DIFFERENT SPECIES, SUCROSE, AND LIGHT IN PLANT SECTION ELONGATION TESTS

Sections from both darkand light-grown seedlings of 11 species were used to test responses to IAA (indoleacetic acid), sucrose, and an inhibitor prepared from cabbage seedlings. Variability among species was great; however, results indicate that many species, light-grown as well as dark-grown, could prove useful in bioassays and probably should be investigated. Although elongation of segments from high-intensity-light-grown cabbage and cucumber hypocotyls and oat coleoptiles had essentially stopped by the time of cutting, their growth and response to IAA as sections were considerable. Neither oat coleoptile nor pea internode sections can be considered representative because of differences in responses to sucrose, of dark-grown sections to light, and to an inhibitor prepared from cabbage. Sucrose generally did not stimulate and even inhibited response of most hypocotyls to IAA. Sucrose was absorbed by sections, increasing final dry weight while not affecting elongation. Sucrose reduiced the rate of respiratory decay in cabbage and sunflower, but IAA did not affect respiration. Changes in length and fresh weight of cucumber hypocotyl sections were comparable. RAPPAPORT, Blumenthal-Goldschmidt, and Hayashi (1966) have criticized the extensive use of oat coleoptiles to the exclusion of other tests for the bioassay of various plant growth promotors and inhibitors. While the intensive study of segments from oat coleoptiles and pea stems has yielded much of interest and value, and the development of many bioassays in addition to section elongation tests was needed and has proved useful, the above criticism is justified. Species other than oat and pea have been used in section elongation tests. Bentley and Housley (1954), Seeley et al. (1956), Heath and Clark (1956), and Barlow, Hancock, and Lacey (1957) have used wheat coleoptiles. Section tests with other species have received but limited study. Yamada (1954) and Wada (1961) used rice coleoptiles. Blackman (1961) measured fresh weight changes in sections of cotton and sunflower hypocotyls as well as in oat and wheat coleoptiles. He referred to, but did not report, weight changes for pea and white mustard. Weight changes also have been used by Venis and Blackman (1966) for cotton, and by Key and Shannon (1964) and Morre (1965) for soybean hypocotyls. Siegel and Porto (1961) used unusually short segments of cucumber hypocotyls and dandelion scapes. White lupine hypocotyls were used by Weinstein et al. (1956). Nitsch and Nitsch (1956) briefly checked cress, sunflower, and bean hypocotyls during their extensive investigation of oat first internodes. Nitsan and Lang (1965) utilized young seedlings to study cell division and cell elongation 1 Received for publication 20 May 1968. Partly supported by National Science Foundation Grants G-9015 and G-22072. in lettuce hypocotyls and lentil first internodes. Purves (1966) used cucumber hypocotyls. Slash pine hypocotyls were employed by Allen (1960), who also reported (personal communication) that he had used similar segments from sweet gum with some success. MAichel (1957) used hypocotyls from cabbage, radish, and turnip. Segments from dark-grown seedlings usually are used; however, light-grown seedlings should not be ignored. Only green pea stem sections have been investigated in anv detail (Galston and Baker, 1951; Brian anid Hemming, 1958; Galston and Kaur, 1961; Ockerse and Galston, 1967). A few years ago segments from several species were checked for possible use as test objects. A brief presentation of the results from this survev seems appropriate. The data suggest that intensive investigation of the responses of some of these species should be worthwhile. MATERIALS AND METHODS-The following 11 species were used: cabbage (Brassica oleracea var. capitata L. 'Golden Acre'), kohlrabi (Brassica caulorapa Pasq. 'White Vienna'), turnip (Brassica rapa L. 'Purple Top White Globe'), radish (Raphanus sativus L. 'Crimson Giant'), pea (Pisumn sativum L. 'Alaska'), tomato (Lycopersicum esculentum Mill. 'Marglobe'), cucumber (Cucumis sativus L. 'Marketer'), sunflower (Helianthus annuus L. 'Mammoth Russian'), bean (Phaseolus vulgaris L. 'Topcrop'), oat (Avena sativa L. 'Victory'), and corn (Zea mays L. 'Golden Bantam'). Seedlings were grown in polystyrene trays of sand. The darkroom was maintained at 24 C with relative humidity generally 70-90 %. Sight-