin and cyanidin-3-glucoside were detected as the main phenolic compounds of ripened fruits. The concentration was always higher in peel tissue, with average values ranging from 1 to 8 mg g⁻¹ dry weight (DW) depending on cultivar. Of the tested varieties, the white-flesh nectarine 'Silver Rome' emerged as the cultivar with the highest amount of total phenolics. Phenolic compounds were also profiled during fruit growth and ripening in the yellow nectarine cv. 'Stark Red Gold', which showed a decreasing concentration during fruit development in both peel and pulp tissues. Average amounts of total phenolics were approximately 25 mg g⁻¹ DW 60 days after full bloom and decreased to 3 mg g⁻¹ DW at ripening in pulp tissue. Differences among peel and pulp composition show the different dietetic and antioxidant potential of fruits consumed unpeeled and peeled.     

Estimation of the bioenergetic costs of fruit and other organ synthesis in apple

The specific bioenergetic cost of apple fruit ( Malus domestica Borkh. cv. Braeburn) growth was calculated from seasonal elemental analysis (for carbon, hydrogen, nitrogen, and sulphur) and ash data. Specific cost changed during fruit development and at harvest was 1.16 g glucose g⁻¹ dry weight of which 0.142 g glucose g⁻¹ dry weight was consumed in growth respiration. Comparisons of those end-of-season values with those from a range of other apple cultivars (early through late maturing, and with a range of sugar/acid ratios) showed little difference, despite variations in elemental composition. Specific costs ranged between 1.15 and 1.16 g glucose g⁻¹ dry weight, and growth respiration between 0.136 and 0.148 g glucose g⁻¹ dry weight. Specific costs were also calculated for leaves (extension and spur), wood (1 and 2 year), and trunk and roots (fine and coarse). Leaves had the greatest cost (mean 1.44 g glucose g⁻¹ dry weight), then wood and trunk (mean 1.38 g glucose g⁻¹ dry weight), and fruit had the smallest. Specific growth costs were also calculated from heats of combustion data. Little difference was observed between the two methods, but the values calculated from the elemental analysis data tended to be higher than those calculated from the heats of combustion data.     

Species of Anguilla as indicators of mercury in the coastal rivers and lakes of Victoria, Australia

Mercury concentrations in the axial muscle tissue of most (243) of the 254 Anguilla australis and most (20) of the 27 A. reinhardtii collected from 30 sites in coastal rivers and lakes in Victoria, Australia, during 1975–78 were well below the Australian statutory health limit (0.5 μg g⁻¹ wet weight). For A. australis the mean mercury concentration was 0.17 μg g⁻¹ (±0.16 s.d. , range 0.01–1.60 μg g⁻¹); for A. reinhardtii the values were 0.37 ± 0.23 μg g⁻¹ (range 0.12–1.10 μg g⁻¹). Statistical analyses showed that variation in mercury concentration due to total length accounted for only 13% of the total variation in A. australis and 2% in A. reinhardtii whereas locality accounted for 54 and 68%, respectively. Both species are thus considered suitable as indicators of mercury pollution.     

Development and accumulation of ABA in fluridone-treated and drought-stressed Vicia faba plants under different light conditions

The effects of fluridone on guard cell morphology, chloroplast ultrastructure and accumulation of drought stress-induced abscisic acid (ABA) were studied in Vicia faba L. plants grown under different light conditions. Drought stress was induced by allowing the leaves to lose 12% of their fresh weight. The appearance of defective and undeveloped stomata, and chloroplasts with a destroyed thylakoid membrane system was found in fluridone-treated plants grown at a photosynthetic photon flux (PPF) of 600 μmol m^-2 s^-1. Plants grown at a PPF of 40 μmol m^-2 s^-1 had diminished levels of ABA after imposition of dehydration. Fluridone treatment reduced the level of ABA in both unstressed and dehydrated leaves. Accumulation of ABA in the control plants was considerably reduced when they were exposed to dark periods of 24, 48 and 72 h just before imposition of the stress. Twenty-four hours after the dark treatment dehydration of the leaves resulted in a 3-fold decrease in the level of stress-induced ABA, and 72 h after dark treatment the amount of stress-induced ABA approximated the prestressed values. Fluridone-treated plants failed to accumulate ABA under water stress. In addition to functionally active chloroplasts, well-developed and functional stomata are required for drought stress to elicit a rise in ABA.     

Anti-bacterial activity of synthetic N-heterocyclic oxidizing compounds

Synthetic chlorochromate derivatives of pyridine and quinoline were active in vitro against type cultures of Escherichia coli (ATCC 128), Staphylococcus aureus (ATCC 14775), Pseudomonas aeruginosa (ATCC 10145) and Bacillus subtilis (NCTC 8236). The minimum inhibitory concentrations (MIC) were 125–250 μg ml⁻¹ and 250–500 μg ml⁻¹ for pyridinium chlorochromate and quinolinium chlorochromate, respectively. An established derivative of quinoline (Perfloxacin) had an MIC of 125–250 μg ml⁻¹. The extinction time for 10⁵ cfu in broth was 90 min for pyridinium chlorochromate and 120 min for quinolinium chlorochromate, except for B. subtilis which survived up to about 180 min and 360 min. A combination of the two compounds produced an antagonistic effect. The 50% lethal dose (LD₅₀ toxicity) in mice was estimated at 76 μg g⁻¹ and 33 μg g⁻¹ body weight for the quinolinium and pyridinium chlorochromates. The compounds also exhibited some potential for suppressing a simulated staphylococcal infection in mice at the dosage levels of ca 22 μg g⁻¹ for pyridinium chlorochromate and 45 μg g⁻¹ for quinolinium chlorochromate.     

Uptake kinetics of iron-phytosiderophores in two maize genotypes differing in iron efficiency

Iron inefficiency in the maize ( Zea mays L.) mutant ysl is caused by a defect in the uptake system for Fe-phytosiderophores. To characterize this defect further, the uptake kinetics of Fe-phytosiderophores in ysl was compared to the Fe-efficient maize cultivar Alice. Short-term uptake of ⁵⁹Fe-labeled Fe-deoxymugineic acid (Fe-DMA) was measured over a concentration range of 0.03 to 300 μM. Iron uptake in Fe-deficient plants followed Michaelis-Menten kinetics up to about 30 μM and was linear at higher concentrations, indicating two kinetically distinct components in the uptake of Fe-phytosiderophores. The saturable component had similar K_m (∼ 10 μM) in both genotypes. In contrast. V_max was 5.5 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in Alice, but only 0.6 μmol Fe-DMA g⁻¹ dry weight [30 min]⁻¹ in _ysl. Uptake experiments with double-labeled ⁵⁹Fe-[¹⁴C]DMA suggest that in both cultivars Fe-DMA was taken up by the roots as the intact chelate. The results indicate the existence of a high-affinity and a low-affinity uptake system mediating Fe-phytosiderophore transport across the root plasma membrane in maize. Apparently, the mutation responsible for Fe inefficiency in ysl affected high-affected uptake and led to a decrease in activity and/or number of Fe-phytosiderophore transporters.     

Regulation of phosphate influx in barley roots: Effects of phosphate deprivation and reduction of influx with provision of orthophosphate

Barley plants were grown in nutrient solutions, which were maintained at either 0 (-P) or 15 μ M orthophosphate (+P). After 11 days phosphate influx into the intact roots of the -P plants began to increase by comparison with +P plants. During this period differences became apparent between the treatments in absolute growth rates, as well as in the root:shoot ratios. Phosphate influx in the -P plants continued to increase as a function of time, to a maximum value of 2.4 μmol (g fresh wt)^-1h^-1 at 16 days after germination. This rate was 6 times higher than influx values for +P plants of the same age. During the period of enhanced uptake phosphate was strongly correlated (r²= 0.77) with root organic phosphate concentration. – The enhancement of inorganic phosphate influx into intact roots of -P plants was rapidly reduced by the provision of 15 μ M orthophosphate. Typically, within 4 h of exposure to this concentration of phosphate, influx values fell from 1.80 ± 0.20 to 0.75 ± 0.03 μmol (g fresh wt)^-1 h^-1, while inorganic phosphate concentrations of the roots increased from 0.12 to 1.15 μmol (g fresh wt)^-1 during the same period. Hill plots of the influx data obtained during this period, treating root inorganic phosphate as an inhibitor of influx, gave Hill coefficients close to 2. The rapidity of the reduction of influx associated with increased root inorganic phosphate together with the Hill plot data provide evidence for an allosteric inhibition of influx by internal inorganic phosphate.     

Antioxidant status of anoxia-tolerant and -intolerant plant species under anoxia and reaeration

The redox potential of the cell, as well as the antioxidant status of the tissue, are considered to be important regulatory constituents in an adaptive response in plants. Here the involvement of active antioxidants ascorbic acid (AA), reduced glutathione (GSH) and α - and β -tocopherols in reactive oxygen species scavenging, and the effect of anoxic stress on their reduction state were studied in 4 anoxia-tolerant and -intolerant plant species: Iris germanica L., Iris pseudacorus L., wheat ( Triticum aestivum L. cv. Leningradka) and rice ( Oryza sativa L. cv. VNIIR). The initial antioxidant content (both AA and GSH) was higher in the rhizomes of the more anoxia-tolerant Iris spp., as compared with that of the roots of the cereals. The predominant form of ascorbate was dehydroascorbic acid (DHA) in the cereals and AA in the Iris spp. Imposition of anoxia with subsequent reoxygenation resulted in an overall depletion of the reduced forms of antioxidants. No concurrent increase in oxidised forms (DHA and conjugated glutathione) was observed in anoxic samples. α -tocopherol content in Iris spp. was in the range 1–2 μg g⁻¹ fresh weight, while β -tocopherol content was higher in the anoxia-intolerant I. germanica (7.2 μg g⁻¹ fresh weight) as compared with the tolerant I. pseudacorus (1.5 μg g⁻¹ fresh weight). In I. pseudacorus , a significant decrease in α - and β -tocopherol levels was observed only after long-term (45 days) anoxia. The results suggested exclusion of AA and GSH from the redox cycling under prolonged anoxia, and a concomitant decrease in the redox state, as well as an anoxia-induced depletion of α - and β -tocopherols.     

Ammonium ion affecting tylosin production by Streptomyces fradiae NRRL 2702 in continuous culture

Nitrogen regulation in tylosin production by Streptomyces fradiae NRRL 2702 was studied in chemostat culture using a soluble synthetic medium. The maximum value of specific tylosin formation rate ( q _TYL) was 1·13 mg g⁻¹ h⁻¹ at the specific growth rate (μ) of 0·05 h⁻¹, and q _TYL decreased with increasing levels of the specific growth rate after reaching a rate of 0·1 h⁻¹. The optimum conditions for tylosin formation were that the specific ammonium ion uptake rate ( q _N) and μ were 0·13 mmol g⁻¹ h⁻¹ and 0·05 h⁻¹, respectively. The specific formation rates of threonine dehydratase (TDT) and tylosin were repressed by high levels of specific ammonium ion uptake rate. This study showed the adaptation to chemostat cultures of the nitrogen regulation of tylosin fermentations.     

The role of light and CO2 in optimising the conditions for shoot proliferation of Actinidia deliciosa in vitro

Proliferating cultures of Actinidia deliciosa A. Chev., C. F. Liang and A. R. Ferguson cv. Tomuri (♂) were grown under photosynthetic photon flux density (PPFD) rates ranging from 30 to 250 μmol m⁻² s⁻¹ in order to determine certain physiological parameters in vitro: CO₂ evolution, photosynthesis at three CO₂ atmospheric concentrations (330, 1450 and 4500 μl l⁻¹), fresh and dry matter accumulation and proliferation rate.
A proportional response in dry weight, dry/fresh weight ratios and PPFD was found. The proliferation rate increased up to 120 μmol m⁻² s⁻¹ but decreased at higher rates. At the highest PPFD, the CO² released from cultures and accumulated in the vessels reached 200 μl l⁻¹ of; at the lowest rate the CO₂ concentration reached 10500 μl l⁻¹ after 28 days of culture. The photosynthetic rate at 1450 and 4500 μl l⁻¹ of CO₂ was nearly 4 times higher than at the lowest concentration tested.     

Changes in pigment levels, Rubisco and respiratory enzyme activity of Ficus benjamina during acclimation to low irradiance

The objective of the present study was to determine the influence of reduced irradiance on the activities of ribulose bisphosphate carboxylase-oxygenase (Rubisco) and respiratory enzymes. Rooted cuttings of the tropical epiphyte. Ficus benjamina L., were grown in a shaded environment that excluded approximately 50% of the natural photosynthetically active irradiance (890 μmol m⁻² s⁻¹) for 4 months. Established plants were transferred and grown for 10 months under a range of irradiance levels with daily average maxima varying from a full-sun environment to 20% full sun (100%−1735; 50%−890; 40%−695; and 20%−303 μmol m⁻²s⁻¹). Chlorophyll, carotenoid and soluble protein content increased in Ficus leaves as irradiance level decreased, while Rubisco increased on a fresh weight basis but decreased on a protein basis. Glycolytic enzymes, enolase and pyruvate kinase, showed higher activities in full-sun plants on a protein and fresh weight basis. However, the activity of two mitochondrial enzymes, aconitase and malate dehydrogenase, was not different under the various irradiance levels. When transferred to a very low irradiance environment (18 μmol m⁻² s⁻¹), mature leaves exhibited increased chlorophyll and carotenoid levels regardless of previous irradiance treatment. Exposure to very low irradiance resulted in a large increase in enolase and pyruvate kinase activities. Only plants grown under full sun conditions showed a decline in Rubisco activity following growth at very low irradiance. Together, these studies demonstrate the ability of mature leaves of Ficus to biochemically adjust photosynthetic and respiratory components over a wide range of irradiance.     

Abscisic acid increases in non-growing and paclobutrazol-treated fruits of seedless mandarins

Clementine ( Citrus reticulata [Hort.] Ex. Tanaka cv. Oroval) is a self-incompatible mandarin with a slow rate of fruit growth and high percentage of fruit abscission. Seedless Satsuma ( Citrus unshiu [Mak] Marc. cv. Clausellina) shows natural parthenocarpy and higher fruit set. Application of 25 μg fruit⁻¹ of paclobutrazol (PP333), an inhibitor of gibberellin biosynthesis, reduced the rate of growth and accelerated fruit abscission in both varieties. In contrast, gibberellin A₃ (GA₃) stimulated fruit growth only in the self-incompatible mandarin. Clementine fruits, in the absence of pollination, showed an approximately 2-fold transient increase in the free abscisic acid (ABA) content shortly after petal fall. In Satsuma, a very small accumulation of ABA was detected. Paclobutrazol treatment induced a 3-fold increase in ABA in Satsuma fruits but did not substantially affect the pattern of ABA accumulation in Clementine. In this variety, GA₃ suppressed the ABA increase observed in untreated fruits. These effects were observed 24 h after treatment. However, in Satsuma fruits, the effect of GA₃ on the ABA content was negligible. In addition, a comparative analysis of growing and non-growing fruits of Clementine showed that ABA, on a per unit weight basis, was always higher in the non-growing fruits. Treatment with 85 μM fluridone, an inhibitor of carotenoid biosynthesis and thus indirectly of ABA, delayed fruit abscission in Clementine, but also decreased fruit growth. Collectively, these observations indicate a relationship between high ABA content and a reduced rate of fruit growth and an acceleration of fruit abscission.