Soluble carbohydrates play a key role as osmolytes and significantly contribute in salt defence mechanism, especially in halophyte species. The objective of this study is to investigate the transcriptional expression of starch-related genes, sugar profile and physiological performances of two contrasting rice genotypes, Pokkali (salt tolerant) and IR29 (salt sensitive), in response to salt stress. Total soluble sugars, glucose and fructose levels in the flag leaf of salt-stressed Pokkali rice were enhanced relative to soluble starch accumulation in plants exposed to EC = 13.25 dS m(-1) (salt stress) for 3 days. In Pokkali, the net photosynthetic rate and starch metabolism may play a key role as energy resources under salt stress. In contrast, photosynthetic performance, indicated by photosynthetic pigment levels and chlorophyll fluorescence parameters, in salt-stressed IR29 was significantly reduced, leading to delayed starch biosynthesis. The reduction in photosynthetic ability and lack of defence mechanisms in IR29 caused growth inhibition and yield loss. Soluble starch and soluble sugar enrichment in Pokkali rice may function alternatively as osmotic adjustment in salt defence mechanism and strengthen carbon energy reserves, greater survival prospects under salt stress and enhanced productivity.
In this study, a rooting protocol was developed for macadamia plantlets with healthy roots and enhanced growth performance, along with enhanced photosynthetic capability. In vitro-grown shoots rooted in vented vessels containing vermiculite as the supporting material exhibited 100% frequency of root induction, whereas when shoots were grown in non-vented vessels containing a solidified Murashige and Skoog (MS) medium, the frequency of root induction was less than 30%. The formation of root with callus, hyperhydricity, and leaf necrosis was observed in this photomixotrophic closed system. The modification of the vented photoautotrophic system with different concentrations of CO 2 and sucrose were investigated using vermiculite as the supporter. The number of roots, root length, root surface area, fresh weight, and dry weight were significantly higher in plantlets grown in CO 2 -enriched (1,000 lmol CO 2 mol -1 ) photoautotrophic conditions. The water content in both root and shoot tissues of plantlets cultured under photoautotrophic conditions was maximized. In addition, shoot and leaf performances were enhanced in plantlets cultured under CO 2 -enriched photoautotrophic conditions. The supplementation of sucrose (29-88 mM) to culture media in both ambient and elevated CO 2 conditions affected a reduction in the shoot and root performance of in vitro plantlets. Chlorophyll a, chlorophyll b, and total carotenoids in the leaf tissues of plantlets acclimatized in CO 2 -enriched photoautotrophic conditions were enriched, leading to increasing photosynthetic abilities, including chlorophyll fluorescence and net photosynthetic rate. From this investigation, a root induction protocol was established and the production of healthy macadamia plantlets was successfully implemented using CO 2 -enriched photoautotrophic conditions.
Anther culture is a biotechnology technique that can be used for the production of pure lines. The aims of this investigation were to induce embryogenic callus from major and minor culms of Thai aromatic rice cultivars and to subsequently regenerate double-haploid green plantlets by the application of exogenous polyamines. Embryogenic callus derived from anther culture was successfully induced in varieties KDML105, Homjan (HJ), and Pathumthani 1 (PT1). Production of embryogenic callus from anthers collected from the major culms was greater than those collected from the minor culms, especially in cultivar HJ. Plantlet regeneration in the three rice cultivars was observed from embryogenic callus and was highest, at 12.1%, from variety HJ treated with 0.5 mM spermidine. Plantlet regeneration from anther-derived embryogenic callus was dependent on the plant genotype, the types of exogenous polyamines, and the interactions of these factors. The percentage of haploid plantlets regenerated in PT1, KDML105, and HJ were 68.1%, 70.7%, and 78.5%, respectively. Only haploid plantlets were treated with colchicine for double-haploid production. This investigation has increased the knowledge of both embryogenic callus induction and plantlet regeneration in aromatic rice and has lead to the development of a pure, double-haploid line for the use in rice breeding programs in Thailand.
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