Effects of water stress on ultrastructure and photosynthetic physiological factors of Potentilla sericea

The leaf ultrastructure of Potentilla sericea under water stress was investigated by transmission electron microscopy. The leaf photosynthetic rate (Pn), transpiration rate (Tr), stomata conductance (Gs), intercellular CO2 concentration and water use efficiency (WUE) were measured by portable photosynthesis system (LI6400). The results showed that the leaf ultrastructure was complete under control. Grana lamellaes of chloroplasts were distinct. The number of granas was abundant and the structure was compact. The thylakoids were compact and the grana stacks of thylakoids were regular. The chloroplasts showed lowly osmiophilic. There were few and small osmiophilic grain in the chloroplasts. With the intensive of drought stress, the grana and envelope damaged, the lamella swelled or dissolved and the grana stacks of thylakoids were disorder. Mitochondrial doublemembranes swelled or rived and its inclusion effused. The net photosynthetic rate was closely related to the change in chloroplast structure. The Pn, Tr and WUE of leaf decrease with the declining of soil water content and the damage of chloroplast.