Heavy metal hyperaccumulation in plants is a poorly understood phenomenon. Transmembrane metal transporters are assumed to play a key role in this process. In the research described in this thesis, genes encoding Zn transporters of Thlaspi<span style='mso-bidi-font-weight:bold'>caerulescens</span><span style='mso-bidi-font-weight:bold;mso-bidi-font-style:italic'>, a heavy metal hyperaccumulator plant,</span>are studied and compared to their orthologues in Arabidopsis thaliana<span style='mso-bidi-font-style:italic'>, a non-hyperaccumulator plant</span>.<o:p></o:p></span>The Tc<span style='mso-bidi-font-style:italic'>ZNT1</span> and Tc<span style='mso-bidi-font-style:italic'>ZNT2</span> genes of T. caerulescens are members of the Zrt, Irt ( ZIP) -like gene family and show 89% and 87% similarity with the At<span style='mso-bidi-font-style:italic'>ZIP4</span> and At<span style='mso-bidi-font-style:italic'>IRT3</span> genes of A. thaliana<span style='mso-bidi-font-style: italic'>,</span>respectively. AtZIP4 and AtIRT3 genes are induced exclusively by Zn-deficiency in Arabidopsis. In limiting Zn conditions both Arabidopsis and Thlaspi show characteristic symptoms of Zn deficiency manifested both in vegetative and reproductive tissues. However, in T. caerulescens , Tc<span style='mso-bidi-font-style:italic'>ZNT1</span> and Tc<span style='mso-bidi-font-style:italic'>ZNT2</span> are constitutively and highly expressed in roots, irrespective of the Zn concentration in the medium. This observation suggested a role for<span class=GramE>these</span>genes in Zn uptake and possibly in explaining the Zn hyperaccumulation trait in Thlaspi . The proteins are localized in the plasma membrane, conferring zinc uptake into the cytoplasm. Tc<span style='mso-bidi-font-style:italic'>ZTP1,</span> another Zn transporter gene shows 85% sequence similarity in its coding region with the At<span style='mso-bidi-font-style: italic'>ZAT</span><span style='mso-bidi-font-style:italic'>/ MTP1 of</span>A. thaliana and is assumed to be localized in the vacuolar membrane. This gene belongs to the Cation Diffusion Facilitator (CDF) family.<o:p></o:p></span>The responses of the over-expression lines of TcZNT1,TcZNT2 and TcZTP1 in A. thaliana<span class=GramE>were</span>investigated with respect to deficiency and toxicity of Zn, Fe and Cd.</span><span lang=EN-GB style='font-family:"Times New Roman";mso-ansi-language:EN-GB'>Over-expression of Tc</span><span lang=EN-US style='font-family:"Times New Roman";mso-ansi-language: EN-US'>ZNT1</span><span lang=EN-GB style='font-family:"Times New Roman"; mso-ansi-language:EN-GB'>showed higher Zn accumulation in A. thaliana , whereas this effect was small and not significant for TcZNT2.TcZNT1 over-expression lines also showed increased Cd accumulation.</span><span lang=EN-US style='font-family:"Times New Roman";mso-ansi-language: EN-US'>In addition, the TcZNT1, TcZNT2 and TcZNT1/TcZNT2 silenced T. caerulescens showed</span><span lang=EN-GB style='font-family:"Times New Roman"; mso-ansi-language:EN-GB'>reduced Zn… Advisors/Committee Members: Wageningen University, Maarten Koornneef, Mark Aarts.

Botrytis cinerea</span><span lang=EN-GB>is the causal agent of grey mould disease on a wide variety of crop plants. It is relatively insensitive to natural and synthetic fungitoxic compounds. This thesis describes how ABC (ATP-binding cassette) transporters contribute to protection by actively secreting toxicants from fungal cells, acting as a firsts aid kit. The expression of twelve ABC transporters and three MFS transporters are differentially induced by plant defence compounds, antibiotics and fungicides. BcatrD can decrease sensitivity to azole fungicides, whereas BcatrB is a true multidrug transporter and can provide protection against the plant defence compounds resveratrol and eugenol, phenylpyrrole fungicides and phenazines antibiotics. By exporting resveratrol BcatrB contributes to virulence of</span><span lang=EN-GB style='font-size:11.0pt; line-height:125%;color:black'>B. cinerea</span><span lang=EN-GB>on grapevine. With their ability to protect against fungicides the ABC transporters BcatrB and BcatrD can contribute to the apparent ease by which</span><span lang=EN-GB style='font-size:11.0pt; line-height:125%;color:black'>B. cinerea</span><span lang=EN-GB>develops resistance against fungicides. The protection against antibiotics is a clear advantage in competition with other microorganisms. Advisors/Committee Members: Wageningen University, Pierre de Wit, M.A. de Waard.