THE AUXIN, 2,4‐DICHLOROPHENOXYACETIC ACID, AS A REGULATOR OF PROTEIN SYNTHESIS AND SENESCENCE IN DETACHED LEAVES OF PRUNUS

Abstract

SUMMARYExperiments on the hormonal regulation of protein synthesis and senescence in detached leaves of Prunus serrulata are described.Senescence is associated with a fall in the content of total protein in the leaf, a loss of chlorophyll and an increase in the soluble nitrogenous fractions. Auxins such as «-hutyl ester of 2,4-dichlorophenoxyacetic acid (2,4-D) effectively retard these changes when supplied to leaves at particular stages of growth and development. 2,4-D is found to stimulate oxygen uptake in young and mature leaves, compared with controls, but has little effect upon oxygen uptake of autumn leaves, while protein levels are maintained by the auxin in freshly detached autumn leaves but not in younger leaves, unless they have already been detached for precise periods of time and considerable protein loss has already taken place.2,4-D prevents protein loss in autumn leaves by maintaining protein synthesis. The incorporation of [i^C] leucine into protein falls by as much as 60% in 7 days in control halves of leaves, but in halves of the same leaves which have been supplied with 2,4-D, the incorporation of [^^C] leucine into protein is sustained at, or above, the original level.It is proposed that auxins participate in the balance of hormonal factors which regulate the metabolism of protein. They would appear to be essential for maintaining the incorporation of amino acids into protein, and at certain stages of leaf development, they would appear to be limiting for the proper functioning of the processes of protein synthesis.The results are discussed in connection with known effects of environment on the auxin content of leaves, and with effects of auxins and other plant growth regulators on protein and nucleic acid metabolism.

Senescence Inhibition and Respiration Induced by Growth Retardants and 6N-Benzyladenine

“…Similar results for mushrooms treated with other chemicals have been reported (9). In a few cases where kinins had little or no effect on senescence, auxins (12) (13), increasing destruction (7), or both.…”

Gene expression during leaf senescence

“…Some reports have indicated that auxins may also be able to delay senescence. For example, a-naphthalene acetic acid retards the senescence of Rhoeo and Mesetnhryanthemum leaf segments (Sacher, 1959) and 2,4-D butyl ester slows down protein breakdown of detached leaves of Prunus serrulata (Osborne & Hallaway, 1964). However, there are numerous cases in which auxins are not very powerful in their effects on senescence, and high concentrations have to be used compared with cytokinins.…”

The Senescence of Detached Leaves of Tropaeolum

“…Unlike Avena, however, kinetin and gibberellic acid, which delay senescence in the dark in both species, do so in Tropaeolum without causing any significant stomatal opening. (10). Virtually all species, however, show delay of senescence by cytokinins.…”

“…Rumex, Taraxicum, and Tropaeolum leaves respond to GA3 by prolonged delay in the rate of senescence (2,3,8,18), while many other plants show little or no response to gibberellins. Leaves of cherry laurel (Prunus cerasus) respond to auxin (10). Virtually all species, however, show delay of senescence by cytokinins.…”