Regeneration of drought-stressed gametophytes of the epiphytic fern, Pyrrosia pilosellodes (L.) Price

The epiphytic habitat represents a highly dynamic environment, and water deficit is one of the common factors that affects growth and development of epiphytes. Gametophytes of the epiphytic fern, Pyrrosia piloselloides (L.) Price, were able to tolerate up to 50 days of drought. Upon rehydration, cells that recovered from water stress were capable of forming new gametophytes. The ability of gametophytes to recover from desiccation plays an important role in the survival and growth of the fern species under natural conditions. Received: 20 May 1998 / Revision received: 5 August 1998 / Accepted: 21 August 1998     

Crassulacean acid metabolism (CAM) in high elevation tropical cactus

Abstract. Several taxa of cacti are distributed in high elevation tropical alpine habitats between 4000–4700 m in central Peru. This region has a marked dry season with soil water potentials as low as – 25 MPa. The barrel type cactus Oroya peruviana and the low ceaspitose Tephrocactus floccosus (both the typical hairy form and a hairless form) all exhibited diurnal fluctuations of malic acid (10–100 μmol/g FW), indicative of CAM photosynthesis. δ³C carbon isotope ratios were – 13 to – 14 suggesting that for these CAM plants the bulk of the net carbon gain is through night-time carbon uptake. This occurs in spite of overnight temperatures below 0°C. CAM activity was observed on nights when air temperature dropped to – 8°C and subepidermal temperatures reached as low as –3°C. In central Peru, the typical form of T. floccosus has a dense covering of long silvery white hairs. Comparisons with an adjacent 'hairless' form showed that the hairy morph maintained a subepidermal temperature several degrees higher during the night. At a site where the 'hairless' morph was rare, the hairy T. floccosus had substantially higher overnight acid accumulation. At another site where the 'hairless' morph was abundant, the hairy T. floccosus had substantially lower acid accumulation relative to the 'hairless' form.     

Effects of growth regulators on the induction of Crassulacean acid metabolism in the facultative halophyte Mesembryanthemum crystallinum L.

The classical induction of Crassulacean acid metabolism (CAM) in Mesembryanthemum crystallinum L. by water stress is observed within one week when fourto five-week-old plants (grown under a 16/8 h photoperiod at ca. 600 mol quanta · m^–2 · s^–1) are irrigated with 350 mM NaCl. The induction of CAM was evaluated by measuring phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31) and NADP-malic enzyme (NADP-ME, EC 4.1.1.82) activities and nocturnal increases in malate content and titratable acidity of leaf extracts, and the daily pattern of CO₂ exchange and stomatal conductance during the 7-d induction period. Three growth regulators, abscisic acid (ABA), farnesol (an antitranspirant and analog of ABA), and benzylaminopurine (BAP), were found to substitute for NaCl for induction of CAM when fed to plants in nutrient media. Daily irrigation with solutions containing micromolar levels (optimum ca. 10 micromolar) of these growth regulators led to the induction of CAM similar to that by high salt. Application of the growth regulators, like NaCl, caused large increases in the activity of NADP-ME and the activity and level of PEPCase, which are components of the biochemical machinery required for CAM. Western immunoblotting showed that the increased activity of PEPCase on addition of ABA, farnesol and BAP was mainly due to increased levels of the CAM-specific isoforms. Also, dehydration of cut leaves over 8.5 h under light resulted in a severalfold increase in PEPCase activity. An equivalent increase in PEPCase activity in excised leaves was also obtained by feeding 150 mM NaCl, or micromolar levels of ABA or BAP via the petiole, which supports results obtained by feeding the growth regulators to roots. However, the increase in PEPCase activity was inhibited by feeding high levels of BAP to cut leaves prior to dehydration, indicating a more complex response to the cytokinin. Abscisic acid may have a role in induction of CAM in M. crystallinum under natural conditions as there is previous evidence that induction by NaCl causes an increase in the content of ABA, but not cytokinins, in leaves of this species.Abbreviations ABA abscisic acid - BAP 6-benzylaminopurine - CAM Crassulacean acid metabolism - Chl chlorophyll - 2,4D 2,4-dichlorophenoxyacetic acid - NADP-ME NADP-malic enzyme - PEPCase phosphoenolpyruvate carboxylase Methyl jasmonate was generously provided by Dr. Vincent Franceschi (Botany Department, Washington State University). The anti-maize leaf PEPCase was kindly supplied by Dr. Tatsuo Sugiyama (Department of Agricultural Chemistry, Nagoya University, Japan) and the anti-Flaveria trinervia leaf PEPCase was kindly supplied by Dr. Samuel Sun (Department of Plant Molecular Physiology, University of Hawaii, Honulu). This work was funded in part by U.S. Department of Agriculture Competitive Grant 90-37280-5706 and an equipment grant (DMB 8515521) from the National Science Foundation. Ziyu Dai was supported in part by Guangxi Agricultural College and Ministry of Agriculture of the People's Republic of China     

Seasonal patterns of water relations and enzyme activity of the facultative CAM plant Portulacaria afra (L.) Jacq.

Abstract. Portulacaria afra (L.) Jacq. is a perennial facultative CAM species showing a seasonal shift from C₃ to CAM photosynthesis. The shift to CAM during the summer occurs despite continued irrigation of the plants. The authors examined the hypothesis that the seasonal shift to CAM occurred because of low transient water potentials. They measured changes in whole leaf water, osmotic and pressure potentials over the course of the shift. They also studied changes in enzyme activity to ascertain if PEP carboxylase and PEP carboxykinase were induced during the seasonal shift to CAM. Water potentials were high, from -0.1 to -0.5 MPa, predawn and midday, when the C₃ pathway of photosynthesis was utilized. Osmotic potentials were constant, from -0.7 to - 0.8 MPa, indicating very little change in turgor. P. afra shifted to CAM indicated by large diurnal acid fluctuations (300 400 meq m⁻²) despite C₃-like predawn water potentials. Midday water potentials usually decreased 0.2-0.7 MPa, while the osmotic potential remained unchanged or decreased slightly. Thus, a midday loss of turgor was associated with the use of the CAM pathway. The results support the hypothesis that the induction of CAM occurred due to low transient water potentials and may be partially mediated through the loss of turgor. The shift to CAM is only a partial induction with PEP carboxykinase showing high activity all year round while PEP carboxylase increases three-to five-fold over C₃ levels. Relatively high levels of CAM enzyme activity enables the utilization of the CAM pathway in the winter and spring in response to high daytime temperatures and increased evaporative demand. These results would lead to an increase in water use efficiency during such periods when compared to other inducible CAM species.     

Crassulacean acid metabolism (CAM) in an epiphytic ant-plant, Myrmecodia beccarii Hook.f. (Rubiaceae)

This study demonstrates unequivocally the presence of crassulacean acid metabolism (CAM) in a species of the Rubiaceae, the fourth largest angiosperm plant family. The tropical Australian endemic epiphytic ant-plant, Myrmecodia beccarii Hook.f., exhibits net CO₂ uptake in the dark and a concomitant accumulation of titratable acidity in plants in the field and in cultivation. Plants growing near Cardwell, in a north Queensland coastal seasonally dry forest of Melaleuca viridiflora Sol. ex Gaertn., accumulated ~50 % of their 24 h carbon gain in the dark during the warm wet season. During the transition from the wet season to the dry season, 24 h carbon gain was reduced whilst the proportion of carbon accumulated during the dark increased. By mid dry season many plants exhibited zero net carbon uptake over 24 h, but CO₂ uptake in the dark was observed in some plants following localised rainfall. In a shade-house experiment, droughted plants in which CO₂ uptake in the light was absent and dark CO₂ uptake was reduced, were able to return to relatively high rates of CO₂ uptake in the light and dark within 12 h of rewatering.     

Enzyme Electrophoretic Evidence for Diploidy in Japanese Woodwardia japonica (L.f.) Sm. (Blechnaceae, Pteridophyte) with 2n= 68

Abstract Enzyme-electrophoretic variation was examined in sporophytes of Woodwardia japonica (2n= 68) and segregation was examined in gametophytes. Despite the high chromosome number, W. japonica displayed disomic segregation of isoenzyme patterns. This and karyotype analyses indicate that W. japonica is a diploid derived from a base number of either x= 17 or x= 34.     

Cobalt stress affects nitrogen metabolism,photosynthesis and antioxidant system in chickpea (Cicer arietinum L.)

Abstract

Plants of chickpea were exposed to varied levels of cobalt (Co) and sampled at the 60-day stage. Cobalt at concentration <100 µM significantly increased the number of nodules, their dry mass, leghemoglobin concentration and the activity of nitrogenase. Similarly, the activities of glutamate dehydrogenase, glutamine synthetase and glutamate synthase also exhibited an increase in the presence of Co <100 µM, in nodules and leaves, respectively. The various photosynthetic attributes in leaves and the activity of antioxidative enzymes both in nodules and leaves were inhibited by Co in a concentration-dependent manner. However, the lipid peroxidation and the content of proline exhibited a significant increase in response to Co and were at a maximum in the plants exposed to 250 µM concentration of cobalt. Since most of the parameters showed a significant increase in response to 50 µM cobalt, this concentration may be regarded as a threshold concentration.     

Effects of sulphur nutrition on nitrogen and carbon metabolism in lucerne (Medicago sativa L.)

Studies were conducted with one-year-old plants of the perennial legume, lucerne ( Medicago sativa L.), to determine the effects of various levels of S (0.3, 1.5, and 7.5 m M ) on N₂-fixation, photosynthesis, herbage free amino acid pools and protein amino acids, levels of protein, and activities of key enzymes of leaf nitrogen and carbon metabolism. Sulphur deficiencies in the 0.3 m M S treatment, as determined by N:S ratios, did not appear until the second growth cycle. This treatment was severely S-deficient by the end of the third growth cycle. Sulphur deficiencies did not occur in the other two treatments over three cycles of growth. By the middle of the second growth cycle acetylene reduction rates of plants grown with 0.3 m M S were lower than those of other treatments. At the end of the third growth cycle acetylene reduction rates of the 0.3 m M S treatment were ca . 30–35% that of the other treatments. There was no effect of S-deficiency on photosynthesis, levels of leaf NADP-isocitrate dehydrogenase and glutamine synthetase activity, or concentrations of leaf protein over the course of the experiments. Levels of NAD-glutamate dehydrogenase, NAD-malate dehydrogenase, and glutamate oxaloacetate trans-aminase activity and concentrations of free methionine, arginine, urea, and ammonia increased, with S-deficiency. Boron concentrations were very high (ca. 300 μg/g dry wt.) in S-deficient plants. The mole percent methiomne in leaf protein decreased slightly and chlorophyll concentration decreased markedly with S-deficiency. This study suggests that N₂-fixation is affected early during S-deprivation of lucerne and that subsequent effects of S-deficiency may be due to loss of fixed nitrogen.     

Corn (Zea mays L.) growth, leaf pigment concentration, photosynthesis and leaf hyperspectral reflectance properties as affected by nitrogen supply

Plant nitrogen (N)deficiency often limits crop productivity. Early detection of plant N deficiency is important for improving fertilizer N-use efficiency and crop yield. An experiment was conducted in sunlit, controlled environment chambers in the 2001 growing season to determine responses of corn (Zea mays L. cv. 33A14) growth and leaf hyperspectral reflectance properties to varying N supply. Four N treatments were: (1) half-strength Hoagland's nutrient solution applied throughout the experiment (control); (2) 20% of control N starting 15 days after emergence (DAE); (3) 0% N starting 15 DAE; and (4) 0% N starting 23 DAE (0% NL). Plant height, the number of leaves, and leaf lengths were examined for nine plants per treatment every 3–4 days. Leaf hyperspectral reflectance, concentrations of chlorophyll a, chlorophyll b,and carotenoids, leaf and canopy photosynthesis, leaf area, and leaf N concentration were also determined during the experiment. The various N treatments led to a wide range of N concentrations (11 – 48 g kg^–1 DW) in uppermost fully expanded leaves. Nitrogen deficiency suppressed plant growth rate and leaf photosynthesis. At final harvest (42 DAE), plant height, leaf area and shoot biomass were 64–66% of control values for the 20% N treatment, and 46-56% of control values for the 0% N treatment. Nitrogen deficit treatments of 20% N and 0% N (Treatment 3) could be distinguished by changes in leaf spectral reflectance in wavelengths of 552 and 710 nm 7 days after treatment. Leaf reflectance at these two wavebands was negatively correlated with either leaf N (r = –0.72 and –0.75^**) or chlorophyll (r = –0.60 and –0.72^**) concentrations. In addition, higher correlations were found between leaf N concentration and reflectance ratios. The identified N-specific spectral algorithms may be used for image interpretation and diagnosis of corn N status for site-specific N management.     

Changes in leaf organisation, photosynthetic performance and wood formation during ex vitro acclimatisation of black mulberry (Morus nigra L.)

Changes in anatomical organisation of the leaf, photosynthetic performance and wood formation were examined to evaluate the temporal and spatial patterns of acclimatisation of micropropagated slow-growing black mulberry ( Morus nigra L.) plantlets to the ex vitro environment. Leaf structure differentiation, the rates of net photosynthesis (P_n), transpiration (E) and stomatal conductance (g_s), and secondary xylem growth were determined in the course of a 56-day acclimatisation. Differentiation of palisade parenchyma was observed 7 days after transfer. At this stage, the rates of P_n, E and g_s reached maximum values, after which the rates of all three gas exchange parameters gradually decreased. The highest proportion of woody area occupied by vessels was also observed 7 days after transfer. An important feature of developing woody tissue is the difference in patterns of vessel distribution from the characteristic differentiation patterns of earlywood and latewood vessels in mature wood of ring-porous trees. Vessels with lumen areas over 3000 μm² were only differentiated in acclimatised plantlets, whereas vessels in stems sampled on days 0 and 7 had very small lumen areas of up to 560 μm². Full acclimatisation, observed 56 days after transfer to the ex vitro environment, was associated with the rapid growth of new in vivo formed leaves, very low rates of E and g_s, and much increased secondary xylem tissue within the stem area.     

Alterations in growth and crassulacean acid metabolism (CAM) activity of in vitro cultured cactus

Unlike C-3 plants, cacti possess a crassulacean acid metabolism (CAM) physiology that can alter the pattern of carbon uptake and affect plant growth under artificial environmental conditions, especially in tissue culture. In vitro-derived plantlets of Coryphantha minima grew 7-fold larger than plants cultured under similar ex vitro conditions. Growth regulators incorporated into the culture media during shoot proliferation stage of micropropagation had a strong influence on this increased growth. Other important factors that contributed to increased growth under in vitro conditions were high relative humidity and sugar in the culture medium. An analysis of gas exchange and daily fluctuations of malic acid levels revealed an increase in net photosynthetic rate, in terms of carbon assimilation, by in vitro plants compared with that of ex vitro plants. This stimulated photosynthesis in the presence of an external carbon source was unexpected but apparently true for cacti exhibiting CAM physiology. Unlike CAM plants grown in ex vitro conditions, net CO₂ uptake by in vitro-cultured cacti occurred continuously in the light as well as the dark. Once regenerated, cacti were transferred to ex vitro conditions where the normal CAM pathway resumed with a concomitant reduction in growth and CO₂ uptake. These results showed that growth of cacti can be considerably accelerated by in vitro culture. This revised version was published online in June 2006 with corrections to the Cover Date.     

Crassulacean acid metabolism,CO2-recycling,and tissue desiccation in the Mexican epiphyte Tillandsia schiedeana Steud (Bromeliaceae)

After 23 days without water in a greenhouse, rates of nocturnal CO₂ uptake in Tillandsia schiedeana decreased substantially and maximum rates occurred later in the dark period eventually coinciding with the onset of illumination. Nocturnal CO₂ uptake accounted for less than half the total nighttime increase in acidity measured in well-watered plants. With increased tissue desiccation, only 11–12% of measured acid accumulation was attributable to atmospheric CO₂ uptake. Plants desiccated for 30 days regained initial levels of nocturnal acid accumulation and CO₂ uptake after rehydration for 10h. These results stress the importance of CO₂ recycling via CAM in this epiphytic bromeliad, especially during droughts.Partially supported by Biomedical Sciences Support Grant RR07037.     

Relationships between root permeability to water,leaf conductance and transpiration rate in sunflower (Helianthus annuus L.) cultivars

Summary The relations between leaf conductance (g_l) transpiration rate and root permeability to water (R_p) of three sunflower (Helianthus annuus L.) cultivars grown in a controlled environment cabinet are described.No differences in transpiration rates were found but it was shown that plants with low values of R_p have active stomatal closure with favourable consequences for water use efficiency under water limiting conditions.R_p was estimated by applying hydrostatic pressure on the root system. Values of R_p per unit root volume ranged from 0.34×10^–5 to 16.75×10^–5 (s MPa^–1). There were significant inter-cultivar differences (P<0.05) in R_p and g_l and an inverse correlation between R_p and the maximum values cf g_l within cultivars.Pressure applied on the root system is proposed as a useful tool for the determination of differences in the root permeability to water amongst sunflower cultivars.     

Plant leaf area expansion and assimilate production in wheat (Triticum aestivum L.) growing under low phosphorus conditions

Under phosphorus deficiency reductions in plant leaf area have been attributed to both direct effects of P on the individual leaf expansion rate and to a reduced availability of assimilates for leaf growth. In this work we use experimental and simulation techniques to identify and quantify these processes in wheat plants growing under P-deficient conditions. In a glasshouse experiment we studied the effects of soil P addition (0–138 kg P₂O₅ ha^-1) on tillering, leaf emergence, leaf expansion, plant growth, and leaf photosynthesis of wheat plants (cv. INTA Oasis) that were not water stressed. Plants were grown in pots containing a P-deficient (3 mg P g^-1 soil) sandy soil. Sowing and pots were arranged to simulate a crop stand of 173 plants m^-2. Experimental results were integrated in a simulation model to study the relative importance of each process in determining the plant leaf area during vegetative stages of wheat. Phosphorus deficiency significantly reduced plant leaf area and dry weight production. Under P-deficient conditions the phyllochron (PHY) was increased up to a 32%, compared to that of high-P plants. In low-P plants the rate of individual leaf area expansion during the quasi-linear phase of leaf expansion (LER) was significantly reduced. The effect of P deficiency on LER was the main determinant of the final size of the individual leaves. In recently expanded leaves phosphorus deficiency reduced the photosynthesis rate per unit leaf area at high radiation (AMAX), up to 57%. Relative values of AMAX showed an hyperbolic relationship with leaf P% saturating at 0.27%. Relative values of the tillering rate showed an hyperbolic relationship with the shoot P% saturating at values above 0.38%. The value of LER was not related to the concentration of P in leaves or shoots. A morphogenetic model of leaf area development and growth was developed to quantify the effect of assimilate supply at canopy level on total leaf area expansion, and to study the sensitivity of different model variables to changes in model parameters. Simulation results indicated that under mild P stress conditions up to 80% of the observed reduction in plant leaf area was due to the effects of P deficiency on leaf emergence and tillering. Under extreme P-deficient conditions the simulation model failed to explain the experimental results indicating that other factors not taken into account by the model, i.e. direct effects of P on leaf expansion, must have been active. Possible mechanisms of action of the direct effects of P on individual leaf expansion are discussed in this work.     

Changes in levels of phosphoenolpyruvate carboxylase with induction of Crassulacean acid metabolism (CAM)-like behavior in the C4 plant Portulaca oleracea

Changes in levels of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31, orthophosphate: oxaloacetate carboxy-lyase, phosphorylating) were followed in leaves and stems of CAM-expressing and non-expressing Portulaca oleracea L. plants. CAM expression was induced by growing plants under an 8-h photoperiod and water stress conditions (SD-WS). Leaves and stems of these plants (designated CAM) expressed nocturnal acidification with an oscillation pattern and an amplitude characteristic of CAM plants. Generally, PEPC activity increased by ca 3-fold during the period of CAM induction. Over the day/night cycle. PEPC activity oscillated in a pattern typical of CAM plants. Treatment of the other plant group (designated as non-CAM) by growth under a 16-h photoperiod and well-watered conditions (LD-WW) did not induce expression of the tested criteria of CAM in plants. In these plants, nocturnal acidification as well as changes in the magnitude of PEPC, activity and fluctuation pattern were undetectable. SDS-PAGE of leaf extracts of the CAM-expressing plants and the corresponding densitometric scans show progressive increase in the amount of PEPC subunit protein (ca 95 kDa) during the period of CAM induction. These results show that induction of CAM-like characteristics in the C₄ plant Portulaca oleracea is also accompanied by increased PEPC activity, which may be partly due to an increase in enzyme synthesis.     

Variation in host susceptibility among and within populations ofPlantago lanceolata L. infected by the fungusPhomopsis subordinaria (Desm.) Trav.

Summary Susceptibility toPhomopsis stalk disease ofPlantago lanceolata genotypes, sampled in three different populations with a variable degree of infection by the fungusPhomopsis subordinaria, was determined under greenhouse conditions. Susceptibility of the host varied within, but not among populations. No relationship between the intensity of the disease in the field and the mean susceptibility of the host genotypes sampled at those locations could be established. Host susceptibility appeared to be composed of the host genotypes sampled at those locations could be established. Host susceptibility appeared to be composed of different (uncorrelated) plant characteristics. Determining whether host genotypes are highly or slightly susceptible can only be achieved by field trials, where the plants are exposed to the whole set of disease inducing factors. The relevance of host susceptibility to the intensity of disease in the field is discussed in relation to the variation in pathogenicity of the fungus and the variation in environmental factors prevailing inP. lanceolata populations underP. subordinaria pathogen pressure. Grassland Species Research Group Number 123     

Activity and quantity of ribulose bisphosphate carboxylase-and phosphoenolpyruvate carboxylase-protein in two Crassulacean acid metabolism plants in relation to leaf age,nitrogen nutrition,and point in time during a day/night cycle

Activity of ribulose 1,5-bisphosphate (RuBP) carboxylase in leaf extracts of the constitutive Crassulacean acid metabolism (CAM) plant Kalanchoe pinnata (Lam.) Pers. decreased with increasing leaf age, whereas the activity of phosphoenolpyruvate (PEP) carboxylase increased. Changes in enzyme activities were associated with changes in the amount of enzyme proteins as determined by immunochemical analysis, sucrose density gradient centrifugation, and SDS gel electrophoresis of leaf extracts. Young developing leaves of plants which received high amounts of NO ₃ ^- during growth contained about 30% of the total soluble protein in the form of RuBP carboxylase; this value declined to about 17% in mature leaves. The level of PEP carboxylase in young leaves of plants at high NO ₃ ^- was an estimated 1% of the total soluble protein and increased to approximately 10% in mature leaves, which showed maximum capacity for dark CO₂ fixation. The growth of plants at low levels of NO ₃ ^- decreased the content of soluble protein per unit leaf area as well as the extractable activity and the percentage contribution of both RUBP carboxylase and PEP carboxylase to total soluble leaf protein. There was no definite change in the ratio of RuBP carboxylase to PEP carboxylase activity with a varying supply of NO ₃ ^- during growth. It has been suggested (e.g., Planta 144, 143–151, 1978) that a rhythmic pattern of synthesis and degradation of PEP carboxylase protein is involved in the regulation of -carboxylation during a day/night cycle in CAM. No such changes in the quantity of PEP carboxylase protein were observed in the leaves of Kalanchoe pinnata (Lam.) Pers. or in the leaves of the inducible CAM plant Mesembryanthemum crystallinum L.Abbreviations CAM Crassulacean acid metabolism - RuBP ribulose 1,5-bisphosphate - PEP phosphoenolpyruvate - G-6-P glucose-6-phosphate     

Availability of water controls Crassulacean acid metabolism in succulents of the Richtersveld (Namib desert,South Africa)

Features of Crassulacean acid metabolism (CAM) were studied in a variety of different succulents in response to climatic conditions between March 1977 and October 1983 in the southern Namib desert (Richtersveld). A screening in 1977 and 1978 revealed that nearly all investigated succulents performed a CAM, but overnight accumulation of malate declined gradually with decreasing soil water potential, tissue osmotic potential, and leaf water content. This was further substantiated by an extended period of insufficient rainfall in 1979 and 1980 which damaged the evergreen CAM succulents between 80 and 100%. In most of the species still living, neither CO₂-gas exchange nor diurnal acid fluctuation, indicative of CAM, could be detected unless an abundant rainfall restored both CAM features. Plants persisted in a stage of latent life.Water supply is one necessary prerequisite for CAM in the Richtersveld. But even well-watered plants with CAM were sensitive to short-term water stress caused by high water-vapour partialpressure deficit (VPD) in the night, which reduced or prevented CO₂ uptake and resulted in a linear relation between overnight accumulated malate and VPD. The results do not support the opinion that, for the Namib succulents, CAM is an adaptive mechanism to water stress since long-term and short-term water stress stopped nocturnal malate synthesis, but instead lead to the conclusion that nocuturnal CO₂ fixation is only performed when the water status of the plant can be improved simultaneously.Abbreviations CAM Crassulacean acid metabolism - VPD water vapour pressure deficit Dedicated to Professor H. Ziegler on the occasion of his 60th birthday     

Indole-3-acetic acid, ethylene, and abscisic acid metabolism in developing muskmelon (Cucumis melo L.) fruit

Hormonal metabolism associated with fruit development in muskmelon was investigated by measuring IAA, ABA, and ACC levels in several tissues at various stages of development. In addition, levels of conjugated IAA and ABA were determined in the same tissues. Ethylene production, which is believed to signal the ripening and senescence of mature fruit, was also measured. Ethylene production was highest in the outer tissue near the rind and gradually declined during maturation, except for a dramatic increase in all fruit tissues at the climacteric. In contrast to ethylene production, ACC levels increased during maturation and remained equal throughout the fruit until the climacteric, when levels in the outer tissues increased nearly 5-fold over levels in the inner tissues. The consistent presence of ACC indicates that ACC oxidase rather than the availability of ACC regulates ethylene production in developing fruits. ABA and ABA esters generally declined during maturation, however an increase in ABA esters associated with the outer mesocarp tissue was observed in fully mature, climacteric fruit. IAA and IAA conjugates were only found in the outer tissue near the rind, and their levels remained low until the fruit was fully mature and entering the climacteric. At that time, increased levels of conjugates were detected. The late burst of hormonal metabolism in the outer mesocarp tissue appeared to signal its degeneration and the deterioration that typically occurs in ripening fruit. The tissue-specific conjugation of IAA and ABA, in addition to the production of climacteric ethylene, may represent part of the signaling mechanism initiating ripening and eventual deterioration of tissues in muskmelon fruits.Abbreviations ABA abscisic acid - ACC 1-aminocylopropane-1-carboxylic acid - DAP days after pollination - IAA indole-3-acetic acid     

A coupled model of photosynthesis,stomatal conductance and transpiration for a rose leaf (Rosa hybrida L.)

The following three models were combined to predict simultaneously photosynthesis, stomatal conductance, transpiration and leaf temperature of a rose leaf: the biochemical model of photosynthesis of Farquhar, von Caemmerer and Berry (1980, Planta 149: 78-90), the stomatal conductance model of Ball, Woodrow and Berry (In: Biggens J, ed. Progress in photosynthesis research. The Netherlands: Martinus Nijhoff Publishers), and an energy balance model. The photosynthetic parameters: maximum carboxylation rate, potential rate of electron transport and rate of triose phosphate utilization, and their temperature dependence were determined using gas exchange data of fully expanded, young, sunlit leaves. The stomatal conductance model was calibrated independently. Prediction of net photosynthesis by the coupled model agreed well with the validation data, but the model tended to underestimate rates of stomatal conductance and transpiration. The coupled model developed in this study can be used to assist growers making environmental control decisions in glasshouse production.