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Burley and flue‐cured tobacco (Nicotiana tabacumL.) cultivars differ in several phenotypic and chemical characteristics. This study was conducted to characterize differences between representative burley and flue‐cured cultivars and to determine the root system influence on shoot physiology. Control and reciprocally grafted plants of burley ‘Ky 14’ and flue‐cared ‘Speight G 28’ were grown in the greenhouse at two levels of N fertilization. Leaves were sampled from 10 days before to 30 days after topping (DAT). At both N levels, the genotype of the root system did not influence any of several parameters measured. This result was clearly indicated by total shoot dry weights that, at the final sampling, were higher at both N levels for G 28 shoots regardless of the genotype of the root system. Chlorophyll concentration was consistently higher for G 28 compared to Ky 14 at both N levels. At high N, CO2exchange rates were similar and declined over time for both tobacco types. At low N, however, higher CO2exchange rates were maintained for G 28 compared to Ky 14 until 20 DAT and this result appeared to be due in part to a differential decline in Rnbisco concentration. Leaf expansion and dry weight accumulation were decreased, and specific leaf weight increased by the low‐N treatment. For Ky 14, but not G 28, low N resulted in cessation of leaf expansion and dry weight accumulation after 20 DAT. For the high‐N treatment, G 28 accumulated leaf dry weight to a greater extent than Ky 14, and at both N levels G 28 had significantly greater specific leaf weight than Ky 14. The results indicated that the burley cultivar was more sensitive to Iow‐N fertility than the flue‐cured cnltivar, and the root system was not a factor in the expression of physiological differences observed in the shoot.

Flue‐cured tobacco (Nicotiana tabacumL.) cultivars produce similar leaf yields compared to hurley tobacco cultivars despite requiring approximately four times less N fertilizer. This study is the second part of an experiment to characterize physiological differences between representative burley and flue‐cured cultivars and to determine the influence of the root system on shoot physiology. Control and reciprocally grafted plants of burley ‘Ky 14’ and flue‐cured ‘Speight G28’ (G28) were grown in soil pots [Maury silt loam (Typic Paleudalfs)] at two levels of N fertilization (580 or 230 mg N week"1)‐ Plants were sampled and divided into laminae, midveins, stalk, and roots from 10 days before to 30 days after topping. Dry weight distribution for the cultivars was similar for all plant parts except laminae. G28 accumulated significantly more lamina dry weight than Ky 14, although leaf area and leaf number were similar for both genotypes. Cultivar differences in lamina dry weight occurred even though lamina and stalk N contents were similar, within an N level. Thus, G28 produced more lamina dry weight based on either units of N fertilizer added or lamina N accumulated. Laminae dry weight differences were explained in large part by higher starch concentration for G28 than Ky 14. Laminae free sugar concentration was low and similar for all treatments. These data inferred that starch metabolism or storage capability was dissimilar for the two tobacco types. The genotype of the root system did not influence any parameter measured for shoots and, thus, differences between cultivars may be expressed at the level of the leaf lamina cell.

Productivity of flue‐cured tobacco (Nicotiana tabacumL.) is similar to that of burley tobacco in spite of the former's lower need for N fertilizer. The objective of this study was to utilize a leaf grafting technique to demonstrate the level of control of an individual leaf with regard to the unique characteristics of burley and flue‐cured tobacco cultivars. Leaves of burley cultivar ‘Ky 14’ were grafted onto shoots of flue‐cured cultivar ‘Speight G28’ (G28) and visa versa and compared to both grafted and nongrafted controls of a particular cultivar. Plants were grown in a greenhouse at two N fertility levels (648 or 144 mg N wk−1). Leaf grafting decreased leaf growth of both the burley and the flue‐cured cultivar compared to nongrafted controls, but relative cultivar differences were maintained. Compared to Ky 14, G28 leaves accumulated more dry weight, due primarily to greater starch accumulation, had higher chlorophyll concentration and, at low N fertility, maintained a higher carbon dioxide exchange rate (CER) and ribulose 1,5‐bisphosphate carboxylase/oxygenase (rubisco) concentration. Grafting a Ky 14 leaf onto a G28 stalk or a G28 leaf onto a Ky 14 stalk did not alter dry weight, starch, or N characteristics of the grafted leaf. Leaf senescence, however, as indicated by loss of chlorophyll, CER, and rubisco, was delayed for Ky 14 leaves grafted onto G28 stalks. For G28 leaves grafted to Ky 14 stalks, loss of chlorophyll was hastened, but declines in CER and rubisco were not altered. The results indicated that cultivar differences in dry weight and starch accumulation were controlled by biochemical or physical factors within an individual leaf, but that senescence characteristics of individual leaves could be influenced by the plant genotype.

The growth and development of an individual soybean [Glycine max(L.) Merr.l seed is an important part of the yield production process; however, the effect of fruit size on the physiological processes controlling seed growth and final seed size are not completely understood. Thus, two experiments were conducted in a greenhouse to evaluate the effect of physical restriction of the fruit on seed growth. The plastic pod restriction device (PPRD) was constructed from a 6.35‐mm diam. plastic drinking straw cut into 4‐cm lengths. The PPRD's were placed over the fruit when the fruit fit tightly into the PPRD. All of the fruits on the treated plants (cv. McCall) were placed in the PPRD's and samples were taken at frequent intervals to determine seed fresh and dry mass. Application of the PPRD's had no effect on the number of fruits or seeds per plant at maturity in either experiment. Final size (mg seed−1) of seeds from the PPRD's was decreased relative to control plants by 30 and 15% in Exp. 1 and 2, respectively. Mature seeds from the PPRD's were cylindrical in shape and had a higher N concentration. The initial seed growth rate (SGR) of seeds in the PPRD's was similar to the control seeds, however, when the seed mass reached 80 (Exp. 1) or 65 (Exp. 2) mg seed−1, the SGR was drastically decreased and there was no further increase in seed water content. However, seed maturation (seeds turning yellow and moisture level reaching 550 g kg−1) did not occur in the PPRD treatments until after the control seeds matured. The PPRD's provide a useful technique to study the effects of physical restraint on seed growth. The data demonstrate that physical restraint has a direct effect on the ability of the seed to accumulate dry matter.