Trehalnse and LEA proteins, representative low MW chemicals that are synthesized under dehydralJon, are known to protect plants from drouBht ~ To compare their effectiveness on enhancin 8 tolerance against various abiotic stresses, we generated tranSl~=nic Chinese cabbase plants overexpressin 8 E. co//trehalose-6-phosphate m/nthase 8erie (ors4) or hot pepper (Capsicum annuum) LEA protein &ene (CaLEA). Both trampnic planl3 exhibited altered phenotype includin 8 stuntedgrowth and aberrant root developmenL When subjected to drousht , salt or heat sb~ss, these plants showed remarkably improved tolerance aj~dnst those stresses compared with nonlTansformants. After dehydra~n b~atment, leaf turgidity and fresh weight was better maintained in both transl~=nic plant~ Cat~-plants performed somewhat better under dehydrated condition, When ~eated with 250 mM NaCI, both ot~4-plants and CaZEA.plants remained equally healthier than nonl]'ansformants in maintaining leaf turgidity and delaying necrosis. Furthermore, leaf Chl content and Fv/Fm was maintained comiderably higher in both tram~enic plant~= than nontransformant~ After heat-treatment at 45~ both Irans~.nk plants appeared much less damased in external shape and PSII funclion, but LEA proteins were more protective. Our results iedicate that although bolh trehalose and LEA proteins are in proteclJng plants against various abiotic stresses, LEA proteins seem to be more promising in generatJn 8 sbess-tolerant ITansl~enic plants.
When the time course for CO2 fixation and 02 evolution in isolated intact spinach chloroplasts was examined, we found a prolonged lag time in the early phase of photosynthesis after heat-treatment in the dark as well as an expected time-dependent decrease in the rate during the subsequent linear phase. Because the lengthening of the lag period was generally attributed to the depletion of sugar phosphates in the chloroplasts, we tested for the possible involvement of Calvin cycle intermediates in the change of the lag phase by heat-treatmenL When triose phosphate was added to the heated chloroplasts, the lag time was re-shortened without the rate in the linear phase being elevated to that measured in the control. Mg-ATP or triose phosphate plus oxaloacetate (previously known as protective chemicals) prevented the lengthening of the lag time when added prior to heat-treatment. Quantification of some metabolites in the chloroplasts confirmed that heavy losses had occurred for triose phosphate, fructose-l,6-bisphosphate, 81ucose-6-phosphate, and fructose-6-phosphate. However, the level of 3-phosphoglyceric acid was increased. The presence of Mg-ATP during heat-treatment alleviated the losses of those sugar phosphates. Therefore, we conclude that the decrease in sugar phosphates in the chloroplasts, as part of the negative effect from heat-treatment, is the primary cause of the lengthened lag time during the initial phase of photosynthesis.
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