Distribution of xylem hydraulic resistance in fruiting truss of tomato influenced by water stress

In this study xylem hydraulic resistances of peduncles (truss stalk), pedicels (fruit stalk) and the future abscission zone (AZ) halfway along the pedicel of tomato (Lycopersicon esculentum L.) plants were directly measured at different stages of fruit development, in plants grown under two levels of water availability in the root environment. The xylem hydraulic connection between shoot and fruits has previously been investigated, but contradictory conclusions were drawn about the presence of a flow resistance barrier in the pedicel. These conclusions were all based on indirect functional measurements and anatomical observations of water-conducting tissue in the pedicel. In the present study, by far the largest resistances were measured in the AZ where most individual vessels ended. Plants grown at low water availability in the root environment had xylem with higher hydraulic resistances in the peduncle and pedicel segments on both sides of the AZ, while the largest increase in hydraulic resistance was measured in the AZ. During fruit development hydraulic resistances in peduncle and pedicel segments decreased on both sides of the AZ, but tended to increase in the AZ. The overall xylem hydraulic resistance between the shoot and fruit tended to increase with fruit development because of the dominating role of the hydraulic resistance in the AZ. It is discussed whether the xylem hydraulic resistance in the AZ of tomato pedicels in response to water stress and during fruit development contributes to the hydraulic isolation of fruits from diurnal cycles of water stress in the shoot

Osmotic potential of Zinnia elegans plant material affects the yield and morphology of tracheary elements produced in vitro

The Zinnia elegans cell suspension culture is excellent for xylogenesis studies at the cellular and molecular level, due to the high and synchronous in vitro differentiation of tracheary elements (TEs). The percentage TE differentiation (%TE) in the culture is, however, influenced by a number of factors before and during cell differentiation. One of the factors that is potentially important but has not gotten much attention is the initial osmolarity of the plant material. To examine whether the growth conditions that determine leaf osmolarity (LO) affect the final %TE, we used three light intensities (50, 70 and 100 mu mol.m(-2)s(-1)) and three electrical conductivity (EC) levels (EC 2, 4 and 6 dS.m(-1)) in hydroponic systems to induce different osmolarities in leaf materials from two cultivars (cvs) of Z. elegans, Envy and Purple Prince. The isolated leaf mesophyll cells were subsequently cultured in a liquid medium (300 mOsm extracellular osmolarity) containing alpha-naphthalene acetic acid (NAA) (1 mg.l(-1)) and benzylaminopurine (BA) (1 mg.l(-1)). The LO increased in both Zinnia cvs with increasing light intensity and increasing EC during growth. Mesophyll cell size correlated negatively with EC, but the correlation was positive with light intensity in both Zinnia cvs. There was an overall positive correlation between % TE and LO although the degree of % TE change versus LO differed between light and EC treatments and also between the two Zinnia cvs. Envy cv is the best known Z. elegans cv for establishing xylogenic cultures. However, it turned out that by subjecting the plants to different growth conditions, the Purple Prince cv produces a higher % TE as compared to the Envy cv. At EC4 the TE differentiation for the Purple Prince cv was 75%, a level that is 25 to 60% higher than those earlier reported. We conclude that light intensity and EC of the root environment affect the LO of Z. elegans which in turn influences the development and therefore dimensions of TEs in an in vitro xylogenic culture. Thus, proper optimization of the growth conditions for the Zinnia plants prior to establishment of xylogenic cultures leads to enhancement of in vitro TE formation

Consequences of diurnal variation in salinity on water relations and yield of tomato

In soilless culture the EC (Electric Conductivity; mS cm -1) is an important measure for the total solute concentration (salinity level) of the nutrient solution in the root environment. This study concentrates on the possibilities of short-term control of the total nutrient concentration (salinity level) in the root environment in relation to the greenhouse climate. A general assumption in this study is that the EC mainly influences plant functioning via its effect on the water relations of the plant: high salinity in the root environment osmotically decreases the availability of water to the roots of the plant. A chapter is included which deals with the current concepts, measures and methods related to the thermodynamic approach of plant water relations and the associated term water potential.The experimental part of this study concentrates on short- and long-term responses of (changes in the) EC on plant growth and functioning. Short-term experiments were done to investigate short-term plant responses (changes in expansion growth, water status and transpiration within a day) upon changes in EC. Long-term experiments were done to investigate the effect of different day and night EC-levels on yield and quality of the fruits during a whole growth season. A simulation model was developed, which is based on the thermodynamic approach of plant water relations, to analyse and integrate the results of the short- and long- term experiments. To obtain reliable measurements of short-term changes in transpiration, water uptake and changes in plant water content (the total amount of water stored in the plant), a new method for simultaneous measurements of water uptake, transpiration and changes in plant water content on one plant was developed.Short-term experiments were done in a growth-chamber and in a greenhouse. Changes in EC were applied in dark and in light, while transpiration, water uptake and plant water content were measured. In dark, a bipartite response was measured on expansion growth: a change in salinity initially changed expansion growth enormously, followed by partial adaptation which occurred in the light: this was interpreted as a direct hydraulic response followed by some adaptation (probably under metabolic control). Salinity changed transpiration clearly in the growth chamber but not in the greenhouse. In the growth-chamber no simple quantitative relationships were found between the changes in plant water status and changes in the rates of transpiration and expansion growth. In the greenhouse, however, the relationship between plant water deficit and transpiration over a day was influenced by salinity. A hysteresis effect over a day was observed on this relationship at low and high salinity level. At low salinity the slope of the relationship was lower than at high salinity and the hysteresis effect was less pronounced. Solute accumulation at the endodermis in the root was raised as a possible explanation for the hysteresis effect and the different slopes at low and high salinity. Simulations, however, showed that solute accumulation was not important enough to be the only cause for the different slopes. The hysteresis effect over a day was clearly simulated by the model. It was concluded that present simulation model needs some adaptation and should probably be combined with metabolic oriented models to be able to describe expansion growth.In the long-term experiments clear positive effects were measured of the intuitive treatment (low salinity during the day and high salinity during the night) on the growth and yield of tomato: yield was increased greatly, mainly by a positive effect on average fruit size, but dry- matter distribution towards the fruits was slightly increased too. Fruit quality was influenced by the intuitive salinity treatment: dry matter percentage of the harvested fruits was decreased, while the incidence of Blossom-End-Rot was greatly decreased.It is concluded that short-term control of the EC mainly influenced expansion growth of the fruits, and that restriction of the supply of macro-nutrients to the dark period did not influence plant growth and production negatively. Short-term control of the EC could probably be well used as a tool to choose between yield and quality in tomato culture

Osmotic potential of Zinnia elegans plant material affects the yield and morphology of tracheary elements produced in vitro

The Zinnia elegans cell suspension culture is excellent for xylogenesis studies at the cellular and molecular level, due to the high and synchronous in vitro differentiation of tracheary elements (TEs).The percentage TE differentiation (%TE) in the culture is, however, influenced by a number of factors before and during cell differentiation. One of the factors that is potentially important but has not gotten much attention is the initial osmolarity of the plant material. To examine whether the growth conditions that determine leaf osmolarity (LO) affect the final %TE, we used three light intensities (50, 70 and 100 μmol.m-2s-1) and three electrical conductivity (EC) levels (EC 2, 4 and 6 dS.m-1 ) in hydroponic systems to induce different osmolarities in leaf materials from two cultivars (cvs) of Z. elegans, Envy and Purple Prince. The isolated leaf mesophyll cells were subsequently cultured in a liquid medium (300 mOsm extracellular osmolarity) containing α-naphthalene acetic acid (NAA) (1 mg.l-1) and benzylaminopurine (BA) (1 mg.l-1). The LO increased in both Zinnia cvs with increasing light intensity and increasing EC during growth. Mesophyll cell size correlated negatively with EC, but the correlation was positive with light intensity in both Zinnia cvs. There was an overall positive correlation between %TE and LO although the degree of %TE change versus LO differed between light and EC treatments and also between the two Zinnia cvs. Envy cv is the best known Z. elegans cv for establishing xylogenic cultures. However, it turned out that by subjecting the plants to different growth conditions, the Purple Prince cv produces a higher %TE as compared to the Envy cv. At EC4 the TE differentiation for the Purple Prince cv was 75%, a level that is 25 to 60% higher than those earlier reported. We conclude that light intensity and EC of the root environment affect the LO of Z. elegans which in turn influences the development and therefore dimensions of TEs in an in vitro xylogenic culture. Thus, proper optimization of the growth conditions for the Zinnia plants prior to establishment of xylogenic cultures leads to enhancement of in vitro TE formation.Keywords: Electrical conductivity, in vitro culture, leaf osmolarity, light intensity, osmotic potential, tracheary element, xylogenesis, Zinnia elegans

Light use efficiency at different wavelengths in rose plants

Current knowledge about the spectral dependence of leaf light use efficiency of leaf photosynthesis (LUE; rate of leaf photosynthesis per unit incident light energy) is based on investigations of mostly arable crops. The leaf LUE depends on the optical properties of the leaf (light absorption), on the fraction of light energy absorbed by photosynthetically active pigments and on the excitation balance of the two photosystems. These properties have hardly been investigated on modern vegetable and especially ornamental greenhouse crops. In this research we investigated the action spectrum of leaf photosynthesis and related leaf optical properties of reddish young leaves and green middle aged leaves of rose ‘Akito’. The crop was grown in a heated greenhouse in Wageningen (The Netherlands, latitude 52°N). The green and reddish leaves had similar total absorptance of 87% on average in the PAR range (400 to 700 nm). In the green leaves, however, leaf absorptance around 550 nm was lower than in the reddish leaves, but slightly higher at longer wavelengths. Red light of 680 nm was found to be the most effective for leaf photosynthesis in the short term. Leaf LUEs were calculated for supplemental light by HPS and 645 and 680 nm LEDs based on their emission spectra and the measured action spectra of leaf photosynthesis. These calculations showed that a 645 nm LED light yielded more improvement in LUE compared to HPS light than 680 nm LED light. This is because the 680 nm LED also emits light >700 nm at which the LUE is much lower. If these calculated improvements in leaf LUE for red LED-light compared to HPS-light are sustained at the crop level during prolonged illumination, substantial energy savings may be realized in rose by supplemental lighting with red LED ligh

Veel rood licht geeft compactere planten : plantlengte te sturen door combinatie van SON-T met rode en blauwe LED's

Lichtkleuren beïnvloeden lengte en vertakking van pot- en perkplanten. Maar sturing daarmee is nog lastig. Wageningen Universiteit heeft onderzoek gedaan om meer zicht te krijgen op de mogelijkheden, met petunia en potchrysant als modelplant

Inzicht in het optreden van bolblad bij chrysant

Jaarlijks treedt vanaf begin november tot en met eind februari op verschillende chrysantenbedrijven bolblad op. Er zijn een aantal chrysanten rassen zeer gevoelig hiervoor. Takken met bolblad hebben een negatieve sierwaarde. Een duidelijke oorzaak is nog niet gevonden. In december 2009 zijn op twee bedrijven in de Bommelerwaard chrysanten met bolblad gemonsterd. Na waarnemingen op de bedrijven blijkt het volgende: 1. De eerste bladeren met bolblad worden al gesignaleerd bij planten in de lange dagperiode. 2. Gedurende de korte dag fase neemt het aantal bladeren met bolblad toe. 3. Na “pluizen” is er een toename van het aantal bladeren met bolblad. Bij het optreden van bolblad wordt gedacht aan de volgende hypothese: Alle planten bouwen gedurende de dag een zetmeelreserve op in bladeren en stengels om de volgende nacht te kunnen overleven. In het donker is er geen fotosynthese en daardoor geen aanmaak van assimilaten. Onderhoudsprocessen in de plant staan echter ’s nachts niet stil en zijn noodzakelijk voor de plant om te kunnen overleven. Planten gebruiken dus ook ’s nacht assimilaten, in het bijzonder voor onderhoud maar ook voor nachtelijke groei. Deze assimilaten komen ’s nachts beschikbaar door zetmeel af te breken. Dit zetmeel wordt overdag opgebouwd. Er is dus een dagelijkse cyclus van opbouw en afbraak van zetmeel in een plant. Planten hebben ingenieuze systemen om opbouw en afbraak van zetmeel op elkaar af te stemmen. Ze reageren op een tekort aan assimilaten aan het einde van de nacht door de daaropvolgende dag meer in licht geproduceerde assimilaten om te zetten in zetmeel en minder in groei. Aan het omgekeerde, een overschot aan zetmeel aan het einde van de nacht, is weinig onderzoek gedaan. In het algemeen wordt aangenomen dat een plant dan het omgekeerde doet: om ophoping van zetmeel te voorkomen worden overdag minder assimilaten naar zetmeel omgezet en kan ook de productie van assimilaten worden verlaagd door efficiëntie van de fotosynthese te verlagen of door de lichtonderschepping te verlagen. Het optreden van bol blad kan worden gezien als het mijden van licht om de fotosynthese te verlagen en daardoor verdere zetmeelophoping te voorkomen. Deze licht-mijding reactie zou het gevolg kunnen zijn van zetmeelophoping in de bladeren met als doel productie en gebruik van assimilaten (en zetmeel) over 24h weer in balans te brengen. Het doel van de ‘scan’ op beide bedrijven was een indruk te krijgen of er zetmeelophoping optreedt in bladeren van belichte chrysant cv ‘Anastasia’ in verschillende teeltfasen en of er een correlatie is met het optreden van ‘bol blad’. Na analyse van de monsters blijkt, dat er sterke zetmeelophoping in de bladeren optreedt gedurende de lange dag fase en op één van de bedrijven na het pluizen in de korte dag. Naast de bemonstering op twee bedrijven is op één chrysantenbedrijf vastgesteld dat daar waar een lagere temperatuur werd gerealiseerd er minder bolblad optrad dan op plaatsen met een hogere ruimtetemperatuur

Effect of growth conditions on post harvest rehydration ability of cut chrysanthemum flowers

Different batches of cut chrysanthemum flowers showed substantial variability in restoring their fresh weight after a moderate water loss. Cutting height strongly affected the rehydration ability of cut flowers, and the hydraulic conductance of the stem and its restoration after air aspiration. Within a batch of flowers, rehydration ability is negatively related with the hydraulic conductance. Rehydration ability of the flowering stems of all experimentst was highly correlated with the restoration of hydraulic conductance of stem segments after air aspiration. This was demonstrated for batches from different harvest dates and cutting heights above root-shoot junction as well as cultivars. Greenhouse temperature and irradiance level affected the ability to recover from air emboli only significantly when differences in treatments were rather extreme. Xylem hydraulic conductance as well as emboli removal (rehydration ability) of cut flowers was rather sensitive to root substrate moisture content during cultivation of the plants

Red and Blue Light Effects during Growth on Hydraulic and Stomatal Conductance in Leaves of Young Cucumber Plants

Many horticultural crops (food and ornamental) are produced year-round in greenhouses at high latitudes, where the limited availability of natural sunlight restricts plant production during large parts of the year. To enable year-round plant production supplemental light is necessary to enhance photosynthesis, the primary process that drives growth and production. It is therefore not surprising that during the last two decades most of the research effort related to light in greenhouse horticulture has been directed towards optimizing the supplemental light use efficiency for photosynthesis, with emphasis on light intensity, duration and since recently also on light quality. For a long time, high pressure sodium (HPS) lamps were the preferred lamps for supplemental lighting. Nowadays, Light Emitting Diodes (LEDs) are gaining importance, mostly because of their potentially higher energy efficiency. Another important, less-well known attribute of LEDs is the much better possibility to control light quality. Besides the effect on photosynthesis, light quality also influences plant morphological and developmental processes, mostly mediated by a set of blue, red and far-red photoreceptors (i.e., cryptochromes, phototropins and phytochromes). Several of these processes, such as for instance internode and petiole elongation growth and leaf expansion have a direct impact on productivity via plant photosynthesis as mediated by light interception. Light quality can also induce leaf deformations and epinasty, which can negatively influence biomass production via reduced light interception. In ornamental crops, such as chrysanthemum, leaf deformations can have severe negative impact on the final ornamental value. Other important effects of light quality involve the development of stomatal density and the control of stomatal aperture, which both attribute to stomatal conductance and therefore potentially influence productivity, while also the leaf hydraulic resistance is influenced by light quality. This paper will overview some plant morphological and developmental processes that are influenced by light quality and are important for plant production in protected environments

Blue light dose–responses of leaf photosynthesis, morphology, and chemical composition of Cucumis sativus grown under different combinations of red and blue light

The blue part of the light spectrum has been associated with leaf characteristics which also develop under high irradiances. In this study blue light dose–response curves were made for the photosynthetic properties and related developmental characteristics of cucumber leaves that were grown at an equal irradiance under seven different combinations of red and blue light provided by light-emitting diodes. Only the leaves developed under red light alone (0% blue) displayed dysfunctional photosynthetic operation, characterized by a suboptimal and heterogeneously distributed dark-adapted Fv/Fm, a stomatal conductance unresponsive to irradiance, and a relatively low light-limited quantum yield for CO2 fixation. Only 7% blue light was sufficient to prevent any overt dysfunctional photosynthesis, which can be considered a qualitatively blue light effect. The photosynthetic capacity (Amax) was twice as high for leaves grown at 7% blue compared with 0% blue, and continued to increase with increasing blue percentage during growth measured up to 50% blue. At 100% blue, Amax was lower but photosynthetic functioning was normal. The increase in Amax with blue percentage (0–50%) was associated with an increase in leaf mass per unit leaf area (LMA), nitrogen (N) content per area, chlorophyll (Chl) content per area, and stomatal conductance. Above 15% blue, the parameters Amax, LMA, Chl content, photosynthetic N use efficiency, and the Chl:N ratio had a comparable relationship as reported for leaf responses to irradiance intensity. It is concluded that blue light during growth is qualitatively required for normal photosynthetic functioning and quantitatively mediates leaf responses resembling those to irradiance intensity