A rate-limiting step in abscisic acid (ABA) biosynthesis in plants is catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED).Here we present the cloning, characterization of a cDNA from dehydrated peanut (Arachis hygogaea L.) leaves that encodes aputative NCED. The 2486-bp full-length cDNA (designated as AhNCED1), obtained by rapid amplification of cDNA ends(RACE), has an open reading frame of 601 amino acid residues and encodes a protein with a calculated molecular weight of66.86 kDa and an isoelectric point of 8.39. Sequence analysis shows that the deduced amino acid sequence of AhNCED1shares high identity with the reported NCED protein sequences. There is a 30-amino-acid chloroplast-targeting peptide at theN-terminus of the AhNCED1 protein predicted by iPSORTalgorithm. Semi-quantification by duplex RT-PCR reveals thatthe expression of AhNCED1 is up-regulated by dehydration and that rehydration represses its expression. The organ specificexpression pattern of AhNCED1 has been examined, which indicates its dominant expression in leaves and stems. Molecularanalysis of the drought-inducible gene of peanut may be useful to investigate the response of agricultural crops to droughtstress.

The transformation of Torenia fournieri L. mediated by Agrobacterium rhizogenes was studied. Almost all roots induced by four bacterial strains,R1000, R1601, A4 and R1205 were putative hairy roots. The effects of bacterial strains, bacterial concentration, acetosyringone, silver nitrate and cocultivationpH on Torenia transformation were investigated. Strain R1000, co-cultivation for 3 days, 30Amol L_1 acetosyringone, 4mg L_1 silvernitrate and pH 6.5 in the cultivation medium provided the optimal conditions under which transformation frequency approached 90%.

The oxidative cleavage of cis-epoxycarotenoids catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED) is considered to be the ratelimitingstep in abscisic acid (ABA) biosynthesis. Here we demonstrate that the expression of AhNCED1 gene in peanut plants is significantlyup-regulated by dehydration and high salinity. The AhNCED1 transcript and endogenous ABA both accumulate predominantlyin leaves and stems of peanut in response to dehydration. The considerable up-regulation of AhNCED1 expression by exogenous applicationof ABA suggests a positive feedback control of ABA biosynthesis in peanut. NAA at high concentration increases ABA biosynthesisin peanut plants through up-regulation of the AhNCED1 gene expression. The constitutive expression of the AhNCED1 gene inwild-type Arabidopsis results in an increase of ABA accumulation in transgenic plants in response to drought stress. Ectopic expression ofAhNCED1 gene in 129B08/nced3 mutant Arabidopsis (with impaired AtNCED3 gene involved in ABA biosynthesis under water stress)driven by the AtNCED3 promoter restores its ability to accumulate ABA during drought stress, and reverts its hypersensitivity to nonionicosmotic stress and soil drought. These results indicate that the expression of AhNCED1 gene plays an important role in theregulation of ABA level during water stress, and that water-stress tolerance of Arabidopsis plants can be improved by ectopic expressionof the AhNCED1 gene causing accumulation of endogenous ABA.

Hairy root s were obtained in vitro 10 days after inoculation of cucumber (Cu-cumis sativ us L.) cotyledon explant s with the st rains of A grobacteri um rhizogenes R1000and R1601. The f requency of the cotyledon explants transformed by R1000 and R1601 wasup to 87.5% and 88.9%, respectively. All hairy root s induced by the st rains of R1000 and R1601 grew rapidly on solid hormone-free MS medium. The root s incited by A. rhizogenesR1000 could be divided into three phenotypes. The roots of phenotype Ⅰwere similar to thenormal ones,but had more numerous lateral root s. Root s of phenotype Ⅲwere much stouterand shorter, they elongated very slowly and were more highly branched than root s of phenol-type Ⅰ. Root s of phenotype Ⅱwere of intermediate in appearance. However, the root s in-cited by A. rhizogenes R1601 appeared similar to phenotype Ⅰroot s incited by A. rhizo-genes R1000. Transformation was confirmed by opine detection.