A study on the floral shoot differentiation process and the changes in nutrient contents in Castanea henryi

Abstract:【Objective】Castanea henryi is a chestnut species belonging to the family of Fagaceae. As one of the important nuts and woody oil species in south China, C. henryi is of significant academic, econimic and ecological values. One of the problems in the production of this nut is that the tree produces too many male flowers and too few female flowers with low production and thus low economic benefits, which has become a bottleneck restrict in C. henryi industry in China. C. henryi flower buds can be mixed flower buds or male flower buds. Female flowers are borne on the base of the mixed flower buds, while male flower buds produce only male flowers. Therefore, the study of C. henryi flower bud differentiation, especially mixed flower bud differentiation, is of great significance. This paper aims to find out the nutrition physiology of bud differentiation in C. henryi so as to provide theoretical basis for artificial regulation of bud differentiation.【Methods】‘Huali 4'was used as the tested materials. Paraffin section method was used to clarify and definite differentiation process in young floral shoot tip and analyze carbohydrates (soluble sugars and starch) , soluble proteins, mineral elements (N, K, Ca, Mg, Mn, Fe and zinc) and the dynamics of C/N in buds of various types. Materials were flower buds and leaf bus from the bearing branches from 7 year old trees of C. henryi under routine management in the experimental field located in Central South Univer-sity of Forestry and Technology, Chenzhou, Hunan, China. Strong mixed flower buds from the trees were collected. 24 h after treatment in FAA fixation solution, the bud samples were subject to ethanol dehydration steps, xylol clearing, paraffin infiltration and embedding. Sections were cut using a Lecias paraffin microtome. After staining with hematoxylin dye, the sections were observed under a digital microscope (BX-51) . Soluble sugar and starch contents in flower buds and leaf buds were analyzed with anthrone colorimetry method, and soluble proteins were determined using coomassie brilliant blue G-250 method. For analysis of nitrogen, samples were heat digested using sulfuric acid and hydrogen peroxide method and analyzed with an automatic analyzer, and the other mineral elements (K, Ca, Mg, Mn, Fe and Zn) digested using perchlorate-nitric acid and determined using a flame atomic absorption spectrophotometer.【Results】The flower bud differentiation in young shoots could be separated into pre-winter inflorescence primordium differentiation (Stage I) , inflorescence primordium differentiation stage in winter (Stage II) , bract primordium differentiation stage (Stage III) and flower cluster primordium differentiation stage (Stage IV) . In the process of flower bud differentiation in young shoots, the content of soluble sugars in mixed flower buds increased at first, then decreased gradually and rose again finally. Soluble sugar content in leaf bud and male flower buds decreased after initial rise and sugars in flower buds and leaf buds peaked in Stage II with peak value reaching up to 11.561 mg·g^-1, 10.14 mg·g^-1and 9.085 mg·g^-1in mixed flower buds, male flower buds and leaf buds, respectively. Soluble protein content accumulated gradually then declined due to consumption and accumulated towards the end of the stage. Soluble protein content in three types of bud peaked in Stage IV. The peak value was 3.314 mg·g^-1, 2.776 mg·g^-1and 1.712 mg·g^-1in mixed flower buds, male flower buds and leaf buds, respectively. Starch content in flower buds and leaf buds showed a drastic change with peak occurring in Stage I and the peak value was 148.286 mg·g^-1, 170.482 mg·g^-1and 189.661 mg·g^-1mixed flower buds, male flower buds and leaf buds, respectively. N, Mg and Fe contents in mixed bud decreased first, then increased, and finally reduced again throughout bud young shoot differentiation. K, Mn and zinc decreased first and then increased; Ca content in Stage IV was the highest reaching 144.05 mg·g^-1. Except for Mn, Fe and Mg, all the tested minerals increased first and decreased afterward in male flower buds. In leaf buds, all the tested but Mn and Mg rose first and decline later. The C/N ratio in flower buds and leaf buds decreased after an initial increase and then rose again.【Conclusion】C. henryi flower bud differentiation is closely related to the accumulation of nutrients, and flower bud differentiation has different nutrients requirements at different stages. A high level of C/N is advantageous to the differentiation of mixed flower bus in C. henryi.