Narendra Kumar

Homalomena aromatica is an economically important essential oil‐producing plant. The rhizome is a commercial source of essential oil useful for high‐grade perfumery and therapeutic applications. It is mainly collected from wild sources. The present study aims to investigate the histochemical localization of oil‐secreting idioblasts and the variability in oil composition in commercial samples. The histochemical study revealed that essential oil is synthesised in oil cells and oil cavities distributed in the rhizome tissues. The larger oil cavities (521 ± 59.4 μm in size) synthesise essential oil and resin, whereas the smaller oil cells (67.2 ± 7.4 μm in size) synthesise only essential oil. The spatial distribution demonstrates that the oil cavities were densely present in the inner ground tissue region, whereas the oil cells were abundant in the cortex ( p < 0.05 ). The different grades of commercial rhizome samples, that is, thickness up to 10 mm (narrow rhizomes, NR), 10 to 20 mm (medium‐sized rhizomes, MR), and 20 to 30 mm (thick rhizomes, TR) showed variation in essential oil yield and composition, fibre content, and distribution of fibre cells. The study demonstrated that the oil yield is negatively correlated with rhizome thickness, fibre content, and density of fibre cells in tissue. The oil of H. aromatica is dominated by linalool (44.18%–61.4%) followed by terpinene‐4‐ol (6.45%–13.16%) in the rhizomes of different thicknesses. These major constituents also negatively correlate with rhizome thickness and significantly decrease in the TR samples. The study concludes that the NR grade rhizomes are better for higher oil yield and linalool and terpinene‐4‐ol content than the TR grade of H. aromatica rhizomes.

Cannabis sativa L. is an important medicinal plant with high commercial value. In recent years, the research interest in cannabidiol (CBD) and terpene‐rich cannabis has been rapidly expanding due to their high therapeutic potential. The present study aims to explore the phytocannabinoids and terpenes diversity in C. sativa collected from different parts of northern India. Our findings revealed that the cannabinoids and terpenes synthesize together in capitate stalked and capitate sessile glandular trichomes, whereas bulbous glands synthesize only terpenes. The North Indian C. sativa is mainly dominated by tetrahydrocannabinol. The CBD‐rich plant diversity is nominal (1.11%) in studied north Indian C. sativa . The essential oil profiling reveals (E)‐caryophyllene (10.30%–36.80%) as the major constituent, followed by α‐humulene (0.50%–15.29%) and α‐bisabolol (0.00%–16.40%) in the North Indian population. The cannabinoids and terpenes content showed significant diversity among and within the five studied populations. The correlation analysis between cannabinoids and terpenes indicates that α‐pinene, β‐pinene and limonene positively correlated with CBD content. Similarly, α‐ and β‐selinene correlate positively with tetrahydrocannabinolic acid content. This study could help to identify the key cultivars from India and establish a consistent chemotype for future breeding programs.

Heterostyly is a specialized reproductive system associated with self‐ and intramorph incompatibility. It reinforces the intermorph breeding system in heterostylous plant species. However, distyly has not been comprehensively studied in Nyctanthes arbor‐tristis . The present study demonstrates the floral traits, breeding system, fruit and seed set, and morph ratio in distylous N. arbor‐tristis . The length of style and filament showed reciprocal herkogamy between long style (L‐morph) and short style (S‐morph). Flower size, corolla tube size, stamen and anther length, ovary length, and pollen diameter were larger in S‐morph. However, the style was longer in L‐morph. Our results demonstrated strongly incompatible self‐ and intramorph pollination combinations. The intermorph pollination was compatible, showing normal pollen tube growth throughout the style and ovary. The embryo formation was also higher in intermorph interaction. Moreover, the fruit setting was higher when the intermorph plants grew in the vicinity of natural conditions. Collectively, all data indicate that N. arbor‐tristis is a distylous species with a self‐incompatible breeding system, resulting in less seed formation in nature.

Pelargonium graveolens L’Hér is an important aromatic plant. The essential oil is secreted in the glandular trichomes distributed mainly on the leaves. In India, P. graveolens is growing only in specific climatic conditions due to the susceptibility of plants to rainfall, high humidity and waterlogging stress. This study aims to analyze rainfall-induced premature senescence in P. graveolens at six phenotypic leaf senescence stages. The physiological and biochemical parameters, cell viability, trichomes density, essential oil yield and variation in chemical constituents were evaluated. Results show a significant increase in chlorophyll-a and b, and a decrease in anthocyanin content. Also, the protein content, MDA, SOD, H2O2, catalase, electrolyte leakage was significantly higher, and cell viability decreased with the progression of senescence. The gland density on leaves was reduced during the advancement of senescence. The GC and GC-MS analysis showed that the senescence significantly modulates oil constituents and oils yield (0.048 to 0.123 %) at different senescence stages. Overall, this study confirms that rainfall induces premature senescence in P. graveolens, significantly affecting essential oil yield and constituents.