| This study examined the physio1ogical and biocl1ernical responses oftomato(LycoPersicon esculentum Mill) to chilling under low light. MeanwhiIe, Inorder to select a photosynthetic index fOr screening genotype with tolerance tochilling under low light, photoSynthetic and chlorophyll fluorescence characteristicsin seven tomato genotypes with different toIerance to chilling were monitOredduring plant groWth, after chilling and during pIan recovery periods. The results areas follows:l Exposure of tomato plants to low temperature (l0t and 5C) under low light(60 u mol .m-'.s-') resulted in a completely inl1ibition of plant growth, and decreasesin vigor of roots, plant heights and the numbers of leaves. ChiI1ing atl0C and 5oCdecreased the dry weights of shoots, but did not decrease the DW During therecovery the groWth of plants for l0oC treat1nent could recover completCly, but tO aless degree fOr 5C treatment.2 Antioxidant enZymes activities were detCrmined in the leaves and roots duringand after chilIing (l0t and 5C) under low light (60 ll mol.m-'.s-'). Chilling at l0C increased the activities of SOD and POD in both leaves and roots. For chilling at5oC, the activities of POD were increased in both 1eaves and roots, and the activitiesof SOD in roots were increased, but the activities of SOD of leaves were decreased.The activities of CAT a coId-sensitive enzyme, were decreased raPidIy in bothleaves and roots after chilling. The activities of SOD, POD and CAT recovered tO orabove the leveI of control Ieaves afler l4 days of recovery at 25oC. However, therewere great differences in the responses of the activities of allioxidant enzymes ofrootS tO chilling. After l4 dnys of recovery at 25C, the activities of SOD and PODin rootS fOr l0oC chilled p1ants were higher tl1an that of control, and the activities ofCAT was as high as those of control. For chilling treatment at 5C, the activities ofboth CAT and POD did not recovery to the value before chiIling. the activities ofSOD, howevef, was increased during the lecovery3 Exposure of tomato pIantS to Iow temperature (l0oC and 5C) under low light(60 u mol .m-2.s-1 ) resulted in an completely inhibition of plant growth anddecreased chlorophylI content, net photosynthetic rate (Pn), stomatal conductal1ce(Gs) and intracellular CO2 (Ci) concentration except Ci fOr the lower 1eaves duringchilling at 5oC. During the recovery Pn fOr l0t treatment arose to a value simiIarto control, but Pn fOr 5C treatment did not. Chilling at l0t did not affect Fv/Fln,but slightly decreased diPSII although it recovered soon after chilling stress.However, chilling at 5C considerabIy decreased Fv/Fm and thPSII, and bothrecovered slowly after chil1ing stress.4 Seven tomato genotypes with different coId tolerance were seIected to comparetheir response to chilling under low light. After chil1ing at l2oC/7C under 60 llmol.m-'.s-', they were transferred to a growth chamber at 25C/18C al1d l000 llmol.m-2.s-I for l0 days. PlastochTOn index, net photosyntl1etic rate, apparent quantumefficiencies(AQE), electron transport rate(ETR), actual photochemical efficiency ofPS lI in the light(th PS II ), photochemical quenching(qP), efficiency of excitationeneng caPture by open PS lI reaction centers(Fv'/Fm') are monitored during plantgrowth. Results showed that there were great differences in their tolerance tochilling under low light and in their recovery ability After chilling under low light,toIerant genotypes mainiained higher Pn. AQE and QPS IIto increasing lightintensity than sensitive genotypes. Meanwhile, tolerant genotypes maintained higherrpPS II and qP than the sensitive genotypes at low temperature under low Iight(l25 P mol.m-'.s-'). The value measured after chilling were significantIy correIatedwith groWth parameteL These results suggest the possibiIity of selecting genotypewith tolerant to low temperature and low light by using chlorophyll fluorescencetechnique... |
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