Endogenous auxin and its manipulation influence in vitro shoot organogenesis of citrus epicotyl explants

Endogenous auxin is an important regulator of in vivo organ development,but its role in in vitro organogenesis is unclear.It has been observed that the basal end of epicotyl cuttings of juvenile citrus seedlings produces fewer shoots than the apical end.Here,we report that elevated endogenous auxin levels in the basal end of citrus epicotyl cuttings are inhibitory for in vitro shoot organogenesis.Using transgenic citrus plants expressing an auxin-inducible GUS reporter gene,we have observed elevated levels of auxin at the basal end of stem cuttings that are mediated by polar auxin transport.Depleting endogenous auxin or blocking polar auxin transport enhances shoot organogenesis.An auxin transport inhibitor,N-1-naphthylphthalamic acid(NPA),can also enhance shoot organogenesis independent of its action on polar auxin transport.Finally,we demonstrate that the promotional effects of depleting endogenous auxin or blocking polar auxin transport on shoot organogenesis are cytokinin-dependent.Our study thus provides meaningful insights into possible roles of endogenous auxin and polar auxin transport,as well as auxin–cytokinin interactions,in in vitro shoot organogenesis.Meanwhile,our results may also provide practical strategies for improving in vitro shoot organogenesis for citrus and many other plant species.

Influence of Water Stress on the Citric Acid Metabolism Related Gene Expression in the Ponkan Fruits

To explore the influence of water stress on fruit quality and gene expression related to citrate metabolism of ponkan. The test were conducted from May 15 to December 24 in 2013 using six-year-old ponkan (C. blanco cv. Ponkan) trees with 40% soil water conditions by taken regular watering as control. The content of acids in fruit were determined by HPLC, and relative expression of related genes of citric acid metabolic were determined by relative fluorescence quantitative PCR. The results showed that the content of citric acid, malic acid, quinic acid and total organic acids per gram sarcocarp were extremely increased by 285.2%, 320%, 480% and 299.1%, and the content of per-fruit organic acid were 77.39%, 89.64%, 117.24% and 75.9% respectively compared to those control in the fruit mature stage. Relative expression of CitCS1, CitCS2 were higher than control, and relative expression of CitAco1, CitAco2, CitAco3 had a certain increase in the late fruit development, were lower in mature stage. Three relative expression of CitIDH gene were higher than control in mature stage. Low CitGAD4 relative expression and undetectable in mature stage, the relative expression of CitGAD5 gene had a role in promoting under water stress. Furthermore, the relative expression of CitCS1, CitCS2, CitACO1, CitACO3, CitIDH1, CitIDH2, CitIDH3, CitGAD4 and CitGAD5 were influenced by water stress through the correlation analysis. Water stress caused the accumulation of citric acid, declined fruit quality, leaded to change of the genetic rela- tive expression about citric acid synthesis and degradation. The down-regulation of CitACO1, CitGAD4 and up-regulation of CitCS1, CitCS2 might be one of the reasons that promoted to the accumulation of citric acid.

Effect of Water Deficit Stress on Isotope ^15N Uptake and Nitrogen Metabolism of Newhall Orange and Yamasitaka Mandarin Seedling

Soil water content significantly influenced uptake and distribution of ^15N in both Newhall and Yamasitaka. The content of ^15N uptake in treated plants was less than that in controlled plants, under 20% soil water content, ^15N was only taken up 16.02% by Newhall and 10.11% by Yamasitaka. The most ^15N was detained in root and old shoots under water stress. Protein concentration in two cultivars significantly decreased by water deficit stress, protein content of Newhall and Yamasitaka in controlled plants was 16.29 mg/g fresh weight and 15.89 mg/g fresh weight, but at 20% of water content, these were 9.60 mg/g fresh weight and 9.02 mg/g fresh weight. Water stress increased concentration of NH3-NH4^＋, Arginine and Proline. Compared with control plants, concentrations of NH3-NH4^＋ in both Newhall and Yamasitaka at 20% water content treatment increased 5.83 fold and 5.71 fold, Arginine increased 197% and 205%, and Proline increased 112% and 132%.

Effects of Plastic Film Mulching on Quality and Appearance of Statuma Mandarin Fruit

Six-year Statuma mandarin (Citrus unshiu Marc. Cv. Miyagawa Wase) trees were used as materials to investigate the effects of plastic film mulching on quality and appearance of Statuma mandarin fruit during three periods of cell division, cell enlargement and mature stages. The results showed that mulching during the cell division and early-mature stages increased total sugar and reduced sugar content of fruit as well as the Vc content, compared to the control. However, the titratable acid content, fruit size, peel weight and single fruit weight were all lower than the control. Film mulching during the cell division phage resulted in higher edible fruit rate, while the fruit shape index was similar to the control. Mulching during the early-mature stage didn’t affect the edible rate of fruit, but caused lower fruit shape index. Compared to the control, film mulching during the cell enlargement period caused lower total and reducing sugar content, titratable acid content and edible rate, while the Vc content was a little bit higher than the control. In addition, the fruit size, peel weight, single fruit weight and fruit shape index were all lower than the control. Mulching during the early-mature period effectively enhanced the content of total and reduced sugar and Vc and decreased the titratable acid content. Hence, it increased fruit quality but had negative effect on fruit appearance.