Osmotic stress and endogenous hormone levels may have a role in shoot organogenesis, but a systematic study has not yet to investigate the links. We evaluated the changes of the endogenous indole-3-acetic acid (IAA) and abscisic acid (ABA) levels in rice (Oryza sativa L. cv. Tainan 5) callus during shoot organogenesis induced by exogenous plant growth regulator treatments or under osmotic stress. Non-regenerable callus showed low levels of endogenous ABA and IAA, with no fluctuation in level during the period evaluated. The addition of 100 lM ABA or 2 mM anthranilic acid (IAA precursor) into Murashige and Skoog basal induction medium containing 10 lM 2,4-D enhanced the regeneration frequency slightly, to 5 and 35%, respectively, and their total cellular ABA or IAA levels were increased significantly, correspondingly to the treatments. However, the regeneration frequency was greatly increased to 80% after treatment with 0.6 M sorbitol or 100 lM ABA and 2 mM anthranilic acid combined. Both treatments produced high levels of total cellular ABA and IAA at the callus stage, which was quickly decreased on the first day after transfer to regeneration medium. Thus, osmotic stress-induced simultaneous accumulation of endogenous ABA and IAA is involved in shoot regeneration in rice callus.

BackgroundShoot regeneration frequency in rice callus is still low and highly diverse among rice cultivars. This study aimed to investigate the association of plant hormone signaling and sucrose uptake and metabolism in rice during callus induction and early shoot organogenesis. The immatured seeds of two rice cultivars, Ai-Nan-Tsao 39 (ANT39) and Tainan 11 (TN11) are used in this study.ResultsCallus formation is earlier, callus fresh weight is higher, but water content is significant lower in ANT39 than in TN11 while their explants are inoculated on callus induction medium (CIM). Besides, the regeneration frequency is prominently higher in ANT39 (~80%) compared to TN11 callus (0%). Levels of glucose, sucrose, and starch are all significant higher in ANT39 than in TN11 either at callus induction or early shoot organogenesis stage. Moreover, high expression levels of Cell wall-bound invertase 1, Sucrose transporter 1 (OsSUT1) and OsSUT2 are detected in ANT39 at the fourth-day in CIM but it cannot be detected in TN11 until the tenth-day. It suggested that ANT39 has higher callus growth rate and shoot regeneration ability may cause from higher activity of sucrose uptake and metabolism. As well, the expression levels of ORYZA SATIVA RESPONSE REGULATOR 1 (ORR1), PIN-formed 1 and Late embryogenesis-abundant 1, representing endogenous cytokinin, auxin and ABA signals, respectively, were also up-regulated in highly regenerable callus, ANT39, but only ORR1 was greatly enhanced in TN11 at the tenth-day in CIM.ConclusionThus, phytohormone signals may affect sucrose metabolism to trigger callus initiation and further de novo shoot regeneration in rice culture.Electronic supplementary materialThe online version of this article (doi:10.1186/1999-3110-54-5) contains supplementary material, which is available to authorized users.

This study aimed to clarify the possible mechanism of endogenous phytohormone signaling and carbohydrate metabolism during shoot organogenesis induced by osmotic stress in rice (Oryza sativa L. cv. Tainung 71) callus. Non-regenerable calli derived from Tainung 71 immature embryos were inoculated on Murashige and Skoog medium containing 10 lM 2,4-D. They turned to highly regenerable calli (HRC) (regeneration frequency more than 75 %) with lower calli fresh weight and water content when 0.6 M sorbitol was supplemented into the medium. The regeneration frequency was prominently decreased to 25 % while an auxin transport inhibitor, 2,3,5-triiodobenzoic acid (TIBA), was added into the sorbitoltreated medium. It suggested that endogenous auxin signal may be involved in the induction of HRC under osmotic stress treatment. As well, HRC showed high levels of glucose, sucrose, and starch and high expression of cell wall-bound invertase 1, sucrose transporter 1 (OsSUT1), OsSUT2, PIN-formed 1, and late embryogenesis abundant 1 (OsLEA1) genes. Their expressions are all dramatic inhibited except OsLEA1 under TIBA treatment. It suggests a key role of auxin may be linked to the effect of shoot regeneration under osmotic stress treatment. Therefore, we present a putative hypothesis for regenerable calli induction by osmotic stress treatment in rice. Osmotic stress may regulate endogenous levels of auxin interacting with abscisic acid, then affect carbohydrate metabolism to trigger callus initiation and further shoot regeneration in rice.

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Once in soil and water, metals can enter the food chain, and the consumption of contaminated crops can pose a serious risk to human health. This study used pot experiments to evaluate the accumulation of metal elements and their influence on levels of antioxidants in vegetables. The current study clearly demonstrates that metals accumulated in the five vegetables that were planted in the contaminated soils, especially so for water spinach. Cd accumulation of all of the vegetables planted in the contaminated soils was greater Cu. The low accumulation rate that was seen in sweet potato leaf, potato, and tomato indicated their suitability for planting in suspected contaminated soil, such as at farms nearby metal industries, in replacement of high accumulators, such as leafy vegetables. The non-carcinogenic HI of Cd exposure from water spinach and sweet potato were >1, whereas those for Cu were <1. This study suggests that residents may experience health risks due to vegetable consumption, and that children are vulnerable to the adverse effects of heavy metal ingestion.