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P S Kerr

Publications and source records attributed to P S Kerr.

23 records · Page 2Linked to original sources
PubMed1984

Effect of N-source on soybean leaf sucrose phosphate synthase, starch formation, and whole plant growth.

Soybeans (Glycine max L. Merr. cv Tracy and Ransom) were grown under N(2)-dependent or NO(3) (-)-supplied conditions, and the partitioning of photosynthate and dry matter was characterized. Although no treatment effects on photosynthetic rates were observed, NO(3) (-)-supplied plants in both cultivars had lower starch accumulation rates than N(2)-dependent plants. Leaf extracts of NO(3) (-)-supplied plants had higher activities of sucrose phosphate synthase (SPS) and cytoplasmic fructose-1,6-bisphosphatase (FBPase) than N(2)-dependent plants. The variation in starch accumulation was correlated negatively with the activity of SPS, but not the activity of FBPase, UDP-glucose pyrophosphorylase, or ADP-glucose pyrophosphorylase. These results suggested that starch accumulation is biochemically controlled, in part, by the activity of SPS. Leaf starch content at the beginning of the photoperiod was lower in NO(3) (-)-supplied plants than N(2)-dependent plants in both cultivars which suggested that net starch utilization as well as accumulation was affected by N source.Total dry matter accumulation and dry matter distribution was affected by N source in both cultivars, but the cultivars differed in how dry matter was partitioned between the shoot and root as well as within the shoot. The activity of SPS was correlated positively with total dry matter accumulation which suggested that SPS activity is related to plant growth rate. The results suggested that photosynthate partitioning is an important but not an exclusive factor which determines whole plant dry matter distribution.

Journal Article↗
PubMed1984

Effect of Photoperiod on Photosynthate Partitioning and Diurnal Rhythms in Sucrose Phosphate Synthase Activity in Leaves of Soybean (Glycine max L. [Merr.]) and Tobacco (Nicotiana tabacum L.).

Studies were conducted to identify the existence of diurnal rhythms in sucrose phosphate synthase (SPS) activity in leaves of three soybean (Glycine max L. [Merr.]) and two tobacco (Nicotiana tabacum L.) cultivars and the effect of photoperiod (15 versus 7 hours) on carbohydrate partitioning and the rhythm in enzyme activity. Acclimation of all the genotypes tested to a short day (7 hours) photoperiod resulted in increased rates of starch accumulation, whereas rates of translocation, foliar sucrose concentrations, and activities of SPS were decreased relative to plants acclimated to long days (15 hours). Under the long day photoperiod, two of the three soybean cultivars (;Ransom' and ;Jupiter') and one of the two tobacco cultivars (;22NF') studied exhibited a significant diurnal rhythm in SPS activity. With the soybean cultivars, acclimation to short days reduced the activity of SPS (leaf fresh weight basis) and tended to dampen the amplitude of the rhythm. With the tobacco cultivars, photoperiod affected the shape of the SPS-activity rhythm. The mean values for SPS activity (calculated from observations made during the light period) were correlated positively with translocation rates and were correlated negatively with starch accumulation rates. Overall, the results support the postulate that SPS activity is closely associated with starch/sucrose levels in leaves, and that acclimation to changes in photoperiod may be associated with changes in the activity of SPS.

Journal Article↗
PubMed1983

Characterization of diurnal changes in activities of enzymes involved in sucrose biosynthesis.

Experiments were conducted with vegetative soybean plants (Glycine max [L.] Merr., ;Ransom') to determine whether the activities in leaf extracts of key enzymes in sucrose metabolism changed during the daily light/dark cycle. The activity of sucrose-phosphate synthase (SPS) exhibited a distinct diurnal rhythm, whereas the activities of UDP-glucose pyrophosphorylase, cytoplasmic fructose-1,6-bisphosphatase, and sucrose synthase did not. The changes in extractable SPS activity were not related directly to photosynthetic rates or light/dark changes. Hence, it was postulated that the oscillations were under the control of an endogenous clock. During the light period, the activity of SPS was similar to the estimated rate of sucrose formation. In the dark, however, SPS activity declined sharply and then increased even though degradation of starch was linear. The activity of SPS always exceeded the estimated maximum rate of sucrose formation in the dark. Transfer of plants into light during the normal dark period (when SPS activity was low) resulted in increased partitioning of photosynthate into starch compared to partitioning observed during the normal light period. These results were consistent with the hypothesis that SPS activity in situ was a factor regulating the rate of sucrose synthesis and partitioning of fixed carbon between starch and sucrose in the light.

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