It has been shown previously ( 15) that photoperiodic induction in Xanthium is inhibited by application of the pyrimidine, 5-fluorouracil (5-FU). More recently (1) it has been demonstrated that the process which is inhibited by 5-FU and which is related to the process of flowering, is the synthesis of ribonucleic acid (RNA) in the Xanthium bud during the first part of the inductive dark period....

Efeito de métodos de extração de compostos fenólicos de Xanthium strumarium L. e suas atividades antioxidantes. The effect of extraction methods and solvents on overall yield, total phenolic content, antioxidant activity, and the composition of the phenolic compounds in Xanthium strumarium extracts were studied. The antioxidant activity was determined by using 2,2-diphenyl-1-picrylhydrazyl radi...

Flowering is induced in Xanthium strumarium by a single dark period exceeding about 8.3 hours in length (the critical night). To study the mechanism which measures this dark period, plants were placed in growth chambers for about 2 days under constant light and temperature, given a phasing dark period terminated by an intervening light period (1 min to several hrs in duration), and finally a te...

It has been suggested that some biological processes are equivalent to computation, but quantitative evidence for that view is weak. Plants must solve the problem of adjusting stomatal apertures to allow sufficient CO(2) uptake for photosynthesis while preventing excessive water loss. Under some conditions, stomatal apertures become synchronized into patches that exhibit richly complicated dyna...

The effect of interrupting darkness with red light in the presence or absence of 0.03% CO(2) was studied in relation to flowering of Xanthium pennsylvanicum and germination of light-sensitive lettuce seeds. The results indicate that CO(2) is essential for red light to be effective in either process.

A cycloheximide-sensitive increase in the activity of phenylalanine ammonia-lyase (EC 4.3.1.5) occurs in Xanthium leaf disks exposed to light. Radioactive ammonia-lyase has been isolated by means of sucrose density gradient centrifugation and starch gel electrophoresis from disks fed l-isoleucine-U-(14)C or l-arginine-U-(14)C. The incorporation of radioactive amino acids into phenylalanine ammo...