Growth and development of juice vesicles grown by in vitro culture in Citrus

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The in vitro culture of juice vesicles could aid in studies on the sugar and acid metabolism in citrus fruit. In this report, juice vesicle explants including some mesocarp tissue excised from young satsuma mandarin (Citrus unshiu Marc.) fruit, were cultured in vitro on MS solid medium under dark conditions at 25 C.1. The juice vesicles grew expansively and turned orange. The juice vesicles accumulated sugar, and disintegrated acid similar to those of fruit grown in the field when cultured on the medium supplemented with 10 % sucrose and incubated for two months. Sugar accumulation occurred in the juice vesicle explants excised from fruitlet at 51 days after full bloom or later and cultured on the medium. Effect of sucrose, glucose and fructose on vesicle growth and sugar accumulation was determined. Fructose was not effective for vesicle growth.2. Juice vesicle explants were cultured on medium with various sucrose concentrations and water potentials. There is a close positive relationship between sugar and acid accumulated by vesicles and sucrose content in the medium with or without adjusting water potential. When cultured under different water potentials on 10 % sucrose concentration, the juice vesicles grew less but accumulated more sugar and acid as the water potential decreased.3. When juice vesicle explants were cultured on medium with various nitrogen levels, there is a negative relationship between sugar content of juice vesicles and nitrogen content in the medium, but a positive one between acid content of juice and nitrogen in the medium.4. Sugar composition in vesicles cultured on various carbohydrates indicates sugar degradation and conversion occurred in vesicle explants. Activities of sugar metabolizing enzymes, SS, SPS and Invertase, were higher in cultured juice vesicles than those of fruit grown in the field, however, the seasonal changes of those enzyme activities in both fruits were similar