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Programmed cell death (PCD) plays an important role during developmental and defense processes in plants. One specific developmental process is the formation of xylem vessels which mainly consist of fused dead, hollow cells called vessel or tracheary elements (TE). These elements are composed of lignified cellulose walls. Anatomical dimensions of these xylem vessels, especially the length and diameter, greatly influence water status of the plant. Manipulation of TE dimensions by e.g. environmental conditions affects the plant's water status and may affect agronomical characteristics (Twumasi et al., Acta Hort 669: 303-311, 2005). PCD is an integral part of the TE differentiation process and we investigated if manipulation of PCD affects the kinetics of TE differentiation and their final dimensions during TE differentiation of Zinnia elegans cv Envy mesophyll cells. Application of E64 (a general protease inhibitor) and Ac-Z-asp-DCB (a broad-range human caspase inhibitor), both well established inhibitors of PCD in plants, resulted in a significant delay in the timing of cell death, the formation of secondary wall thickenings and significantly affected the final TE dimensions (length and area). We found the effects to be directly proportional to the drug concentrations within the non-lethal boundaries. Both inhibitors were effective at 10nM concentration in the mesophyll suspension cultures. The timing and role of PCD in relation to the formation of secondary wall thickening is discussed |
