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...

BACKGROUND The androgen comprises a group of hormones that play roles in male reproductive activity as well as personal characteristics. OBJECTIVE We investigated the androgenic activity of various herbal medicines in human prostate cancer 22Rv1 cells. MATERIALS AND METHODS Herbal extracts of Trichosanthes kirilowii (TK), Asarum sieboldii (AS), Sanguisorba officinalis (SO), and Xanthium str...

Acetolactate synthase (ALS) was isolated from a field population of cocklebur (Xanthium strumarium) that developed resistance to the herbicide Scepter following three consecutive years of application. The active ingredient of Scepter, imazaquin, gave an inhibitor concentration required to produce 50% inhibition of the enzyme activity that was more than 300 times greater for the resistant enzyme...

A growth regulator (G; 4-ethyl-1-hydroxy-4,8,8,10,10 pentamethyl-7,9-dioxo-2,3 dioxyabicyclo (4.4.0) decene-5) from Eucalyptus grandis (Maiden) reduced stomatal conductance and also photosynthetic capacity when fed through the transpiration stream of detached leaves. The concentration of G required for this effect was high (10(-4) molar), but the amount of G taken up (dose) was below the level ...