RESPIRATORY TRENDS IN PERIANTH SEGMENTS OF MAGNOLIA GRANDIFLORA

Abstract

STUDIES OF floral respiration have in general been carried out to indicate the trend in respiration rate over a period of days or weeks. James and Beevers (1950) observed in the immature tissue of Arum spadix a gradual decrease in respiration followed by a sharp rise during the period of maturation. Siegelman et al. (1958) found a similar pattern in disks of rose petals during development. The trend in respiration appeared to be similar to the climacteric curve of several fruits as described by Biale (1958). However, in work done on excised mature flowers or floral parts of camellias by Bonner and Honda (1950), of roses by Siegelman (1952), and of Cattleya mossiae Hook. by Sheehan (1954), there was a continual drop in respiration with no increase comparable to a climacteric. In this study the relationship of metabolic activity, as indicated by oxygen consumption, to stages in floral development and to cytological changes is reported for the perianth segments of Magnolia grandiflora . MATERIALS AND METHODS.-Six trees in the Los Angeles area served as source for flowers. The blooming season in this region is May, June, and July. The work reported here was done during June and July of 1956. The flowers were selected at random and labeled on the first morning of bloom. This day was designated as the first day of bloom and all measurements were referred to this time. To determine the approximate age of buds in relation to the first day of bloom, a large group of buds from a given area on one tree was tagged and their length was recorded by daily measurements. Buds for respiration determinations were taken from the same region on the tree and their age, in relation to the first day of bloom, was estimated by comparison with those carried through to bloom. Flowers were collected and their age recorded in days and hours, with midnight prior to the first morning of bloom designated as the zero point. A lapse of from '70 to 90 min. occurred between picking and the beginning of a test in Warburg vessels; the data were recorded as of the time of picking. Respiration rate was based on oxygen uptake, measured by the Warburg manometric method and recorded as Qo2 (microliters of oxygen per milligram of dry weight per hour). Disks about 9 mm. in diameter were cut from the inner perianth segments with a cork borer. Between 15 and 18 of these disks, whose total weight varied between 390 and 410 mg., were used in each flask; in older flowers, due to desiccation, more disks had to be