Promoting root induction and growth of in vitro macadamia (<Emphasis Type="Italic">Macadamia tetraphylla</Emphasis> L. ‘Keaau’) plantlets using CO<Subscript>2</Subscript>-enriched photoautotrophic conditions

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 CO₂ 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 CO₂-enriched (1,000 μmol CO₂ 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 CO₂-enriched photoautotrophic conditions. The supplementation of sucrose (29–88 mM) to culture media in both ambient and elevated CO₂ 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 CO₂-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 CO₂-enriched photoautotrophic conditions.     

Proteomic analysis of drought-responsive proteins in rice reveals photosynthesis-related adaptations to drought stress

Drought stress inhibits rice growth and biomass accumulation. To identify novel regulators of drought-stress responses in rice, we conducted a proteome-level study of the stress-susceptible (SS) Oryza sativa L. cv. ‘Leung Pratew 123’ and its stress-resistant (SR) somaclonal mutant line. In response to osmotic-stress treatments, 117 proteins were differentially accumulated, with 62 and 49 of these proteins detected in the SS and SR rice lines, respectively. There were six proteins that accumulated in both lines. The proteins in the SS line were mainly related to metabolic processes, whereas the proteins identified in the SR line were primarily related to retrotransposons. These observations suggest that retrotransposons may influence the epigenetic regulation of gene expression in response to osmotic stress. To identify the biological processes associated with drought tolerance in rice, we conducted a co-expression network analysis of 55 proteins that were differentially accumulated in the SR line under osmotic-stress conditions. We identified a major hub gene; LOC_Os04g38600 (encoding a glyceraldehyde-3-phosphate dehydrogenase), suggesting that photosynthetic adaptation via NADP(H) homeostasis contributes to drought tolerance in rice.     

In vitro acclimatization of Curcuma longa under controlled iso-osmotic conditions

In vitro acclimatization has been validated as the successful key to harden the plantlets before transplanting to ex vitro conditions. In the present study, we investigated the potential of different sugar types (glucose, fructose, galactose, sucrose) in regulating morphological, physiological and biochemical strategies, survival percentage and growth performance, and rhizome traits of turmeric under iso-osmotic potential. Leaf greenness (SPAD value) in acclimatized plantlets (4% glucose; −1.355 MPa osmotic potential) of ‘ST018’ was retained and greater than in ‘PB009’ by 1.69-fold, leading to maintain high F_v/F_m (maximum quantum yield of PSII), Φ_PSII (photon yield of PSII) and P_n (net photosynthetic rate) levels, and retained shoot height, leaf length, leaf width, shoot fresh weight and shoot dry weight after one month upon transplanting to ex vitro conditions. In addition, P_n, C_i (intracellular CO₂), g_s (stomatal conductance) and E (transpiration rate) in acclimatized plantlets (6% sucrose; −1.355 MPa osmotic potential) of ‘PB009’ were stabilized as physiological adapted strategies, regulating the shoot and root growth and fresh and dry weights of mini-rhizome. Interestingly, the accumulation of total curcuminoids in mini-rhizome derived from 6% sucrose acclimatized plantlets of ‘ST018’ was greater than in ‘PB009’ by 3.76-fold. The study concludes that in vitro acclimation of turmeric ‘PB009’ and ‘ST018’ using 6% sucrose and 4% glucose, respectively, promoted percent survival, physiological adaptations, and overall growth performances under greenhouse conditions.