An Effect of Kinetin on the Translocation if 14C-Labelled Photosynthate in Citrus

Abstract

This study indicates that the application of kinetin to a recently formed fruit enhances its ability to import photosynthetic assimilates. Cytokinins are known to influence .the transport of plant metabolites (Letham 1967), and in the case of vine shoots Shindy and Weaver (1967) have recently demonstrated an effect of the kinin 6-(benzylamino)-9-(2-tetrahydropyranyl)-9H-purine on the translocation of 14C_ labelled assimilates. The present paper reports an effect of kinetin (6-furfurylaminopurine) on the accumulation of14C-labelled substrates by citrus fruits (cv. Washington Navel). In such crops the newly formed fruitlet is often unable to compete successfully with adjacent expanding leaves for substrates and this is thought to result in early fruit drop (Haas 1949;Sauer 1954). Materials and M ethod8The experiments made use of 2-year-old rooted cuttings of cv. Washington Navel raised in the glasshouse according to the method of Gates, Bouma, and Groenewegen (1961). A current growth flush had produced groups of two or three fruitlets at five points along a single welldeveloped shoot and these were designated groups 1-5 basipetally. Starting 25 days after the blossoms opened, kinetin was applied at 0 and 500 p.p.m. to the newly formed fruits.The kinetin was first dissolved in a minimum volume of 0 ·IN HCI and the solution adjusted to pH 6·0 during dilution. A wetting agent was added to the final solutions and they were applied to the fruits with a camel-hair brush. Successive groups of fruits along the shoot had from one to five applications spaced at 3-or 4-day intervals.Following the final kinetin application to a given group, 14C02 generated from 2 mg Ba14COs with a specific activity of 1· 5 mc/m-mole was supplied to a nearby leaf, and the fed leaf and adjacent fruits were harvested 24 hr later. After measuring fresh weight, the fruits were sectioned and dried between filter paper at room temperature together with the source leaf and other tissues. The mounted specimens were then exposed to Kodak medical X-ray film which was developed after 3-8 days, depending on the level of radioactivity.Prior to exposure, the source leaf was masked with transparent adhesive tape so that the image of adjacent tissues would not be obscured on the X-ray film. At the time of harvest, samples of fruit were taken for dry weight and moisture determination (dried at 80°C for 3 days), and this dried material was then ground to a fine powder and 5-mg subsamples, weighed to ± 0·05 mg and known to afford maximum counting efficiency for this type of material, were assayed for radioactivity in a Packard liquid scintillator. Re8ult8 and Di8cU88ion

Use of High Performance Liquid Chromatography for the Determination of Endogenous Hormone Levels in Solanum tuberosum L. Subjected to Carbon Dioxide Enrichment of the Root Zone

“…The decrease of both trans zeatin and zeatin riboside in the roots suggests the possibility that CO2 treatments may cause a conversion of trans zeatin to zeatin riboside and, in turn, also enhance the translocation of zeatin riboside to the top of the plant. This is consistent with the increase in dry matter content resulting from CO2 applications previously noted (1) and is supported by previous evidence that cytokinins are mobilizing agents of stored reserves (6,9,17). This is also in agreement with the findings of Meidner ( 11) who showed an increase in photosynthesis with applications of cytokinins.…”

Benzyladenine-induced Movement of 14C-Labeled Photosynthate into Roots of Vitis vinifera

“…2), indicating that BA has a general effect on the movement of different types of compounds. Our results support the hypothesis that transport of photosynthetically assimilated "CO2 is controlled by plant hormones (3,10,17,22,29). Benzyladenine has been shown to increase the movement of "C-assimilates into fruit clusters (39), shoot tips (32,33), and leaves (34) of grapevines.…”

“…Kriedemann et al (17) and Saito and Kasai (30) found that rapidly expanding grape leaves, such as the apical leaves used in our experiments, incorporate the greatest proportion of "CO, into organic acids, with smaller amounts going into amino acids and sugars. Fully expanded leaves, in contrast, incorporate "CO2 mostly into sugars (7).…”

Growth Regulator Induced Movement of Photosynthetic Products Into Fruits of `Black Corinth' Grapes

“…Little such work has been done with flowers or fruits. However, Kriedemann (9) recently has shown that the application of kinetin to a voung fruit of orange cv. Washington Navel enhances its ability to import photosvnthetic assimilates.…”