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Browsing by Subject "xylem"

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  • Exploration of cell types and xylem development regulators during Arabidopsis thaliana root secondary growth with single-cell transcriptome technique 
    Mäkelä, Meeri (2024)
    Secondary growth in plant vasculature tissues originate from meristematic tissue vascular cambium. Vascular cambium produces xylem inwards and phloem outwards in the plant root and stem. Vascular cambium regulatory mechanisms are not completely known, and while plants and especially trees are dependent on the mechanical support and transportation systems the vasculature provide, increased knowledge of the vascular cambium and especially xylem development is valuable. In this thesis, I explored Arabidopsis thaliana single-cell RNA-sequencing data from secondary growth stage via cloning transcriptional reporter lines, and later utilized the transcriptomics data to find potential xylem development regulators. By loss-of-function mutant and inducible overexpression line screening, I found two genes in a family of MYB transcription factors to be potential regulators in xylem development. Loss-of-function mutant did not show significant phenotype, but overexpression lines under constitutive 35S promoter showed extreme halt of growth, and a stain-filled vessel phenotype in a fixed and resin-embedded Arabidopsis cross-section. Under developing xylem -specific promoters, inducible overexpression lines showed the same phenotype, and while grown to the secondary growth stage, I detected some patterning defects. Thus, these results indicate, that these MYBs expressed in the xylem parenchyma in the single-cell transcriptomics data, might have a function in xylem development.
  • Puun vesipotentiaalin komponenttien vuorokautinen vaihtelu ja nilan osmoottisen potentiaalin mittaaminen : mittaussarja männyllä (Pinus sylvestris L.) sekä koemittauksia pilaritervalepällä (Alnus glutinosa F. pyramidalis) 
    Paljakka, Teemu (2013)
    In consequence of transpiration vast amounts of water moves from tree roots to the atmosphere via stem and leaves. Water does not only move directly from roots towards canopy. It is essential element in the maintenance of cells and fuel to solute transport in phloem. Movement of water inside the tree is caused by differences in water potential between cells and tissues. Water moves towards lower pressure potential in the xylem. Pressure is the main component of water potential in the xylem. Phloem transport is also driven by hydrostatic pressure gradient. Water moves from xylem to the phloem when the water potential is lower in the phloem than xylem. Osmotic potential is the main component of phloem water potential. Osmotic potential, practically the osmotic strength, of a cell is related to the soluble sugar and water content in the phloem. Therefore, the main components of tree water potential are pressure and the osmotic strength of a cell. Phloem is the transport pathway of sugars and other important compounds many which role is yet unknown. The dynamics of water and sugar transport is still an enigma for researchers. Understanding of water and sugar transport is vital because they appear to affect other physiological functions in trees, i.e. the function of stomata and cell growth. The research of phloem is very challenging because phloem content is easily contaminated when collected. Phloem cells have several defend reaction when disturbed. Some methods are in use in phloem research but these methods can only be used in laboratory conditions or with specific tree species. Especially few research is been carried out in situ due to its damaging effect when collecting phloem samples. Promising method to assess phloem transport is to utilize diameter measurements. Modeling of phloem transport with xylem diameter data does not disturb the function of phloem. Essential missing piece of information is quantitative data of osmotic strength in the phloem. The topic of this thesis is to examine the diurnal changes of the main components of tree water potential. Emphasis is on examining the osmotic strength of phloem and the testing of new method for studying osmotic strength of phloem. The measurements are mainly carried out with scots pine (Pinus sylvestris L.) and test evaluations are carried out with pillar black alder (Alnus glutinosa F. pyramidalis). The measurements are made with phloem pieces collected from different heights of the tree examined and with leaves from the canopy. Also the leaf water potential is measured which is related to diameter changes of the xylem. The former are compared to the osmotic strength of phloem pieces and leaves. The method used in this thesis is apparently not used in literature. The difference with methods in the literature is the freezing and thawing of phloem pieces before sampling with sentrifuge. Method brings out similar results of phloem osmotic strength found in the literature. The values might be slighlty underestimated due to the method used. According to these results the water potential of phloem are closely related to the xylem water potential with scots pine. The strongest relation with the xylem is in the phloem beneath the canopy and weakest in the phloem collected in the base of a trunk. The phloem water potential of a branch was most difficult to intepret. The osmotic strength and water content of needles were strongly related to the needle water potential. The results support the idea of a strong interaction between phloem and xylem.

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