Cellular and Morpho-histological Foundations of In Vitro Plant Regeneration

Flower structure, anatomy, and sexuality of Chrysophyllum gonocarpum (Sapotaceae)

The Sapotaceae are a significant component of the humid forests of the Neotropics and have many species of economic interest. Chrysophyllum gonocarpum is one of them and its edible fruits have currently acquired a high commercial value. Since there are no studies that cover its floral anatomy and elucidate its sexual system, the objective of the present study is to describe these aspects based on field observations and a detailed anatomical analysis of their flowers. Conventional techniques of plant anatomy are implemented. The results indicate that the species presents cryptic dioecy, showing specimens with morphologically and functionally pistillate flowers (with reduced staminodes), and trees with morphologically hermaphrodite and functionally staminate flowers. In addition, data on floral nectaries and laticiferous are provided.

Transcriptome Analysis of Melocactus glaucescens (Cactaceae) Reveals Metabolic Changes During in vitro Shoot Organogenesis Induction

Melocactus glaucescens is an endangered cactus highly valued for its ornamental properties. In vitro shoot production of this species provides a sustainable alternative to overharvesting from the wild; however, its propagation could be improved if the genetic regulation underlying its developmental processes were known. The present study generated de novo transcriptome data, describing in vitro shoot organogenesis induction in M. glaucescens. Total RNA was extracted from explants before (control) and after shoot organogenesis induction (treated). A total of 14,478 unigenes (average length, 520 bases) were obtained using Illumina HiSeq 3000 (Illumina Inc., San Diego, CA, USA) sequencing and transcriptome assembly. Filtering for differential expression yielded 2,058 unigenes. Pairwise comparison of treated vs. control genes revealed that 1,241 (60.3%) unigenes exhibited no significant change, 226 (11%) were downregulated, and 591 (28.7%) were upregulated. Based on database analysis, more transcription factor families and unigenes appeared to be upregulated in the treated samples than in controls. Expression of WOUND INDUCED DEDIFFERENTIATION 1 (WIND1) and CALMODULIN (CaM) genes, both of which were upregulated in treated samples, was further validated by real-time quantitative PCR (RT-qPCR). Differences in gene expression patterns between control and treated samples indicate substantial changes in the primary and secondary metabolism of M. glaucescens after the induction of shoot organogenesis. These results help to clarify the molecular genetics and functional genomic aspects underlying propagation in the Cactaceae family.

Leaf heteroblasty in Passiflora edulis as revealed by metabolic profiling and expression analyses of the microRNAs miR156 and miR172

BACKGROUND AND AIMS

Juvenile-to-adult phase transition is marked by changes in leaf morphology, mostly due to the temporal development of the shoot apical meristem, a phenomenon known as heteroblasty. Sugars and microRNA-controlled modules are components of the heteroblastic process in Arabidopsis thaliana leaves. However, our understanding about their roles during phase-changing in other species, such as Passiflora edulis, remains limited. Unlike Arabidopsis, P. edulis (a semi-woody perennial climbing vine) undergoes remarkable changes in leaf morphology throughout juvenile-to-adult transition. Nonetheless, the underlying molecular mechanisms are unknown.

METHODS

Here we evaluated the molecular mechanisms underlying the heteroblastic process by analysing the temporal expression of microRNAs and targets in leaves as well as the leaf metabolome during P. edulis development.

KEY RESULTS

Metabolic profiling revealed a unique composition of metabolites associated with leaf heteroblasty. Increasing levels of glucose and α-trehalose were observed during juvenile-to-adult phase transition. Accumulation of microRNA156 (miR156) correlated with juvenile leaf traits, whilst miR172 transcript accumulation was associated with leaf adult traits. Importantly, glucose may mediate adult leaf characteristics during de novo shoot organogenesis by modulating miR156-targeted PeSPL9 expression levels at early stages of shoot development.

CONCLUSIONS

Altogether, our results suggest that specific sugars may act as co-regulators, along with two microRNAs, leading to leaf morphological modifications throughout juvenile-to-adult phase transition in P. edulis.

Morpho-histological development of the somatic embryos of Typha domingensis

Background

Sustainable methods of propagation of Typha domingensis through somatic embryogenesis can help mitigate its current condition of ecological marginalization and overexploitation. This study examined whether differentiation up to coleoptilar embryos could be obtained in an embryogenic line proliferated with light and high auxin concentration.

Methods

Murashige and Skoog medium at half ionic strength and containing 3% sucrose and 0.1% ascorbic acid was used for the three embryogenic phases. Induction started with aseptic 9-day-old germinated seeds cultured in 0.5 mg L⁻¹ 2,4-dichlorophenoxyacetic (2,4-D). Proliferation of the embryogenic callus was evaluated at 2,4-D concentrations ranging from 0 to 2 mg L⁻¹ in cultures maintained in the dark. The dominant embryogenic products obtained in each treatment were used as embryogenic lines in the third phase. Thus, maturation of the somatic embryos (SEs) was analyzed using four embryogenic lines and under light vs. dark conditions. Embryogenic differentiation was also monitored histologically.

Results

Proliferation of the nine morphogenetic products was greater in the presence of 2,4-D, regardless of the concentration, than in the absence of auxin. Among the products, a yellow callus was invariably associated with the presence of an oblong SE and suspended cells in the 2,4-D treatments, and a brown callus with scutellar somatic embryos (scSEs) in the treatment without 2,4-D. During the maturation phase, especially the embryogenic line but also the light condition resulted in significant differences, with the highest averages of the nine morphogenetic products obtained under light conditions and the maximum concentration of auxin (YC3 embryogenic line). Only this line achieved scSE growth, under both light and dark conditions. Structurally complete coleoptilar somatic embryos (colSEs) could be anatomically confirmed only during the maturation phase.

Discussion

In the embryogenic line cultured with the highest auxin concentration, light exposure favored the transdifferentiation from embryogenic callus to scSE or colSE, although growth was asynchronous with respect to the three embryogenic phases. The differentiation and cellular organization of the embryos were compatible with all stages of embryogenic development in other monocotyledons. The growth of colSEs under light conditions in the YC3 embryogenic line and the structurally complete anatomic description of colSEs demonstrated that differentiation up to coleoptilar embryos could be obtained. The diversity of embryogenic products obtained in the YC3 embryogenic line opens up the opportunity to synchronize histological descriptions with the molecules associated with the somatic embryogenesis of Typha spp.