Silencing of the ACC synthase gene ACACS2 causes delayed flowering in pineapple [Ananas comosus (L.) Merr.]

Flowering is a crucial developmental stage in the plant life cycle. A number of different factors, from environmental to chemical, can trigger flowering. In pineapple, and other bromeliads, it has been proposed that flowering is triggered by a small burst of ethylene production in the meristem in response to environmental cues. A 1-amino-cyclopropane-1-carboxylate synthase (ACC synthase) gene has been cloned from pineapple (ACACS2), which is induced in the meristem under the same environmental conditions that induce flowering. Two transgenic pineapple lines have been produced containing co-suppression constructs designed to down-regulate the expression of the ACACS2 gene. Northern analysis revealed that the ACACS2 gene was silenced in a number of transgenic plants in both lines. Southern hybridization revealed clear differences in the methylation status of silenced versus non-silenced plants by the inability of a methylation-sensitive enzyme to digest within the ACACS2 DNA extracted from silenced plants, indicating that methylation is the cause of the observed co-suppression of the ACACS2 gene. Flowering characteristics of the transgenic plants were studied under field conditions in South East Queensland, Australia. Flowering dynamics studies revealed significant differences in flowering behaviour, with transgenic plants exhibiting silencing showing a marked delay in flowering when compared with non-silenced transgenic plants and control non-transformed plants. It is argued that the ACACS2 gene is one of the key contributors towards triggering 'natural flowering' in mature pineapples under commercial field conditions.

Muscle glycogen inharmoniously regulates glycogen synthase activity, glucose uptake, and proximal insulin signaling

Muscle glycogen inharmoniously regulates glycogen synthase activity, glucose uptake, and proximal insulin signaling. Am J Physiol Endocrinol Metab 290: E154-E162, 2006. First published August 23, 2005; doi:10.1152/ajpendo. 00330.2005.-Insulin-stimulated glucose uptake and incorporation of glucose into skeletal muscle glycogen contribute to physiological regulation of blood glucose concentration. In the present study, glucose handling and insulin signaling in isolated rat muscles with low glycogen (LG, 24-h fasting) and high glycogen (HG, refed for 24 h) content were compared with muscles with normal glycogen (NG, rats kept on their normal diet). In LG, basal and insulin-stimulated glycogen synthesis and glycogen synthase activation were higher and glycogen synthase phosphorylation (Ser645, Ser649, Ser653, Ser657) lower than in NG. GLUT4 expression, insulin-stimulated glucose uptake, and PKB phosphorylation were higher in LG than in NG, whereas insulin receptor tyrosyl phosphorylation, insulin receptor substrate-1-associated phosphatidylinositol 3-kinase activity, and GSK-3 phosphorylation were unchanged. Muscles with HG showed lower insulin-stimulated glycogen synthesis and glycogen synthase activation than NG despite similar dephosphorylation. Insulin signaling, glucose uptake, and GLUT4 expression were similar in HG and NG. This discordant regulation of glucose uptake and glycogen synthesis in HG resulted in higher insulin-stimulated glucose 6-phosphate concentration, higher glycolytic flux, and intracellular accumulation of nonphosphorylated 2-deoxyglucose. In conclusion, elevated glycogen synthase activation, glucose uptake, and GLUT4 expression enhance glycogen resynthesis in muscles with low glycogen. High glycogen concentration per se does not impair proximal insulin signaling or glucose uptake. Insulin resistance is observed at the level of glycogen synthase, and the reduced glycogen synthesis leads to increased levels of glucose 6-phosphate, glycolytic flux, and accumulation of nonphosphorylated 2-deoxyglucose.

Carotenoid content of pandanus fruit cultivars and other foods of the Republic of Kiribati

Background: Kiribati, a remote atoll island country of the Pacific, has serious problems of vitamin A deficiency (VAD). Thus, it is important to identify locally grown acceptable foods that might be promoted to alleviate this problem. Pandanus fruit (Pandanus tectorius) is a well-liked indigenous Kiribati food with many cultivars that have orange/yellow flesh, indicative of carotenoid content. Few have been previously analysed. Aim: This study was conducted to identify cultivars of pandanus and other foods that could be promoted to alleviate VAD in Kiribati. Method: Ethnography was used to select foods and assess acceptability factors. Pandanus and other foods were analysed for beta- and alpha-carotene, beta-cryptoxanthin, lutein, zeaxanthin, lycopene and total carotenoids using high-performance liquid chromatography. Results: Of the nine pandanus cultivars investigated there was a great range of provitamin A carotenoid levels (from 62 to 19 086 mu g beta-carotene/100 g), generally with higher levels in those more deeply coloured. Seven pandanus cultivars, one giant swamp taro (Cyrtosperma chamissonis) cultivar and native fig (Ficus tinctoria) had significant provitamin A carotenoid content, meeting all or half of estimated daily vitamin A requirements within normal consumption patterns. Analyses in different laboratories confirmed high carotenoid levels in pandanus but showed that there are still questions as to how high the levels might be, owing to variation arising from different handling/preparation/analytical techniques. Conclusions: These carotenoid-rich acceptable foods should be promoted for alleviating VAD in Kiribati and possibly other Pacific contexts where these foods are important. Further research in the Pacific is needed to identify additional indigenous foods with potential health benefits.