Effects of drought stress on growth, photosynthetic physiological features and stomata characters of cucumber seedlings.

The responses of morphological indexes,photosynthetic gas exchange,chlorophyll fluorescence,physiological indexes and stomata characters to different water stress(70%-80% of field capacity as no stress,40%-50% of field capacity as light stress,20%-30% of field capacity as high stress) in seedlings of two cucumber cultivars(var.'Qianqiu No.5' and var.'Qianchun No.7').The growth of the two cultivars was inhibited under the drought stress.The water stress resulted in progressively decreases in relative water content of leaves,net photosynthesis rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),the actual photosynthesis efficiency of PSⅡ in the light(ΦPSⅡ),the electron transport rate(ETR),photochemical quenching(qP) and proportion of PSⅡ photochemistry(P),but the non-photochemical quenching(NPQ) and proportion of antenna heat dissipation(D) increased.The intercellular CO2 concentration(Ci) decreased at light stress,but increased at high stress,which indicated that the decline of Pn was considered as a result of stomatal restriction under light stress,but non-stomatal restriction under high stress.The leaf pigment decreased,but increased for the contents of malon-dialdehyde,the proline as well as the activities of superoxide dismutase,peroxidase and catalase.The density of leaf stomata,open stomata proportion decreased progressively.The stomata were of smaller,low density,and most closed.Density of trichomes decreased.The cucumber cv.'Qianchun No.7' was more drought-tolerant than var.'Qianqiu No.5'.