The cotyledons of soybean begin to develop photosynthetic capacity shortly after emergence. The cotyledons develop nitrate reductase (NR) activty in parallel with an increase in chlorophyll and a decrease in protein.In crude extracts of 5-to 8-day-old cotyledons, NR activity is greatest with NADH as electron donor. In extracts of older cotyledons, NR activity is greatest with NADPH. Blue-Sepharose was used to purify and separate the NR activities into two fractions. When the blue-Sepharose was eluted with NADPH, NR activity was obtained which was most active with NADPH as electron donor. Assays of the NADPH-eluted NR with different concentrations of nitrate revealed that the highest activity was obtained in 80 millimolar KNO3. Thus, this fraction has properties similar to the low nitrate affinity NAD(P)H:NR of soybean leaves. When 5-to 8-day-old cotyledons were extracted and purified, further elution of the blue-Sepharose with KNO3, subsequent to the NADPH elution, yielded an NR fraction most active with NADH. Assays of this fraction with different nitrate concentrations revealed that this NR had a higher nitrate affinity and was similar to the NADH:NR of soybean leaves. The KNO3-eluted NR fraction which was purified from the extracts of 9-to 14-day-old cotyledons, was most active with NADPH. The analysis of these fractions prepared from the extracts of older cotyledons indicated that residual NAD(P)H:NR contaminated the NADH:NR. Despite this complication, the pattern of development of the purified NR fractions was consistent with the changes observed in the crude extract NR activities. It was concluded that NADH:NR was most active in young cotyledons and that as the cotyledons aged the NAD(P)H:NR became more active.

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The effects of storage temperature, inhibition of ethylene action by treatment with 1-methylcyclopropene (1-MCP) and ultra low oxygen (ULO) atmosphere on chilling injury (CI), fruit firmness and ethylene production in the astringent 'Rojo Brillante' persimmon fruit were investigated. CI symptoms were manifested as a very dramatic loss of firmness after fruit transfer from cold storage to shelf-life conditions (18 °C). During cold storage, fruit softening appeared more rapidly in fruit stored at the intermediate temperature of 10 °C than at 1 °C or 14.5 °C. Ethylene production increased with storage time at the chilling temperature (1 °C) but a sharp increase took place upon fruit transfer from 1 °C to ambient temperature. This ethylene increase was accompanied by a loss of fruit firmness associated with chilling damage development. A pre-treatment with the competitive inhibitor of ethylene action 1-MCP, at 1 μL/L, reduced firmness loss and mitigated CI damage but considerably increased ethylene production in fruit transferred to shelf-life conditions after a prolonged cold storage period. Collectively, these results suggest a role of ethylene in the reduction of flesh firmness and consequently in the induction of CI in persimmon fruit. Moreover, ethylene exerts a negative feedback regulation of cold-induced ethylene biosynthesis. Storage of 'Rojo Brillante' persimmon fruit under ULO (1.3-1.8% O₂, v/v) atmosphere did not affect the incidence of CI but reduced fruit astringency, suggesting that ULO may be an alternative postharvest storage system for 'Rojo Brillante' persimmon fruit.

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