| Tomato cultivation in facilities is often suffered by low night temperature, which causes retarded growth and the decline of yield and quality, and it is important to investigate the effects of low night temperature on cold-resistant characteristics, cDNA microarray, and carbohydrate metabolism in different genotypes tomatoes. Chilling-tolerant wild tomato (Lycopersicoum hirsutum) "LA1777" and chilling-sensitive tomato (Lycopersicon esculentum Mill.) "Moneymaker" were used in this research, the effects on cold-resistant characteristics (osmotic regulation substances, praline content, antioxidative enzymes activities and chlorophyll fluorescence parameters), cDNA microarray, carbohydrate metabolism accumulation, metabolism and related gene expression in different genotypes tomatoes at 15℃(control),9℃and 6℃were studied. To clarify the mechanism of different genotypes tomatoes responsed to low night temperature, and provide theoretical basis for regulation on tomato growth under low night temperature. The main results are as followes:1. After short-time low night temeperature treated, proline content, POD and CAT activities increased in two different genotypes tomatoes, but the variation scope of proline content, POD and CAT activities in LA 1777 is greater than those of Moneymaker. SOD activity in LA1777 was lower than control, otherwise, the SOD activity in Moneymaker was higher than control. The increase of MDA content in Moneymaker leaves was greater than LA1777, indicating the enhanced membrane lipid peroxidation in Moneymaker. These results demonstrate that the cold resistant tomato seedlings exerted higher level of POD activity and proline content to acclimate chilling stress under short-time low temperature.2. The chlorophyll a, b content and chlorophyll a/b in two genotypes tomato leaves were significantly decreased under low night temperature stress, and the chlorophyll a and b content in Moneymaker significantly decreased than control after 1d low night temperature treated. The Fo and NPQ increased in two tomatoes leaves under low night temperature, however, Fv/Fm,ΦPSII, ETR and qP were decreased significantly after low night temperature treated. Only NPQ in two tomatoes had the same trend, other fluorescence parameters in Moneymaker leaves had greater changed scale than LA1777. The results showed that PSII activity and electron transfer in cold-sensitive tomato leaves were influenced under low night temperature, and PSⅡactivity decreased significantly, but its decline scale was lower in cold-tolerant tomato.3. The changes of cDNA Microarray in different genotypes tomatoes at 6℃(15℃as control) for 6h were investigated. The results showed that the sum of up-regulated and down-regulated genes in LA 1777 after 6℃treated for 6h was about the same as Moneymaker. However, the number of down-regulated genes in LA1777 was higher than Moneymaker, the number of up-regulated genes and the average fold changes was lower than Moneymaker.4. It is clear that the genes which involved in amoid acid metabolism, secondary metabolism, carbohydrate metabolism, energy metabolism and lipid metabolism were siginificantly changed at 6℃for 6h in two different genotypes tomatoes. ADC1, ADC2, Super1/yucca5, AT3G10340, SAMDC, NCED3 and NCED9 were significatly up-regulated. In carbohydrate metabolism, CT-AMY gene was markedly up-regulated in two genotypes. AT4G22110, UGE3 and UGE1 genes were significantly down-regulated in LA1777, MVA1, AT5G11720 and ALDH2B7 genes were significantly down-regulated.5. It is clear that there were 20 functional categories (including clones that do not belong to any chosen category "others", and no precise function or no BLAST results "Unknown function") genes expression. The genes involved in secondary metabolism, amoid acid metabolism and energy metabolism were significantly changed. The genes involved in carbohydrate metabolism in two genotypes were 2%-3% in functional categories.6. Fructose, glucose, sucrose content in two genotypes and starch content in Moneymaker increased after low night temperature, but the starch content in LA1777 decreased after low night temperature. After 6℃treated for 3h, SAI activity in Moneymaker was lower than control, and no significantly difference between treated seedlings and control seedlings after treated for 12h. The changes of NI and SS (hydrolysis direction) activities were similarly to SAI activity. SAI, NI and SS (hydrolysis direction) activities were higher than control level after 9℃treated 6h and 6℃treated 9h, there was significantly difference in SAI activities between treated seedlings and control after 12h. CWI activities increased in two genotypes. SS (synthesis direction) and SPS activity in Moneymaker increased at 9℃and 6℃after treated 9h, and SS (synthesis direction) and SPS activity in LA1777 at 9℃after treated 6h and 6℃after treated 9h were higher than control level. After treated 12h, there was no different between treated seedlings and control seedlings.7. The relative expression level of tiv-1 gene in two genotypes was significantly inhibited under low night temperature, but no significantly difference between treated seedlings and control seedlings after treated for 12h. The relative expression level of sus2, sus3 and hkl also increased under low night temperature stress, and the highest level at 6℃. The relative expression level of lin5 in Moneymaker seedlings at 6℃after treated 9h was higher than control level, but it was higher than control level after treated for 12h in LA1777 seedlings. The relative expression level of lin8 in Moneymaker seedlings was higher than control at 6℃after treated for 6h and at 9℃after treated for 9h, and that of LA1777 increased after treated 6h, and the highest level at 6℃, and then decreased. After treated for 12h, the relative expression level of lin8 in LA1777 was no significant difference between treated seedling and control. The relative expression level of hk2, hk4 and fk2 were different in two genotypes. The relative expression level of hk2 in Moneymaker increased after low night temperature treated, and the relative expression level of hk4 were higher than control at 6℃treated for 6h and at 9℃treated 9h. The relative expression level of fk2 was higher than control level after 6℃treated for 3h and 9℃treated for 9h. The relative expression level of hk2, hk4 and fk2 decreased under low night temperature stress, and no significant difference between treated seedling and control after treated for 12h. |
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