Structural and functional changes in some species of Lamiaceae family in the process of in vitro genebank development

Due to the high content of essential oils and biologically active substances in the tissues of Lamiaceae species, they are widely used in medicine, perfumery, cosmetics, and food industries. The deposition of such plant objects in vitro by creating a genebank of valuable species and cultivars and breeding forms in its turn expands the possibilities of bioresource collections preservation ex situ. The aim of our work was to determine morphological, histological, and physiological characteristics of lavender and lavandin microshoots under the long-term preservation in vitro with subsequent assessment of their viability. The studies included explants of two Lavandula L. cultivars from the Nikita Botanical Gardens collection: Record (L. angustifolia Mill.) and Rabat (L. × intermedia Emeric. ex Loisel). Deposition was carried out on 1/4 MS culture medium supplemented with sucrose (60-90 g L^‑1) and CCC (0.2-0.4 g L^‑1). The explants were maintained in cold chambers at low positive temperatures from 4 to 14°C, light intensity 1.25-3.75 μM m^‑2 s^‑1, and 16-h photoperiod. Explants parameters were recorded after 6 and 12 months of preservation. The shoot length was 2.5-4.8 cm, the total number of leaves 7-10 pcs shoot^‑1. Leaf blades were small (up to 0.6 cm long), linear-lanceolate. Their thickness reduced to 54-92 μm, intercellular spaces in the chlorenchyma became large; in most of the leaf blades, homogeneous mesophyll was noted. Chloroplasts arrangement in the cells was diffuse, less often - near the cell wall. A thin cuticle (up to 3 μm) and trichomes structurally were the same as in native plants. Leaf structure varied from hypostomatic to amphistomatic type. Preservation of viability at 95% was revealed during deposition at 4 and 6°С. The growth kinetics was slowed down 3-4 times, compared to the control, the relative photosynthetic activity was (Fm-Fst)/Fm = 0.42 ... 0.54 a.u.