Effects of kinetin on plant growth and chloroplast ultrastructure of two Pteris species under arsenate stress

Cytokinins (CTKs) are effective in alleviating abiotic stresses on plants, but little information is available regarding the effects of CTKs on arsenic (As) accumulation and changes of chloroplast ultrastructure in plants with different As-accumulating ability. Here a hydroponic experiment was designed to evaluate the effects of different concentration of kinetin (KT, 0–40 mg/L) on growth and chloroplast ultrastructure of As hyperaccumulator Pteris cretica var. nervosa and non-hyperaccumulator Pteris ensiformis treated by 5 mg/L arsenate for 14 days. The growth parameters, As accumulation, contents of photosynthetic pigments and chloroplast ultrastructure were examined. The results showed that KT promoted the growth of two plants, and significantly increased As accumulation and translocation in P. cretica var. nervosa and P. ensiformis at 5 and 20 mg/L, respectively. Additionally, the contents of chlorophyll a and carotenoid in two plants showed no significant difference at 20 mg/L KT compared to the control. Chloroplast ultrastructure of P. cretica var. nervosa was integral with KT application. Comparatively, the swollen chloroplasts were increased, plasmolysis appeared, and chloroplast grana slice layers and stroma lamellas were clearly separated or distorted at 5 mg/L KT in P. ensiformis. The length and width of chloroplasts in P. cretica var. nervosa were significantly increased with KT addition compared to the control. However, the length of chloroplasts in P. ensiformis was significantly decreased but their width showed no significant change. Furthermore, the deterioration of chloroplast ultrastructure in P. ensiformis was ameliorated by 40 mg/L KT. These results suggested that KT increased As accumulation and was beneficial to maintain the photosynthetic pigments for a good growth of plants. Therefore, KT could maintain and reorganize the ultrastructure integrality of As-stressed chloroplasts to some extent for the two plants, especially at high concentration.