The metabolism and composition of skeletal muscle tissue is of special interest because it is a primary site of insulin action and plays a key role in the pathogenesis of insulin resistance. Intramyocellular (IMCL) triglyceride stores are an accessible form of energy that may decrease skeletal muscle glucose utilization, thereby contributing to impaired glucose metabolism. Because of the invasive nature of muscle biopsies, there is limited, if any, information about intramuscular lipid stores in children. The development of 1 H nuclear magnetic resonance (NMR) spectroscopy provides a unique noninvasive alternative method that differentiates intracellular fat from intercellular fat in muscle tissue. The present study was performed to determine whether IMCL and extramyocellular (EMCL) lipid contents are increased early in the development of juvenile obesity and to explore the relationships between IMCL and EMCL to in vivo insulin sensitivity, independently of total body fat and central adiposity in obese and nonobese adolescents. Eight nonobese (BMI 21 kg/m 2 , age 11-16 years) and 14 obese (BMI 35 ؎ 1.5 kg/m 2 , age 11-15 years) adolescents underwent 1) 1 H-NMR spectroscopy to noninvasively quantify IMCL and EMCL triglyceride content of the soleus muscle, 2) a 2-h euglycemic-hyperinsulinemic clamp (40 mU ⅐ m ؊2 ⅐ min ؊1 ) to assess insulin sensitivity, 3) a dual-energy X-ray absorptiometry scan to measure total percent body fat, and 4) magnetic resonance imaging to measure abdominal fat distribution. Both the IMCL and EMCL content of the soleus muscle were significantly greater in the obese adolescents than in the lean control subjects. A strong inverse correlation was found between IMCL and insulin sensitivity, which persisted and became even stronger after controlling for percent total body fat and abdominal subcutaneous fat mass (partial correlation r ‫؍‬ ؊0.73, P < 0.01) but not when adjusting for visceral fat (r ‫؍‬ ؊0.54, P < 0.08). In obese adolescents, increase in total body fat and central adiposity were accompanied by higher IMCL and EMCL lipid stores. The striking relationships between both IMCL and EMCL with insulin sensitivity in childhood suggest that these findings are not a consequence of aging but occur early in the natural course of obesity. Diabetes

No abstract

Should root and shoot temperature vary in synchrony to optimize nutrient uptake, particularly when there is a large difference in temperature from day to night (DIF) of air and soil? To answer this question, tomato (Lycopersicon esculentum Mill.) seedlings were grown in greenhouses with the air heated to give either a +14°C DIF or a +5°C DIF in air temperature with a 16°C mean. The root medium was either unheated except by the air, or heated to 21°C constantly, only in the day, or only in the night. Experiments were repeated in early March and April in two years. Overall, growth was faster and there were higher concentrations of elements in leaves under +5°C compared with +14°C air DIF. Root‐zone heating significantly increased growth and nutrition, compared with no heating. There was a trend in growth and nutrient concentration with timing of root heating: constant > day > night. These differences in growth and nutrition were similar under a +5°C or +14°C air DIF, and they were slight compared with no root‐zone heating. For most nutrients, coordination of root and shoot activity related to uptake and metabolism did not require synchronous variation of air and soil temperature. Uptake and transport of nitrate was an exception. Heating roots in the day resulted in the highest nitrate concentration in leaves under a +14°C air DIF, whereas heating constantly was optimal under a +5°C DIF. Our results indicate nitrate metabolism did benefit from synchronous variation in air and root temperature.

Kernel size (KS), an important yield component of wheat (Triticum aestivum L.), depends on assimilate availability and the capacity of the kernel to use assimilates. The objective of this study was to evaluate the response of wheat cultivars with different KS (20 to 43 mg kernel −1,) to sink manipulation. Twenty cultivars grown at two locations were partially degrained by removal of all spikelets from one side of only one spike per plant. Control spikes were left intact. Partial degraining decreased kernel number (KN) by 51%. Relative compensatory kernel growth tended to increase with decreasing KS. However, the KS of five cultivars was unaffected by partial degraining, and the relative growth response of one small‐ and one large‐kernel cultivar each deviated markedly from the predicted response. Partial degralning enhanced kernel N of all cultivars, with an estimated 19 to 80% of the increase in KS attributed to greater accumulation of N compounds. For selected caltivars, the KS distribution and flag‐leaf abscisic acid (ABA) were determined to evaluate the relationship of sink size to these traits. Partial degraining altered KS distributions; for all but one of seven cultivars evaluated, partially degrained cultivars had the largest 5% of kernels and the single largest kernel. Compensatory kernel growth was unrelated to flag‐leaf ABA, indicating partial degraining had no adverse effects on assimilate supply related to excessive ABA levels in the flag leaf. These results demonstrate variable cultivar response to partial degraining; apparently, kernel growth of some cultivars is source limited, while other cultivars are at their capacity to accumulate assimilates.