荔枝果皮对外源钙和蔗糖吸收及向细胞壁沉着的研究

利用放射性同位素示踪技术研究荔枝果皮对外源钙和蔗糖的吸收及细胞壁构建规律。结果表明,进入果皮的蔗糖主要被用以构建细胞壁,但随果实发育,蔗糖用于构建细胞壁比例减少,更多分布于果皮组织的可溶性成分中;果梗向果实运输钙的效率远远低于蔗糖运输效率;NAA处理果实短期内可明显促进蔗糖向果实运输,但不能促进果梗的钙进入果实,说明蔗糖和钙向果实运输有不同调控机制;施于果实表面的钙虽可被吸收并成为细胞壁的结构钙,但比例不到千分之一;硝酸(根)离子和NAA可一定程度促进外源钙向细胞壁沉着;抗裂的怀枝果皮细胞壁的钙含量比易裂的糯米糍高,其细胞壁结合外源钙的能力也强于后者,说明前者细胞壁中果胶半乳糖醛酸残基含量高于后者,也是怀枝具有较强抗裂性的物质基础之一;2品种14C-蔗糖向果皮细胞壁沉着均在果实发育初期最活跃,怀枝细胞壁构建也只是在果实发育初期比糯米糍更活跃,这就意味着抗裂性形成的关键时期是在果皮发育的初期。

A study on the absorption of exogenous calcium and sucrose and their deposit onto the cell walls in litchi pericarp

Absorption of exogenous calcium and sucrose and their deposit onto the cell walls in litchi pericarp were studied by using radioisotope tracer technique. The results showed that most of the 14C-sucrose in litchi pericarp was mobilized for cell wall construction, but with fruit development, the percentage of 14C-sucrose deposited onto the cell walls decreased while more 14C-sucrose was distributed in the soluble fraction of pericarp tissues. The translocation efficiency of 45Ca to fruit through the peduncle was by far lower than that of 14C-sucrose. NAA (naphthaleneacetic acid) treatment on fruit significantly increased the translocation of 14C-sucrose introduced from the peduncle to fruit but not in the case of 45Ca, indicating that different regulation mechanisms were involved in the transport of sucrose and calcium to fruit. Very little (less than 0.1%) calcium sprayed on the fruit surface could be absorbed and deposited onto the cell walls. However, the presence of NAA and nitrate promoted the deposit of the exogenous calcium onto the cell walls of the pericarp. Concentration of structural calcium in the cell walls of pericarp was higher in the cracking-resistant Huaizhi than in the cracking-susceptible cultivar Nuomici. The higher capacity in binding exogenous calcium in the former cultivar suggests that the pericarp cell walls of Huaizhi have a higher concentration of negatively charged structural component, i.e. galacturonic acid residues which can be one of the material bases of its cracking resistance. Incorporation of 14C-sucrose into the cell walls of pericarp was most active in the early stages of fruit development in both cultivars, and it was only in the early stages that more 14C-sucrose was incorporated into the cell walls of pericarp in Huaizhi than in Nuomici, while no difference between them was found in other stages. It is suggested that early fruit development stages with active cell wall construction is the critical period to form cracking resistance.