Low light stress is one of the most important factors affecting photosynthesis and growth in winter production of cucumber(Cucumis sativus L.) in solar greenhouses in northern China. Here, two genotypes of cucumber(Deltastar and Jinyan 2) are used to determine the effect of low light stress on Rubisco expression and photosynthesis of leaves from emergence to senescence. During leaf development, the net photosynthetic rate(PN), stomatal conductance(gs), Rubisco initial activity and activation state, transcript levels of rbcL and rbcS, and the abundance of rbcL and rbcS DNA in these two genotypes increase rapidly to reach maximum in 10-20 d, and then decrease gradually. Meanwhile, the actual photosystem II effi ciency(ФPSII) of cucumber leaves slowly increased in the early leaf developing stages, but it declined quickly in leaf senescent stages, accompanied by an increased non-photochemical quenching(NPQ). Moreover, PN, gs, initial Rubisco activity, and abundance of protein, mRNA and DNA of Rubisco subunits of leaves grown under 100 μmol m-2 s-1 are lower, and require more time to reach their maxima than those grown under 600 μmol m-2 s-1 during leaf development. All these results suggest that lower ph otosynthetic capacity of cucumber leaves from emergence to senescence under low light stress is probably due to down-regulated Rubisco gene expression in transcript and protein levels, and decreased initial and total activity as well as activation state of Rubisco. Deltastar performs better than Jinyan 2 under low light stress.
SUN Jian-leiSUI Xiao-leiHUANG Hong-yuWANG Shao-huiWEI Yu-xiaZHANG Zhen-xian
Low temperature and high salinity are the major abiotic stresses that restrict cucumber growth and production,breeding materials with multiple abiotic resistance are in greatly need.Here we investigated the effect of introducing the LOS5 gene,a key regulator of ABA biosynthesis in Arabidopsis thaliana,under the stress-responsive RD29A promoter into cucumber(Cucumis sativus L.cv.S516).We found that T 1 RD29A-LOS5 transgenic lines have enhanced tolerance to cold and salt stresses.Specifically,transgenic lines exhibited dwarf phenotypes with reduced leaf number,shorter internode,decreased length of the biggest leaf,fewer female flowers,shorter fruit neck and lower vitamin C(Vc).The increased cold tolerance can be reflected from the significantly decreased cold index,the reduced electrolyte leakage index and the MDA content upon cold treatment as compared to those in the control.This may result from the accumulation of internal ABA,soluble sugars and proline,and the enhanced activities of protective enzymes superoxide dismutase(SOD),peroxidase(POD) and catalase(CAT) in the transgenic lines.Under salt treatment,the transgenic lines exhibited increased germination index,vigor index,more lateral roots and increased root fresh weight.Moreover,RD29A-LOS5 transgenic plants displayed quicker responses in salt stress than that in low-temperature stress.
LIU Li-yingDUAN Liu-shengZHANG Jia-changMI Guo-quanZHANG Xiao-lanZHANG Zhen-xianREN Hua-zhong
Micro RNAs(mi RNAs) are ~21 nucleotide(nt), endogenous RNAs that regulate gene expression in plants. Increasing evidence suggests that mi RNAs play an important role in species-specific development in plants. However, the detailed mi RNA profile divergence has not been performed among tomato species. In this study, the small RNA(s RNA) profiles of Solanum lycopersicum cultivar 9706 and Solanum habrochaites species PI 134417 were obtained by deep sequencing. Sixty-three known mi RNA families were identified from these two species, of which 39 were common. Further mi RNA profile comparison showed that 24 known non-conserved mi RNA families were species-specific between these two tomato species. In addition, six conserved mi RNA families displayed an apparent divergent expression pattern between the two tomato species. Our results suggested that species-specific, non-conserved mi RNAs and divergent expression of conserved mi RNAs might contribute to developmental changes and phenotypic variation between the two tomato species. Twenty new mi RNAs were also identified in S. lycopersicum. This research significantly increases the number of known mi RNA families in tomato and provides the first set of small RNAs in S. habrochaites. It also suggests that mi RNAs have an important role in species-specific plant developmental regulation.
FAN Shan-shanLI Qian-nanGUO Guang-junGAO Jian-changWANG Xiao-xuanGUO Yan-meiJohn C.SnyderDU Yong-chen
