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

One-dimensional wave spectrum analysis of wind waves off Cape Town

Wind waves in the vicinity of Cape Town, South Africa, were measured by means of an N.I.O. (England) ship-borne wave recorder, in water depths varying from 12 - 140 metres. One dimensional frequency spectra were computed from the records, by power spectrum analysis, based on the method of Blackman and Tukey, using an I.B.M. 1130 Computer. Assumptions of normality and stationarity were tested. The Gaussian assumption of the waves was found to be acceptable for the waters off Cape Town. At the 5% critical level, using the chi-square test, 3 out of 23 records tested were found to be non-Gaussian. No significant difference between the Gaussian properties of the deep and the shallow stations was found. Tests for stationarity applied to 3 selected records showed 1 record as clearly non-stationary. However, this recording was obtained under fluctuating wind conditions. Comparison of the total variances of the power spectra obtained in shoaling water showed a systematic decrease of variance with depth. Normalised spectra did not show a systematic selective attenuation of the variances with frequency. Factors which might have caused the systematic reduction of the total variances with depth have been examined. The bottom friction factor for this coast was estimated. The mean value of the bottom friction is 0.22. This is higher than found by other workers

Percolation of a strongly connected component in simple directed random graphs with a given degree distribution

We study site and bond percolation on directed simple random graphs with a given degree distribution and derive the expressions for the critical value of the percolation probability above which the giant strongly connected component emerges and the fraction of vertices in this component

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

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

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