Presence Of Gibberellins Research Articles

Interactions in vitro between gibberellins and DNA : II. Optical rotatory profile of the thermal denaturation of DNA-gibberellin complexes

The formation of gibberellin-DNA complexes was assayed by measurement of optical rotation profiles of pea DNA. In the presence of gibberellin A 7, the cotton peak of pea DNA at 282 nm decreased at higher melting temperatures. This temperature shift indicated a stabilization of the DNA duplex by gibberellin A 7. Gibberellin A 3 was inactive in this respect.

GROWTH HORMONES IN POLLEN, STYLES AND OVARIES OF PETUNIA HYBRIDA AND OF LILIUM SPECIES

SUMMARY The presence of auxins has been demonstrated in extracts from pollen and styles of Petunia hybrida. The presence of gibberellins was demonstrated in extracts of pollen, styles and ovaries of Petunia hybrida as well as of three Lilium species. Pollen contains relatively high amounts of auxins as well as bibberellins compared with styles or ovaries. No significant effect was found of either compatible or incompatible pollinations in Petunia on the auxin and the gibberellin content of the pollinated styles, since the small increases of auxins and gibberellins found could be attributed to the auxins and gibberellins present in the pollen used for pollination. The gibberellin content of pollen of Lilium henryi dropped sharply during the first hour of germination, indicating the importance of gibberellins for germination.

The Presence of Gibberellins in Excised Tomato Roots

Substances having similar physiological properties to the gibberellins (located by the ‘Meteor’ dwarf pea bio-assay) have been detected in extracts from excised tomato root. The chromatographic behaviour of the most active zone is similar to that of gibberellin A1. Experiments using the d-1 and d-5 mutants of mazie did not indicate the presence of substances with differential effects on these two mutants.

THE CHANGING CONCEPT OF AUXIN

Kefford, N. P., and P. L. Goldacre. (Division of Plant Industry, C.S.I.R.O., Canberra, Australia.) The changing concept of auxin. Amer. Jour. Bot. 48(7): 643–650. Illus. 1961.—Recent findings in auxin research are interpreted as follows: The concept of auxin as only a cell‐enlargement regulator can no longer accommodate the variety of growth phenomena controlled by auxin. In isolated tissues, auxin interacts with gibberellin in the control of cell enlargement, and auxin and kinin interact in initiating cell division. Some evidence suggests a single site of auxin action for both processes. It is proposed that auxin is not a determining agent but a predisposing agent, causing the production of something in limiting amount which is required in both processes —in the presence of kinin, cell division is activated; in the presence of gibberellin, cell enlargement is activated. In the presence of limiting amounts of auxin, there could be competition between the 2 processes, the outcome depending on the balance of kinin and gibberellin. The possibility of competition in the presence of supraoptimal auxin concentrations is also suggested. Difficulties arise in the application of this concept to observations on intact plants, where cause and effect relationships are not readily established; the use of excised plant parts shows the relationships more clearly. The role of auxin in cell and organ differentiation is also discussed. The primary auxin reaction is not yet known. The biological assay for auxins is discussed with reference to this and to natural auxins. The function of auxin in the correlation of tissue and organ growth through the auxin transport system is stressed, and it is pointed out that if transport is a necessary requirement of a native auxin, indole‐3‐acetic acid is at present the only substance known to qualify.