Effects of alternative stress of drought and waterlogging on rice leaf anatomical structure at tillering stage

Abstract: Vascular bundle is the main microstructure of rice plants, which is conducive to the growth of leaf and photosynthetic rate, and the greater the vascular bundle, the more the number, the better the supply of nutrients. Pot experiments were performed to research the effects of alternative stress of drought and waterlogging at tillering stage on rice leaf anatomical structure, including the number, area and perimeter of large (small) vascular bundles, sectional area and perimeter of major vein, area of bulliform cell group and sectional area of side blade, and 2 treatments were set up in 2013: waterlogging - light drought (LD) and waterlogging - severe drought (HD), in which the water depth of waterlogging was 10 cm, using regular irrigation (CK) as the control. The experiments were conducted in the greenhouse of Key Laboratory of Efficient Irrigation-Drainage and Agricultural Soil-Water Environment in Southern China (Hohai University), Ministry of Education. The results showed that alternative stress of drought and waterlogging decreased the number of large (small) vascular bundles, but there was no significant difference compared to the CK; after the first drought for 5 d (Stage I), the sectional area of major vein of LD treatment was reduced by 31.13% compared to the CK (P<0.05), and that of HD treatment was reduced by 13.9?104 μm2, which yet had no significant difference with the CK; the area and perimeter of large vascular bundle of side blade were reduced by 28.87% and 15.79% for LD treatment, respectively, and by 24.74% and 13.16% for HD treatment, respectively, and the area and perimeter of small vascular bundle of side blade for LD and HD treatments were also lower than that of the CK. After waterlogging for 5 d (Stage II), the perimeter of small vascular bundle of side blade for LD and HD treatments had no significant difference with the CK, and that of LD treatment was reduced by 0.13?102 μm compared to HD treatment. Except large vascular bundle, other indices of HD treatment were all over than the CK, indicating that leaf development showed a certain compensation effect. Five days after waterlogging (Stage III), the sectional area of major vein of LD and HD treatments was significantly reduced by 24.6?104 and 29.1?104 μm2 respectively compared to the CK, and the development of side blade organ was also behind the CK. After the second drought for 5 d (Stage IV), the area of large vascular bundle of major vein for LD and HD treatments was significantly reduced by 19.42% and 29.13% respectively compared to the CK; the area and perimeter of large vascular bundle of side blade under LD treatment had no significant difference with the CK, and those under HD treatment were significantly lower than LD treatment and CK. The areas of bulliform cell group of LD and HD treatments were lower than the CK when the rice was in drought, and especially in Stage III, the areas of bulliform cell group were significantly reduced by 0.38?102 and 0.57?102 μm2, respectively; the sectional areas of side blade of LD and HD treatments in Stage I, III and IV were lower than the CK, while in Stage II, the sectional area of side blade of HD treatment was higher than the CK, but the difference was not significant. After the water stress, the development of the main vein's large vascular bundle was inhibited, and the development of side blade was also subject to certain persecution, but the persecution of rice leaves under severe drought treatment was increased after the second drought stage, while it was reduced under light drought treatment, indicating that the rice drought tolerance was enhanced, and after the drought stress, the waterlogging tolerance of rice was still strong. The results of this study can provide the basis for the development of appropriate water management plan and the research of rice photosynthesis.