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Somatic embryogenesis (SE) can be readily induced in leaf explants of the Jemalong 2HA genotype of the model legume Medicago truncatula by auxin and cytokinin, but rarely in wild-type Jemalong. Gibberellic acid (GA), a hormone not included in the medium, appears to act in Arabidopsis as a repressor of the embryonic state such that low ABA (abscisic acid): GA ratios will inhibit SE. It was important to evaluate the GA effect in M. truncatula in order to formulate generic SE mechanisms, given the Arabidopsis information. It was surprising to find that low ABA:GA ratios in M. truncatula acted synergistically to stimulate SE. The unusual synergism between GA and ABA in inducing SE has utility in improving SE for regeneration and transformation in M. truncatula. Expression of genes previously shown to be important in M. truncatula SE was not increased. In investigating genes previously studied in GA investigations of Arabidopsis SE, there was increased expression of GA2ox and decreased expression of PICKLE, a negative regulator of SE in Arabidopsis. We suggest that in M. truncatula there are different ABA:GA ratios required for down-regulating the PICKLE gene, a repressor of the embryonic state. In M. truncatula it is a low ABA:GA ratio while in Arabidopsis it is a high ABA:GA ratio. In different species the expression of key genes is probably related to differences in how the hormone networks optimise their expression.

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This study proposes a photovoltaic (PV) systems de-loaded margin online calculation method that allows PVs to participate in isolated power system frequency regulation with a proper de-loaded margin. The de-loaded margin determines PVs' frequency regulation capacity. The larger de-loaded margin of PVs provides more reserve capacity for frequency regulation, while more economic benefits are sacrificed correspondingly. Therefore, a tradeoff between PVs' economic benefit and their frequency regulation reserve capacity is necessary. Taking into account these two factors, a dynamic calculation method of PVs optimal de-loaded margin based on the systems real-time operation condition is proposed. Real-time monitoring of the systems operation condition is realised by wide-area measurement system. The calculated de-loaded margin can meet the system frequency regulation requirement with PVs' minimum economic loss. RTDS simulation is conducted in an actual industrial isolated system driven by thermal power and PVs to verify the effectiveness of the proposed method.