Effects of darkness on ultrastructure in chloroplast of watermelon seedling leaves

The ultrastructural changes in chloroplast of watermelon seedling leaves under darkness were observed by transmission electron microscopy(TEM).TEM observations indicated that ultrastructural damages in chloroplast became severe when it is kept under darkness.After 2-day treatment with darkness,the chloroplast expanded,the stroma lamellae decreased and arranged unregularly,the starch particles disappeared.After 4-day treatment with darkness,the lamellae were distorted or even disintegrated.After 6-day treatment with darkness,the lamellae disappeared completely,the chloroplast became spherical,the membrane of chloroplast became disintegrated and the chloroplast tended to disintegrated.When transferred to normal light(150μmol/m~2·s~(-1)) for 2 days,the starch particles started to accumulate,which indicated that the function of photosynthesis of chloroplast began to recover.However the grana were few and obscured.After 6 days of recovery in the light,the grana were clear and stacked increasingly.The ultrastructure in chloroplast recovered fast if dark-treated time was short.