P. Twumasi : "Hydraulic properties of Zinnia elegans: from cellular development in vitro to performance in planta"

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8 May 2007 16:00
Unit: Wageningen University
Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen
Organisation: Wageningen University
Promotor: prof.dr. O. van Kooten (Horticultural Production Chains)
Co Promotor: A.M.C. Emons (promotor), J.H.N. Schel, W. van Ieperen

 The vessel properties of the xylem, such as length and diameter, are important for hydraulic conductance in the stems of a plant. Especially in cut flowers, the preservation of continuous hydraulic conductance is necessary for maintaining a long vase life which is an important parameter to determine cut flower quality. The worldwide losses in cut flower value, accrued in a year due to the poor maintenance of postharvest water balance in the stems, runs into millions of US dollars. To better understand the regulation of xylem vessel element development and how to influence this developmental process, by use of environmental factors for an efficient post harvest hydraulic conductivity, this thesis focused on studying the in vitro cellular differentiation of Zinnia elegans mesophyll cells into the fundamental units of the xylem vessels called tracheary elements (TEs) with emphasis on regulating their dimensions by drought stress and cell death inhibitors. It also considered the regulation of the dimensions of whole plant xylem vessels in cut flowers of Zinnia elegans by water stress and temperature. By reducing drought stress or inhibiting cell death in the in vitro experiments, the size (length and area) of the xylem elements produced increased by up to 300%, although with 24-48 h delay in the differentiation process, coupled with a reduction in the number of cells that became xylem elements. Such an extensive anatomical modification implies significant adjustments in the potential water transport capacity. In the whole plant experiments, drought stress induced narrower and more xylem vessels, resulting in the production of cut flowers with a higher post harvest quality, measured as vase life, as compared to the non-stressed cut flowers. Also, by increasing the temperature during growth, there were corresponding increases in the whole xylem vessel length (an increase of 130% when temperature increased from 17 oC to 25 oC) and average vessel element length (an increase of 20% when temperature increased from 17 oC to 25 oC). Thus, there was a greater change in the whole vessel length with temperature as compared to the average vessel element length and this, therefore, makes the rate of fusion of the individual vessel elements an important factor in determining xylem vessel length using growth temperatures.

Title thesis: "Hydraulic properties of Zinnia elegans: from cellular development in vitro to performance in planta "
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