Genes homologous to the auxin-inducible Ntl03 glutathione S-transferase (GST) gene of tobacco, were isolated from a genomic library of Arabidopsis thaliana. We isolated a 2 clone containing an auxininducible gene, AtlO3-1a, and part of a constitutively expressed gene, AtlO3-1b. The coding regions of the Arabidopsis genes were highly homologous to each other and to the coding region of the tobacco gene but distinct from the GST genes that have been isolated from arabidopsis thusfar. Overexpression of a cDNA clone in Escherichia coli revealed that the AT103-1A protein had GST activity.

Agrobacterium rhizogenes-mediated introduction of the wild-type allele of the gene encoding granulebound starch synthase (GBSS) into the amylose-free starch mutantamf of potato leads to restoration of GBSS activity and amylose synthesis, which demonstrates thatAmf is the structural gene for GBSS. Amylose was found in columella cells of root tips, in stomatal guard cells, tubers, and pollen, while in the control experiments using only vector DNA, these tissues remained amylose free. This confirms the fact that, in potato, GBSS is the only enzyme responsible for the presence of amylose, accumulating in all starch-containing tissues. Amylose-containing transformants showed no positive correlation between GBSS activity and amylose content, which confirms that the former is not the sole regulating factor in amylose metabolism.

The gene defender against apoptotic death (DAD‐1) prevents programmed cell death in animal cells. We investigated the expression pattern of DAD‐1 in petals of iris (Iris × hollandica cv. Blue Magic) and carnation (Dianthus caryophyllus cv. Etarro). DAD‐1 expression in Iris petals was strongly reduced by the time of visible senescence, which occurs 4 days after flower opening. Microscopic analysis showed that most mesophyll cells had died prior to a clear decrease in DAD‐1 expression and that epidermis cells started to die by that time. In carnation petals DAD‐1 expression also decreased by the time of massive cell death. After ethylene treatment, DAD‐1 expression in carnation again decreased concomitant with the advance in massive cell death. In conclusion, DAD‐1 is not an early regulator of petal cell death. Its expression may be required for the programmed dismantling of cells, as it ceases only just prior to, or concomitant with, cell death.

The expression of the auxin-inducible NtlOJ-1 gene of tobacco was studied inArabidopsis thaliana. For this purpose we introduced a gene fusion between the promoter of the gene and the P-glucuronidase reporter gene (GUS) into Arabidopsis thaliana. The expression and location of GUS activity were studied histochemically in time and after incubation of seedlings on medium containing auxins or other compounds. The auxins 2,4-dichlorophenoxyacetic acid (2,4-D), indole-3-acetic acid (IAA), and 1-naphthylacetic acid (l-NAA) were able to induce GUS activity in the root tips of transgenic seedlings. The auxin transport inhibitor 2,3,5-triiodobenzoic acid was able to induce GUS activity not only in the root tip, but also in other parts of the root. Induction by the inactive auxin analog 3,5-dichlorophenoxyacetic acid was much weaker. Compounds like glutathione and the heavy metal CuSO4 were weak inducers. GUS activity observed after induction by glutathione was located in the transition zone. Salicylic acid and compounds increasing the concentration of hydrogen peroxide in the cell were also very well able to induce GUS activity in the roots. The possible involvement of hydrogen peroxide as a second messenger in the pathway leading to the induction of the NtZO3-1 promoter is discussed.

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