SEASONAL VARIATIONS IN RESERVE AND STRUCTURAL COMPONENTS OF PINUS RESINOSA CONES

Changes in reserve materials, lignin, hemicellulose, and cellulose of lst-year conelets and 2ndyear cones of red pine (Pinus resinosa Ait.) were studied by chemical extraction of the respective fractions. During the first 11 months after emergence of conelets, reserve materials, primarily carbohydrates, constituted approximately half of the dry weight of cones. Cellulose and hemicellulose contents were low but cells were highly lignified. During summer of the 2nd year of cone development, marked compositional changes occurred. A rapid surge of cone growth, possibly triggered by resumption of pollen-tube growth and fertilization, occurred from mid-June to early August and was accompaniel by transformation of reserve materials into cellulose and, to a lesser extent, into hemicellulose and lignin. During this transformation, the thickening and lignification of cells responsible for the opening of cone scales probably occurred. The developing seeds also mobilized readily available cone reserves during this time. THE PISTILLATE strobilus or cone of pinesbasically a woody axis on which paired bracts and ovule-bearing scales are arranged-requires 2 years to mature. In central Wisconsin the conelet of Pinus resinosa Ait. first becomes externally visible at the distal end of a growing shoot in late May or early June. Pollination occurs shortly thereafter while the ovuliferous scales are separated from one another. The cone begins to enlarge after pollination and the scales become tightly closed. By late July the conelet has lengthened from 4 mm to 10-12 mm. Very little dimensional growth occurs thereafter during the 1st year (Lyons, 1956). Meanwhile the pollen grains have germinated, but the pollen tube soon ceases growing and appears to lie in a quiescent state during the late summer and winter (Stanley, 1958). Megaspores are not formed until approximately 3 weeks after emergence of the pistillate strobilus. Successive cell and nuclear divisions of one of the megaspores result in an enlarged megagametophyte. An overwinter period of dormancy follows (Sarvas, 1962). Growth of cones resumes early in the spring of the second season. The cone attains its final length of 40-50 mm by early July and then dries and turns chestnut brown before seeds are released (Lyons, 1956). Growth of the megagametophyte also resumes in early spring, but no growth of the pollen tube takes place until just before fertilization (Sarvas, 1962). Fertilization occurs in mid-June of the 2nd year, almost 13 months after pollination (Ferguson, 1904). 1 Received for publication 11 October 1968. The cooperation of the Wisconsin Department of Natural Resources is acknowledged. Publication is approved by the Director of the Wisconsin Agricultural Experiment Station. Embryo development follows and the seeds are ripe by early September. Work in our laboratory has shown that carbohydrates utilized by growing Pinus resinosa cones during their 2-year period of development are mobilized from two sources: needle and stem reserves and currently produced photosynthate, mostly from the 1-year-old needles (Dickmann and Kozlowski, 1968). These studies have now been extended to an investigation of the seasonal pattern of storage of carbohydrates by cones and conversion of reserves into structural components. Changes in reserve materials, lignin, hemicellulose, and cellulose were observed for lstand 2nd-year cones during the 1966 growing season. METHODs-Beginning on 14 April, cones were collected at 2-week intervals during the 1966 growing season from 25to 30-year-old windbreak Pinus resinosa trees at the Griffith State Forest Nursery in central Wisconsin. The trees were growing on Plainfield sand soil with south or west exposure. On each sampling date five cones from each of 10 trees were removed from the mid-portion of the crown, placed in polyethylene bags, and brought to the laboratory. The cones were then dried at 75 C and ground in a Wiley mill to pass a 4-mm-pore diameter sieve. Threeto 4-g samples of this granular cone material were then redried at 75 C and weighed on an analytical balance. The samples were boiled for 2 hr in an aqueous mixture of 5 % trichloroacetic acid, TCA, (w/v) and 35 % methanol (v/v) to hydrolyze reserve polysaccharides and then extracted with water for 8 hr in a Soxhlet apparatus (Priestley, 1965). The residue was dried at 75 C, weighed, and weight loss determined to give an estimate of