We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen eontent. The method prediets glucose equivalents, the amount of glucose required to provide earbon skeletons and r-eduetant to synthesize a quantity of organic produet. Glueose equivalents have previously been ealculated frorn the elemental eomposition of tissue. We define construetion cost as the amount of glueose requir-ed to provide carbon skeletons, reduetant and ATP for synthesizing the organie eompounds in a tissue via standard biochemieal pathways. The fraetion of the total construetion eost of a eompound or tissue (excluding costs of transporting eompounds) that is reflected in its glueose equivalents is the biosynthetie efficieney (£"). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total eonstruetion cost ean be estimated to +6% of the value obtained from bioehemical pathway analysis.Construction costs of leaves ot" three ehaparral species -were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differenees were probably due to a eornbination of inaeeuracy in the estimated biosynthetie efficiency and teehnieal difficulties with bioehernieal analysis, one of the older methods of determining construction cost.

We present a method for estimating the construction costs of plant tissues from measurements of heat of combustion, ash content, and organic nitrogen eontent. The method prediets glucose equivalents, the amount of glucose required to provide earbon skeletons and r-eduetant to synthesize a quantity of organic produet. Glueose equivalents have previously been ealculated frorn the elemental eomposition of tissue. We define construetion cost as the amount of glueose requir-ed to provide carbon skeletons, reduetant and ATP for synthesizing the organie eompounds in a tissue via standard biochemieal pathways. The fraetion of the total construetion eost of a eompound or tissue (excluding costs of transporting eompounds) that is reflected in its glueose equivalents is the biosynthetie efficieney (£"). This quantity varies between 0.84 and 0.95 for tissues with a wide range of compositions. Using the new method, total eonstruetion cost ean be estimated to +6% of the value obtained from bioehemical pathway analysis.Construction costs of leaves ot" three ehaparral species -were estimated using the proposed method and compared to previously published values, derived using different methods. Agreement among methods was generally good. Differenees were probably due to a eornbination of inaeeuracy in the estimated biosynthetie efficiency and teehnieal difficulties with bioehernieal analysis, one of the older methods of determining construction cost.

The present studies showed that about 80% of the indole-3-acetic acid extractable from Avena kernels by aqueous acetone was estenfied to polymers precipitable by ammonium sulfate and ethanol or acetone. The polymers were positively charged, being adsorbed to cation exchange columns at a pH of 3, or below, and eluted at a pH greater than 4. The polymers were heterogeneous with respect to size, about 5,000 to 20,000 daltons, and charge, exhibiting apparent pKa values of 4.2 and 4.7. The polymer fractions contained esterified IAA, anthrone-reactive material that liberated glucose upon acid hydrolysis, phenolic compounds, and peptidic material with a high proportion of hydrophobic amino acids. Since the esterified IAA was unstable, establishing polymer purity was not possible, and the designation IAA-glucoprotein fraction was adopted.Dehusked Avena kernels contained 8 mg/kg total IAA of which 5.5% was free and 94.5% esterified. IAA 26 radiometer p1-i meter. GLC was done with an F and M model 402 or a Varian 2740 gas chromatograph. both with flameionization detectors and nitrogen as the carrier gas. Combined GLC-mass spectrometry was performed NNith an LKB 9000. mmol) and 1.3 to 1 .5 mg indole-3-butyric acid were added to the first extraction. For free IAA determinations, the aqueous condensate (40-50 ml) was adjusted to pH 2.5 with 5 N HC1. the IAA extracted three times into 75 ml of ether and then purified as described (4). except omitting the Sepharose column. For estimation of bound IAA. NaOH pellets were added to the aqueous condensate to make the extract 1 N or 7 N in base. The 1 N base treatment was at room temperature for 1 hr while the 7 N base extracts were flushed with N., then heated in a sealed hydrolysis tube for 3 hr at 100 C. The alkaline extracts were partitioned three times against 75 ml of ether, adjusted to pH 2.5 with 12 N H.SO4, the IAA partitioned into ether (3 x 70 ml) and purified by DEAE and lipophylic Sephadex chromatography. TLC, and GLC (4). Plant Physiol. Vol. 58. 1976 IAA as previously described (4,22). Combined GLC-mass spectrometry of trimethylsilylated samples was as described previously (4). except that the samples were chromatographed with a program of 10 degrees/min, starting at 180 C. The IAA derivative emerged at an oven temperature of 220 C. Assay Procedures. IAA was determined with the Salkowski reagent (4). or with the Ehmann reagent. The latter reagent (A.Ehmann. unpublished) consisted of 3 parts Salkowski reagent and 1 part Ehrlich reagent (v/v). The samples were dissolved in no more than 50 gl of 50% ethanol, and 0.2 ml of reagent was added. Mixtures were heated at 45 C for 30 min, and then diluted with 0.6 ml 50% ethanol. Absorbancies of the solutions were measured at 615 nm and, under these conditions, the assay is linear up to 10 ,ug.IAA contents of fractions from the crude ester isolation. described below. were determined by taking aliquots to dryness wxith 25 nCi['4C]IAA and saponifying them in 1 ml of 1 N NaOH at room temperature for 1 hr. Samples were t...

Abstract. Wild radish plants deprived of, and continuously supplied with solution NO−3 for 7 d following 3 weeks growth at high NO−3 supply were compared in terms of changes in dry weight, leaf area, photosynthesis and the partitioning of carbon and nitrogen (NH2‐N and NO−3‐N) among individual organs. Initial levels of NO−3‐N accounted for 25% of total plant N. Following termination of NO−3 supply, whole plant dry weight growth was not significantly reduced for 3 d, during which time plant NH2‐N concentration declined by about 25% relative to NO−3‐supplied plants, and endogenous NO−3‐N content was reduced to nearly zero. Older leaves lost NO−3 and NH2‐N, and roots and young leaves gained NH2‐N in response to N stress. Relative growth rate declined due both to decreased net assimilation rate and a decrease in leaf area ratio. A rapid increase in specific leaf weight was indicative of a greater sensitivity to N stress of leaf expansion compared to carbon gain. In response to N stress, photosynthesis per unit leaf area was more severely inhibited in older leaves, whereas weight‐based rates were equally inhibited among all leaf ages. Net photosynthesis was strongly correlated with leaf NH2‐N concentration, and the relationship was not significantly different for leaves of NO3−‐supplied compared to NO−3‐deprived plants. Simulations of the time course of NO−3 depletion for plants of various NH2‐N and NO−3 compositions and relative growth rates indicated that environmental conditions may influence the importance of NO−3 accumulation as a buffer against fluctuations in the N supply to demand ratio.