Ozone-induced oxidative stress: Mechanisms of action and reaction. -Physiol. Plant. 100: 264-273.In this review we explore several models which might explain ozone (03)-induced injury to plant foliage. Ozone enters the cell through the wall and plasma membrane where active oxygen species are generated. If the concentration of O3 is very high, unregulated cell death will occur. Alternatively, the active oxygen species, or succeeding reaction products, may serve as elicitors of regulated plant responses. These regulated responses include the induction of ethylene which could serve as a primary signal for -or a facilitator of -subsequent responses. The role of regulated suppression of photosynthetic genes and induction of chitinases and y5-l,3-glucanase in programmed cell death is explored. Induction of antioxidants, enzymes of lignification and glutathione-5-transferase are discussed in the context of 03-induced cell repair or cell protection. A second model is postulated to explain induction of accelerated foliar senescence by low levels of O3. The notion that 03-induced elicitation of responses in the nucleus might lead to increased oxidative stress in the chloroplast is considered as a mechanism for accelerating the rate of degradation of ribulose-l,5-bisphosphate carboxylase/oxygenase (Rubisco). The mechanisms by which O3 induces loss of Rubisco, and the relationship to accelerated foliar senescence are discussed.

We describe a modified Agrobacterium-mediated method for the efficient transformation of Agaricus bisporus. Salient features of this procedure include cocultivation of Agrobacterium and fruiting body gill tissue and use of a vector with a homologous promoter. This method offers new prospects for the genetic manipulation of this commercially important mushroom species.

1-Aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14) is the key regulatory enzyme in the ethylene biosynthetic pathway. The identification and characterization of a full-length cDNA (pAIM-1) 1941 bp in length for indole-3-acetic acid (IAA)-induced ACC synthase is described in this paper. The pAIM-1 clone has an 87 bp leader and a 402 bp trailing sequence. The open reading frame is 1452 bp long encoding for a 54.6 kDa polypeptide (484 amino acids) which has a calculated isoelectric point of 6.0. In vitro transcription and translation experiments support the calculated molecular weight and show that the enzyme does not undergo processing. Eleven of the twelve amino acid residues which are conserved in aminotransferases are found in pAIM-1. The sequence for pMAC-1 which is one of the 5 genes we have identified in mung bean is contained in pAIM-1. pAIM-1 shares between 52 to 65% homology with previously reported sequences for ACC synthase at the protein level. There is little detectable pAIM-1 message found in untreated mung bean tissues; however, expression is apparent within 30 min following the addition of 10 microM IAA reaching a peak after approximately 5 h with a slight decrease in message after 12 h. These changes in message correlate with changes in ACC levels found in these tissues following treatment with 10 microM IAA.

1983. The effect of brassinosteroid on auxin-induced ethylene production by etiolated mung bean segments. -Physiol. Plant. 59: 539-544.Brassinosteroid, an analogue of brassinolide, (BR) (2a, 3a. 22|5, 23(5-tctrahydroxyindole-3-acctic acid (IAA), naphthaleneacetic ac-id (NAA), 2,4-dichlorophcnoxyacetic acid (2.4-D), indolc-3-butyric acid (IBA). indole-3-propionic acid (IPA). indole-3-pyruvic acid (IPyA), indole-3-aldchydc (tAld), indolc-3-carbiiiol (tCB) or tryptophan (TRP) lor its effects on ethylene piodtiction by etiolated mung bean IAA, or NAA (these increases were 2580, 2070, 890, and 30t)%. respectively), decrease in the percentage stimulation by BR. Both IPyA and IPA had different percentage stimulations (1430 and 1580%) were greatest with 5 [iM IPyA and 10 [iM IPA, respectively. There was a marked reduction in the percentage stimulation by BR with either 100 [LM IPyA or IPA. The inactive indoles (IAld. ICB, or TRP) did not synergi/.e with BR at any of the concentrations tested. Four hours tollovving treatment those segments in contact with 1 yiM BR with or without the addition of 10 f.iM IAA began to show a stimulation in ethylene production above the control and this stimulation became greater over the following 20 h. It was necessary for BR to be ethylene production. When segments excised from greater distances below the hypocotyl hook, were treated with cither IAA alone or in combination with BR, effect of hypocotyl length on BR stimulation of auxin-induced ethylene production; R. N. Arteca (reprint requests),

The rate‐limiting enzyme in the ethylene biosynthesis pathway is 1‐aminocyclo‐propane‐1‐carboxylate (ACC) synthase. We have investigated an ozone (O3)‐induced ACC synthase gene in Arabidopsis thaliana. Four previously reported ACC synthase genes from A. thaliana (ACS1, ACS2, ACS4 and ACS5) were not induced in response to O3 stress. An O3‐induced 1 098‐bp cDNA encoding ACC synthase was isolated from foliage of A. thaliana; this sequence was identical to that of ACS6 which could be induced by multiple stimuli including touch. When plants were treated with 350 nl l−1 of O3 for 2 or 6 h. the evolution of ethylene became maximal after 1.5 h and gradually decreased thereafter. Similarly, the mRNA transcript of O3‐induced ACC synthase was detected after 30 min of exposure, attained a maximum level after 1 h, and then declined. Visible damage in O3‐treated plants was observed at the end of the 2‐h exposure. This ACC synthase gene in A. thaliana provides a useful tool for studying O3‐induced responses related to ethylene production at the molecular and genetic levels.