Anatomical survey of the formation of primary xylem and nutrients supply to the reproductive apple bud

Frazenburg, Madelaine (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: Apple (Malus domestica Borkh.) is a deciduous fruit species, which is subject to dormancy before bud break occurs in spring. Although not noticed externally, anatomical changes occur in the reproductive bud during this dormant period, including formation of the carpels, enlargement of the petals and carpel and anther elongation. In this study, we determined i) the time of primary xylem formation as influenced by cultivar, month and/or climate (expressed by winter chilling) and ii) the distribution and quantification of a selected nutrient calcium (Ca) in, (a) the primary xylem tissue as well as (b) in reserve tissues (spur, leaf and apical meristem). Four different commercial apple cultivars were selected for this investigation. Golden Delicious and Braeburn represented cultivars with typical Ca deficiency symptoms in the fruit if additional Ca is not applied, whereas Royal Gala and Cripps Pink represented cultivars in which Ca related problems occur less frequently. Golden Delicious and Royal Gala are cultivars associated with high chilling requirements, and Braeburn and Cripps Pink, with medium chilling requirements. Sampling of dormant buds occurred during June, July, August and September in 2012, 2014 and 2015. The different cultivars used for this investigation were cultivated in Stellenbosch and Elgin. Although these regions are both in the Western Cape Province, the Elgin region is an area with a higher chill unit accumulation than Stellenbosch. Light, fluorescence and scanning electron microscopy imaging techniques were used to study the anatomy of primary xylem development. To differentiate the degree of lignification in primary xylem from secondary xylem, samples were imaged with a Zeiss LSM880 confocal microscope equipped with ZEN 2 software. Scanning electron microscopy images were acquired using a Zeiss Merlin FEG Scanning Electron Microscope (SEM). After the time (month) of primary xylem establishment in the bud was identified, Ca concentration (%) was quantified in reproductive apple bud tissues of all four cultivars during three seasons (2012, 2014 and 2015). Ca concentration was quantified with Wavelength Dispersive Spectrometer (Oxford Instrument® Wave Dispersive X-ray Spectrometer). Ca was simultaneously quantified with Electron Dispersive X-ray (Oxford Instrument ® Energy Dispersive X-ray). In Golden Delicious and Braeburn, the process of secondary xylem development commenced earlier than in Cripps Pink and Royal Gala. While this process is slow in Cripps Pink, xylem development proceeds much faster in Royal Gala and changes from having only primary xylem in July to having secondary xylem a month later. The timing and duration of xylem development in Cripps Pink and Royal Gala were similar in the Stellenbosch and Elgin regions in June, but differed in July and August in all three seasons. Results clearly show differences in Ca distribution and Ca concentration in the tissues of dormant reproductive apple buds of the four cultivars studied. High Ca levels were noted in the spur transport tissue of Royal Gala, Cripps Pink and Braeburn during June, with considerably lower levels of Ca in the same region in Golden Delicious. Cripps Pink and Royal Gala have a higher Ca concentration in the xylem in June, followed by an increase in Ca concentration towards September. The reduction in Ca concentration in the spur during the same period may indicate that reserve Ca from the spur is allocated towards the xylem. This needs further investigation. Although trends were not as clear in Golden Delicious and Braeburn and did not always follow the same pattern, observations in these cultivars differed from those in Cripps Pink and Royal Gala, confirming the higher presence of primary xylem reported previously. Thus, later formation or presence of primary xylem in the dormant bud of these cultivars may partly explain the lower Ca concentrations and difference in Ca distribution between tissues compared to Cripps Pink and Braeburn.

AFRIKAANS OPSOMMING: Appel (Mallus domestica Borkh.) is ʼn bladwisselende vrug spesie, wat onderhewig is aan rus voordat knoppe in die lente oopbreek. Alhoewel dit nie ekstern waargeneem word nie, vind anatomiese verandering in die reproduktiewe knop plaas gedurende hierdie rustende periode, insluitend die vorming van vrugblare, vergroting van kroonblare en vrugblaar en meeldraad verlenging. In hierdie studie het ons die volgende bepaal: i) die tyd van primêre xileem vorming soos beïnvloed deur kultivar, maand en/of klimaat (uitgedruk as winter verkoeling) en ii) die verspreiding en kwantifisering ʼn geselekteerde voedingstof kalsium (Ca) in (a) die primêre xileemweefsel asook (b) in reserwe weefsels (spoor, blaar en apikale meristeem). Vier verskillende kommersiele appel kultivars is geselekteer vir hierdie ondersoek. Golden Delicious en Braeburn het kultivars verteenwoording met tipies Ca tekort simptome in vrugte indien addisionele Ca nie toegedien word nie, terwyl Royal Gala en Cripps Pink kultivars verteenwoordig het waarin Ca verwante probleme minder algemeen voorkom. Golden Delicious en Royal Gala is kultivars geassosieer met ʼn hoë verkoeling behoefte, en Braeburn en Cripps Pink, met medium verkoelings behoeftes. Insameling van rustende knoppe het tydens Junie, Julie, Augustus en September van 2012, 2014 en 2015 plaasgevind. Die verskillende kultivars wat vir hierdie ondersoek gebruik is, is in Stellenbosch en Elgin gekweek. Alhoewel hierdie omgewings beide in die Weskaap Provinsie is, is die Elgin steek ʼn area met ʼn hoëre verkoelingseenheid akkumulasie as Stellenbosch. Lig-, fluoressensie- en skandeerelektronmikroskoop beeldvasleggings tegnieke is gebruik om die anatomie van primêre xileem ontwikkeling te bestudeer. Om die graad van lignifikasie van primêre en sekondêre xileem te differensieer, is monsters afgeneem met ʼn Zeiss LSM880 konfokale mikroskoop toegerus met ZEN 2 sagteware. Skandeerelektronmikroskoop fotos is verkry deur gebruik te maak van ʼn Zeiss Merlin FEG skandeerelektronmikroskoop (SEM). Nadat die tyd (maand) van primêre xileem vestiging in die knoppe geidentifiseer is, is Ca konsentrasie (%) in reproduktiewe appelknop weefsels vir al vier kultivars tydens drie seisoene (2012, 2014 en 2015) gekwantifiseer. Ca konsentrasie is gekwantifiseer deur Golflengte Versreidende X-straal Spektrometrie (Oxford Instrument® Wave Dispersive X-ray Spectrometer). Ca is gelyktydig gekwantifiseer met Elektron Verspreidings X-strale (Oxford Instrument ® Energy Dispersive X-ray). In Golden Delicious en Braeburn het die proses van sekondêre xileem ontwikkeling vroeër begin as in Cripps Pink en Royal Gala. Terwyl die proses stadig is in Cripps Pink, het xileem ontwikkeling baie vinniger plaasgevind in Royal Gala en het verander van slegs die besit van primêre xileem in Julie na die besit van sekondêre xileem ʼn maand later. Die tyd en duur van xileemontwikkeling in Cripps Pink en Royal Gala was eenders in die Stellenbosch en Elgin omgewing in Junie, maar het verskil in Julie en Augustus in al drie seisoene. Resultate wys duidelik verskille in Ca verspreiding en Ca konsentrasie in die weefsels van rustende reproduktiewe appel knoppe van die vier kultivars wat bestudeer is. Hoë Ca vlakke is opgemerk in die spoor vervoerweefsel van Royal Gala, Cripps Pink en Braeburn gedurende Junie, met aansienlik laer vlakke van Ca in dieselfde area in Golden Delicious. Cripps Pink en Royal Gala het hoër Ca konsentrasie in Junie gehad, gevolg deur ʼn toename in Ca konsentrasie na September toe. Die reduksie in die Ca konsentrasie in die spoor gedurende dieselfde periode mag aandui dat reserwe Ca van die spoor aan die xileem geallokeer is. Dit benodig verdere ondersoek. Alhoewel neigings nie duidelik was in Golden Delicious en Braeburn nie, en nie altyd dieslfde patroon gevolg het nie, het waarnemings in hierdie kultivars verskil van dié in Cripps Pink en Royal Gala, wat die hoër teenwoordigheid van primêre xileem wat vroeër gerapporteer is ondersteun. Dus, die later vorming en teenwoordigheid van primêre xileem in die rustende knoppe van hierdie kultivars mag deels die laer Ca konsentrasies en verskille in Ca verspreiding tussen weefsels vergeleke met Cripps Pink en Braeburn verduidelik.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101019
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