Effects of Low Light Stress on Morphological Trait,Physiological Characters and Leaf Ultrastructure of Tomato(Lycopersicon esculentum L.) Seedlings

Two tomato cultivars were selected for the study,the whole-plant morphology,physiological characters as well as leaf ultrastructure of two tomato cultivars to differential light availabilities were examined in controlled environment.The results showed that,under the low light stress,the growth of the plants was inhibited.The total plant dry weight declined significantly and the reduction was 22.43% of the common tomato(Meifen-2) and 28.87% of the cherry tomato(Hongsheng),and the healthy index decreased 33.53% of Meifen-2 and 51.48% of Hongsheng,respectively.Chl and Car content of the two cultivars grown under low light condition increased significantly,the Chl a/b ratio decreased during acclimation.Compared with control plants,the amount of soluble proteins and soluble sugars were drastically decreased by low light treatment.As the light intensity was lower,the net photosynthesis rate(Pn) and stomatal conductance(Gs) decreased,but intercellular CO2 concentration(Ci) increased.The decrease of net photosynthetic rate was considered as a result of non-stomatal restriction.The blade thickness became thinner under low light stress,and the thickness rate of palisade and sponge tissue declined.The number of chloroplast and starch grain decreased as a result of low light intensity,the number of grana and lamella increased,the size of chloroplast and starch grain minished.The objective of this study revealed the relationship between photosynthetic system characters and low light stress,which could tolerate low light stress.