Morphological Structure And Developmental Regularity Of Glandular Prickles Of The Rosa Genus

Rosa plants have important ornamental value and economic value,and are widely used in landscaping,cut flowers,pharmaceutical and aromatic industries.However,most of the Rosa plants have sharp prickles and do not fall off,which causes great inconvenience in field cultivation management,harvesting,transportation and processing.According to the presence or absence of glandular structure,the types of prickles were classified into nonglandular prickles(NGPs)and glandular prickles(GPs).At present,domestic and foreign researchers lack a clear and unified understanding of the morphological development and organizational structure of the Rosa prickles,and basically focus on the study of NGPs,while there are few reports on the morphology and anatomy of GPs.In this study,R.damascena,R.gallica ‘Cardinal de Richelieu’and R.hybrida ‘Spirit of Freedom’ were used as materials.Detailed morphological and histological descriptions of GPs on the stems of these three materials were performed,so as to clarify the basic characteristics and developmental rules of the morphological structure of GPs.In order to provide new ideas and theoretical basis for further exploring the molecular mechanism of the formation of prickles in genus Rosa.The main research results are as follows:1.Investigation of different types of prickles in the genus RosaThe types of prickles were accurately described in the genus Rosa germplasm repository.R.multiflora was the representative material with only NGPs on its stem,while R.damascena had both NGPs and GPs on its stem.In addition,we found that NGPs of some genotypes covered trichomes,such as R.bracteata and R.cymosa var.puberula.2.Morphological and developmental study of GPsThe key morphological events during the development of GPs on stem surfaces of R.damascena,R.gallica ‘Cardinal de Richelieu’ and R.hybrida ‘Spirit of Freedom’ were characterized by stereoscopic microscope and scanning electron microscopy.The results showed that the development process of GPs in the three materials were similar.In the initial stage,The primordia of GPs were smaller and gave rise to the “cylindrical” bumps.Compared with the early development stage,the basal part of GPs at the mature stage were not significantly widened,the GPs were shown as “needle-like” or “column-like”bulges.Moreover,compared with NGPs,GPs were more abundant and more densely distributed on stems.In addition,NGPs usually appeared below the petiole base,and the location of NGPs had certain regularity,while the distribution of GPs was basically irregular.3.The histoanatomical study of GPsThe anatomical characteristics of the initiation and development of GPs of R.damascena and R.hybrida ‘Spirit of Freedom’ were analyzed in detail.The results showed that GPs arose from protoepidermal cells and basic meristem cells at the stem apex.Glandular cells(a specific structure of GPs)originated from the “cylindrical” raised structures in the early stages of prickle development.The upper end of protoderm divided and differentiated into precursor glandular cells,which further develop to form the characteristic “glandular head” structure of GPs.4.Distribution and deposition patterns of lignin and cellulose in GPsThe results of lignin staining showed that there was no lignin accumulation in the glandular head and epidermal cell layer during the whole process of GPs development.Moreover,the initial lignification of GPs occurred in the middle stage of prickle development,when the degree of lignification was relatively mild.With prickles developing,the lignification of GPs continued to deepen,starting from the upper end of the glandular stalk and gradually expanding to the base.Finally,GPs were completely lignified and became hardened mature prickles.The results of cellulose staining showed that cellulose was first enriched in the cell wall of epidermal cells at the early stage of prickle development,and the content of cellulose in epidermal cells was significantly higher than that in internal parenchyma cells.With prickles developing,cellulose accumulated in the parenchyma cells inside the prickles in a non-uniform manner.5.Submicroscopic structure of GPsTransmission electron microscopy(TEM)was used to observe the submicroscopic structure of GPs of R.damascena and R.hybrida ‘Spirit of Freedom’.The results showed that there were obvious plasmodesmata on the adjacent wall of the outer epidermal cells of the glandular head structure.In addition,the cells had dense cytoplasm and large central vacuolus,which were closely connected with the cell wall.6.Division of developmental stages of GPsBased on the results of morphological characteristics,anatomical structure,chemical composition and ultrastructure,the genesis and development of GPs were further defined as five overlapping stages,namely the initial stage(stage Ⅰ),the morphogenesis stage(stage Ⅱ),the rapid growth stage(stage Ⅲ),the maturity stage(stage Ⅳ)and the senescence stage(stage Ⅴ).The morphological and anatomical evidence provided in this study clearly indicates that GPs and NGPs belong to two different types of prickles,and they have their own independent development process.NGPs are not developed from GPs with gland structure.This conclusion is different from the current mainstream hypothesis.