Comparison of stomatal structure among five citrus cultivars including Cara Cara Navel Orange.

To study the microstructure of leaf epidermis and stomata in citrus,paraffin sections,ultrathin sections and transmission electron microscopy,scanning electron microscopy,and improved temporary slide method were adopted on 1/2 expanded and fully expanded spring leaves of 5 cultivars,including Cara Cara Navel Orange(Citrus sinensis),Meigui Cheng(C.sinensis),Inaba Wase(C.unshiu),Okitsu No.44(C.reticulata × C.sinensis) and HB Pummelo(C.grandis).Results showed that most stomata distributed on the leaf lower epidermis while only a few distributed on the upper epidermis alongside the mid rib.The anatomic structure of stomatal pore was funnel-shaped(cross section) and was similar among the 5 cultivars.The stomatal aperture depended on the length of the stomatal inner pore.Cluster analysis was carried out based on the following parameters: the length of the stomatal complex,the width of the stomatal complex,and the number of the sunken subsidiary cells.Stomatal complex of the 5 cultivars could be clearly divided into two types(Type-Ⅰ and Type-Ⅱ).The length and width of stomatal outer/inner pore,the size of stomatal complex and the number of the subsidiary cell of Type-Ⅰ stomatal complex were significantly different from that of Type-Ⅱ.The differentiation time and cell fate of the two types' stomatal guard cells were different from each other.Degeneration of the Type-Ⅰ stomatal guard cells at late stage of leaf expansion might be related to resistance enhancement to bacterial disease in C.sinensis.