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The decapitated primary root of 3‐day‐old Alaska pea seedlings has been used as a test system to determine the activities on lateral root formation of six auxins, six cytokinins and several other naturally‐occurring compounds. Their effects were assessed on (1) the initiation of lateral root primordia, (2) the emergence of visible lateral roots, and (3) the elongation of these laterals. All the auxins, at the optimum concentration of 10‐4M, promoted the initiation of lateral root primordia, and all except 3‐indolylpropionic acid inhibited the elongation of the resulting lateral roots. Their effects on the emergence of laterals were small and varied. All the cytokinins, at 10‐6M and above, inhibited both the initiation and the emergence of lateral roots, zeatin being the most powerful inhibitor. The emergence process was about twice as sensitive as the initiation of primordia to the presence of cytokinins. The cytokinin ribosides were generally less active than the free bases. Abscisic acid and xanthoxin inhibited both emergence and elongation, the concentration for 50% decrease of emergence being about 10‐4M. Gibberellic acid had little clear effect on any of the three criteria. Nicotinic acid and thiamine at 10‐3M promoted both the initiation of primordia and their emergence: pyridoxal phosphate stimulated both emergence and elongation but did not influence the initiation of primordia. Adenine and guanine had little effect but decreased root elongation some 25%. The strong inhibiting effect of the cytokinins may well be the basis for the marked inhibition exerted by the root‐tip on lateral root formation, while the promoting effects of auxins may explain the previously observed promotion of lateral root formation by the young shoot and cotyledons.

Qualitative analysis by gas chromatography-mass spectrometry (GC-MS) of the auxins present in the root, cotyledons and epicotyl of 3-dold etiolated pea (Pisum sativum L., cv. Alaska) seedlings has shown that all three organs contain phenylacetic acid (PAA), 3-indoleacetic acid (IAA) and 4-chloro-3-indoleacetic acid (4Cl-IAA). In addition, 3-indolepropionic acid (IPA) was present in the root and 3-indolebutyric acid (IBA) was detected in both root and epicotyl. Phenylacetic acid, IAA and IPA were measured quantitatively in the three organs by GC-MS-single ion monitoring, using deuterated internal standards. Levels of IAA were found to range from 13 to 115 pmol g(-1) FW, while amounts of PAA were considerably higher (347-451 pmol g(-1) FW) and the level of IPA was quite low (5 pmol g(-1) FW). On a molar basis the PAA:IAA ratio in the whole seedling was approx. 15:1.

In barley seedlings, tryptophan is the precursor of the simple indole alkaloid gramine, and also of tryptamine, which is important as a potential precursor of the plant growth hormone 3-indoleacetic acid. The present investigation was designed to study the distribution of free tryptophan and its derivatives within the seedlings, and to follow the changes in these compounds with time. Development of the enzyme tryptophan decarboxylase, which catalyzes the conversion of tryptophan to tryptamine, was also studied. An increase in free tryptophan was detected within 2 h of soaking the seed; this compound reached high values in very young tissues, and then declined. Gramine and its precursors, 3-aminomethylindole and N-methyl-3-aminomethylindole, were confined to the shoots; all three compounds appeared together at the inception of shoot growth. Quantitatively, gramine was the most important compound present and reached a concentration of 623 μg/g fresh weight (25 times that of free tryptophan) on the 9th day, and then declined. Isolated embryos were capable of synthesizing gramine at about one quarter the normal rate, indicating that these embryos have a considerable inherent capacity for tryptophan synthesis and are not wholly dependent on tryptophan released by the endosperm. Tryptophan decarboxylase and tryptamine were found only in the shoot, and both enzyme and product appeared after the 1st week of growth, when the rate of gramine synthesis was beginning to decline. 5-Hydroxytryptamine began to accumulate in both shoot and root after about 2 weeks of growth, and N-methyl-5-hydroxytryptamine was also present in the roots. The close parallel between the gramine pathway of the barley shoot and the analagous hordenine pathway of the root, in which tyrosine is the precursor amino acid, is discussed.

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