To understand better the plant response to ozone, we isolated and characterized an ozone-sensitive (ozs1) mutant strain from a set of T-DNA-tagged Arabidopsis thaliana ecotype Columbia. The mutant plants show enhanced sensitivity to ozone, desiccation and sulfur dioxide, but have normal sensitivity to hydrogen peroxide, low temperature and high light levels. The T-DNA was inserted at a single locus which is linked to ozone sensitivity. Identification of the genomic sequences flanking the T-DNA insertion revealed disruption of a gene encoding a transporter-like protein of the tellurite resistance/C(4)-dicarboxylate transporter family. Plants with either of two different T-DNA insertions in this gene were also sensitive to ozone, and these plants failed to complement ozs1. Transpiration levels, stomatal conductance levels and the size of stomatal apertures were greater in ozs1 mutant plants than in the wild type. The stomatal apertures of ozs1 mutant plants responded to light fluctuations but were always larger than those of the wild-type plants under the same conditions. The stomata of the mutant and wild-type plants responded similarly to stimuli such as light, abscisic acid, high concentrations of carbon dioxide and ozone. These results suggest that OZS1 helps to close stomata, being not involved in the responses to these signals.

This study explained about machining parameters of Al5086/Flyash/Sic hybrid metal matrix composites by the Taguchi technique. Al5086 reinforced in SiC (5–10 wt %) and 8% weight of flyash are retained as constants. The specimens are prepared with the help of the stir casting method. The material removal rate was examined by electrochemical machining under various parameters such as feed rate (0.15–0.30 mm/min), voltage (10–20 V), and electrolyte concentration (20–35 g/litre). Taguchi’s L16 orthogonal array was selected for design of experiments (DOEs), and 16 experimental tests were conducted to examine the effect of the selected machining parameters employed to identify the best optimal levels and also to investigate the effect of electrochemical machining parameters on MRR determined by Minitab-18.

An ozone-sensitive mutant was isolated from T-DNA-tagged lines of Arabidopsis thaliana. The T-DNA was inserted at a locus on chromosome 3, where two genes encoding glycolate oxidases, GOX1 and GOX2, peroxisomal enzymes involved in photorespiration, reside contiguously. The amounts of the mutant's foliar transcripts for these genes were reduced, and glycolate oxidase activity was approximately 60% of that of the wild-type plants. No difference in growth and appearance was observed between the mutant and the wild-type plants under normal conditions with ambient air under a light intensity of 100 µmol photons m-2 s-1. However, signs of severe damage, such as chlorosis and ion leakage from the tissue, rapidly appeared in mutant leaves in response to ozone treatment at a concentration of 0.2 µl l-1 under a higher light intensity of 350 µmol photons m-2 s-1 that caused no such symptoms in the wild-type plant. The mutant also exhibited sensitivity to sulfur dioxide and long-term high-intensity light. Arabidopsis mutants with deficiencies in other photorespiratory enzymes such as glutamate:glyoxylate aminotransferase and hydroxypyruvate reductase also exhibited ozone sensitivities. Therefore, photorespiration appears to be involved in protection against photooxidative stress caused by ozone and other abiotic factors under high-intensity light.

In general, antimicrobial agents are often used in micropropagation techniques to obtain contaminant free clones. The objective of the present study was to evaluate the effects of bavistin and cefotaxime on producing contaminant free plants of Ruellia tuberosa cultured on MS supplemented with phytohormones. Field grown nodal explants of Ruellia tuberosa was used to regenerate entire plants via direct organogenesis. Among the decontaminants tested, the fungicide bavistin along with higher concentration of BAP (2.0 mg/l) and lower concentration of NAA (1.0 mg/l) was the most effective in regeneration and producing contaminant free shoots from cultured explants. This fungicide at 300 mg/l minimised fungal contamination with survival rate of 54%. While the addition of decontaminant cefotaxime at low concentration (200 mg/l) along with same concentration of BAP and NAA stimulated the bud formation and controlled the bacterial contamination. However, its increasing concentration adversely affected the survival rate of Ruellia tuberosa. These findings clearly showed that low concentrations of bavistin and cefotaxime were not only non-toxic but also facilitated bud regeneration. The results achieved showed the decisive role not only of the use of successful fungicides and antibiotics, but also of their sufficient doses were very important in reducing contamination and helping multiple shoot proliferation. Plant Tissue Cult. & Biotech. 31(1): 1-12, 2021 (June)