Molecular Characterization of <Emphasis Type="Italic">Arabidopsis</Emphasis> and <Emphasis Type="Italic">Brassica juncea</Emphasis> Cu/Zn-Superoxide Dismutases Reveals Their Regulation of Shoot Regeneration

Superoxide dismutases (SODs) are ubiquitous metalloenzymes that catalyze the dismutation of superoxide radicals (O₂^-) to molecular oxygen (O₂) and hydrogen peroxide (H₂O₂). In this study we characterized an Arabidopsis thaliana CuZnSOD (CSD1), a close ortholog of a previously identified Brassica juncea CuZnSOD (MSOD1). CSD1 and other two homologs CSD2 and CSD3 were spatially regulated in Arabidopsis, and CSD1 exhibited distinct expression patterns in response to different stress treatments. To investigate the in vivo function of SOD, transgenic Arabidopsis plants, expressing sense and antisense MSOD1 RNAs, were generated and those with altered SOD activity were selected for further characterization. Although SOD transgenic plants exhibited normal phenotypes, the shoot regeneration response in transgenic explants was significantly affected by the modulated SOD activity and the corresponding H₂O₂ levels. Transgenic explants with downregulated SOD activity were poorly regenerative, whereas those with upregulated SOD activity were highly regenerative. These results suggest that shoot regeneration in vitro is regulated by the SOD activity.     

Categorization of low cardiorespiratory fitness using obesity indices in non-smoking Singaporean women

Objective: To revisit cut‐off values of BMI, waist circumference (WC), and waist‐to‐stature ratio (WSR) based on their association with cardiorespiratory fitness (CRF). The derived cut‐off points were compared with current values (BMI, 25.0 kg/m²; WC, 80 cm) as recommended by the World Health Organization. Research Methods and Procedures: Anthropometric indices were measured in a cross sectional study of 358 Singaporean female employees of a large tertiary hospital (63% Singaporean Chinese, 28% Malays, and 9% Indians). CRF was determined by the 1‐mile walk test. Receiver operating characteristic curves were constructed to determine cut‐off points. Results: The cut‐off points for BMI, WC, and WSR were 23.6 kg/m², 75.3 cm, and 0.48, respectively. The areas under the curve of BMI, WC, and WSR were 0.68, 0.74, and 0.74, respectively. For a given BMI, women with low CRF had higher WSR compared with women with high CRF. Discussion: These findings provide convergent evidence that the cut‐off points for Singaporean women were lower than the World Health Organization's criteria but were in good agreement with those reported for Asians.     

Modulation of SAMDC expression in Arabidopsis thaliana alters in vitro shoot organogenesis

S -Adenosylmethionine decarboxylase (SAMDC, EC 4.1.4.50) is a rate-limiting enzyme in the biosynthesis of polyamines (PAs) from putrescine. To gain more insight into the role of PAs in shoot organogenesis, a reverse genetic approach has been used to study in vitro shoot organogenesis by manipulating SAMDC expression in Arabidopsis . Up- and downregulation of SAMDC expression was achieved by transferring sense, antisense and double-stranded Arabidopsis SAMDC complementary DNA constructs back into Arabidopsis via Agrobacterium tumefaciens . Results show that the biosynthesis of PAs and ethylene is mutually antagonistic by manipulation of SAMDC expression. Further results demonstrate that increased shoot organogenesis seems to be directly related to PA accumulation. This effect of PA may be further enhanced with reduced ethylene. It also suggests that spermidine is involved in the process of acquiring organogenesis competence through downregulation of ethylene production and shoot organogenesis, which might result from the concerted action of PAs and plant hormones such as auxin, cytokinins and ethylene.     

The Never ripe Mutant Provides Evidence That Tumor-Induced Ethylene Controls the Morphogenesis of Agrobacterium tumefaciens-Induced Crown Galls on Tomato Stems

We confirm the hypothesis that Agrobacterium tumefaciens-induced galls produce ethylene that controls vessel differentiation in the host stem of tomato (Lycopersicon esculentum Mill.). Using an ethylene-insensitive mutant, Never ripe (Nr), and its isogenic wild-type parent we show that infection by A. tumefaciens results in high rates of ethylene evolution from the developing crown galls. Ethylene evolution from isolated internodes carrying galls was up to 50-fold greater than from isolated internodes of control plants when measured 21 and 28 d after infection. Tumor-induced ethylene substantially decreased vessel diameter in the host tissues beside the tumor in wild-type stems but had a very limited effect in the Nr stems. Ethylene promoted the typical unorganized callus shape of the gall, which maximized the tumor surface in wild-type stems, whereas the galls on the Nr stems had a smooth surface. The combination of decreased vessel diameter in the host and increased tumor surface ensured water-supply priority to the growing gall over the host shoot. These results indicate that in addition to the well-defined roles of auxin and cytokinin, there is a critical role for ethylene in determining crown-gall morphogenesis.     

Plasticity and variability in the patterns of phytolith formation in Asteraceae species along a large rainfall gradient in Israel

Silicification and phytolith formation in Poaceae species growing in arid and semi-arid regions are commonly thought to be positively correlated with silica and water availabilities and with transpiration. To expand our understanding of this phenomenon, we chose to study species of the Asteraceae, the largest dicotyledonous family. We measured phytolith concentrations in eight Asteraceae species (three non-spiny and five spiny) and one Poaceae species (Avena sterilis), as reference, along a large climatic gradient of 80–900 mm mean annual rainfall in Israel.